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Degradation Rates of Plastics in the Environment

Cite this: ACS Sustainable Chem. Eng. 2020, 8, 9, 3494–3511
Publication Date (Web):February 3, 2020
https://doi.org/10.1021/acssuschemeng.9b06635

Copyright © 2022 American Chemical Society. This publication is licensed under CC-BY.

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Abstract

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Plastic waste is currently generated at a rate approaching 400 Mt year–1. The amount of plastics accumulating in the environment is growing rapidly, yet our understanding of its persistence is very limited. This Perspective summarizes the existing literature on environmental degradation rates and pathways for the major types of thermoplastic polymers. A metric to harmonize disparate types of measurements, the specific surface degradation rate (SSDR), is implemented and used to extrapolate half-lives. SSDR values cover a very wide range, with some of the variability arising due to degradation studies conducted in different natural environments. SSDRs for high density polyethylene (HDPE) in the marine environment range from practically 0 to approximately 11 μm year–1. This approach yields a number of interesting insights. Using a mean SSDR for HDPE in the marine environment, linear extrapolation leads to estimated half-lives ranging from 58 years (bottles) to 1200 years (pipes). For example, SSDRs for HDPE and polylactic acid (PLA) are surprisingly similar in the marine environment, although PLA degrades approximately 20 times faster than HDPE on land. Our study highlights the need for better experimental studies under well-defined reaction conditions, standardized reporting of rates, and methods to simulate polymer degradation using.

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Synopsis

Reported degradation rates of common plastics were harmonized using the specific surface degradation rate (SSDR), which was then used to estimate half-lives.

Introduction

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Synthetic polymers are made by linking together hundreds or thousands of organic subunits (“monomers”) via strong covalent chemical bonds. The first fully synthetic polymer, Bakelite (made by a condensation reaction of phenol with formaldehyde) dates to the early 20th century, but true mass production of polymers began only in the 1950s. Since then, global manufacturing has grown exponentially, reaching 380 Mt year–1 in 2015. (1) Today, thousands of polymer grades are produced on commercial scales. (2) The largest market shares belong to low-cost, commodity thermoplastic polymers, henceforth referred to as “plastics.” They include polyethylene terephthalate (PET), high, low, and linear-low density polyethylene (HDPE, LDPE, and LLDPE), polyvinyl chloride (PVC), polypropylene (PP), and polystyrene (PS).
The vast majority of plastics produced today, including all of the aforementioned commodity polymers, are made from nonrenewable petrochemicals, so named because they are derived from fossil oil, natural gas, and coal. Although these plastics are inexpensive, each is a highly engineered material with precise physical properties. They can be molded into virtually any desired shape through rotation, injection, extrusion, compression, blowing, or thermoforming. Their material properties are adjusted during and/or after synthesis to achieve the desired strength, permeability, porosity, opacity, and color. Polyolefins are particularly durable, due to their chemical and biological inertness, which is a result of their high molecular weight and hydrophobicity, and the absence of functional groups that are susceptible to attack by microbial enzymes, light, water, etc. (3,4) The recalcitrance and impermeability of these plastics make them ideal for applications such as food packaging, sterile medical uses, and construction, among others, but also make them particularly long-lived when they are discarded. Various antioxidants and stabilizers, which are used to prolong the working life of plastics, slow environmental degradation of plastics waste even further. (1,5,6)
Consequently, the very properties that make plastics so versatile for humans has also created an emerging threat to the environment. (7) Globally, only 18% of plastics waste are recycled, and 24% are incinerated. The remaining 58% are either landfilled or enter the natural environment, where plastics accumulate and persist for a long period of time. (1) In the United States, where the landfill rate for discarded plastics exceeds 75%, such polymers are now responsible for a significant fraction (19%) of all municipal solid waste. (8) At current growth rates, the accumulation of plastics waste in landfills and/or in the natural environment is projected to reach nearly 12,000 Mt globally by 2050. (1,9)
The amount of plastic waste entering the oceans has emerged as a major concern. Large-scale concentrated accumulations of plastics have been found in the South Pacific subtropical gyre and the Eastern Pacific Ocean gyre. (10−12) Even in a medium waste-to-debris conversion rate scenario, the total amount of plastics waste in the ocean is expected to grow from 50 Mt in 2015 to 150 Mt by 2025. (13) The sources of this material are highly correlated with the absence of effective waste management infrastructures. It has been estimated that nearly 90% of the plastics entering the ocean comes from just 10 rivers, all located in Asia or Africa. (14) Ocean plastic debris is associated with persistent organic pollutants (POPs), including polychlorinated biphenyls (PCB), pesticides, and polycyclic aromatic hydrocarbons (PAHs), due to the higher affinity of these hydrophobic molecules for plastics compared to their affinities for sediments or water. (15,16) Finally, nearly 700 marine species have been observed to interact directly with plastics marine debris through ingestion, entanglement, and/or smothering. (17)
There are often vast differences between plastics degradation rates reported in the peer-reviewed literature and those reported by the popular press. A few media reports acknowledge the deficit of knowledge about the degradation rates of plastics, (18,19) but more often, they present degradation times as known, despite the paucity of scientific evidence. Media estimates of degradation times for plastic bags tend to fall into one of two ranges: 10–20 years (20) or 500–1000 years, (21) while that for “plastic” bottles is reported as over 70 up to 450 years. (21) Some media have reported that “plastics” do not degrade at all. (22) In these claims, however, the type of plastics is often unclear, and the environmental conditions are not specified. Also, the extrapolation method is unknown. Each of these factors has a large impact on degradation times. Furthermore, scientific studies of plastics degradation times are evolving, and estimated lifetimes can change dramatically based new evidence. For example, a recent study found that polystyrene exposed to sunlight degrades on much shorter time scales than the thousands of years in previous estimates. (23)
This study aims to present an overview of plastics degradation pathways in the environment and to summarize current knowledge about degradation rates for different types of commodity plastics under various environmental conditions. The results should help researchers and policymakers to more accurately describe the times needed for various plastics to degrade in the environment.

Abiotic Degradation Pathways

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The environmental degradation mechanisms for plastics can be classified as either (i) physical, referring to changes in the bulk structure, such as cracking, embrittlement, and flaking, or (ii) chemical, referring to changes at the molecular level such as bond cleavage or oxidation of long polymer chains to create new molecules, usually with significantly shorter chain lengths. The potential environmental hazards associated with the soluble chemical byproducts of plastics degradation must be considered, (24) as well as with the leaching of small molecules added during product formulation. Typically, chemical degradation at near-ambient temperatures in the environment involves either hydrolysis (requiring H2O) or oxidation (requiring O2), both of which can be accelerated by microbial action, heat, light, or combinations thereof. (25,26) In the sections below, we focus on natural abiotic processes that lead to the chemical degradation of polyethylene (PE), polyethylene terephthalate (PET), and polylactic acid (PLA). Although biotic degradation pathways are also undoubtedly important, (27) degradation is typically initiated abiotically (light, heat, acids, etc.). (28,29) Abiotic and biotic processes often work in tandem, with abiotic degradation leading to smaller molecules that are subsequently mineralized by microbes. (30) In this section, we focus on degradation pathways for PE, PET, and PLA due to the high relative number of studies of these plastics described later in this Perspective. Degradation mechanisms for other commodity plastics (including polyvinyl chloride (PVC), (31,32) polypropylen (PP), (33−35) and polystyrene (PS) (36,37)) have been reviewed elsewhere. (38)

Polyethylene (PE)

Although PE is the most inert of the polyolefins, it does degrade slowly in the natural environment. The backbone chains of PE are constructed exclusively from C–C single bonds which do not readily undergo hydrolysis and which resist photo-oxidative degradation due to the lack of UV–visible chromophores. Adventitious impurities or structural defects that form in PE during its manufacturing, or during subsequent weathering, (38) can act as chromophores. (39) PE may also contain a small number of unsaturated (C═C) bonds in the main chain or at the chain ends (typically, vinyl groups in HDPE and vinylidenes in LDPE). These sites are readily oxidized by O3, NOx, or other tropospheric radicals, often to highly unstable hydroperoxides, which are then converted to more stable UV-absorbing carbonyl groups. (40) An increased rate of photo-oxidation was reported for LDPE, relative to HDPE, due to the higher frequency of reactive branch points in the low density polymer. (41) In the absence of sunlight, thermal oxidative degradation of PE does not occur at appreciable rates at temperatures below 100 °C. (42) Since the role of light in photo-oxidative degradation is only to initiate chain reactions, (42) similar product distributions are generated in both photochemical and thermal processes (Figure 1). In environments lacking both sunlight and oxygen (e.g., landfills), anaerobic thermal degradation is unlikely to proceed naturally due to the high temperatures required (≥350 °C). (43,44)

Figure 1

Figure 1. Common products in the thermal- and photo-oxidative degradation pathways for polyethylene (R, R′, and R′′ are polymer chains of variable length).

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The mechanism of photo-oxidative degradation begins when an excited state (localized at a carbonyl or other structural defect) in PE abstracts a hydrogen atom from the polymer backbone, generating a reactive carbon-based alkyl radical. The first step in the subsequent radical chain mechanism is the reaction of the alkyl radical with O2 to form a peroxy radical, which abstracts a hydrogen atom from another polymer chain (or from a distant site on the same polymer chain) to form a hydroperoxide and a new alkyl radical. Subsequent O–O bond scission in the hydroperoxide leads to alkoxy and hydroxyl radicals, each of which can abstract another hydrogen atom and generate a new alkyl radical. Finally, termination occurs through bimolecular radical recombination. (24)
Carbonyl defects introduced into polyethylene via oxidative reactions can also lead to Norrish Type I reactions (Figure 2a), in which photochemically induced homolytic cleavage leads to free radical intermediates, or Norrish type II reactions, in which intramolecular γ-H abstraction generates ketones and vinylidenes (Figure 2b). (45,46) Although HDPE, LDPE, and LLDPE all have nominally the same chemical compositions, they have very different degrees of crystallinity. The rate of degradation depends strongly on the amorphous fraction of the polymer. Thus, degradation is far slower for crystalline HDPE, whose lower chain mobility promotes radical recombination at the expense of radical propagation reactions. (47)

Figure 2

Figure 2. Photo-oxidative degradation of PE containing carbonyl impurities, via (a) a Norrish type I mechanism or (b) a Norrish type II mechanism. (c) Radical recombination to form cross-linked chains. (38) R, R′, and R′′ are polymer chains of variable length.

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Polyethylene Terephthalate (PET)

The chemical structure of polyethylene terephthalate (PET) consists of alternating ethylene glycolate and terephthalate subunits, linked via ester bonds. It therefore belongs to the class of polymers known as polyesters. In the natural environment, PET can degrade by thermal oxidation, but hydrolytic cleavage and photo-oxidation initiated by UV light are more common under ambient conditions. (48) In particular, the low temperatures typical of the marine environment mean that floating plastics degrade primarily by slow, photo-oxidative degradation. When PET is landfilled, or sinks below the upper regions of the ocean penetrated by sunlight, the buried polymer obviously cannot undergo photodegradation. Under these conditions, slow thermal oxidative degradation and hydrolysis may occur together, or sequentially. If PET is landfilled in an oxygen-poor environment, anaerobic degradation is unlikely to occur naturally due to the high temperatures required (≥200 °C). (36) The chemical products resulting from each of these processes are compared in Figure 3.

Figure 3

Figure 3. Small molecule products of the three common degradation routes in the environmental degradation of polyethylene terephthalate. R and R′ are polymer chains of variable length.

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Hydrolysis of PET forms shorter carboxylic acid-terminated and alcohol-terminated chains, leading ultimately to terephthalic acid and ethylene glycol. In the near-neutral pH of the marine environment, hydrolytic cleavage of PET is very slow, (49,50) but the rate is strongly enhanced under acidic conditions. (51) In landfills, ester hydrolysis can induce a local drop in pH if the amount of moisture is insufficient to dilute the carboxylic acid products, resulting in autocatalytic acceleration. (24)
In the presence of O2, thermal degradation may proceed via a free-radical mechanism, initiated when the α-H of the ester is abstracted by an excited carbonyl group. The resulting carbon-centered radical reacts rapidly with O2 to give a peroxy radical which abstracts another α-H to form a new hydroperoxide and perpetuate the chain reaction. The final products are mostly small molecule carboxylic acids, aldehydes, and other oxygenates. (52) In the absence of O2, α-H abstraction can also trigger the cleavage of ester linkages, resulting in carboxylic acid-terminated and vinyl-terminated chains. Subsequent anaerobic reactions generate small molecule oxygenates with higher overall aldehyde contents relative to the carboxylic acids. (36,49)
Degradation of PET initiated by photolytic cleavage of an ester bond results in the release of CO, CO2, terephthalic acid, anhydrides, carboxylic acids, and esters (Figure 3). As expected, higher yields of CO2 are observed in aerobic environments. (53) Both aerobic and anaerobic photodegradations follow a Norrish type II mechanism (similar to that shown in Figure 2b), in which an excited state carbonyl abstracts an α-H to yield carboxylic acid and vinyl chain ends. In the presence of O2, hydroxyl radicals formed by hydroperoxide O–O bond cleavage can react with the aromatic rings in the polymer backbone to form hydroxyterephthalate groups. Radical intermediates and products can recombine to form cross-links and new chromophores, which can lead to polymer embrittlement and discoloration (but not necessarily mineralization). (24,49)

Polylactic Acid (PLA)

Bioderived polyesters such as PLA are interesting alternatives to petrochemical-based polyesters, due in part to their appreciable rates of degradation under industrial composting conditions (>60 °C, in the presence of O2 and moisture). (54) Analogous to PET, PLA degradation typically proceeds through either hydrolysis or thermal-oxidative or photo-oxidative degradation (Figure 4). Degradation can also occur under anaerobic thermal conditions but only at temperatures much higher than those normally found in the natural environment (≥230 °C). (36,55)

Figure 4

Figure 4. Common products in the hydrolytic and photo-oxidative degradation pathways of polylactic acid (R and R′ are polymer chains of variable length).

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Slow hydrolysis of the PLA ester linkages occurs during exposure to moisture at temperatures of at least 30 °C, leading to the release of smaller oligomers and monomers. (56) The hydrolysis reactions initially take place in amorphous regions within the polymer, (57) where they lead to an increased concentration of carboxylic acid chain ends. PLA exposed to the resulting lower pH conditions experiences accelerated degradation due to autocatalysis (58) but ultimately yields the same lactic acid monomer (Figure 5).

Figure 5

Figure 5. Mechanism of PLA degradation by chain-end scission in acidic environments. Adapted from de Jong et al., 2001. (58)

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PLA is unlikely to hydrolyze in marine environments, where the temperature rarely reaches 30 °C. Consequently, the predominant degradation pathway in marine environments is photo-oxidative. The carbonyl group of PLA absorbs UV radiation below 280 nm, making the polymer susceptible to photodegradation. (59) The Norrish type II mechanism results in C–O bond dissociation, similar to PET and PE (Figure 2b). (60) Random chain scission nevertheless occurs more readily in amorphous regions, which experience less radical recombination than rigid crystalline regions. (56,60) In addition to the Norrish type II products, hydroperoxide intermediates arise from activation of the methine group of the PLA backbone and insertion of O2. They subsequently degrade to carboxylic acids, anhydrides, and diketones. (61) Analogous to PET, on land and in the presence of O2, thermal-oxidative degradation occurs through a free-radical mechanism and results in the similar product distribution to photo-oxidative degradation. (56,62)

Methods for Assessing Plastics Degradation

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The approaches reported for the analysis of plastics degradation can be grouped into methods associated with assessing the elimination of small molecules, methods which assess chemical changes (hydrophobicity, functional groups) in the polymer structure, and methods which record physical changes in materials properties (tensile strength, surface morphology, crystallinity, etc.).

Assessing Bond Cleavage

Mass Loss

The simplest and most direct way to quantify the extent of degradation of polymers involves measuring changes in their mass. Quantification of mass loss has been used to assess degradation in soil, (63−66) in compost, (67,68) and in microbially enriched lab settings. (28,69−71) Because degradation takes place at the surface, the rate of mass loss is closely related to (and is typically proportional to) the surface area of the plastic piece. (72,73) Partial conversion to small molecules (including but not limited to CO2 and H2O) and their resulting volatilization or solubilization leads to a reduction in the mass of nonvolatile or insoluble polymeric material. (74) However, the overall mass loss convolutes the liberation of small molecules with the flaking of larger, insoluble pieces, including microplastics (0.5- 5 mm) and mesoplastics (5–200 mm). (25,75) Our understanding of how plastics fragment and the generation of microplastics is far from complete. However, recent reports suggest that the shape of the plastic piece influences its fragmentation behavior in the ocean and that small pieces with low aspect ratios fragment faster because their isotropic motion inhibits biofilm development. (76)
Little or no mass loss may be observed in the initial phases of degradation. (77) Instead, the mass may actually increase at short exposure times due to oxygen incorporation and/or the attachment of microorganisms. (78,79) Clinging biomass and other debris can also accumulate in surface cracks and pits that develop during degradation. Thus, extremely long experimental times are usually necessary to obtain meaningful results. Since mass loss measurements alone are not easy to interpret or extrapolate, it is desirable to combine this method with some of the other analytical techniques described below. (80)

CO2 Evolution

CO2 is the ultimate fate of carbon under aerobic polymer degradation conditions (81−84) (although polyesters can produce some CO2 under anaerobic conditions). (85,86) Its formation is frequently used as an indicator of biological degradation. In anaerobic conditions, soluble carbon compounds are metabolized by methanogens or sulfate reducers, producing CH4 and CO2, respectively. (3,4) The polymer degradation rate is inferred by measuring the CO2 liberated during abiotic or biotic mineralization in a controlled environment. (87−89) CO2 can be quantified by trapping and titration methods (90) or by analytical techniques such as gas chromatography with thermal conductivity detection (GC-TCD) (84) and IR spectroscopy. (91) The CO2 yield is defined as in eq 1:
(1)
where nCO2,test is the total accumulated amount of CO2 product from polymer degradation, nCO2,control is the amount of CO2 released in a blank experiment, and nCO2,theoretical is the total amount of CO2 that would be liberated by complete mineralization of the polymer sample. (92) However, at short time scales, it is unlikely that polymer carbon is fully oxidized to CO2. Therefore, the use of CO2 evolution as a probe to measure the kinetics of polymer degradation must be applied with caution.

Gel Permeation Chromatography (GPC)

This method reveals changes in the molecular weight, an important parameter in polymer degradation, by size exclusion. (89,93,94) Reduction in the molecular weight of partially degraded polymers has been observed during both biotic and abiotic degradation processes, which increase the concentration of chain ends and can lead to mineralization of the smaller polymer chains. (27) GPC requires the polymer to be dissolved in a carrier solvent, which for polyolefins requires high temperatures. Care must be taken to ensure that dissolution of the polymer or the high-temperature measurement conditions do not cause further degradation. (95)

Assessing Changes in Chemical Functionality

Chemical Analysis

Nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies can readily detect the presence and concentration of certain functional groups in polymers, even at low concentrations. (96−99) For example, 13C CP/MAS NMR reveals the formation of cross-linked polymer chains (via a peak at 39.7 ppm) upon γ-irradiation of HDPE. (100) IR is particularly valuable for detecting polar functional groups, such as ketones and ester carbonyls (intense peaks at ca. 1715 and 1735 cm–1, respectively), which are typical of oxidative degradation pathways. (101−104) The extent of oxidation during degradation can be quantified from the change in absorbance for the carbonyl stretch relative to the C–H stretching modes, (105,106) although a recent study suggests that this Carbonyl Index may be less accurate than other modes, such as methyl deformation in the case of PP, to quantify the extent of oxidation. (107)

Contact Angle

Changes in the surface density of polar functional groups, for example, those formed during oxidative degradation, cause changes in the surface energy, which are reflected in the contact angle with liquids. (108,109) Hydrophilic surfaces, with their high wettability, have higher surface energies and give lower contact angles with water. Thus, formation of polar functional groups in polymers due to environmental weathering effects (e.g., UV exposure) results in a decrease in contact angle. Increased hydrophilicity promotes the attachment of microorganisms to the polymer surface, further accelerating the degradation rate. (110)

Assessing Changes in Materials Properties

Dynamic Mechanical Analysis (DMA)

This technique is typically used to characterize polymer strength. Changes in the tensile strength and elongation at break are also indicators of physical deterioration during polymer degradation. (111,112) Changes in these mechanical properties are associated with the formation of cracks and pores at the surface, as well as a reduction in molecular weight. (113)

Thermal Analysis

This method generally involves heating or cooling a sample at a controlled rate while monitoring its physical characteristics. (114−116) Differential scanning calorimetry (DSC) measures heat capacity (Cp), melting temperature (Tm), and glass transition temperature (Tg). (117) A decrease in Tg during polymer degradation results from a decrease in the average chain length, due to the higher motility of shorter chains. (118) Thermal gravimetric analysis (TGA) records mass changes that occur upon heating. When coupled with product analysis, this method can provide information on the nature of the decomposition, such as oxidation or loss of volatiles, during thermal degradation. (119)

Surface Analysis

Surface modification of polymers during degradation can be detected with scanning electron microscopy (SEM) and atomic force microscopy (AFM). (120−122) These methods can directly image topographical changes at the polymer surface, such as the formation of holes and cracks, increases in roughness, or even attachment of microbes to the surface. (123) Typical changes in polymer morphology are visible as cracks and cavities; surface degradation and deterioration of HDPE films can be seen after 6 months in the marine environment. (124)

Rates of Plastics Degradation and Extrapolated Lifetimes

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Describing Degradation Rates

In the literature, the term degradation may include depolymerization, chemical modification, alteration of physical properties, overall mass loss by any and all mechanisms, or complete mineralization to CO2 and H2O. For the purposes of this study, we limit the definition of degradation to overall mass loss from the initial polymer piece. However, it must be noted that this definition is most appropriate for large plastic pieces. Recent studies suggest that surface ablation may be important for small plastic pieces in the marine environment. (125) Loss of microplastic or nanoplastic fragments reduces the initial mass, without changing the total amount of plastic present.
The polymer degradation rate, rd, is the differential mass loss per unit time
(2)
Since degradation occurs principally at exposed surfaces, we assume the degradation rate to be proportional to the surface area SA and the rate constant k to have dimensions kg s–1 m–2. Therefore, the rate of degradation depends not only on the intrinsic properties of the plastics (polymer type, molecular weight, fillers, etc.) and environmental conditions such as the temperature, presence of moisture and air, etc. but also on the extrinsic properties such as the size and shape of the material.
Samples with the same composition and mass but different surface areas can show very different rates. For example, a common HDPE produce bag has a thickness of 0.015 mm and dimensions of 25 cm × 38 cm, corresponding to a total (interior and exterior) surface area (SA) of ca. 3800 cm2 and a volume (V) of 2.9 cm3 (Figure 6a). A spherical HDPE resin bead with a radius of 8.8 mm (Figure 6b) represents the same polymer volume but with a SA of only 9.7 cm2. If degradation takes place only at the polymer surface, with a rate that is linearly proportional to the SA, (72) the initial degradation rate for the bead will be nearly 400 times slower than that of the bag.

Figure 6

Figure 6. Representative structures for (a) a section of a flat produce bag with total thickness h and (b) a sphere of radius r. The specific surface degradation rate (SSDR) is defined as the volume of material lost by removal of a layer of thickness Δd in a specified time.

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We define a surface degradation speed kd with dimensions m s–1, obtained by dividing k by the density ρ in kg m–3. The rate law becomes
(3)
The constant kd is the specific surface degradation rate (SSDR), and it resembles the linear growth rate in crystallography. (126) In contrast to a conventional reaction rate (i.e., the rate at which reactants are converted to products), the SSDR is a linear rate representing the perpendicular depth of plastic (Δd, Figure 6) degraded per unit time. For the thin film described above, the surface area (and the rate) may be considered essentially constant for most of the degradation time. If we also assume constant density, then integration and rearrangement yield simple algebraic solutions for the mass as a function of time and the time for complete degradation td (eqs 4 and 5)
(4)
(5)
Using a value of kd = 4.3 μm year–1 (median estimated degradation rate for HDPE in the marine environment, vide infra) leads to a predicted time for complete degradation of the HDPE film td of just 1.8 years.
The assumption of constant surface area is not appropriate for the HDPE bead. The decreases in radius r and SA with time are incorporated into eq 6, which is formulated in terms of the bead’s mass m:
(6)
Integration and rearrangement (also assuming constant density) give the algebraic solutions in eqs 7 and 8 for the mass as a function of time and the complete degradation time
(7)
(8)
Using eq 8 and the same value for kd, 4.3 μm year–1, the time required for complete degradation of the shrinking HDPE bead is estimated to be 2000 years. Of course, such values do not account for spontaneous fragmentation, resulting in a discontinuity where the surface area, and degradation rate, abruptly increase.
For plastic fibers, a cylinder is a better approximation of the shape. If the aspect ratio is large (i.e., radius r ≪ height h), we can assume SA ≈ 2 πrh. If we further assume that h is essentially invariant with time, we obtain the corresponding equations for mass loss and estimated complete degradation time shown in eqs 9 and 10
(9)
(10)
A cylindrical HDPE fiber of volume 2.9 cm3 (r = 2 mm, h = 23 cm, SA = 29 cm2) would require an estimated 465 years for complete degradation.
Thus, an HDPE film should degrade completely 260 times faster than a fiber of the same mass and crystallinity, and 1100 times faster than a comparable bead, in the absence of significant fragmentation, crystallization, or shape dependence of the SSDR. The ratios of the initial degradation rates (based on surface area ratios) are 390:3:1 for the film, fiber, and bead, respectively. However, the degradation rates of the fiber and the bead decrease as their radii shrink, so their “average” degradation rates are even lower. In addition, the exceedingly long extrapolations for the fiber and the bead result in errors with a far greater magnitude, in years, than the short extrapolation for the film. Thus, if the relative error in kd is 20%, the film will degrade in 1.8 ± 0.4 years, while the fiber will degrade in 465 ± 100 years and the bead in 2000 ± 400 years. We can also reasonably assume that kd will vary far more in the course of two millennia than it will during the first decade, making the actual error for the bead even larger. The shape-dependent degradation profiles are compared in Figure 7.

Figure 7

Figure 7. Comparison of predicted degradation profiles for HDPE pieces with the same mass, density, and SSDR but different shapes (thin film, fiber, and bead). The dashed lines correspond to extrapolations assuming constant surface area; the solid lines correspond to a model which assumes the radius, and therefore the surface area, decrease over time.

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Some additional points are worth mentioning. First, the surface roughness is unlikely to remain constant over time. Polymers that are melt processed may have initially smooth surfaces. However, as degradation proceeds, the surface will become pitted, and cracks will appear, increasing the surface area and hence the degradation rate. Such cracks can also lead to surface ablation and mass loss due to the release of microplastic fragments. Second, an amorphous polymer (whose surface abundance may or may not be the same as the bulk) will undergo faster degradation than a crystalline polymer, requiring the addition of a scaling factor to eqs 3 and 6 to represent the amorphous surface area fraction (aSA, 0 ≤ a ≤ 1). Once the amorphous polymer is eliminated, degradation in the remaining crystalline regions may be much slower. Furthermore, partial polymer degradation can lead to cross-linking and/or crystallization in the amorphous regions adjacent to crystallites, (107) thereby slowing degradation, although this effect cannot be quantified or modeled at this time.
Clearly, polymer degradation times in the environment should be tremendously sensitive to the shape and size of the material, in addition to its intrinsic chemical reactivity. Nevertheless, for plastics pieces of different sizes and compositions but with similar aspect ratios, it is possible to compare initial degradation rates via the SSDR, which is inversely proportional to the degradation time for a material whose surface area remains approximately constant. This assumption is discussed further below.

Analysis of Reported Degradation Rates

Of the hundreds of published papers screened for this Perspective, only 25 reported all of the information needed to calculate an SSDR (mass loss, sample dimensions, experiment duration). (71,79,127−149) The resulting 54 data points are organized in Figure 8. The data are arranged according to plastics type and degradation environment (Landfill/soil/compost, Marine, Biological, or Sunlight). While these categories are not completely orthogonal, they are useful to represent the four major categories of polymer degradation experiments that have been conducted: on land (without exposure to sunlight), in water (in freshwater or seawater with exposure to sunlight), in a lab using enzymes or microbes, or with exposure exclusively to sunlight and air. Data for plastics type 7 (“others”) includes the nominally biodegradable plastics PLA, polyhydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), Mater-Bi and polycaprolactone (PCL). The presence of a filler component (e.g., starch, PLA, etc.) or accelerating conditions (e.g., UV pretreatment, thermal pretreatment, or microbial incubation) in each study is noted. Two of the papers used to construct Figure 8 studied the degradation of blends of polypropylene (132) and polyethylene (149) with a biodegradable filler (5 or 10 wt % starch, respectively). The authors assumed that the filler indirectly increases the degradation rate of the plastic, possibly by causing the surface area of the plastic to increase as the starch component degrades. The problems of inferring plastics degradation rates in this way are discussed further below. Data for PET, PP, and PS degradation are sparse. Finally, only one report for PVC degradation met our criteria, regardless of the environment, and it found no measurable degradation after 32 years. (148)

Figure 8

Figure 8. Specific surface degradation rates for various plastics, in μm year–1. Vertical columns represent different environmental conditions (L, landfill/compost/soil; M, marine; B, biological; S, sunlight) and plastics types (represented by their resin identification codes). Plastics type 7, “others”, corresponds to various nominally biodegradable plastics. The range and average value for plastics types 1–6 are shown on the right as lines and squares, respectively, as well as for biodegradable “others”. Data points representing degradation rates that were unmeasurably slow are shown on the x-axis. Gray columns represent combinations for which no data were found.

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Considering only the nonzero values, the SSDR values for all plastics types, regardless of environment, vary over several orders of magnitude. Overall, the average reported values for accelerated degradation in each environmental condition are slightly higher than their nonaccelerated counterparts, as expected, although the differences may not be statistically significant. For accelerated degradations (filled circles, Figure 8), involving polymer pretreatment or a filler, the rates still vary by about an order of magnitude in most cases. The variation is especially noticeable for LDPE decomposing on land, where the range is a factor of 50. The highest reported accelerated SSDR for LDPE, 83 μm year–1, is for a blend with 20 wt % PLA decomposing under composting conditions (37 °C). (144) The lowest reported accelerated SSDR for LDPE is 3.7 μm year–1, measured after addition of P. aeruginosa to the soil. Interestingly, the SSDR for the LDPE/PLA blend (83 μm year–1) is higher than the SSDR for pure PLA (21 μm year–1), (138) both measured in composting conditions at 37 °C. However, the durations of the two experiments differed (28 days for the LDPE/PLA blend, compared to 365 days for the pure PLA). The discrepancy could also be due to differences in crystallinity, since blending can increase the volume fraction of amorphous regions, which show higher degradation rates. (57)
Extrapolated degradation rates for plastics blended with degradable fillers (e.g., starch) assume constant degradation rates, but this may be highly inaccurate. Such fillers are typically degraded by microorganisms first. Once the readily accessible filler is consumed, the remaining plastics degrades much more slowly through a combination of environmental degradation (e.g., photo-oxidative, hydrolysis, etc.) and microbial action. (150) The degradation should therefore be described as a multiphase kinetic process. (151) The variable durations and rates of these phases depend on the dimensions of the material, type and concentration of the filler, degradation environment and conditions, etc. Abiotic degradation of plastics may be enhanced relative to the unfilled polymer due to greatly increased surface area after removal of the filler. (150) Despite the convenience of shorter time scales, great caution should be used when interpreting degradation kinetics of blended polymers, and they should not be used to infer mechanisms and degradation rates for pure polymers.
Although biodegradable plastics such as PHB and PLA show large average SSDRs in compost and landfill conditions (59 and 21 μm year–1, respectively), their degradation in marine environments is significantly slower and may even be comparable to the degradation rates of their petrochemical counterparts. For example, the average SSDR of PLA in the marine environment, 7.5 μm year–1, is similar to the averages for HDPE (4.3 μm year–1) and LDPE (15 μm year–1). Although PLA and other “biodegradable” plastics are expected to fully degrade in industrial composting conditions (≥ 60 °C, and moist), the temperature in marine environments rarely exceeds 20 °C and therefore lacks the thermal energy for depolymerization. In soil conditions, however, the average SSDR of PLA is notably higher (21 μm year–1) than the corresponding values for petrochemical-based plastics (e.g., HDPE, 1.0 μm year–1). Temperatures in landfills have been reported to reach 80–100 °C, (152) which is sufficient to degrade plastics like PLA as long as moisture is present.

Extrapolated Degradation Times

Two methods have been widely used to estimate polymer lifetimes, defined here as the time required for complete degradation (>99% loss of the initial polymer mass): (1) Arrhenius extrapolation of accelerated aging result, and (2) extrapolation based on initial rates measured under environmentally relevant conditions. Both make important and often poorly justified assumptions which limit their validity.
The first method assumes that degradation rate constants have Arrhenius-like temperature dependences. (153) A polymer lifetime at ambient temperature is extrapolated from the faster degradation rates that are more readily measured at higher temperatures, ca. 25–200 °C. For example, the lifetime of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) at 25 °C in distilled water was predicted to be 300 d, based on extrapolation of decreases in tensile strength (154,155) and molecular weight measured at temperatures of 25–50 °C. (156) However, lifetime estimation by Arrhenius extrapolation assumes that the same degradation mechanism is operative at all relevant temperatures. For PE and PP, the Arrhenius plots are nonlinear, (157−159) suggesting a change in mechanism and/or rate-determining step with temperature. (160)
Arrhenius extrapolation is less useful for estimating biodegradation rates, because enzymatic degradation processes take place only under biologically relevant reaction conditions; they usually do not occur at elevated temperatures. Therefore, biodegradation lifetimes are generally predicted by the second method, using initial degradation rates obtained over prolonged measurement times instead. (148,161) For instance, the degradation rates of LDPE–starch blends were calculated by measuring weight loss as a function of time over a period of 125 days in composting conditions, and this rate was used to predict the complete degradation time using a linear extrapolation. (120) However, since relatively rapid biodegradation of the starch component should be followed by much slower degradation of the remaining LDPE, extrapolation based on initial measurements could be highly misleading. The accuracy of the method is compromised by the occurrence of several phases of degradation, with very different rates. (162) Thus, information on degradation rates for each component in a mixture is necessary to make accurate lifetime estimates.
Although extrapolation from initial rates is inaccurate, it is the simplest method to estimate plastics lifetimes in the environment. The approach requires knowledge of the rate law but does not account for dependence on the shape of the material. The shrinking core model (common in TGA studies of phase transformations) assumes that the volume, and hence the surface area, change as the reaction proceeds. (163) While it may be more realistic, it does not take into account changes in surface roughness, which may be considerable. Applications of the shrinking core model to plastics degradation have so far focused on high temperature catalytic degradation, which is not directly relevant to plastics degradation in the natural environment. (164,165)
Since experimental assessment of polymer degradation rate laws would require kinetic studies that last multiple decades or even longer, we assume a simple first-order dependence on SA (eq 3) and further assume that SA is constant over time (i.e., pseudo-zeroth-order behavior). However, we must point out that these assumptions have substantial consequences and can lead to extrapolation errors that represent decades or even centuries of additional lifetime. For example, a 100 μm thick film with a SSDR of 1 μm year–1 would require 100 years to degrade completely following a pseudo-zeroth-order rate law (constant surface area), while the same film would be 99% degraded in nearly 500 years if the reaction is first-order degradation. The error is much less important at lower extents of the reaction: using the same SSDR, pseudo-zeroth-order degradation would require 50 years to reach 50% completion, compared to 68 years for first-order degradation.
In addition, we note that the polymer is likely to have undergone extensive chemical and morphological changes as the reaction approaches high conversion. For example, disintegration into smaller pieces (e.g., microplastics) may alter the rate of reaction dramatically. Although little is known about the details of such processes, recent reports suggest that mechanical forces can cause the flaking of weathered, or oxidized, surfaces, leading to ablation, in addition to macrofragmentation. (166) Studies of several polymer types in a weathering chamber revealed exponential growth in the numbers of nanometer- and micron-sized particles released over several weeks. (125,167) However, since nearly two-thirds of microplastics in the ocean are estimated to originate from the washing of synthetic fabrics and the abrasion of rubber tires, (168) fragmentation of bottles, bags, pipes, and other large rigid pieces may not be major sources of microplastics and nanoplastics.
No extrapolation model is likely to describe the rates of complex phenomena involved in polymer degradation accurately. Consequently, we choose to compare degradation rates by calculating the first half-life, or the time in which the material loses 50% of its original mass. The values are still associated with large uncertainties but are probably much more accurate than attempting to extrapolate the time for “complete” degradation. Subsequent half-lives may be very different from the first half-life, depending on the rate law. In addition, the representativeness of literature values for degradation rates is unknown, and averaging them does not allow us to assess uncertainties in a statistically meaningful way. Nevertheless, in view of the public interest in estimated plastics lifetimes, we averaged the available SSDRs for each plastics type under each type of degradation condition in Figure 8 in order to estimate a first half-life for several common household plastic items, shown in Table 1. Ranges for these half-lives, obtained by multiplying SSDRs based on reported minimum and maximum values for degradation rates by the typical thickness of each plastics type for the specified application, highlight the large uncertainty in the extrapolation. The degradation was assumed to be unidirectional, proceeding from the exterior of the material toward the center. According to Table 1, common single-use plastics items like LDPE plastic bags and HDPE milk bottles and laundry detergent containers have estimated half-lives of 5 and 250 years, respectively, in landfill/compost/soil conditions. In the marine environment, the estimated half-lives are shorter, at 3.4 and 58 years, respectively. All values are subject to additional uncertainty because some data suggest much longer lifetimes, based on degradation rates that were immeasurably slow in both landfill/compost/soil and marine environments. For heavier industrial items like HDPE pipes, complete degradation may require thousands of years, regardless of the environment (we note that the durability of such items is often desirable for their intended purpose).
Table 1. Estimated Half-Lives of Common Plastic Itemsa
   Estimated Specific Surface Degradation Rate (min–max; μm year–1)bEstimated half-lives (min–max; year)
Plastics typeCommon applicationsTypical thickness (μm)Land (buried)Land (accel. by UV/heat)cMarineMarine (accel. by UV/heat)cLand (buried)Land (accel. by UV/heat)cMarineMarine (accel. by UV/heat)c
1. PETSingle-use water bottle5000––110>2500d––2.3
2. HDPEPlastic bottles5001.0 (0.91–1.1)1.3 (0.55–2.6)4.3 (0–11)9.5 (4.5–22)250 (230–280)190 (95–460)58 (23 to >2500)26 (12–55)
2. HDPEPipes10,0001.0 (0.91–1.1)1.3 (0.55–2.6)4.3 (0–11)9.5 (4.5–22)5000 (4600–5500)3900 (1900–9000)1200 (450 to >2500)530 (230–1100)
3. PVCPipes10,0000–––>2500d–––
4. LDPEPlastic bags1001122 (1.6–83)15 (0–37)10 (9.0–12)4.62.3 (0.6–32)3.4 (1.4 to >2500)5 (4.2–5.5)
5. PPFood storage container800–0.517.54.6–7805387
6. PSInsulating packaging20,0000–––>2500d–––
7. OthersBiodegradable plastic bag100270 (20–1400)32016 (7.5–29)1800.19 (0.035–2.5)0.163.1 (1.7–6.7)0.29
a

Half-life refers to conversion of the first 50% of the polymer mass, assuming pseudo-zeroth-order kinetics (i.e., invariant SA). According to eq 10, assuming cylindrical geometry and decreasing radius (but not height) over time predicts half-lives that are twice as long. Entries shown as (−) correspond to conditions for which no published data were found. Values in parentheses correspond to the range based on published reports. All values were rounded to two significant figures.

b

Values of 0 μm year–1 correspond to reports in which no degradation was observed; however it is likely that the duration of the experiment was too short to measure an appreciable weight loss. These values were included in calculations of average degradation rates and in the corresponding time ranges for complete degradation.

c

Corresponds to data collected in the presence of a degradation accelerant (e.g., UV pretreatment, thermal pretreatment, or microbial incubation) and/or for plastics containing a rapidly degrading filler (e.g., starch, PLA, etc.).

d

>2500 indicates that the relevant studies detected no measurable degradation, possibly due to the duration of the experiment being too short, allowing only an estimated lower limit for the extrapolated degradation time. The value 2500 years was obtained by calculating a SSDR based on the sensitivity of the balance used in the study and extrapolating a half-life for the thinnest material (100 μm, ca. 2500 years).

In order to obtain estimated times for complete degradation, we can assume a constant rate of degradation, a constant surface area:volume ratio, a constant reaction order, uniform crystallinity, and a mechanism for microplastic degradation identical to that of the parent material. These assumptions make such estimates highly uncertain. Nevertheless, the complete degradation of an HDPE bottle is estimated to require 500 and 116 years in the land and marine environments, respectively.

Environmental Effects on Degradation Rates

Prolonged exposure to environmental factors such as moisture, heat, light, or microbial action causes polymers to be abraded into smaller pieces (eventually to microplastics) as well as cleaved into small molecules. (11) The effect of a particular environmental factor on the degradation rate depends strongly on the type of plastic. For example, some studies of petrochemical-based polymers show that degradation rates are lower in the marine environment compared to landfills. (169,170) The differences are typically attributed to lower ambient temperatures and low dissolved oxygen concentrations in the marine environment. (25) However, our literature analysis shows that average degradation rates for HDPE and LDPE are actually slightly higher in marine environments compared to degradation on land (Table 1), although the differences could be statistically insignificant due to the large uncertainties of the averages. The effects of lower temperatures and oxygen concentrations in the ocean may be outweighed by the more intense UV radiation, relative to a landfill.
In other situations, plastics exposed to sunlight on land can experience “heat buildup”, reaching temperatures higher than the surrounding air and experiencing accelerated degradation. (171) Temperatures in some landfills and industrial composters have been reported to reach 80–100 °C, (152) accelerating degradation rates provided sufficient oxygen and/or moisture are present for the thermal-oxidative degradation and hydrolysis pathways, respectively. For example, PLA undergoes ester hydrolysis under industrial composting conditions (≥60 °C), although it is very slow to degrade at lower temperatures. (56) Consequently, PLA appears to be just as recalcitrant as its petrochemical counterparts in marine environments, where temperatures are well below 60 °C (Figure 8).
Landfill/soil/compost conditions typically apply to buried materials that experience little solar UV radiation, hindering photodegradation. Biofouling can hinder the rate of photodegradation by decreasing sunlight penetration. (25,139,171) In the ocean, biofouling can also increase the overall density of plastic pieces, causing them to sink (172,173) (although some plastics, including PET, PVC, PLA, do not float anyway). (174−177) The process may be time dependent, as plastic debris has been observed to undergo repeated cycles of sinking and floating. After the fouled plastic debris sinks in the water column, it can undergo defouling due to the absence of sunlight needed to maintain the film, causing the density to decrease and the debris to resurface. (174) Such studies have been largely conducted on petrochemical-based plastics, but similar changes in buoyancy are expected to affect the degradation kinetics of biodegradable plastics as well. Interestingly, average photodegradation rates for “biodegradable” plastics do not differ much from those for petrochemical-based plastics.

Effects of Accelerating Conditions

UV Irradiation

Solar UV radiation is necessary to initiate photo-oxidation of most polymers, (37) which proceeds via a radical chain mechanism that results in bond cleavage and a decrease in molecular weight (see above). Shorter chains, often with oxygen-containing functional groups at the chain ends, are more prone to attack by microorganisms and mineralization due to their increased hydrophilicity (which enhances microbial adhesion). (178) Several experimental studies reported synergy between photo-oxidation and biodegradation of polyethylene. (179−181) In another study, the abundance of carbonyl groups in polyethylene increased upon exposure to UV radiation for 60 h, then decreased when the photo-oxidized polyethylene was subsequently incubated with microorganisms, suggesting microbial degradation. (182)

Transient Thermal Treatment

Moderate heating in air enhances rates of polyolefin oxidative degradation significantly. The increase in polymer hydrophilicity arising from incorporation of oxygen-containing functional groups facilitates surface attachment of microorganisms. (27,178) In a study conducted in a soil culture over 12 months, films of LDPE, HDPE, or PP that were thermally pretreated at 80 °C for 10 days showed enhanced biodegradation rates of 12, 4.5, and 2.7 μm year–1, respectively, compared to 6.3, 1.8, and 0.1 μm year–1, respectively, without thermal pretreatment. (130) In the marine environment, LDPE and HDPE films thermally pretreated at 80 °C in an oven for 10 days showed 4- to 7-fold increases in marine bacterial colonization compared to the untreated materials over six months. Higher mass losses were also observed for thermally pretreated LDPE and HDPE (17% and 5.5%, respectively), compared to the untreated materials (10% and 1%, respectively) over the same time period. (135)

Humidity

Elevated humidity levels accelerate polyester degradation by promoting hydrolysis. For example, chain scission of a PET in a plastic bottle was 5 times greater at 60 °C and 100% relative humidity compared to 45% relative humidity. However, at temperatures of 80 °C or higher, there was no significant increase in the rate of hydrolysis with increased humidity, since the rate of thermal-oxidative degradation outpaces that of hydrolysis at these elevated temperatures. (153) Humidity has also been shown to accelerate the photodegradation of PLA, (183) and polyolefins such as PE, (184) PP, (185) and PVC, (186) by promoting an increase in the concentration of hydroxyl radicals.

Conclusions

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Each year, 400 Mt of plastic waste is generated, of which 175 Mt enters landfills and the natural environment. (1) The amount of plastics that enters landfills and the environment is sufficient for rebuilding the currently standing Great Wall of China with a span of 6000 km (187) every 12 months. Despite this massive scale, the literature on plastics degradation under environmental conditions is disproportionately thin. Relatively little has been reported in the literature regarding the following: How quickly do plastics degrade in the environment? What are the degradation pathways? What are the factors affecting the degradation processes? What are the degradation byproducts? When juxtaposed, existing literature on plastics degradation rates shows a wide range of numbers.
Furthermore, the various degradation byproducts may include larger molecules, as well as microscale and nanoscale plastics with increased bioavailability and associated potential adverse impacts to ecosystems throughout the food web. Additional research is needed to better understand the mechanisms of polymer degradation under various environmental conditions. Given the long life-span of plastics, methods to use short-term experimental results to predict long-term degradation pathways and methods to simulate degradation, for example, using modern computational chemistry techniques, must also be further refined and vetted.
Our review highlights the need to standardize the metrics and the experimental conditions used in plastics degradation research. Studies on plastics degradation often omit key information, such as the temperature, microbial loading, and the size and shape of the sample, which are essential to interpret the results properly. These deficiencies, combined with the sparseness of the literature, limit the ability to conduct meaningful meta-analyses. The SSDR metric proposed here is a step in that direction; however, it only measures how much material, or mass, is lost from the sample. Therefore, neither structural changes nor the extent of mineralization of plastics can be addressed using SSDR alone. Furthermore, extrapolations are fraught with uncertainty. We anticipate the need for development and implementation of multiple well-defined standard metrics to quantify the rates of polymer degradation in the environment.

Author Information

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  • Corresponding Authors
  • Authors
    • Ali Chamas - Department of Chemistry & Biochemistry, , and , University of California, Santa Barbara, Santa Barbara, California 93106, United States;  Orcidhttp://orcid.org/0000-0001-8739-8880
    • Hyunjin Moon - Department of Chemical Engineering, , and , University of California, Santa Barbara, Santa Barbara, California 93106, United States
    • Jiajia Zheng - Bren School of Environmental Science and Management, , and , University of California, Santa Barbara, Santa Barbara, California 93106, United States
    • Yang Qiu - Bren School of Environmental Science and Management, , and , University of California, Santa Barbara, Santa Barbara, California 93106, United States
    • Tarnuma Tabassum - Department of Chemistry & Biochemistry, , and , University of California, Santa Barbara, Santa Barbara, California 93106, United States
    • Jun Hee Jang - Department of Chemical Engineering, , and , University of California, Santa Barbara, Santa Barbara, California 93106, United States;  Orcidhttp://orcid.org/0000-0002-1879-0544
    • Mahdi Abu-Omar - Department of Chemistry & Biochemistry  and  Department of Chemical Engineering, , and , University of California, Santa Barbara, Santa Barbara, California 93106, United States;  Orcidhttp://orcid.org/0000-0002-4412-1985
  • Notes
    The authors declare no competing financial interest.

Biographies

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Ali Chamas

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Ali Chamas is completing his Ph.D. in Chemistry at the University of California, Santa Barbara. He received his B.S. in biochemistry also from the University of California, Santa Barbara. His research focuses on kinetic and mechanistic studies of catalytic lignin depolymerization and recently plastic waste upcycling. Ali has been the recipient of several awards and fellowships, including the U.S. Department of Energy, Office of Science Graduate Student Research Program for in-residence research at the Pacific Northwest National Laboratory. The UC Santa Barbara Crossroads Fellowship has allowed him to work in a multidisciplinary team on understanding plastic waste degradation.

Hyunjin Moon

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Hyunjin Moon is currently a Ph.D. student in chemical engineering at the University of California, Santa Barbara. He received his M.S. in mechanical engineering (2016) at Seoul National University, Korea. His Master’s thesis focused on electrochemical synthesis of metal/polymer-based nanomaterials for energy storage devices. Currently, his Ph.D. research investigates valorizing lignocellulosic biomass by controlling polarities at solid–liquid interfaces. During his graduate career, he has been recognized with several fellowships including the Global Ph.D. fellowship and UC-RWTH IRES fellowship. His expertise lies in synthesis of nanoscale and microscale materials for efficient catalytic conversions and their characterization through physicochemical methods.

Jiajia Zheng

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Jiajia Zheng is currently a Ph.D. student at the Bren School of Environmental Science and Management at the University of California, Santa Barbara. She obtained her Master’s degree in environmental engineering from Fudan University, China. Jiajia’s research focuses on the assessment of technological opportunities for carbon mitigation. As part of the research, her recent publication in Nature Climate Change addresses the strategies to reduce the global carbon footprint of plastics. (9)

Yang Qiu

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Yang Qiu is a Ph.D. student at the Bren School of Environmental Science and Management at the University of California, Santa Barbara. Yang has been working in the field of industrial ecology for his Ph.D., and his research focuses on understanding the economic and environmental trade-offs of low-carbon transitions in the energy system. Additionally, he is also interested in understanding the implication of technology development on consumption and circularity of critical metals.

Tarnuma Tabassum

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Tarnuma Tabassum is currently a Ph.D. candidate in the Department of Chemistry and Biochemistry at the University of California, Santa Barbara. Her research interests lie in the surface characterization of supported catalytic materials using magnetic resonance spectroscopy. Specifically, she is working towards using electron paramagnetic resonance to investigate the spatial distribution of hydroxyl groups on silica and applying solid state nuclear magnetic resonance in combination with dynamic nuclear polarization to elucidate the structural characteristics of P-modified zeolites and alumina-supported vanadia. As an IRES and Chateaubriand Fellow, she has had the opportunity to conduct research as a visiting student at RWTH Aachen (Germany) and the University of Lille (France), respectively. The Crossroads Fellowship Program allowed her to broaden her scope of knowledge by offering an interdisciplinary platform that merges chemistry, chemical engineering, and environmental sciences, such that she could explore an area different from her primary research investigation.

Jun Hee Jang

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Jun Hee Jang is currently a Ph.D. candidate in chemical engineering at the University of California, Santa Barbara (UCSB). Prior to joining UCSB, he received a M.S. at Seoul National University with a research project focused on the microscale- and nanoscale-patterned membranes for wastewater treatment. In the Abu-Omar research group at UCSB, his research project aims at developing renewable materials for energy and environmental applications. His research areas include the synthesis of inorganic heterogeneous catalysts (metal and metal oxide catalysts), materials characterization with a variety of analytical techniques, biomass valorization, optimization of catalytic reactions, and polymer degradation.

Mahdi Abu-Omar

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Mahdi Abu-Omar holds the Duncan and Suzanne Mellichamp Chair in Green Chemistry at the University of California, Santa Barbara. His research accomplishments include selective conversion of biomass lignin to biophenols and the creation of renewable plastics based on lignin. He has authored/coauthored nearly 200 original research articles in peer-reviewed scientific journals, supervised more than 40 Ph.D. students, and held faculty appointments at Purdue University and the University of California, Los Angeles (UCLA). Mahdi is the founder of Spero Renewables, a clean tech company that provides cost-effective and renewable substitutes to petrochemicals (sperorenewables.com/). Mahdi was elected Fellow of the American Association for Advancement of Science (AAAS) in 2012 and was a Senior Fulbright Fellow at the Weismann Institute in 2008. Dr. Abu-Omar completed a Ph.D. from Iowa State University (1996) and a postdoc from Caltech.

Susannah L. Scott

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Susannah L. Scott holds the Duncan and Suzanne Mellichamp Chair in Sustainable Catalysis at the University of California, Santa Barbara, and is jointly appointed as a Distinguished Professor in both the Departments of Chemical Engineering and Chemistry and Biochemistry. She earned a B.S. in chemistry from the University of Alberta (Canada) and a Ph.D. in inorganic chemistry from Iowa State University. Her research interests include the design of heterogeneous catalysts with well-defined active sites for the efficient conversion of conventional and emerging feedstocks, as well as environmental catalysts to promote air and water quality. At the University of California, Santa Barbara, she founded the interdisciplinary Mellichamp Academic Initiative in Sustainable Manufacturing and Product Design.

Sangwon Suh

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Sangwon Suh is a Professor at the Bren School of Environmental Science and Management at the University of California, Santa Barbara, where he also serves as the director of the Chemical Life Cycle Collaborative (CLiCC) that developed an online tool for sustainability assessment of chemicals (clicc.net). He earned a B.E. in civil and environmental engineering and an M.E. in environmental engineering from Ajou University (South Korea) and a Ph.D. in industrial ecology from Leiden University (The Netherlands). His research focuses on the interface between technologies and the environment. In particular, his work concerns the sustainability of human–nature complexity through understanding the materials and energy exchanges between them.

Acknowledgments

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The authors acknowledge funding from the NSF (DGE-1633764 and CBET-1604095). H.M., J.Z., and Y.Q. thank the UC Santa Barbara’s Mellichamp Academic Initiative in Sustainability for partial fellowship support. Y.Q., J.Z., and S.S. are supported by the U.S. Environmental Protection Agency’s Science to Achieve Results (STAR) Program under Grant No. 83557907.

References

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    A review. One of the most ubiquitous and long-lasting recent changes to the surface of our planet is the accumulation and fragmentation of plastics. Within just a few decades since mass prodn. of plastic products commenced in the 1950s, plastic debris has accumulated in terrestrial environments, in the open ocean, on shorelines of even the most remote islands and in the deep sea. Annual clean-up operations, costing millions of pounds sterling, are now organized in many countries and on every continent. Here we document global plastics prodn. and the accumulation of plastic waste. While plastics typically constitute approx. 10% of discarded waste, they represent a much greater proportion of the debris accumulating on shorelines. Mega- and macro-plastics have accumulated in the highest densities in the Northern Hemisphere, adjacent to urban centers, in enclosed seas and at water convergences (fronts). We report lower densities on remote island shores, on the continental shelf seabed and the lowest densities (but still a documented presence) in the deep sea and Southern Ocean. The longevity of plastic is estd. to be hundreds to thousands of years, but is likely to be far longer in deep sea and non-surface polar environments. Plastic debris poses considerable threat by choking and starving wildlife, distributing non-native and potentially harmful organisms, absorbing toxic chems. and degrading to micro-plastics that may subsequently be ingested. Well-established annual surveys on coasts and at sea have shown that trends in mega- and macro-plastic accumulation rates are no longer uniformly increasing: rather stable, increasing and decreasing trends have all been reported. The av. size of plastic particles in the environment seems to be decreasing, and the abundance and global distribution of micro-plastic fragments have increased over the last few decades. However, the environmental consequences of such microscopic debris are still poorly understood.
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    Cole, M.; Lindeque, P.; Halsband, C.; Galloway, T. S. Microplastics as Contaminants in the Marine Environment: A Review. Mar. Pollut. Bull. 2011, 62 (12), 2588– 2597,  DOI: 10.1016/j.marpolbul.2011.09.025
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    Microplastics as contaminants in the marine environment: A review
    Cole, Matthew; Lindeque, Pennie; Halsband, Claudia; Galloway, Tamara S.
    Marine Pollution Bulletin (2011), 62 (12), 2588-2597CODEN: MPNBAZ; ISSN:0025-326X. (Elsevier Ltd.)
    A review. Since the mass prodn. of plastics began in the 1940s, microplastic contamination of the marine environment was a growing problem. Here, a review of the literature was conducted with the following objectives: (1) to summarize the properties, nomenclature and sources of microplastics; (2) to discuss the routes by which microplastics enter the marine environment; (3) to evaluate the methods by which microplastics are detected in the marine environment; (4) to assess spatial and temporal trends of microplastic abundance; and (5) to discuss the environmental impact of microplastics. Microplastics are both abundant and widespread within the marine environment, found in their highest concns. along coastlines and within mid-ocean gyres. Ingestion of microplastics was demonstrated in a range of marine organisms, a process which may facilitate the transfer of chem. additives or hydrophobic waterborne pollutants to biota. The authors conclude by highlighting key future research areas for scientists and policymakers.
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    Thompson, R. C.; Swan, S. H.; Moore, C. J.; vom Saal, F. S. Our Plastic Age. Philos. Trans. R. Soc., B 2009, 364 (1526), 1973– 1976,  DOI: 10.1098/rstb.2009.0054
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    Our plastic age
    Thompson Richard C; Swan Shanna H; Moore Charles J; vom Saal Frederick S
    Philosophical transactions of the Royal Society of London. Series B, Biological sciences (2009), 364 (1526), 1973-6 ISSN:.
    Within the last few decades, plastics have revolutionized our daily lives. Globally we use in excess of 260 million tonnes of plastic per annum, accounting for approximately 8 per cent of world oil production. In this Theme Issue of Philosophical Transactions of the Royal Society, we describe current and future trends in usage, together with the many benefits that plastics bring to society. At the same time, we examine the environmental consequences resulting from the accumulation of waste plastic, the effects of plastic debris on wildlife and concerns for human health that arise from the production, usage and disposal of plastics. Finally, we consider some possible solutions to these problems together with the research and policy priorities necessary for their implementation.
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    Advancing Sustainable Materials Management: 2014 Fact Sheet; U.S. Environmental Protection Agency, 2016.
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    Zheng, J.; Suh, S. Strategies to Reduce the Global Carbon Footprint of Plastics. Nat. Clim. Change 2019, 9 (5), 374– 378,  DOI: 10.1038/s41558-019-0459-z
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    Eriksen, M.; Maximenko, N.; Thiel, M.; Cummins, A.; Lattin, G.; Wilson, S.; Hafner, J.; Zellers, A.; Rifman, S. Plastic Pollution in the South Pacific Subtropical Gyre. Mar. Pollut. Bull. 2013, 68 (1-2), 71– 76,  DOI: 10.1016/j.marpolbul.2012.12.021
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    Plastic pollution in the South Pacific subtropical gyre
    Eriksen, Marcus; Maximenko, Nikolai; Thiel, Martin; Cummins, Anna; Lattin, Gwen; Wilson, Stiv; Hafner, Jan; Zellers, Ann; Rifman, Samuel
    Marine Pollution Bulletin (2013), 68 (1-2), 71-76CODEN: MPNBAZ; ISSN:0025-326X. (Elsevier Ltd.)
    Plastic marine pollution in the open ocean of the southern hemisphere is largely undocumented. Here, we report the result of a (4489 km) 2424 nautical mile transect through the South Pacific subtropical gyre, carried out in March-Apr. 2011. Neuston samples were collected at 48 sites, averaging 50 nautical miles apart, using a manta trawl lined with a 333 μm mesh. The transect bisected a predicted accumulation zone assocd. with the convergence of surface currents, driven by local winds. The results show an increase in surface abundance of plastic pollution as we neared the center and decrease as we moved away, verifying the presence of a garbage patch. The av. abundance and mass was 26,898 particles km-2 and 70.96 g km-2, resp. 88.8% of the plastic pollution was found in the middle third of the samples with the highest value of 396,342 particles km-2 occurring near the center of the predicted accumulation zone.
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    Law, K. L.; Morét-Ferguson, S. E.; Goodwin, D. S.; Zettler, E. R.; DeForce, E.; Kukulka, T.; Proskurowski, G. Distribution of Surface Plastic Debris in the Eastern Pacific Ocean from an 11-Year Data Set. Environ. Sci. Technol. 2014, 48 (9), 4732– 4738,  DOI: 10.1021/es4053076
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    11
    Distribution of Surface Plastic Debris in the Eastern Pacific Ocean from an 11-Year Data Set
    Law, Kara Lavender; Moret-Ferguson, Skye E.; Goodwin, Deborah S.; Zettler, Erik R.; DeForce, Emelia; Kukulka, Tobias; Proskurowski, Giora
    Environmental Science & Technology (2014), 48 (9), 4732-4738CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    We present an extensive survey of floating plastic debris in the eastern North and South Pacific Oceans from more than 2500 plankton net tows conducted between 2001 and 2012. From these data we defined an accumulation zone (25 to 41°N, 130 to 180°W) in the North Pacific subtropical gyre that closely corresponds to centers of accumulation resulting from the convergence of ocean surface currents predicted by several oceanog. numerical models. Maximum plastic concns. from individual surface net tows exceeded 106 pieces km-2, with concns. decreasing with increasing distance from the predicted center of accumulation. Outside the North Pacific subtropical gyre the median plastic concn. was 0 pieces km-2. We were unable to detect a robust temporal trend in the data set, perhaps because of confounded spatial and temporal variability. Large spatiotemporal variability in plastic concn. causes order of magnitude differences in summary statistics calcd. over short time periods or in limited geog. areas. Utilizing all available plankton net data collected in the eastern Pacific Ocean (17.4°S to 61.0°N; 85.0 to 180.0°W) since 1999, we estd. a min. of 21 290 t of floating microplastic.
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    Kaiser, J. The Dirt on Ocean Garbage Patches. Science 2010, 328 (5985), 1506– 1506,  DOI: 10.1126/science.328.5985.1506
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    The dirt on ocean garbage patches
    Kaiser Jocelyn
    Science (New York, N.Y.) (2010), 328 (5985), 1506 ISSN:.
    There is no expanded citation for this reference.
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    Jambeck, J. R.; Geyer, R.; Wilcox, C.; Siegler, T. R.; Perryman, M.; Andrady, A.; Narayan, R.; Law, K. L. Plastic Waste Inputs from Land into the Ocean. Science 2015, 347 (6223), 768– 771,  DOI: 10.1126/science.1260352
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    Plastic waste inputs from land into the ocean
    Jambeck, Jenna R.; Geyer, Roland; Wilcox, Chris; Siegler, Theodore R.; Perryman, Miriam; Andrady, Anthony; Narayan, Ramani; Law, Kara Lavender
    Science (Washington, DC, United States) (2015), 347 (6223), 768-771CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Plastic debris in the marine environment is widely documented, but the quantity of plastic entering the ocean from waste generated on land is unknown. By linking worldwide data on solid waste, population d., and economic status, we estd. the mass of land-based plastic waste entering the ocean. We calc. that 275 million metric tons (MT) of plastic waste was generated in 192 coastal countries in 2010, with 4.8 to 12.7 million MT entering the ocean. Population size and the quality of waste management systems largely det. which countries contribute the greatest mass of uncaptured waste available to become plastic marine debris. Without waste management infrastructure improvements, the cumulative quantity of plastic waste available to enter the ocean from land is predicted to increase by an order of magnitude by 2025.
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    Schmidt, C.; Krauth, T.; Wagner, S. Export of Plastic Debris by Rivers into the Sea. Environ. Sci. Technol. 2017, 51 (21), 12246– 12253,  DOI: 10.1021/acs.est.7b02368
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    Export of Plastic Debris by Rivers into the Sea
    Schmidt, Christian; Krauth, Tobias; Wagner, Stephan
    Environmental Science & Technology (2017), 51 (21), 12246-12253CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    A review. A substantial fraction of marine plastic debris originates from land-based sources and rivers potentially act as a major transport pathway for all sizes of plastic debris. We analyzed a global compilation of data on plastic debris in the water column across a wide range of river sizes. Plastic debris loads, both microplastic (particles <5 mm) and macroplastic (particles >5 mm) are pos. related to the mismanaged plastic waste (MMPW) generated in the river catchments. This relation is nonlinear where large rivers with population-rich catchments delivering a disproportionately higher fraction of MMPW into the sea. The 10 top-ranked rivers transport 88-95% of the global load into the sea. Using MMPW as a predictor we calc. the global plastic debris inputs form rivers into the sea to range between 0.41 and 4×106 t/y. Due to the limited amt. of data high uncertainties were expected and ultimately confirmed. The empirical anal. to quantify plastic loads in rivers can be extended easily by addnl. potential predictors other than MMPW, for example, hydrol. conditions.
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    Rios, L. M.; Jones, P. R.; Moore, C.; Narayan, U. V. Quantitation of Persistent Organic Pollutants Adsorbed on Plastic Debris from the Northern Pacific Gyre’s “Eastern Garbage Patch.. J. Environ. Monit. 2010, 12 (12), 2226– 2236,  DOI: 10.1039/c0em00239a
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    Quantitation of persistent organic pollutants adsorbed on plastic debris from the Northern Pacific Gyre's "eastern garbage patch"
    Rios, Lorena M.; Jones, Patrick R.; Moore, Charles; Narayan, Urja V.
    Journal of Environmental Monitoring (2010), 12 (12), 2226-2236CODEN: JEMOFW; ISSN:1464-0325. (Royal Society of Chemistry)
    Floating marine plastic debris was found to function as solid-phase extn. media, adsorbing and concg. pollutants out of the water column. Plastic debris was collected in the North Pacific Gyre, extd., and analyzed for 36 individual PCB congeners, 17 organochlorine pesticides, and 16 EPA priority PAHs. Over 50% contained PCBs, 40% contained pesticides, and nearly 80% contained PAHs. The PAHs included 2, 3 and 4 ring congeners. The PCBs were primarily CB-11, 28, 44, 52, 66, and 101. The pesticides detected were primarily p,p-DDTs and its metabolite, o,p-DDD, as well as BHC (a,b,g and d). The concns. of pollutants found ranged from a few ppb to thousands of ppb. The types of PCBs and PAHs found were similar to those found in marine sediments. However, these plastic particles were mostly polyethylene which is resistant to degrdn. and although functioning similarly to sediments in accumulating pollutants, these had remained on or near the ocean surface. Particles collected included intact plastic items as well as many pieces less than 5 mm in size.
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    Fisner, M.; Taniguchi, S.; Moreira, F.; Bícego, M. C.; Turra, A. Polycyclic Aromatic Hydrocarbons (PAHs) in Plastic Pellets: Variability in the Concentration and Composition at Different Sediment Depths in a Sandy Beach. Mar. Pollut. Bull. 2013, 70 (1), 219– 226,  DOI: 10.1016/j.marpolbul.2013.03.008
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    Polycyclic aromatic hydrocarbons (PAHs) in plastic pellets: Variability in the concentration and composition at different sediment depths in a sandy beach
    Fisner, Mara; Taniguchi, Satie; Moreira, Fabiana; Bicego, Marcia C.; Turra, Alexander
    Marine Pollution Bulletin (2013), 70 (1-2), 219-226CODEN: MPNBAZ; ISSN:0025-326X. (Elsevier Ltd.)
    Plastic pellets have the ability to adsorb org. pollutants such as PAHs. This study analyzed the variability in the concn. and compn. of PAHs on plastic pellets sampled up to 1 m deep in the sediment of a sandy beach. The toxic potential of PAHs was analyzed, and the possible sources of contamination are discussed. The total PAHs varied, with the highest concns. in the surface layer; the priority PAHs showed a different pattern. PAHs at greater depths did not reach toxicity levels above the PEL. The compn. of PAHs differed between pellets from the shallower and from deeper sediment layers, and was suggested a mixt. of sources. These results provided the first information on the depth distribution of PAHs in sandy beaches, assocd. with plastic pellets; and evidenced the potential environmental risk. Similarly to the abundance of pellets, the toxic potential is underestimated in surface samples.
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    Gall, S. C.; Thompson, R. C. The Impact of Debris on Marine Life. Mar. Pollut. Bull. 2015, 92 (1), 170– 179,  DOI: 10.1016/j.marpolbul.2014.12.041
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    The impact of debris on marine life
    Gall, S. C.; Thompson, R. C.
    Marine Pollution Bulletin (2015), 92 (1-2), 170-179CODEN: MPNBAZ; ISSN:0025-326X. (Elsevier Ltd.)
    Marine debris is listed among the major perceived threats to biodiversity, and is cause for particular concern due to its abundance, durability and persistence in the marine environment. An extensive literature search reviewed the current state of knowledge on the effects of marine debris on marine organisms. 340 original publications reported encounters between organisms and marine debris and 693 species. Plastic debris accounted for 92% of encounters between debris and individuals. Numerous direct and indirect consequences were recorded, with the potential for sublethal effects of ingestion an area of considerable uncertainty and concern. Comparison to the IUCN Red List highlighted that at least 17% of species affected by entanglement and ingestion were listed as threatened or near threatened. Hence where marine debris combines with other anthropogenic stressors it may affect populations, trophic interactions and assemblages.
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    How Long Does It Take for a Plastic Bag to Break down? Toronto Environmental Alliance. https://www.torontoenvironment.org/how_long_does_it_take_for_a_plastic_bag_to_break_down (accessed Nov 23, 2018).
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    Lapidos, J. Do Plastic Bags Really Take 500 Years to Break down in a Landfill? Slate. https://slate.com/news-and-politics/2007/06/do-plastic-bags-really-take-500-years-to-break-down-in-a-landfill.html (accessed Nov 23, 2018).
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    Pocket Guide to Marine Debris. The Ocean Conservancy. https://www.mass.gov/files/documents/2016/08/pq/pocket-guide-2003.pdf (accessed Nov 23, 2018).
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    How Long Does It Take a Plastic Bottle to Biodegrade? Postconsumers , 2011. https://www.postconsumers.com/2011/10/31/how-long-does-it-take-a-plastic-bottle-to-biodegrade/ (accessed Nov 23, 2018).
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    Ward, C. P.; Armstrong, C. J.; Walsh, A. N.; Jackson, J. H.; Reddy, C. M. Sunlight Converts Polystyrene to Carbon Dioxide and Dissolved Organic Carbon. Environ. Sci. Technol. Lett. 2019, 6, 669,  DOI: 10.1021/acs.estlett.9b00532
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    Sunlight Converts Polystyrene to Carbon Dioxide and Dissolved Organic Carbon
    Ward, Collin P.; Armstrong, Cassia J.; Walsh, Anna N.; Jackson, Julia H.; Reddy, Christopher M.
    Environmental Science & Technology Letters (2019), 6 (11), 669-674CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)
    Numerous international governmental agencies that steer policy assume that polystyrene persists in the environment for millennia. Here, we show that polystyrene is completely photochem. oxidized to carbon dioxide and partially photochem. oxidized to dissolved org. carbon. Lifetimes of complete and partial photochem. oxidn. are estd. to occur on centennial and decadal time scales, resp. These lifetimes are orders of magnitude faster than biol. respiration of polystyrene and thus challenge the prevailing assumption that polystyrene persists in the environment for millennia. Additives disproportionately altered the relative susceptibility to complete and partial photochem. oxidn. of polystyrene and accelerated breakdown by shifting light absorbance and reactivity to longer wavelengths. Polystyrene photochem. oxidn. increased approx. 25% with a 10° increase in temp., indicating that temp. is unlikely to be a primary driver of photochem. oxidn. rates. Collectively, sunlight exposure appears to be a governing control of the environmental persistence of polystyrene, and thus, photochem. loss terms need to be included in mass balance studies on the environmental fate of polystyrene. The exptl. framework presented herein should be applied to a diverse array of polymers and formulations to establish how general these results are for other plastics in the environment.
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    Gewert, B.; Plassmann, M. M.; MacLeod, M. Pathways for Degradation of Plastic Polymers Floating in the Marine Environment. Environ. Sci. Process. Impacts 2015, 17 (9), 1513– 1521,  DOI: 10.1039/C5EM00207A
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    Pathways for degradation of plastic polymers floating in the marine environment
    Gewert, Berit; Plassmann, Merle M.; MacLeod, Matthew
    Environmental Science: Processes & Impacts (2015), 17 (9), 1513-1521CODEN: ESPICZ; ISSN:2050-7895. (Royal Society of Chemistry)
    Each year vast amts. of plastic are produced worldwide. When released to the environment, plastics accumulate, and plastic debris in the world's oceans is of particular environmental concern. More than 60% of all floating debris in the oceans is plastic and amts. are increasing each year. Plastic polymers in the marine environment are exposed to sunlight, oxidants and phys. stress, and over time they weather and degrade. The degrdn. processes and products must be understood to detect and evaluate potential environmental hazards. Some attention has been drawn to additives and persistent org. pollutants that sorb to the plastic surface, but so far the chems. generated by degrdn. of the plastic polymers themselves have not been well studied from an environmental perspective. In this paper we review available information about the degrdn. pathways and chems. that are formed by degrdn. of the six plastic types that are most widely used in Europe. We extrapolate that information to likely pathways and possible degrdn. products under environmental conditions found on the oceans' surface. The potential degrdn. pathways and products depend on the polymer type. UV-radiation and oxygen are the most important factors that initiate degrdn. of polymers with a carbon-carbon backbone, leading to chain scission. Smaller polymer fragments formed by chain scission are more susceptible to biodegrdn. and therefore abiotic degrdn. is expected to precede biodegrdn. When heteroatoms are present in the main chain of a polymer, degrdn. proceeds by photo-oxidn., hydrolysis, and biodegrdn. Degrdn. of plastic polymers can lead to low mol. wt. polymer fragments, like monomers and oligomers, and formation of new end groups, esp. carboxylic acids.
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    Andrady, A. L. Microplastics in the Marine Environment. Mar. Pollut. Bull. 2011, 62 (8), 1596– 1605,  DOI: 10.1016/j.marpolbul.2011.05.030
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    Microplastics in the marine environment
    Andrady, Anthony L.
    Marine Pollution Bulletin (2011), 62 (8), 1596-1605CODEN: MPNBAZ; ISSN:0025-326X. (Elsevier Ltd.)
    This review discusses the mechanisms of generation and potential impacts of microplastics in the ocean environment. Weathering degrdn. of plastics on the beaches results in their surface embrittlement and microcracking, yielding microparticles that are carried into water by wind or wave action. Unlike inorg. fines present in sea water, microplastics conc. persistent org. pollutants (POPs) by partition. The relevant distribution coeffs. for common POPs are several orders of magnitude in favor of the plastic medium. Consequently, the microparticles laden with high levels of POPs can be ingested by marine biota. Bioavailability and the efficiency of transfer of the ingested POPs across trophic levels are not known and the potential damage posed by these to the marine ecosystem has yet to be quantified and modelled. Given the increasing levels of plastic pollution of the oceans it is important to better understand the impact of microplastics in the ocean food web.
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    Lucas, N.; Bienaime, C.; Belloy, C.; Queneudec, M.; Silvestre, F.; Nava-Saucedo, J.-E. Polymer Biodegradation: Mechanisms and Estimation Techniques – A Review. Chemosphere 2008, 73 (4), 429– 442,  DOI: 10.1016/j.chemosphere.2008.06.064
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    Polymer biodegradation: Mechanisms and estimation techniques
    Lucas, Nathalie; Bienaime, Christophe; Belloy, Christian; Queneudec, Michele; Silvestre, Francoise; Nava-Saucedo, Jose-Edmundo
    Chemosphere (2008), 73 (4), 429-442CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)
    A review. Within the frame of the sustainable development, new materials are being conceived to increase their biodegradability properties. Biodegrdn. is considered to take place throughout 3 stages: biodeterioration, biofragmentation, and assimilation, without neglect the participation of abiotic factors. However, most of the techniques used by researchers in this area are inadequate to provide evidence of the final stage: assimilation. In this review, the different stages of biodegrdn. are described and several techniques are stated used by some authors working in this domain. Validate assimilation (including mineralization) is an important aspect to guarantee the real biodegradability of items of consumption (in particular friendly environmental new materials). The aim of this review is to emphasize the importance of measure as well as possible, the last stage of the biodegrdn., to certify the integration of new materials into the biogeochem. cycles. Finally, a perspective is given to use the natural labeling of stable isotopes in the environment, by a new methodol. based on the isotopic fractionation to validate assimilation by microorganisms.
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    Shah, A. A.; Hasan, F.; Hameed, A.; Ahmed, S. Biological Degradation of Plastics: A Comprehensive Review. Biotechnol. Adv. 2008, 26 (3), 246– 265,  DOI: 10.1016/j.biotechadv.2007.12.005
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    Biological degradation of plastics: A comprehensive review
    Shah, Aamer Ali; Hasan, Fariha; Hameed, Abdul; Ahmed, Safia
    Biotechnology Advances (2008), 26 (3), 246-265CODEN: BIADDD; ISSN:0734-9750. (Elsevier B.V.)
    A review. Lack of degradability and the closing of landfill sites as well as growing water and land pollution problems have led to concern about plastics. With the excessive use of plastics and increasing pressure being placed on capacities available for plastic waste disposal, the need for biodegradable plastics and biodegrdn. of plastic wastes has assumed increasing importance in the last few years. Awareness of the waste problem and its impact on the environment has awakened new interest in the area of degradable polymers. The interest in environmental issues is growing and there are increasing demands to develop material which do not burden the environment significantly. Biodegrdn. is necessary for water-sol. or water-immiscible polymers because they eventually enter streams which can neither be recycled nor incinerated. It is important to consider the microbial degrdn. of natural and synthetic polymers in order to understand what is necessary for biodegrdn. and the mechanisms involved. This requires understanding of the interactions between materials and microorganisms and the biochem. changes involved. Widespread studies on the biodegrdn. of plastics have been carried out in order to overcome the environmental problems assocd. with synthetic plastic waste. This paper reviews the current research on the biodegrdn. of biodegradable and also the conventional synthetic plastics and also use of various techniques for the anal. of degrdn. in vitro.
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    Lee, B.; Pometto, A. L.; Fratzke, A.; Bailey, T. B. Biodegradation of Degradable Plastic Polyethylene by Phanerochaete and Streptomyces Species. Appl. Environ. Microbiol. 1991, 57 (3), 678– 685,  DOI: 10.1128/AEM.57.3.678-685.1991
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    Biodegradation of degradable plastic polyethylene by Phanerochaete and Streptomyces species
    Lee, Byungtae; Pometti, Anthony L., III; Fratzke, Alfred; Bailey, Theodore B., Jr.
    Applied and Environmental Microbiology (1991), 57 (3), 678-85CODEN: AEMIDF; ISSN:0099-2240.
    The ability of lignin-degrading microorganisms to attack degradable plastics was investigated in pure shake flask culture studies. The degradable plastic used in this study was produced com. by using the Archer-Daniels-Midland POLYCLEAN masterbatch and contained pro-oxidant and 6% starch. The known lignin-degrading bacteria Streptomyces viridosporus T7A, S. badius 252, and S. setonii 75Vi2 and fungus Phanerochaete chrysosporium were used. Pro-oxidant activity was accelerated by placing a sheet of plastic into a drying oven at 70° under atm. pressure and air for 0, 4, 8, 12, 16, or 20 days. The effect of 2-, 4-, and 8-wk longwave UV irradn. at 365 nm on plastic biodegradability was also investigated. For shake flask cultures, plastics were chem. disinfected and incubated-shaken at 125 rpm at 37° in 0.6% yeast ext. medium (pH 7.1) for Streptomyces spp. and at 30° for the fungus in 3% malt ext. medium (pH 4.5) for 4 wk along with an uninoculated control for each treatment. Wt. loss data were inconclusive because of cell mass accumulation. For almost every 70° heat-treated film, the Streptomyces spp. demonstrated a further redn. in percent elongation and polyethylene mol. wt. av. when compared with the corresponding uninoculated control. Significant redns. were demonstrated for the 4- and 8-day heat-treated films by all three bacteria. Heat treated-films incubated with P. chrysosporium consistently demonstrated higher percent elongation and mol. wt. av. than the corresponding uninoculated controls, but were lower than the corresponding zero controls (heat-treated films without 4-wk incubation). The 2- and 4-wk UV-treated films showed the greatest biodegrdn. by all three bacteria. Virtually no degrdn. by the fungus was obsd. This is the first report demonstrating bacterial degrdn. of these oxidized polyethylenes in pure culture.
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    Gautam, R.; Bassi, A. S.; Yanful, E. K. A Review of Biodegradation of Synthetic Plastic and Foams. Appl. Biochem. Biotechnol. 2007, 141 (1), 85– 108,  DOI: 10.1007/s12010-007-9212-6
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    A review of biodegradation of synthetic plastic and foams
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    Applied Biochemistry and Biotechnology (2007), 141 (1), 85-108CODEN: ABIBDL; ISSN:0273-2289. (Humana Press Inc.)
    A review. Synthetic polymeric foams have pervaded every aspect of modern life. Although foams provide numerous benefits, they also cause a significant environmental litter problem because of their recalcitrant and xenobiotic nature. Biodegrdn. may provide soln. to the problem, but not enough is known about the biodegrdn. process of synthetic plastic and plastic-based foams. This review provides the current state of plastic foam biodegrdn. Several biodegrdn. pathways of a few select synthetic polymers are also presented along with a discussion on some of the physico-chem. factors that can influence the biodegrdn. of plastic foams.
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    The influence of biotic and abiotic environments on the degradation of polyethylene
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    Progress in Polymer Science (1990), 15 (2), 177-92CODEN: PRPSB8; ISSN:0079-6700.
    A review with 45 refs., including the authors' recent works, comparing environmental degrdn. of polyethylene films in biol. and nonbiol. sites. The samples were labeled with 14C for monitoring CO2 evolution, and the effects of additives and pre-irradn. were considered.
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    Close, L. G.; Gilbert, R. D.; Fornes, R. E. Poly(Vinyl Chloride) Degradation — A Review. Polym.-Plast. Technol. Eng. 1977, 8 (2), 177– 198,  DOI: 10.1080/03602557708545035
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    Polymer-Plastics Technology and Engineering (1977), 8 (2), 177-98CODEN: PPTEC7; ISSN:0360-2559.
    A review with 72 refs. The mechanism of PVC [9002-86-2] degrdn., and the degrdn. of PVC by uv light and heat are discussed.
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    Yu, J.; Sun, L.; Ma, C.; Qiao, Y.; Yao, H. Thermal Degradation of PVC: A Review. Waste Manage. 2016, 48, 300– 314,  DOI: 10.1016/j.wasman.2015.11.041
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    Yu, Jie; Sun, Lushi; Ma, Chuan; Qiao, Yu; Yao, Hong
    Waste Management (Oxford, United Kingdom) (2016), 48 (), 300-314CODEN: WAMAE2; ISSN:0956-053X. (Elsevier Ltd.)
    This review summarized various chem. recycling methods for PVC, such as pyrolysis, catalytic dechlorination and hydrothermal treatment, with a view to solving the problem of energy crisis and the impact of environmental degrdn. of PVC. Emphasis was paid on the recent progress on the pyrolysis of PVC, including co-pyrolysis of PVC with biomass/coal and other plastics, catalytic dechlorination of raw PVC or Cl-contg. oil and hydrothermal treatment using subcrit. and supercrit. water. Understanding the advantage and disadvantage of these treatment methods can be beneficial for treating PVC properly. The dehydrochlorination of PVC mainly happed at low temp. of 250-320 °C. The process of PVC dehydrochlorination can catalyze and accelerate the biomass pyrolysis. The intermediates from dehydrochlorination stage of PVC can increase char yield of co-pyrolysis of PVC with PP/PE/PS. For the catalytic degrdn. and dechlorination of PVC, metal oxides catalysts mainly acted as adsorbents for the evolved HCl or as inhibitors of HCl formation depending on their basicity, while zeolites and noble metal catalysts can produce lighter oil, depending the total no. of acid sites and the no. of accessible acidic sites. For hydrothermal treatment, PVC decompd. through three stages. In the first region (T < 250 °C), PVC went through dehydrochlorination to form polyene; in the second region (250 °C < T < 350 °C), polyene decompd. to low-mol. wt. compds.; in the third region (350 °C < T), polyene further decompd. into a large amt. of low-mol. wt. compds.
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    The mechanism of the low-temperature oxidation of polypropylene
    Gijsman, Pieter; Hennekens, Jan; Vincent, Jef
    Polymer Degradation and Stability (1993), 42 (1), 95-105CODEN: PDSTDW; ISSN:0141-3910.
    The peroxides (as detected by an iodometric titrn.) formed in the oxidn. of polypropylene (I) at 50-90° are of 2 types; fast-decompg. and slow-decompg. When both of these peroxides are present, the oxidn. rate is controlled by the fast-decompg. peroxides. During the induction period, the slow-decompg. peroxides are formed initially; the decompn. of these peroxides leads to primary oxidn. products. Due to the restricted mobility, these oxidn. products will preferentially be oxidized, which leads to fast-decompg. peroxides. Chem. analyses show that these peroxides are peracids. Thus, the increase in the oxidn. rate of I after the induction period is not, as generally accepted, due to the accumulation of hydroperoxides, but can be ascribed to the faster decompn. of peracids which result from the oxidn. of primary oxidn. products.
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    Oswald, H. J.; Turi, E. The Deterioration of Polypropylene by Oxidative Degradation. Polym. Eng. Sci. 1965, 5 (3), 152– 158,  DOI: 10.1002/pen.760050312
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    Deterioration of polypropylene by oxidative degradation
    Oswald, H. J.; Turi, E.
    (1965), 5 (3), 152-8 ISSN:.
    The effect of small amts. of absorbed O on the mech. properties of polypropylene is discussed. The sample holder of the ASTM O absorption app. was modified to facilitate simultaneous detn. of the deterioration of the mech. properties and the amt. of O absorbed. This test is more realistic for screening stabilizers and permits the use of small samples. Mostly, unstabilized polymers were used, but some were stabilized with 1.0% Topanol and 0.1% 2-ethylhexyl octylphenyl phosphite. The stabilizer was dissolved in a suitable solvent, added to the polymer, and stirred to complete dryness. Samples were compression-molded into 25 mil-thick films at 250° for 4 min. Specimens cut from these films were placed into the modified sample holder, exposed to O or to Ar at 75, 100, 120, and 140°, vol. changes were measured, and the amt. of absorbed O was detd. Specimens were tested for tensile properties at 2 in./min. Instron head speed; CO and OH concn. by ir; mol. wt. calcd. from intrinsic viscosity in Decalin at 135°; and d. Initial oxidn. sets in at the amorphous or less ordered segments and results in the formation of hydroperoxide groups at the tertiary C atoms, which then decomp. into alkoxy and OH free radicals. The alkoxy radical stabilizes itself through rearrangement into an alkyl radical and ketone formation. The formation of CO groups can thus be equated with the no. of chain scissions in a first approxn. CO concn. accounted for only 8-15% of the total O absorbed in the initial stages of oxidn. A broader mol. wt. distribution was attained by oxidative chain scission below the m.p. than by thermal degradation in the melt at temps. >250° in an inert atm. Chain scission results in an increase in crystallinity as shown by d. increase. Decreases in ultimate elongation and tensile strength were also due to chain scission and subsequent crystn. The embrittlement of the polymer was followed by plotting the retention of the product of the ultimate elongation and the ultimate tensile strength vs. time. The absorption of only 1.1 mg. O/g. polymer coincided with the 20% loss of the original properties in all cases. For unstabilized polypropylene, an extrapolation beyond the 75° data, using an apparent activation energy of 30-32 kcal./mole, would yield a life expectancy of 2 months and >6 years for 50 and 25° in air, resp. Polypropylene should be stabilized prior to pelletizing. Extrapolation of elevated temp. data can be safely accomplished over a temp. range of 140-50° if allowance is made for the discrepancy between the induction time of the O absorption technique and the retention of the mech. properties at the 80% or 50% level, but extrapolation beyond 50° is unwarranted. All data were the result of oxidative degradation in the absence of uv light. Stability against uv radiation can be greatly improved by a combination of an antioxidant stable to uv radiation and a uv absorber. In general, the O absorption technique overest. the life expectancy of polymers with respect to mech. properties.
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    Carlsson, D. J.; Wiles, D. M. The Photooxidative Degradation of Polypropylene. Part II. Photostabilization Mechanisms. J. Macromol. Sci., Polym. Rev. 1976, 14 (2), 155– 192,  DOI: 10.1080/15321797608065768
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    A detailed investigation of the products of the thermal degradation of polystyrene
    McNeill, I. C.; Zulfiqar, M.; Kousar, T.
    Polymer Degradation and Stability (1990), 28 (2), 131-51CODEN: PDSTDW; ISSN:0141-3910.
    The amts. of volatile liq. and cold ring fraction (CRF) products in the degrdn. of several anionic and a free radical polystyrene (I) sample were detd. gravimetrically for degrdns. in vacuum at 300°, over the range 5-60% volatilization. The ratio fell sharply from a value indicating a predominance of monomer over CRF products, dependent on the initial mol. wt. of the polymer, and reached a const. value in the range 0.8-1.0 for all the samples. Volatile liq. products in degrdns. of I at 300, 350, and 420° were sepd. and identified using GC-MS. Among the minor products from Na naphthalenide-initiated I were established several which could clearly be related to the head-to-head linkage. The major and minor CRF products were also characterized. The degrdn. mechanism of I was reconsidered in the light of the new evidence. Initially, intramol. transfer (which generated CRF products) was impeded by the high melt viscosity, and intermol. transfer (which led to a fall in mol. wt.) was favored. After ∼25% volatilization, however, intermol. transfer was of little importance and intramol. transfer became the main transfer reaction, so that the proportion of CRF products was greater. The secondary I macroradical was regarded as the main source of volatile and CRF products. The reactions of the primary I macroradical were discussed.
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    Yousif, E.; Haddad, R. Photodegradation and Photostabilization of Polymers, Especially Polystyrene: Review. SpringerPlus 2013, 2 (1), 398,  DOI: 10.1186/2193-1801-2-398
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    Photodegradation and photostabilization of polymers, especially polystyrene: review
    Yousif Emad; Haddad Raghad
    SpringerPlus (2013), 2 (), 398 ISSN:2193-1801.
    Exposure to ultraviolet (UV) radiation may cause the significant degradation of many materials. UV radiation causes photooxidative degradation which results in breaking of the polymer chains, produces free radical and reduces the molecular weight, causing deterioration of mechanical properties and leading to useless materials, after an unpredictable time. Polystyrene (PS), one of the most important material in the modern plastic industry, has been used all over the world, due to its excellent physical properties and low-cost. When polystyrene is subjected to UV irradiation in the presence of air, it undergoes a rapid yellowing and a gradual embrittlement. The mechanism of PS photolysis in the solid state (film) depends on the mobility of free radicals in the polymer matrix and their bimolecular recombination. Free hydrogen radicals diffuse very easily through the polymer matrix and combine in pairs or abstract hydrogen atoms from polymer molecule. Phenyl radical has limited mobility. They may abstract hydrogen from the near surrounding or combine with a polymer radical or with hydrogen radicals. Almost all synthetic polymers require stabilization against adverse environmental effects. It is necessary to find a means to reduce or prevent damage induced by environmental components such as heat, light or oxygen. The photostabilization of polymers may be achieved in many ways. The following stabilizing systems have been developed, which depend on the action of stabilizer: (1) light screeners, (2) UV absorbers, (3) excited-state quenchers, (4) peroxide decomposers, and (5) free radical scavengers; of these, it is generally believed that excited-state quenchers, peroxide decomposers, and free radical scavengers are the most effective. Research into degradation and ageing of polymers is extremely intensive and new materials are being synthesized with a pre-programmed lifetime. New stabilizers are becoming commercially available although their modes of action are sometimes not thoroughly elucidated. They target the many possible ways of polymer degradation: thermolysis, thermooxidation, photolysis, photooxidation, radiolysis etc. With the goal to increase lifetime of a particular polymeric material, two aspects of degradation are of particular importance: Storage conditions, and Addition of appropriate stabilizers. A profound knowledge of degradation mechanisms is needed to achieve the goal.
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    Hartley, G. H.; Guillet, J. E. Photochemistry of Ketone Polymers. I. Studies of Ethylene-Carbon Monoxide Copolymers. Macromolecules 1968, 1 (2), 165– 170,  DOI: 10.1021/ma60002a012
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    Photochemistry of ketone polymers. I. Studies of ethylene-carbon monoxide copolymers
    Hartley, G. H.; Guillet, J. E.
    Macromolecules (1968), 1 (2), 165-70CODEN: MAMOBX; ISSN:0024-9297.
    The photolysis of copolymers of C2H4 and CO contg. 1-9 mole % CO has been studied in soln. and in the solid phase. Irradn. of the copolymer with 3130 A. light results in mol.-wt. degradation. evolution of CO, and formation of terminal vinyl groups. These effects are explained in terms of the Norrish type I and type II reactions of ketones. The type II reaction, an intramol. elimination, appears to be independent of temp. and phase and is not quenched by atm. O. In the glass-transition region, however, the type II reaction is inhibited, probably due to restriction of the freedom of internal motion of the polymer chain. The type I reaction produces free radicals and is temp. dependent. At 120°, the 2 processes make approx. equal contributions to a total quantum yield for reaction of ∼0.05. However, at ambient temp., the type II process accounts for the major part of the reaction. 24 references.
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    Craig, I. H.; White, J. R.; Shyichuk, A. V.; Syrotynska, I.
    Polymer Engineering and Science (2005), 45 (4), 579-587CODEN: PYESAZ; ISSN:0032-3888. (John Wiley & Sons, Inc.)
    The mol. degrdn. characteristics of three different polyethylenes were detd. by deriving chain scission and crosslinking concns. from gel permeation chromatog. mol. wt. distributions obtained after 3 wk and 6 wk lab. UV exposure. Injection-molded bars (3 mm thick) made from a low-d. polyethylene (LDPE), a linear low-d. polyethylene (LLDPE), and a high-d. polyethylene (HDPE) were used and all showed strong depth variations in degrdn. Degrdn. was rapid near the exposed surfaces but very little change occurred in the bar centers, due to oxygen starvation. The most rapid rises in scission and crosslink concns. were obsd. with LDPE, for which the concns. after 6 wk exposure were approx. double those measured after 3 wk. With LLDPE and HDPE the scission and crosslink concns. after 6 wk exposure were very much greater than twice those after 3 wk. Scission dominated over crosslinking at all depths and for all materials the scission/crosslink ratio was always ≥3, with a value of ∼9 recorded for HDPE near the exposed surface after 6 wk exposure.
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    Gardette, M.; Perthue, A.; Gardette, J.-L.; Janecska, T.; Földes, E.; Pukánszky, B.; Therias, S. Photo- and Thermal-Oxidation of Polyethylene: Comparison of Mechanisms and Influence of Unsaturation Content. Polym. Degrad. Stab. 2013, 98 (11), 2383– 2390,  DOI: 10.1016/j.polymdegradstab.2013.07.017
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    Photo- and thermal-oxidation of polyethylene: Comparison of mechanisms and influence of unsaturation content
    Gardette, Melanie; Perthue, Anthony; Gardette, Jean-Luc; Janecska, Tunde; Foldes, Eniko; Pukanszky, Bela; Therias, Sandrine
    Polymer Degradation and Stability (2013), 98 (11), 2383-2390CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    The behavior of polyethylene with different contents in vinyl and t-vinylene groups have been studied by photooxidn. with λ ≥ 300 nm light or by thermooxidn. at 100 °C. The oxidn. was studied by IR spectroscopy and it was shown that the same oxidn. products were obtained, but with different relative concns. depending on the conditions of aging, i.e. photochem. or thermal conditions. The mechanisms by which the oxidn. products are formed were recalled. The differences between photo- and thermo-oxidn. were evidenced on the basis of the stability of ketones that do not accumulate in photochem. conditions, as a result of Norrish reactions. The influence of the initial amt. of unsatd. groups on the rates of oxidn. was characterized. It was shown that the concn. of unsaturations had no effect on the rate of photooxidn. but dramatically influenced the stability in thermooxidative conditions.
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    Onwudili, J. A.; Insura, N.; Williams, P. T. Composition of Products from the Pyrolysis of Polyethylene and Polystyrene in a Closed Batch Reactor: Effects of Temperature and Residence Time. J. Anal. Appl. Pyrolysis 2009, 86 (2), 293– 303,  DOI: 10.1016/j.jaap.2009.07.008
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    Composition of products from the pyrolysis of polyethylene and polystyrene in a closed batch reactor: Effects of temperature and residence time
    Onwudili, Jude A.; Insura, Nagi; Williams, Paul T.
    Journal of Analytical and Applied Pyrolysis (2009), 86 (2), 293-303CODEN: JAAPDD; ISSN:0165-2370. (Elsevier B.V.)
    The compns. of the pyrolysis products of pure low-d. polyethylene (LDPE) and polystyrene (PS) and their mixts. have been investigated over a temp. range from 300 to 500 °C. The pyrolysis expts. were carried out in a closed batch reactor under inert nitrogen atm. to study the effects of reaction temp. and residence time. LDPE was thermally degraded to oil at 425 °C however, beyond this temp. the proportion of oil product decreased as a result of its conversion to char and hydrocarbon gas. Compositional anal. of the oil products showed that aliph. hydrocarbons were the major components, but the proportion of arom. compds. increased at higher temps. and residence times. On the other hand, PS degraded at around 350 °C, mainly into a viscous dark-colored oil. The formation of char only increased marginally until 425 °C, but was dramatically enhanced at 450 and 500 °C, reaching up to 30 wt.%. The oil product from PS even at 350 °C consisted almost entirely of arom. compds. esp. toluene, ethylbenzene and styrene. Under increasing temps. and residence times, the oil product from PS was preferentially converted to char, while gas formation was preferred for the oil from LDPE. For instance at 500 °C, PS produced about twice the amt. of char obtained from LDPE indicating the role of arom. compds. in char formation via condensation of the arom. ring structure. During the co-pyrolysis of a 7:3 mixt. of LDPE and PS, wax product was obsd. at 350 °C leading to oil at 400 °C, indicating that the presence of PS influenced the conversion of LDPE by lowering its degrdn. temp. The mixt. produced more oil and less char than the individual plastics at 450 °C.
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    Ahmad, I.; Khan, M. I.; Khan, H.; Ishaq, M.; Tariq, R.; Gul, K.; Ahmad, W. Pyrolysis Study of Polypropylene and Polyethylene into Premium Oil Products. Int. J. Green Energy 2015, 12 (7), 663– 671,  DOI: 10.1080/15435075.2014.880146
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    Pyrolysis Study of Polypropylene and Polyethylene Into Premium Oil Products
    Ahmad, Imtiaz; Khan, M. Ismail; Khan, Hizbullah; Ishaq, M.; Tariq, Razia; Gul, Kashif; Ahmad, Waqas
    International Journal of Green Energy (2015), 12 (7), 663-671CODEN: IJGECR; ISSN:1543-5075. (Taylor & Francis, Inc.)
    Pyrolysis of polypropylene (PP) and high d. polyethylene (HDPE) into fuel like products was investigated over temp. range of 250- 400°C. The product yields as a function of temp. were studied. Total conversion as high as 98.66% (liq.; 69.82%, gas; 28.84%, and residue; 1.34%) was achieved at 300°C in case of PP and 98.12% (liq.; 80.88%, gas; 17.24%, and residue; 1.88%) in case of HDPE at 350°C. The liq. fractions were analyzed by FTIR and GC-MS. The results showed that the liq. fractions consisted of a wide range of hydrocarbons mainly distributed within the C6-C16. The liq. product obtained in case of PP is enriched in the naphtha range hydrocarbons. Similarly, the liq. product obtained in case of HDPE is also enriched in naphtha range hydrocarbons with preponderance in gasoline and diesel range hydrocarbons. The% distribution of paraffinic, olefinic, and naphthenic hydrocarbons in liq. product derived from PP is 66.55, 25.7, and 7.58%, resp., whereas in case HDPE, the% distribution is 59.70, 31.90, and 8.40%, resp. Upon comparing the hydrocarbon group type yields, PP gave high yield of paraffinic hydrocarbons while HDPE gave high yields of olefins and naphthenes. The whole liq. fractions and their corresponding distillates fractions were also analyzed for fuel properties. The results indicated that the derived liq. fractions were fuel-like meeting the fuel grade criteria.
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    Norrish, R. G. W.; Bamford, C. H.
    Nature (London, United Kingdom) (1937), 140 (), 195-6CODEN: NATUAS; ISSN:0028-0836.
    cf. C. A. 28, 2270.5; 30, 1304.7, 2493.5; 31, 1703.1. Aldehydes and ketones decompose in the gas phase in two main ways: (1) RCOR' → CO + (RR + RR' + R'R'), (2) the long hydrocarbon chain cracks α-β to the CO group, giving a lower carbonyl compd. and an olefin. MeEtCO and Et2CO in 10% liquid-paraffin soln. show no photolysis at 20°, but decompose according to type (1) at 100°. The products consist only of CO, RH and R'H. The free radical fragments react with the solvent, causing an unsatn. in the solvent. In the decompn. of MeEtCO, there is a deficiency of CH4 and of CO, due to the formation of MeCO, followed by the reaction MeCO + CnH2n+2 → MeCHO + CnH2n+1. Aldehydes undergo type (1) photolysis at room temp., yielding the same gas products in soln. as in the gas phase (AcH → CH4 + CO; PrCHO ≃ CO + C3H8; Me2CHCH2CHO → CO + Me3CH). Both aldehydes and ketones decompose simultaneously according to both types, with the same proportion of each type as in the gas phase, and unchanged in the liquid between 20° and -80°. The former conclusions (1) that the hydrocarbon is produced from aldehydes in one step, RCHO → RH + CO, and (2) that in ketones free radicals are first formed, were verified.
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    Restrepo-Flórez, J.-M.; Bassi, A.; Thompson, M. R. Microbial Degradation and Deterioration of Polyethylene – A Review. Int. Biodeterior. Biodegrad. 2014, 88, 83– 90,  DOI: 10.1016/j.ibiod.2013.12.014
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    Restrepo-Florez, Juan-Manuel; Bassi, Amarjeet; Thompson, Michael R.
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    A review. The ability of microorganisms to use polyethylene as a carbon source has only been recently established. This result has significance both from an environmental point of view, due to the accumulation of millions of tons of waste plastics every year, but also regarding the conservation of integrity for infrastructures incorporating this plastic. A no. of microorganisms with the ability to grow on polyethylene have been isolated. The effects of these microorganisms on the physiochem. properties of this polymer have been described; these include changes in crystallinity, mol. wt., topog. of samples and the functional groups found on the surface. Although the bio-degrdn. and bio-deterioration of polyethylene has been demonstrated by several researchers, the enzymes involved and mechanisms assocd. with these phenomena are still unclear. Nevertheless, it is recognized that both enzymic and abiotic factors (such UV light) can mediate the initial oxidn. of polyethylene chains, and given the chem. similarity between polyethylene and olefins it has been suggested that the metabolic pathways for degrdn. of hydrocarbons can be used once the size of polyethylene mols. decrease to an acceptable range for enzyme action (typically from 10 to 50 carbons). The long-range structure and morphol. of polyethylene have shown important roles, with amorphous regions being more prone to microbial attack than cryst. ones. This review focuses on the recent hypotheses and exptl. findings regarding the biodegrdn. of polyethylene.
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    Allen, Norman S.; Edge, Michael; Mohammadian, Mehrdad; Jones, Ken
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    The degrdn. of amorphous poly(ethylene terephthalate) sheet material was studied under various environmental conditions [dry, wet soil, 100% and 45% relative humidity (RH), and UV irradn.] by measuring the rate of chain scission using viscometric anal. at several temps. Using the Arrhenius expression, the lifetime of the polyester was very dependent upon the environmental conditions, with hydrolysis being a dominant process at lower temps. Negligible degrdn. was obsd. at temps. below the glass transition (∼80°) in dry conditions. From d. measurements at 45 and 100% RH, the crystallinity exhibited an initial facile increase due to plasticization by the moisture and annealing followed by an inflection which increased from 26 to 40% with the severity of the degrdn. conditions. This inflection was consistent under all degrdn. conditions at 0.5 of a chain scission and was then followed by a much lower rate due to combined hydrolytic degrdn./oxidn. of the polymer chains. The initial rapid increase was faster at lower rates of chain scission because of an annealing/plasticization effect by the moisture.
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    Rosmaninho, M. G.; Jardim, E.; Moura, F. C. C.; Ferreira, G. L.; Thom, V.; Yoshida, M. I.; Araujo, M. H.; Lago, R. M. Surface Hydrolysis of Postconsumer Polyethylene Terephthalate to Produce Adsorbents for Cationic Contaminants. J. Appl. Polym. Sci. 2006, 102 (6), 5284– 5291,  DOI: 10.1002/app.24790
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    Journal of Applied Polymer Science (2006), 102 (6), 5284-5291CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
    The surface hydrolysis of post-consumer polyethylene terephthalate (PET) was used to produce an ion exchange material to adsorb cationic contaminants from water. The PET surface hydrolyzes were carried out in neutral, alk., and acid media (NaOH or HNO3 at 7, 10, and 15 mol L-1) under reflux producing surface carboxylic acid sites (-COOH) characterized by ATR-IR, pyridine adsorption, titrn., TG, and DSC analyses. Acid hydrolysis produced high concns. of -COOH (up to 0.5 mmol g-1PET), whereas no significant concn. of carboxylic acid sites was obtained by neutral and alk. hydrolysis. SEM analyses suggest that the acid sites are likely located at the cracks and defects produced on the PET surface by acid hydrolysis. Neutral or alk. hydrolysis produced a very regular and smooth PET surface with very low acid site concns. The adsorption isotherms of Cd+2 as a model of heavy metal and the dye methylene blue as a model of large org. cationic mols. showed high adsorption capacities for the HNO3-hydrolyzed PET, whereas no adsorption takes place on the neutral- or alk.-hydrolyzed polymer.
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    The prepn. of resilient and dimensionally stable poly(ethylene terephthalate) fibers from di-Me terephthalate and ethylene glycol was described and the stability of the polyester toward a variety of degradative reactions was discussed. The nature of thermal, hydrolytic, oxidative and radiation-induced degradative reactions was discussed and compared with the results obtained with model compds. such as ethylene dibenzoate, 2-hydroxyethyl benzoate, and diethylene glycol dibenzoate. 45 references.
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    Day, M.; Wiles, D. M. Photochemical Degradation of Poly(Ethylene Terephthalate). II. Effect of Wavelength and Environment on the Decomposition Process. J. Appl. Polym. Sci. 1972, 16 (1), 191– 202,  DOI: 10.1002/app.1972.070160117
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    Day, M.; Wiles, D. M.
    Journal of Applied Polymer Science (1972), 16 (1), 191-202CODEN: JAPNAB; ISSN:0021-8995.
    Crosslinking and discoloration occurred when poly(ethylene terephthalate) [25038-59-9] film was uv irradiated in vacuum or in N, but in the presence of air chain scissions and fluorescent material buildup resulted and no crosslinking and only slight discoloration was obsd. The importance of wavelength <315 nm in causing deterioration was shown by surface crazing and ultimate fracture under stress.
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    Musioł, M.; Sikorska, W.; Adamus, G.; Janeczek, H.; Richert, J.; Malinowski, R.; Jiang, G.; Kowalczuk, M. Forensic Engineering of Advanced Polymeric Materials. Part III - Biodegradation of Thermoformed Rigid PLA Packaging under Industrial Composting Conditions. Waste Manage. 2016, 52, 69– 76,  DOI: 10.1016/j.wasman.2016.04.016
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    Forensic engineering of advanced polymeric materials. Part III - Biodegradation of thermoformed rigid PLA packaging under industrial composting conditions
    Musiol, Marta; Sikorska, Wanda; Adamus, Grazyna; Janeczek, Henryk; Richert, Jozef; Malinowski, Rafal; Jiang, Guozhan; Kowalczuk, Marek
    Waste Management (Oxford, United Kingdom) (2016), 52 (), 69-76CODEN: WAMAE2; ISSN:0956-053X. (Elsevier Ltd.)
    This paper presents a forensic engineering study on the biodegrdn. behavior of prototype packaging thermoformed from PLA-extruded film and plain PLA film under industrial composting conditions. Hydrolytic degrdn. in water was conducted for ref. The effects of composting duration on changes in molar mass, glass transition temp. and degree of crystallinity of the polymeric material were monitored using gel permeation chromatog. (GPC) and differential scanning calorimetry (DSC). The chem. structure of water sol. degrdn. products of the polymeric material was detd. using NMR (NMR) and electrospray ionization mass spectrometry (ESI-MS). The results show that the biodegrdn. process is less dependent on the thermoforming process of PLA and more dependent on the composting/degrdn. conditions that are applied. The increase in the dispersity index, leading to the bimodal molar mass distribution profile, suggests an autocatalytic hydrolysis effect at the early stage of the composting process, during which the bulk hydrolysis mechanism dominantly operates. Both the prototype PLA-packaging and PLA rigid film samples were shown to have a gradual increase in opacity due to an increase in the degree of crystallinity.
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    Kopinke, F.-D.; Remmler, M.; Mackenzie, K.; Möder, M.; Wachsen, O. Thermal Decomposition of Biodegradable Polyesters—II. Poly(Lactic Acid). Polym. Degrad. Stab. 1996, 53 (3), 329– 342,  DOI: 10.1016/0141-3910(96)00102-4
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    Thermal decomposition of biodegradable polyesters. II. Poly(lactic acid)
    Kopinke, F. -D.; Remmler, M.; Mackenzie, K.; Moeder, M.; Wachsen, O.
    Polymer Degradation and Stability (1996), 53 (3), 329-342CODEN: PDSTDW; ISSN:0141-3910. (Elsevier)
    The thermal decompn. of the biol. degradable polymer poly(lactic acid) (PLA) was investigated by several thermoanal. techniques: thermogravimetry, differential scanning calorimetry, time resolved pyrolysis-MS and pyrolysis-GC/MS. The results mainly confirm reaction mechanisms proposed in the literature. The dominant reaction pathway is an intramol. transesterification for pure PLA (Tmax = 360°), giving rise to the formation of cyclic oligomers. In addn., acrylic acid from cis-elimination as well as carbon oxides and acetaldehyde from fragmentation reactions were detected. PLA samples contaminated with residual Sn from the polymn. process show a preceding selective depolymn. step (Tmax = 300°) which produces lactide exclusively. The GC anal. of the oligomers gives insight into the stereochem. of the original polymer chain with respect to the configuration of the asym. C atoms, as well as into the stereochem. of decompn. reactions. Other exptl. findings, which do not fit the proposed reaction mechanisms, are also discussed.
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    Castro-Aguirre, E.; Iñiguez-Franco, F.; Samsudin, H.; Fang, X.; Auras, R. Poly(Lactic Acid)—Mass Production, Processing, Industrial Applications, and End of Life. Adv. Drug Delivery Rev. 2016, 107, 333– 366,  DOI: 10.1016/j.addr.2016.03.010
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    Poly(lactic acid)-Mass production, processing, industrial applications, and end of life
    Castro-Aguirre, E.; Iniguez-Franco, F.; Samsudin, H.; Fang, X.; Auras, R.
    Advanced Drug Delivery Reviews (2016), 107 (), 333-366CODEN: ADDREP; ISSN:0169-409X. (Elsevier B.V.)
    A review. Global awareness of material sustainability has increased the demand for bio-based polymers like poly(lactic acid) (PLA), which are seen as a desirable alternative to fossil-based polymers because they have less environmental impact. PLA is an aliph. polyester, primarily produced by industrial polycondensation of lactic acid and/or ring-opening polymn. of lactide. Melt processing is the main technique used for mass prodn. of PLA products for the medical, textile, plasticulture, and packaging industries. To fulfill addnl. desirable product properties and extend product use, PLA has been blended with other resins or compounded with different fillers such as fibers, and micro- and nanoparticles. This paper presents a review of the current status of PLA mass prodn., processing techniques and current applications, and also covers the methods to tailor PLA properties, the main PLA degrdn. reactions, PLA products' end-of-life scenarios and the environmental footprint of this unique polymer.
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    Chu, C. C. Hydrolytic Degradation of Polyglycolic Acid: Tensile Strength and Crystallinity Study. J. Appl. Polym. Sci. 1981, 26 (5), 1727– 1734,  DOI: 10.1002/app.1981.070260527
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    Hydrolytic degradation of polyglycolic acid: tensile strength and crystallinity study
    Chu, C. C.
    Journal of Applied Polymer Science (1981), 26 (5), 1727-34CODEN: JAPNAB; ISSN:0021-8995.
    The hydrolytic degrdn. of polyglycolic acid (PGA) [26124-68-5] was studied by examg. the changes of tensile strength and the level of crystallinity of the suture material. The breaking stress decreased from 6.369 × 10-1 at 0 day to 3.97 × 10-3 Newton/Tex at 49 days. The sigmoidal shape of the stress-strain curves gradually disappeared with increase in the duration of in vitro degrdn. The endpoint titrn. method used to assess the degree of degrdn. beyond the period of measurable tensile strength showed that the percent of PGA degraded were 42, 56, and 70% at 49, 60, and 90 days, resp. The level of crystallinity of PGA at various durations of degrdn. exhibited an initial increase in the degree of crystallinity from 40% at 0 day to an upper limit of 52% at 21 days, then gradual decrease to 23% at 90 days. This observation is essentially parallel to hydrolysis of cellulose and polyethylene terephthalate. The concept of microfibrillar structure of fibers provides the basis for the proposed degrdn. mechanism of PGA in vitro. Apparently, that degrdn. proceeds through 2 main stages which are different in rate of degrdn.
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    de Jong, S. J.; Arias, E. R.; Rijkers, D. T. S.; van Nostrum, C. F.; Kettenes-van den Bosch, J. J.; Hennink, W. E. New Insights into the Hydrolytic Degradation of Poly(Lactic Acid): Participation of the Alcohol Terminus. Polymer 2001, 42 (7), 2795– 2802,  DOI: 10.1016/S0032-3861(00)00646-7
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    New insights into the hydrolytic degradation of poly(lactic acid): participation of the alcohol terminus
    De Jong, S. J.; Arias, E. R.; Rijkers, D. T. S.; Van Nostrum, C. F.; Kettenes-Van den Bosch, J. J.; Hennink, W. E.
    Polymer (2001), 42 (7), 2795-2802CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
    The hydrolytic degrdn. of monodisperse lactic acid oligomers was studied in vitro to gain insight into the degrdn. of oligolactic acid grafted to dextran, which we use for the prepn. of hydrogels based on phys. interactions, or the degrdn. of PLA/PLGA. The decrease in the amt. of oligomer and the formation of degrdn. products was monitored by HPLC and MS. The amt. of lactic acid oligomer decreased according to pseudo-first-order kinetics and was dependent on the dielec. const. of the medium and the pH. The OH end group was found to play a crucial role in the hydrolytic degrdn.; when the OH was blocked no significant degrdn. was obsd. At acidic pH, hydrolysis was shown to proceed by chain-end scission whereas in alk. medium, lactoyl lactate was split off. The possible consequences of these findings for the degrdn. of PLA matrixes are discussed.
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    Ikada, E. Relationship between Photodegradability and Biodegradability of Some Aliphatic Polyesters. J. Photopolym. Sci. Technol. 1999, 12 (2), 251– 256,  DOI: 10.2494/photopolymer.12.251
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    Relationship between photodegradability and biodegradability of some aliphatic polyesters
    Ikada, Eiji
    Journal of Photopolymer Science and Technology (1999), 12 (2), 251-256CODEN: JSTEEW; ISSN:0914-9244. (Technical Association of Photopolymers, Japan)
    Aliph. polyesters such as polycaprolactone are now widely utilized as a green polymer to avoid serious environmental pollution due to diffusion of plastics waste. Such a polyester contains a carbonyl group in each repeating unit. The Norrish-type photo decompn., therefore, is expected to occur in these polyester polymers. Accordingly, photo irradn. by a medium pressure mercury lamp was done to the polyester film. It was found that the aliph. polyester could be utilized for a photodegradable plastic. Photodegrdn. behavior of the aliph. polyesters was compared with the biodegrdn. behavior by means of electron microscopy.
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    Tsuji, H.; Echizen, Y.; Nishimura, Y. Photodegradation of Biodegradable Polyesters: A Comprehensive Study on Poly(l-Lactide) and Poly(ε-Caprolactone). Polym. Degrad. Stab. 2006, 91 (5), 1128– 1137,  DOI: 10.1016/j.polymdegradstab.2005.07.007
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    Photodegradation of biodegradable polyesters: A comprehensive study on poly(-lactide) and poly(.vepsiln.-caprolactone)
    Tsuji, Hideto; Echizen, Yoshihisa; Nishimura, Yoshiro
    Polymer Degradation and Stability (2006), 91 (5), 1128-1137CODEN: PDSTDW; ISSN:0141-3910. (Elsevier B.V.)
    The photodegrdn. of melt-crystd. and amorphous-made poly(L-lactide) (PLLA-C and PLLA-A, resp.) and cast-crystd. poly(.vepsiln.-caprolactone) (PCL) was investigated comprehensively for the periods up to 200 h using gel permeation chromatog., differential scanning calorimetry, tensile testing, and polarization optical microscopy. The photodegrdn. of PLLA and PCL films proceeds via a bulk erosion mechanism, indicating that UV penetrates the specimens with no significant redn. in its intensity, irresp. of the chem. structure and the crystallinity of biodegradable polyesters. The photodegradability of PCL chains was higher than that of PLLA chains. This strongly suggests that the chem. structure of the two sequential groups adjacent to the ester oxygen rather than the d. of ester group is crucial to det. the photodegradability of biodegradable polyesters. Although PLLA chains are photodegradable even in the cryst. regions, their photodegradability is lower than that in the amorphous regions. The significant increase in wt.-av. mol. wt. (M w)/no.-av. mol. wt. (M n) was obsd. for PLLA-A and PCL films, even when the decrease in M n by UV irradn. was small. Most of the tensile properties of PLLA and PCL films remained unchanged during UV irradn., while solely the elongation at break of PCL film significantly decreased. This result reflects that among the tensile properties the elongation at break was most sensitive to the change in mol. characteristics of biodegradable polyesters by UV irradn. The contrast between bright and dark parts of Maltese crosses remained unchanged for the spherulites in PLLA-C and PCL films even after UV irradn. for 200 h. This result exhibits that the cleaved fraction of the tie chains was too low to cause the traceable disorientation of lamellae.
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    Janorkar, A. V.; Metters, A. T.; Hirt, D. E. Degradation of Poly(L-Lactide) Films under Ultraviolet-Induced Photografting and Sterilization Conditions. J. Appl. Polym. Sci. 2007, 106 (2), 1042– 1047,  DOI: 10.1002/app.24692
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    Degradation of poly(L-lactide) films under ultraviolet-induced photografting and sterilization conditions
    Janorkar, Amol V.; Metters, Andrew T.; Hirt, Douglas E.
    Journal of Applied Polymer Science (2007), 106 (2), 1042-1047CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
    The degrdn. of polymers under UV irradn. has been a great concern for biomaterial and agricultural applications. The major objective of this research was to study the effect of UV irradn. on the representative bulk and surface properties of poly(L-lactide) (PLA) films. Two UV sources with different spectral outputs and intensities were chosen so that one of them could be used for surface modification and the other could be used for UV sterilization of the PLA films. The results established that the mol. wt. of PLA decreased significantly during irradn. from the photografting lamp under atm. conditions. Irradn. through a Pyrex container was shown to minimize polymer degrdn. during UV exposure from the photografting lamp. The PLA films UV-irradiated under the sterilization lamp for 12 h revealed a similar redn. in the mol. wt. and no change in the surface hydrophilicity. However, significantly less photodegrdn. was obsd. under the sterilization lamp when the samples were held in a Pyrex container.
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    European Polymer Journal (2014), 50 (), 109-116CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
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    Plastic degradation by thermophilic Bacillus sp. BCBT21 isolated from composting agricultural residual in Vietnam
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    Three different kinds of plastic bags HL, VHL, and VN1 with different chem. nature were degraded by a novel thermophilic bacterial strain isolated from composting agricultural residual in Vietnam in shaking liq. medium at 55 °C after 30 d. The new strain was classified in the Bacillus genus by morphol. property and sequence of partial 16Sr RNA coding gene and named as Bacillus sp. BCBT21. This strain could produce extracellular hydrolase enzymes including lipase, CMCase, xylanase, chitinase, and protease with different level of activity in the same media. After a 30-d treatment at 55 °C with Bacillus sp. BCBT21, all characteristics including properties and morphol. of treated plastic bags had been significantly changed. The wt. loss, structure and surface morphol. of these bags as well as the change in the av. mol. wt. of VHL bag were detected. Esp., the av. mol. wt. of VHL bag was significantly reduced from 205 000 to 116 760. New metabolites from the treated bags indicated biodegrdn. occurring with the different pathways. This finding suggests that there is high potential to develop an effective integrated method for plastic bags degrdn. by a combination of extracellular enzymes from bacteria and fungi existing in the composting process.
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    A degrdn. of compost bags strips made of supposedly degradable polyethylene and nondegradable low-d. and high-d. polyethylene were evaluated in soil mixed with 50% (wt./wt.) mature municipal solid waste compost supplied from municipal refuse. Plastic films were buried during 15 mo at room temp. in 2 L desiccator jars contg. soil adjusted to 40% of max. water holding capacity. Degrdn. of plastics was detd. by the wt. loss of sample, tensile strength, carbon dioxide prodn., chem. changes measured in IR spectrum and bacterial activity in soil. The examd. films can be ranged in order of decreasing susceptibility: degradable polyethylene >>> low d. polyethylene > high d. polyethylene.
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    Eight kinds of biodegradable plastics were compared for their degradability in controlled lab. composting conditions. A thin film of each plastic was mixed into the composting material, and wt.-loss was calcd. from the wt. changes of the film during composting. Wt. loss varied significantly depending on the type of plastic; two were very high, four moderate, and the remaining two very slight. The most easily degradable plastic degraded by 81.4% over 8 days. By comparing wt.-loss degradability with ultimate degradability, which is defined as the molar ratio of C loss as CO2 to the total C contained in the plastic, the order of ease of degrdn. of the plastics differed.
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    Since last few decades the uncontrolled use of plastics for various purposes such as packaging, transportation, industry and agriculture in rural as well as urban areas, has elevated serious issue of plastic waste disposal and its pollution. The efficient decompn. of plastic bags takes about 1000 years. Plastic causes pollution and global warming not only because of increase in the problem of waste disposal and land filling but also release CO2 and dioxins due to burning. Commonly used methods for plastic disposal were proved to be inadequate for effective plastic waste management, and hence there is growing concern for use of efficient microorganisms meant for biodegrdn. of non-degradable synthetic polymer. The biodegradable polymers are designed to degrade fast by microbes due their ability to degrade the most of the org. and inorg. materials, including lignin, starch, cellulose and hemicelluloses. The present review discusses the current status, mechanisms of biodegrdn. of plastics, techniques for characterizing degraded plastics and factors affecting their biodegrdn.
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    Environmental Science & Technology (2014), 48 (23), 13776-13784CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Polyethylene (PE) has been considered nonbiodegradable for decades. Although the biodegrdn. of PE by bacterial cultures has been occasionally described, valid evidence of PE biodegrdn. has remained limited in the literature. We found that waxworms, or Indian mealmoths (the larvae of Plodia interpunctella), were capable of chewing and eating PE films. Two bacterial strains capable of degrading PE were isolated from this worm's gut, Enterobacter asburiae YT1 and Bacillus sp. YP1. Over a 28-day incubation period of the 2 strains on PE films, viable biofilms formed, and the PE films' hydrophobicity decreased. Obvious damage, including pits and cavities (0.3-0.4 μm in depth), was obsd. on the surfaces of the PE films using SEM and at. force microscopy (AFM). The formation of carbonyl groups was verified using XPS and microattenuated total reflectance/FTIR (micro-ATR/FTIR) imaging microscope. Suspension cultures of YT1 and YP1 (108 cells/mL) were able to degrade approx. 6.1±0.3% and 10.7±0.2% of the PE films (100 mg), resp., over a 60-day incubation period. The mol. wts. of the residual PE films were lower, and the release of 12 water-sol. daughter products was also detected. The results demonstrated the presence of PE-degrading bacteria in the guts of waxworms and provided promising evidence for the biodegrdn. of PE in the environment.
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    Plastic waste constitutes the third largest waste vol. in Malaysian municipal solid waste (MSW), next to putrescible waste and paper. The plastic component in MSW from Kuala Lumpur avs. 24% (by wt.), whereas the national mean is about 15%. The 144 waste dumps in the country receive about 95% of the MSW, including plastic waste. The useful life of the landfills is fast diminishing as the plastic waste stays un-degraded for more than 50 years. In this study the compostability of polyethylene and pro-oxidant additive-based environmentally degradable plastics (EDP) was investigated. Linear low-d. polyethylene (LLDPE) samples exposed hydrolytically or oxidatively at 60°C showed that the abiotic degrdn. path was oxidative rather than hydrolytic. There was a wt. loss of 8% and the plastic has been oxidized as shown by the addnl. carbonyl group exhibited in the Fourier transform infra red (FTIR) Spectrum. Oxidn. rate seemed to be influenced by the amt. of pro-oxidant additive, the chem. structure and morphol. of the plastic samples, and the surface area. Composting studies during a 45-day expt. showed that the percentage elongation (redn.) was 20% for McD samples [high-d. polyethylene, (HDPE) with 3% additive] and LL samples (LLDPE with 7% additive) and 18% redn. for totally degradable plastic (TDP) samples (HDPE with 3% additive). Lastly, microbial expts. using Pseudomonas aeruginosa on carbon-free media with degradable plastic samples as the sole carbon source, showed confirmatory results. A pos. bacterial growth and a wt. loss of 2.2% for degraded polyethylene samples were evident to show that the degradable plastic is biodegradable.
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    Hidalgo-Ruz, V.; Gutow, L.; Thompson, R. C.; Thiel, M. Microplastics in the Marine Environment: A Review of the Methods Used for Identification and Quantification. Environ. Sci. Technol. 2012, 46 (6), 3060– 3075,  DOI: 10.1021/es2031505
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    Environmental Science & Technology (2012), 46 (6), 3060-3075CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    This review of 68 studies compares the methodologies used for the identification and quantification of microplastics from the marine environment. Three main sampling strategies were identified: selective, vol.-reduced, and bulk sampling. Most sediment samples came from sandy beaches at the high tide line, and most seawater samples were taken at the sea surface using neuston nets. Four steps were distinguished during sample processing: d. sepn., filtration, sieving, and visual sorting of microplastics. Visual sorting was one of the most commonly used methods for the identification of microplastics (using type, shape, degrdn. stage, and color as criteria). Chem. and phys. characteristics (e.g., specific d.) were also used. The most reliable method to identify the chem. compn. of microplastics is by IR spectroscopy. Most studies reported that plastic fragments were polyethylene and polypropylene polymers. Units commonly used for abundance ests. are "items per m2" for sediment and sea surface studies and "items per m3" for water column studies. Mesh size of sieves and filters used during sampling or sample processing influence abundance ests. Most studies reported two main size ranges of microplastics: (i) 500 μm-5 mm, which are retained by a 500 μm sieve/net, and (ii) 1-500 μm, or fractions thereof that are retained on filters. We recommend that future programs of monitoring continue to distinguish these size fractions, but we suggest standardized sampling procedures which allow the spatiotemporal comparison of microplastic abundance across marine environments.
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    ter Halle, A.; Ladirat, L.; Gendre, X.; Goudouneche, D.; Pusineri, C.; Routaboul, C.; Tenailleau, C.; Duployer, B.; Perez, E. Understanding the Fragmentation Pattern of Marine Plastic Debris. Environ. Sci. Technol. 2016, 50 (11), 5668– 5675,  DOI: 10.1021/acs.est.6b00594
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    Understanding the Fragmentation Pattern of Marine Plastic Debris
    ter Halle, Alexandra; Ladirat, Lucie; Gendre, Xavier; Goudouneche, Dominique; Pusineri, Claire; Routaboul, Corinne; Tenailleau, Christophe; Duployer, Benjamin; Perez, Emile
    Environmental Science & Technology (2016), 50 (11), 5668-5675CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    The global estn. of microplastic afloat in the ocean is only approx. 1% of annual global plastic inputs. This reflects fundamental knowledge gaps in the transformation, fragmentation, and fates of microplastics in the ocean. In order to better understand microplastic fragmentation we proceeded to a thorough physicochem. characterization of samples collected from the North Artlantic subtropical gyre during the sea campaign Expedition seventh Continent in May 2014. The results were confronted with a math. approach. The introduction of mass distribution in opposition to the size distribution commonly proposed in this area clarify the fragmentation pattern. The math. anal. of the mass distribution points out a lack of debris with mass lighter than 1 mg. Characterization by means of microscopy, microtomog., and IR microscopy gives a better understanding of the behavior of microplastic at sea. Flat pieces of debris (2 to 5 mm in length) typically have one face that is more photodegraded (due to exposure to the sun) and the other with more biofilm, suggesting that they float in a preferred orientation. Smaller debris, with a cubic shape (below 2 mm), seems to roll at sea. All faces are evenly photodegraded and they are less colonized. The breakpoint in the math. model and the exptl. observation around 2 mm leads to the conclusion that there is a discontinuity in the rate of fragmentation: we hypothesized that the smaller microplastics, the cubic ones mostly, are fragmented much faster than the parallelepipeds.
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    A review. Co-polymers of lactide and glycolide, referred to as PLGA, have generated tremendous interest because of their excellent biocompatibility, biodegradability and mech. strength. Various polymeric devices like microspheres, microcapsules, nanoparticles, pellets, implants, and films had been fabricated using these polymers. They could be transformed by spinning into filaments for subsequent fabrication of desirable textile structures. Spinning might be accomplished by various routes. The fibers might be fabricated into various forms and may be used for implants and other surgical applications such as sutures. They were also easy to formulate into various delivery systems for carrying a variety of drug classes. The present article presented a review on the prodn. of PLGA fiber by various methods, along with correlations between structure and properties of the fibers. The applications of these fibers in biomedical domains were also discussed.
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    Laycock, B.; Nikolić, M.; Colwell, J. M.; Gauthier, E.; Halley, P.; Bottle, S.; George, G. Lifetime Prediction of Biodegradable Polymers. Prog. Polym. Sci. 2017, 71, 144– 189,  DOI: 10.1016/j.progpolymsci.2017.02.004
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    Lifetime prediction of biodegradable polymers
    Laycock, Bronwyn; Nikolic, Melissa; Colwell, John M.; Gauthier, Emilie; Halley, Peter; Bottle, Steven; George, Graeme
    Progress in Polymer Science (2017), 71 (), 144-189CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    The detn. of the safe working life of polymer materials is important for their successful use in engineering, medicine and consumer-goods applications. An understanding of the phys. and chem. changes to the structure of widely-used polymers such as the polyolefins, when exposed to aggressive environments, has provided a framework for controlling their ultimate service lifetime by either stabilizing the polymer or chem. accelerating the degrdn. reactions. The recent focus on biodegradable polymers as replacements for more bio-inert materials such as the polyolefins in areas as diverse as packaging and as scaffolds for tissue engineering has highlighted the need for a review of the approaches to being able to predict the lifetime of these materials. In many studies the focus has not been on the embrittlement and fracture of the material (as it would be for a polyolefin) but rather the products of degrdn., their toxicity and ultimate fate when in the environment, which may be the human body. These differences are primarily due to time-scale. Different approaches to the problem have arisen in biomedicine, such as the kinetic control of drug delivery by the bio-erosion of polymers, but the similarities in mechanism provide real prospects for the prediction of the safe service lifetime of a biodegradable polymer as a structural material. Common mechanistic themes that emerge include the diffusion-controlled process of water sorption and conditions for surface vs. bulk degrdn., the role of hydrolysis vs. oxidative degrdn. in controlling the rate of polymer chain scission and strength loss and the specificity of enzyme-mediated reactions.
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    Sudhakar, M.; Trishul, A.; Doble, M.; Suresh Kumar, K.; Syed Jahan, S.; Inbakandan, D.; Viduthalai, R. R.; Umadevi, V. R.; Sriyutha Murthy, P.; Venkatesan, R. Biofouling and Biodegradation of Polyolefins in Ocean Waters. Polym. Degrad. Stab. 2007, 92 (9), 1743– 1752,  DOI: 10.1016/j.polymdegradstab.2007.03.029
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    High d. polyethylene (HDPE), low d. polyethylene (LDPE), and polypropylene (PP) coupons were immersed for 6 mo in Bay of Bengal near Chennai Port (Port) and Fisheries Survey of India (FSI) sites. Samples were retrieved monthly and the extent of biofouling and biodegrdn. were monitored by measuring biol. and physicochem. parameters. Dissolved O2 and redox potential were higher at Port vs. FSI sites. Total suspended solids and org. matter were higher on PP followed by HDPE and LDPE, indicating hydrophobic surfaces favored biofouling. Pseudomonas species, anaerobic, heterotrophic, and Fe-reducing bacteria were obsd. on polymer surfaces. Biofouling depended on season; loading was highest in Aug. Chlorophyll was higher at FSI than at Port due to higher pollution levels and closeness to shore. Max. wt. loss was obsd. in LDPE (1.5-2.5%), followed by HDPE (0.5-0.8%) and PP (0.5-0.6%) samples deployed at Port in the 6 mo study period.
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    The distribution of oxygen and carbon dioxide gases in the unsatd. zone provides a geochem. signature of aerobic hydrocarbon degrdn. at petroleum product spill sites. The fluxes of these gases are proportional to the rate of aerobic biodegrdn. and are quantified by calibrating a math. transport model to the oxygen and carbon dioxide gas concn. data. Reaction stoichiometry is assumed to convert the gas fluxes to a corresponding rate of hydrocarbon degrdn. The method is applied at a gasoline spill site in Galloway Township, New Jersey, to det. the rate of aerobic degrdn. of hydrocarbons assocd. with passive and bioventing remediation field expts. At the site, microbial degrdn. of hydrocarbons near the water table limits the migration of hydrocarbon solutes in groundwater and prevents hydrocarbon volatilization into the unsatd. zone. In the passive remediation expt. a site-wide degrdn. rate est. of 34,400 g yr-1 (11.7 gal. yr-1) of hydrocarbon was obtained by model calibration to carbon dioxide gas concn. data collected in Dec. 1989. In the bioventing expt., degrdn. rate ests. of 46.0 and 47.9 g m-2 yr-1 (1.45 × 10-3 and 1.51 × 10-3 gal. ft. -2 yr-1) of hydrocarbon were obtained by model calibration to oxygen and carbon dioxide gas concn. data, resp. Method application was successful in quantifying the significance of a naturally occurring process that can effectively contribute to plume stabilization.
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    Polymer Testing (2006), 25 (8), 1006-1016CODEN: POTEDZ; ISSN:0142-9418. (Elsevier B.V.)
    An automatic direct measurement respirometric system was built, calibrated and tested to det. polymer biodegrdn. under simulated environmental conditions. The amt. of carbon dioxide produced during biopolymer biodegrdn. was converted to percentage of mineralization, and used as an indicator of the polymer biodegrdn. Poly(lactide) (PLA) bottles were used as the test material, and the results were compared with those from corn starch powder and poly(ethylene terephthalate) (PET) bottles. The respirometric system ran for more than 63 days without any user intervention, very stable and efficiently. At 63 days of exposure at 58 ± 2°C and 55 ± 5% relative humidity, PLA, corn starch, and PET achieved 64.2 ± 0.5%, 72.4 ± 0.7%, and 2.7 ± 0.2% mineralization, resp. Based on ASTM D 6400 and ISO14855, PLA bottles qualify as biodegradable since mineralization was greater than 60%.
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    Kunioka, M.; Ninomiya, F.; Funabashi, M. Biodegradation of Poly(Butylene Succinate) Powder in a Controlled Compost at 58 °C Evaluated by Naturally-Occurring Carbon 14 Amounts in Evolved CO2 Based on the ISO 14855–2 Method. Int. J. Mol. Sci. 2009, 10 (10), 4267– 4283,  DOI: 10.3390/ijms10104267
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    International Journal of Molecular Sciences (2009), 10 (10), 4267-4283CODEN: IJMCFK; ISSN:1422-0067. (Molecular Diversity Preservation International)
    The biodegradabilities of poly(butylene succinate) (PBS) powders in a controlled compost at 58° have been studied using a Microbial Oxidative Degrdn. Analyzer (MODA) based on the ISO 14855-2 method, entitled "Detn. of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions-Method by anal. of evolved carbon dioxide-Part 2: Gravimetric measurement of carbon dioxide evolved in a lab.-scale test". The evolved CO2 was trapped by an addnl. aq. Ba(OH)2 soln. The trapped BaCO3 was transformed into graphite via a serial vaporization and redn. reaction using a gas-tight tube and vacuum manifold system. This graphite was analyzed by accelerated mass spectrometry (AMS) to det. the percent modern carbon [pMC (sample)] based on the 14C radiocarbon concn. By using the theory that pMC (sample) was the sum of the pMC (compost) (109.87%) and pMC (PBS) (0%) as the resp. ratio in the detd. period, the CO2 (respiration) was calcd. from only one reaction vessel. It was found that the biodegradabilities detd. by the CO2 amt. from PBS in the sample vessel were about 30% lower than those based on the ISO method. These differences between the ISO and AMS methods are caused by the fact that part of the carbons from PBS are changed into metabolites by the microorganisms in the compost, and not changed into CO2.
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    Yagi, H.; Ninomiya, F.; Funabashi, M.; Kunioka, M. Anaerobic Biodegradation Tests of Poly(Lactic Acid) under Mesophilic and Thermophilic Conditions Using a New Evaluation System for Methane Fermentation in Anaerobic Sludge. Int. J. Mol. Sci. 2009, 10 (9), 3824– 3835,  DOI: 10.3390/ijms10093824
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    International Journal of Molecular Sciences (2009), 10 (9), 3824-3835CODEN: IJMCFK; ISSN:1422-0067. (Molecular Diversity Preservation International)
    Anaerobic biodegrdn. tests of poly(lactic acid) (PLA) powder were done at the thermophilic (55 °C) and mesophilic temp. (35 °C) under aquatic conditions [total solid concns. of the used sludge were 2.07% (at 55 °C) and 2.24% (at 35 °C)] using a newly developed evaluation system. With this system, the evolved biogas is collected in a gas sampling bag at atm. pressure. This method is more convenient than using a pressure transducer or inverted graduated cylinder submerged in water. PLA was degraded about 60% in 30 days, about 80% in 40 days and about 90% in 60 days at 55 °C. On the other hand, the PLA degrdn. started in 55 days at 35 °C and degrdn. rate was much slower than at 55 °C.
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    Strotmann, U.; Reuschenbach, P.; Schwarz, H.; Pagga, U. Development and Evaluation of an Online CO2 Evolution Test and a Multicomponent Biodegradation Test System. Appl. Environ. Microbiol. 2004, 70 (8), 4621– 4628,  DOI: 10.1128/AEM.70.8.4621-4628.2004
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    Well-established biodegrdn. tests use biogenously evolved carbon dioxide (CO2) as an anal. parameter to det. the ultimate biodegradability of substances. A newly developed anal. technique based on the continuous online measurement of cond. showed its suitability over other techniques. It could be demonstrated that the method met all criteria of established biodegrdn. tests, gave continuous biodegrdn. curves, and was more reliable than other tests. In parallel expts., only small variations in the biodegrdn. pattern occurred. When comparing the new online CO2 method with existing CO2 evolution tests, growth rates and lag periods were similar and only the final degree of biodegrdn. of aniline was slightly lower. A further test development was the unification and parallel measurement of all three important summary parameters for biodegrdn.-i.e., CO2 evolution, detn. of the BOD, and removal of dissolved org. carbon (DOC)-in a multicomponent biodegrdn. test system (MCBTS). The practicability of this test method was demonstrated with aniline. This test system had advantages for poorly water-sol. and highly volatile compds. and allowed the detn. of the carbon fraction integrated into biomass (heterotrophic yield). The integrated online measurements of CO2 and BOD systems produced continuous degrdn. curves, which better met the stringent criteria of ready biodegradability (60% biodegrdn. in a 10-day window). Furthermore the data could be used to calc. maximal growth rates for the modeling of biodegrdn. processes.
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    Yabannavar, A. V.; Bartha, R. Methods for Assessment of Biodegradability of Plastic Films in Soil. Appl. Environ. Microbiol. 1994, 60 (10), 3608– 3614,  DOI: 10.1128/AEM.60.10.3608-3614.1994
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    Methods for assessment of biodegradability of plastic films in soil
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    Applied and Environmental Microbiology (1994), 60 (10), 3608-14CODEN: AEMIDF; ISSN:0099-2240.
    Traditional and novel techniques were tested and compared for their usefulness in evaluating biodegradability claims made for newly formulated degradable plastic film products. Photosensitized polyethylene (PE), starch-PE, extensively plasticized PVC, and polypropylene (PP) films were incorporated into aerobic soil. Biodegrdn. was measured for 3 mo under generally favorable conditions. Carbon dioxide evolution, residual wt. recovery, and loss of tensile strength measurements were supplemented, for some films, by gas chromatog. measurements of plasticizer loss and gel permeation chromatog. (GPC) measurement of polymer mol. size distribution. Six- and 12-wk sunlight exposures of photosensitized PE films resulted in extensive photochem. damage that failed to promote subsequent mineralization in soil. An 8% starch-PE film and the plasticized PVC film evolved significant amts. of CO2 in biodegrdn. tests and lost residual wt. and tensile strength, but GPC measurements demonstrated that all these changes were confined to the additives and the PE and PVC polymers were not degraded. Carbon dioxide evolution was found to be a useful screening tool for plastic film biodegrdn., but for films with additives, polymer biodegrdn. needs to be confirmed by GPC. Photochem. crosslinking of polymer strands reduces soly. and may interfere with GPC measurements of polymer degrdn.
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    Castellani, F.; Esposito, A.; Stanzione, V.; Altieri, R. Measuring the Biodegradability of Plastic Polymers in Olive-Mill Waste Compost with an Experimental Apparatus. Adv. Mater. Sci. Eng. 2016, 2016, 6909283,  DOI: 10.1155/2016/6909283
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    Calmon, A.; Dusserre-Bresson, L.; Bellon-Maurel, V.; Feuilloley, P.; Silvestre, F. An Automated Test for Measuring Polymer Biodegradation. Chemosphere 2000, 41 (5), 645– 651,  DOI: 10.1016/S0045-6535(99)00491-9
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    The biodegradability of polymer materials as evaluated by the modified Sturm test is labor-intensive, cumbersome and costly and also tends to cumulate errors. An automated system for the measurement of carbon dioxide would overcome many of these disadvantages. We describe here a method in which CO2 was detd. by IR spectroscopy. We compared the results with those from trapping CO2 in a soln. of barium hydroxide (Ba(OH)2) followed by manual titrn. The automated system was more reproducible, less costly and more compact. The automated system could also be employed to measure the biodegradability of other substances such as oils and detergents.
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    Lefaux, S.; Manceau, A.; Benguigui, L.; Campistron, I.; Laguerre, A.; Laulier, M.; Leignel, V.; Tremblin, G. Continuous Automated Measurement of Carbon Dioxide Produced by Microorganisms in Aerobic Conditions: Application to Proteic Film Biodegradation. C. R. Chim. 2004, 7 (2), 97– 101,  DOI: 10.1016/j.crci.2003.10.008
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    Continuous automated measurement of carbon dioxide produced by microorganisms in aerobic conditions: application to proteic film biodegradation
    Lefaux, Sandra; Manceau, Annick; Benguigui, Ludovic; Campistron, Irene; Laguerre, Albert; Laulier, Marc; Leignel, Vincent; Tremblin, Gerard
    Comptes Rendus Chimie (2004), 7 (2), 97-101CODEN: CRCOCR; ISSN:1631-0748. (Editions Scientifiques et Medicales Elsevier)
    An automated set-up based on the original Sturm test was developed for detg. the biodegradability of proteic mulching films. This method is based on the measurement of released (respiratory metab. of microorganisms) CO2 to det. film biodegradability. Maintenance of const. aerobic conditions in thermoregulated bioreactors and continuous measurement of released CO2 with an IR differential gas analyzer were the main advantages of this set-up. It was verified with a plasticized proteic film that soil exts. could be used as microbial sources instead of activated sludge that was usually used in lab. biodegrdn. tests.
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    Kale, G.; Auras, R.; Singh, S. P. Degradation of Commercial Biodegradable Packages under Real Composting and Ambient Exposure Conditions. J. Polym. Environ. 2006, 14 (3), 317– 334,  DOI: 10.1007/s10924-006-0015-6
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    Kale, Gaurav; Auras, Rafael; Singh, Sher Paul
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    The use of long-lasting polymers as packaging materials for short lived applications is not entirely justified. Plastic packaging materials are often soiled due to foodstuffs and other biol. substances, making phys. recycling of these materials impractical and normally unwanted. Hence, there is an increasing demand for biodegradable packaging materials which could be easily renewable. Use of biopolymer based packaging materials allows consideration of eliminating issues such as landfilling, sorting, and reprocessing through taking advantage of their unique functionality, that is compostability. Composting allows disposal of biodegradable packages and is not as energy intensive compared to sorting and reprocessing for recycling, although it requires more energy than landfilling. We studied the degrdn. of 3 com. available biodegradable packages made of poly (LD-lactide) (PLA) under real compost conditions and under ambient exposure by visual inspection, gel permeation chromatog., differential scanning calorimetry, and thermal gravimetric anal. A novel technique to study the degradability of these packages and to track the degrdn. rate under real compost conditions was used. The packages were subjected to composting for 30 days, and the degrdn. of the phys. properties was measured at 1, 2, 4, 6, 9, 15, and 30 days. PLA packages made of 96% L-lactide exhibited lower degrdn. than PLA packages made of 94% L-lactide, mainly due to their highly ordered structure, therefore, higher crystallinity. The degrdn. rate changed as the initial crystallinity and the L-lactide content of the packages varied. Temp., relative humidity, and pH of the compost pile played an important role in the total degrdn. of the packages. A first order degrdn. of the mol. wt. as a function of time was obsd. for the 3 packages.
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    Bandyopadhyay, P. K.; Shaw, M. T.; Weiss, R. A. Detection and Analysis of Aging and Degradation of Polyolefins: A Review of Methodologies. Polym.-Plast. Technol. Eng. 1985, 24 (2–3), 187– 241,  DOI: 10.1080/03602558508070065
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    A review with 193 refs. on the various exptl. techniques employed in following the course of aging and degrdn. of unstabilized and additive-free polyolefins. The mechanism of polymer degrdn. and the various models used in predicting polymer lifetimes from exptl. results were presented and discussed.
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    Hoshino, A.; Tsuji, M.; Fukuda, K.; Nonagase, M.; Sawada, H.; Kimura, M. Changes in Molecular Structure of Biodegradable Plastics during Degradation in Soils Estimated by FT-IR and NMR. Soil Sci. Plant Nutr. 2002, 48 (4), 469– 473,  DOI: 10.1080/00380768.2002.10409228
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    Changes in molecular structure of biodegradable plastics during degradation in soil estimated by FT-IR and NMR
    Hoshino, Akira; Tsuji, Masao; Fukuda, Kazuhiko; Nonagase, Miki; Sawada, Hideo; Kimura, Makoto
    Soil Science and Plant Nutrition (Tokyo, Japan) (2002), 48 (4), 469-473CODEN: SSPNAW; ISSN:0038-0768. (Japanese Society of Soil Science and Plant Nutrition)
    The biodegradable plastic specimens (poly(3-hydroxybutylate-valerate) (PHB/V), poly(.vepsiln.-caprolactone) (PCL), poly(butylene succinate) (PBS), poly(butylene succinate adipate) (PBSA), and poly-lactide (PLA)) were placed in soils for 1 yr at 19 sites in Japan. The specimens were studied for chem. structure changes, using FT-IR, 1H-NMR, and 13C-NMR. No differences in the main absorbency bands of the at. groups were shown by FT-IR for any of the plastic specimens tested. Both 1H-NMR and 13C-NMR analyses suggested that the mol. structure of the PHB/V specimens changed after 1 yr placement in soils. Based on the assignment of the resp. signals of chem. shifts derived from valerate, selective degrdn. of the valerate moiety in the PHB/V specimens was obsd. In contrast, although wt. loss, and/or a decrease in tensile strength and elongation were obsd. after the placement in soils for the PCL, PBS, PBSA, and PLA specimens, the analyses of these specimens by FT-IR, 1H-NMR, and 13C-NMR did not reveal any changes in their mol. structure.
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    Bennett, R. L.; Keller, A.; Stejny, J.; Murray, M. Study of the Direct Detection of Crosslinking in Hydrocarbons by 13C-NMR. II. Identification of Crosslink in Model Compound and Application to Irradiated Paraffins. J. Polym. Sci., Polym. Chem. Ed. 1976, 14 (12), 3027– 3033,  DOI: 10.1002/pol.1976.170141216
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    Bennett, R. L.; Keller, A.; Stejny, J.; Murray, M.
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    The 13C-NMR signal due to tertiary C atom representing a crosslink remote from mol. ends was identified in the model compd., 1,1,2,2-tetra(tridecyl)ethane [61625-16-9], and the identification was used to det. crosslinks in irradiated linear paraffins, hexadecane [544-76-3] and eicosane [112-95-8], as a preliminary for future study of crosslinks in irradiated polyethylene. The crosslinking could be assocd. with corresponding changes in mol. wt. as shown by discrete peaks in the gel permeation chromatograms of the samples and randomness of the crosslinking process in the liq. state being inferred.
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    Ammala, A.; Bateman, S.; Dean, K.; Petinakis, E.; Sangwan, P.; Wong, S.; Yuan, Q.; Yu, L.; Patrick, C.; Leong, K. H. An Overview of Degradable and Biodegradable Polyolefins. Prog. Polym. Sci. 2011, 36 (8), 1015– 1049,  DOI: 10.1016/j.progpolymsci.2010.12.002
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    An overview of degradable and biodegradable polyolefins
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    Progress in Polymer Science (2011), 36 (8), 1015-1049CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    A review. The use of engineering plastics, esp. polyolefins has increased significantly in recent decades largely due to their low cost, good mech. properties and light wt. However, this increase in usage has also created many challenges assocd. with disposal and their impact on the environment. This is because polyolefins do not easily degrade in the natural environment and hence the need for degradable polyolefins has become a major topic of research. Degradable polyolefins are designed to retain functionality as a commodity plastic for the required service life but degrade to non-toxic end products in a disposal environment. They are typically designed to oxo-degrade while undergoing changes in chem. structure as a result of oxidn. in air, thus causing the breakdown of the mols. into small fragments that are then bioassimilated. This article presents (i) a comprehensive review of the chem. of additives for the degrdn. of polyolefins, (ii) a patent and scientific literature summary of technologies including com. available systems, (iii) the mechanisms of degrdn. and biodegrdn., (iv) testing methods and (v) toxicity.
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    Celina, M.; Ottesen, D. K.; Gillen, K. T.; Clough, R. L. FTIR Emission Spectroscopy Applied to Polymer Degradation. Polym. Degrad. Stab. 1997, 58 (1–2), 15– 31,  DOI: 10.1016/S0141-3910(96)00218-2
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    FTIR emission spectroscopy applied to polymer degradation
    Celina, M.; Ottesen, D. K.; Gillen, K. T.; Clough, R. L.
    Polymer Degradation and Stability (1997), 58 (1-2), 15-31CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Science Ltd.)
    The thermal degrdn. of some common polymers was investigated using IR emission spectroscopy. The potential of the technique to contribute to polymer degrdn. studies is demonstrated by measuring the spectroscopic changes that occur during thermal degrdn., oxidn. or decompn. of polymers under air at temps. ranging from 150 to 250°C. Polymer types studied include EPDM and nitrile rubbers (com. materials contg. some inorg. fillers), PMMA, polyacrylonitrile, polyamide, PVC and polystyrene. The resulting qual. changes in the polymers were easily detected, and were correlated with the current knowledge on the degrdn. mechanisms of these materials. These include simple carbonyl formation and related oxidative reactions, wt. loss and volatilization, as well as formation of conjugation and specific polymer reactions. Some fundamental aspects and limitations of the technique are discussed to demonstrate the intrinsic difficulties of attempting to det. precise emittances and ultimately quant. spectroscopic information. FTIR emission appears to be promising for studying in situ polymer degrdn.
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  103. 103
    Moldovan, A.; Pa, S.; Buican, R.; Tierean, M. Characterization of Polyolefins Wastes by FTIR Spectroscopy. Bull. Transilvania Univ. Brasov, Ser. I 2012, 5 (54), 65– 72
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    Characterization of polyolefins wastes by FTIR spectroscopy
    Moldovan, A.; Patachia, S.; Buican, R.; Tierean, M. H.
    Bulletin of the Transilvania University of Brasov, Series I: Engineering Sciences (2012), 5 (2), 65-72, 8 pp.CODEN: BTUBBC ISSN:. (Transilvania University Press)
    In this paper the Fourier transform IR spectroscopy (FTIR) method has been used to assess the degrdn. state (oxidn. degree) of different polyolefinic plastic wastes from construction industry, sepd. in d. fractions. Polyolefin oxidn. has been identified and quantified by the presence of a strong absorption band assigned to carbonyl groups and its possible influence on the properties and behavior of the polymer wastes has been critically assessed.
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    Ioakeimidis, C.; Fotopoulou, K. N.; Karapanagioti, H. K.; Geraga, M.; Zeri, C.; Papathanassiou, E.; Galgani, F.; Papatheodorou, G. The Degradation Potential of PET Bottles in the Marine Environment: An ATR-FTIR Based Approach. Sci. Rep. 2016, 6, 23501,  DOI: 10.1038/srep23501
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    The degradation potential of PET bottles in the marine environment: An ATR-FTIR based approach
    Ioakeimidis, C.; Fotopoulou, K. N.; Karapanagioti, H. K.; Geraga, M.; Zeri, C.; Papathanassiou, E.; Galgani, F.; Papatheodorou, G.
    Scientific Reports (2016), 6 (), 23501CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
    The dominance and persistence of plastic debris in the marine environment are well documented. No information exists in respect to their lifespan in the marine environment. Nevertheless, the degrdn. potential of plastic litter items remains a crit. issue for marine litter research. In the present study, polyethylene terephthalate bottles (PETs) collected from the submarine environment were characterized using ATR-FTIR in respect to their degrdn. potential attributed to environmental conditions. A temporal indication was used as indicative to the years of presence of the PETs in the environment as debris. PETs seem to remain robust for approx. fifteen years. Afterwards, a significant decrease of the native functional groups was recorded; some even disappear; or new-not typical for PETs-are created. At a later stage, using the PET time series collected from the Saronikos Gulf (Aegean Sea-E. Mediterranean), it was possible to date bottles that were collected from the bottom of the Ionian Sea (W. Greece). It is the first time that such a study has been conducted with samples that were actually degraded in the marine environment.
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    Reddy, M. M.; Gupta, R. K.; Gupta, R. K.; Bhattacharya, S. N.; Parthasarathy, R. Abiotic Oxidation Studies of Oxo-Biodegradable Polyethylene. J. Polym. Environ. 2008, 16 (1), 27– 34,  DOI: 10.1007/s10924-008-0081-z
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    Abiotic Oxidation Studies of Oxo-biodegradable Polyethylene
    Reddy, M. M.; Gupta, Rahul K.; Gupta, Rakesh K.; Bhattacharya, S. N.; Parthasarathy, R.
    Journal of Polymers and the Environment (2008), 16 (1), 27-34CODEN: JPENFW; ISSN:1566-2543. (Springer)
    The best approach to induce oxo-biodegrdn. in polyethylene is the use of special additives known as pro-oxidants. Pro-oxidants accelerate abiotic oxidn. and subsequent polymer chain cleavage rendering the product apparently more susceptible to biodegrdn. In this work, the abiotic oxidn. is studied to understand how the addn. of nanoclay affects the oxidn. rate and the degrdn. mechanism of oxo-biodegradable polyethylene. In order to achieve this, the following materials were used in this study: (1) polyethylene (PE), (2) oxo-biodegradable polyethylene (OPE), (3) polyethylene nanocomposite (PENac), and (4) oxo-biodegradable polyethylene nanocomposite (OPENac). Wide-Angle x-ray scattering (WAXS) and TEM studies reveal that grafting in the prepn. of composites helps to achieve mixed intercalated/exfoliated morphol. in PENac and OPENac. Abiotic oxidn. was carried out in an oven for a period of 14 days at 70° with air supply. The effect of abiotic oxidn. was evaluated by measuring the changes in tensile strength, elongation at break, carbonyl index and mol. wt. Results show that OPE and OPENac are more susceptible to oxidn. than PENac. The mol. wt. distribution data obtained from GPC reveal that the addn. of nanoclay does not alter the oxidn. mechanism in OPE significantly.
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    Ojeda, T.; Freitas, A.; Birck, K.; Dalmolin, E.; Jacques, R.; Bento, F.; Camargo, F. Degradability of Linear Polyolefins under Natural Weathering. Polym. Degrad. Stab. 2011, 96 (4), 703– 707,  DOI: 10.1016/j.polymdegradstab.2010.12.004
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    Degradability of linear polyolefins under natural weathering
    Ojeda, Telmo; Freitas, Ana; Birck, Katia; Dalmolin, Emilene; Jacques, Rodrigo; Bento, Fatima; Camargo, Flavio
    Polymer Degradation and Stability (2011), 96 (4), 703-707CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    High d. polyethylene (HDPE), linear low d. polyethylene (LLDPE), and isotactic polypropylene (PP) contg. antioxidant additives at low or zero levels were extruded and blown molded as films. An HDPE/LLDPE com. blend contg. a pro-oxidant additive (i.e., an oxo-biodegradable blend) was taken from the market as supermarket bag. These four polyolefin samples were exposed to natural weathering for one year during which their structure and thermal and mech. properties were monitored. This study shows that the real durability of olefin polymers may be much shorter than centuries, as in less than one year the mech. properties of all samples decreased virtually to zero, as a consequence of severe oxidative degrdn., that resulted in substantial redn. in molar mass accompanied by a significant increase in content of carbonyl groups. PP and the oxo-bio HDPE/LLDPE blend degraded very rapidly, whereas HDPE and LLDPE degraded more slowly, but significantly in a few months. The main factors influencing the degradability were the frequency of tertiary carbon atoms in the chain and the presence of a pro-oxidant additive. The primary (sterically hindered phenol) and secondary (phosphite) antioxidant additives added to PP slowed but did not prevent rapid photo-oxidative degrdn., and in HDPE and LLDPE the secondary antioxidant additive had little influence on the rate of abiotic degrdn. at the concns. used here.
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    Rouillon, C.; Bussiere, P.-O.; Desnoux, E.; Collin, S.; Vial, C.; Therias, S.; Gardette, J.-L. Is Carbonyl Index a Quantitative Probe to Monitor Polypropylene Photodegradation?. Polym. Degrad. Stab. 2016, 128, 200– 208,  DOI: 10.1016/j.polymdegradstab.2015.12.011
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    Is carbonyl index a quantitative probe to monitor polypropylene photodegradation?
    Rouillon, C.; Bussiere, P.-O.; Desnoux, E.; Collin, S.; Vial, C.; Therias, S.; Gardette, J.-L.
    Polymer Degradation and Stability (2016), 128 (), 200-208CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    For several decades, authors relied upon the carbonyl index to monitor the photo-oxidn. of polypropylene and to account for the degrdn. of the mech. properties. This paper starts from one question: is the carbonyl band at 1712 cm-1 in IR spectroscopy really appropriate to quant. measure the extent of oxidn. of polypropylene. This article brings a neg. answer to this question, and the results given in this paper suggest that carbonyl detection by IR spectroscopy, despite it has been used for years, is not the abs. probe to monitor the photooxidn. of polypropylene. Hence, the article aims to provide new relevant and quant. criteria. These criteria allow the photo-oxidn. of PP to be correlated with properties degrdn., the one of interest in this case being the gloss loss, which reflects the loss of the surface mech. properties. These criteria give an early warning of the degrdn. and permit anticipating the loss of polypropylene functional properties. There are various criteria that can be proposed, the Me band at 1456 cm-1 being the easiest way to measure the oxidn. It is shown that the modifications of the Me absorbance fit quite well the increase of crystallinity, mol. wt., and it quite-well reflects the micro-hardness, this last parameter being well correlated to the loss of gloss.
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    Weikart, C. M.; Yasuda, H. K. Modification, Degradation, and Stability of Polymeric Surfaces Treated with Reactive Plasmas. J. Polym. Sci., Part A: Polym. Chem. 2000, 38 (17), 3028– 3042,  DOI: 10.1002/1099-0518(20000901)38:17<3028::AID-POLA30>3.0.CO;2-B
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    Modification, degradation, and stability of polymeric surfaces treated with reactive plasmas
    Weikart, Christopher M.; Yasuda, Hirotsugu K.
    Journal of Polymer Science, Part A: Polymer Chemistry (2000), 38 (17), 3028-3042CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
    The degrdn., modification, and stability of polymeric surfaces, i.e., low-d. polyethylene, polyoxymethylene, PMMA, poly(ethylene terephthalate) and silicone rubber, exposed to chem. reactive O and H2O-vapor plasmas were investigated. Specifically, the effects of these plasmas on etching rate, surface morphol., wetting instability, and fluid-holding capability were studied. Wetting instability is reflected by hydrophobic recovery and can be examd. by the Wilhelmy balance method. Although hydrophobic recovery is usually attributed to surface configuration change, there are actually two types: reversible and permanent. Reversible hydrophobic recovery is caused by surface configuration change, whereas permanent hydrophobic recovery is caused by the creation of oxidized surface oligomers. The two are distinguished by identifying differences in the shapes of the corresponding Wilhelmy force loops and in the fluid-holding parameter. The presence of surface oligomers was most detrimental to wetting stability and fluid-holding capability but could be controlled via the type of reactive gas, the discharge conditions, and the polymer substrate. In general, polymers most susceptible to O-plasma etching had the least surface oligomers and vice versa, whereas H2O-vapor plasma suppressed surface oligomers on polymers less susceptible to etching.
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    Biresaw, G.; Carriere, C. J. Correlation between Mechanical Adhesion and Interfacial Properties of Starch/Biodegradable Polyester Blends. J. Polym. Sci., Part B: Polym. Phys. 2001, 39 (9), 920– 930,  DOI: 10.1002/polb.1067
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    Correlation between mechanical adhesion and interfacial properties of starch/biodegradable polyester blends
    Biresaw, G.; Carriere, C. J.
    Journal of Polymer Science, Part B: Polymer Physics (2001), 39 (9), 920-930CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
    Biopolymers are preferred ingredients for the manuf. of materials because they are based on abundantly available and renewable raw materials that have benign environmental problems assocd. with their prodn., fabrication, use, and disposal; however, the wide use of biopolymers in engineering applications has not been achieved, mainly because of the inferior quality of many biopolymer-based products. To overcome this limitation, studies were initiated on blends of biopolymers and biodegradable synthetic polymers. The authors used the contact angle of probe liqs. to measure the surface energy of polystyrene, the biodegradable polyesters polycaprolactone, poly(hydroxybutyrate-co-hydroxyvalerate), polylactic acid, polybutylene adipate terephthalate, and adipic poly(hydroxy ester ether), and normal starch. The surface energies were used to est. the starch/polymer interfacial energy and work of adhesion. The calcd. starch/polyester work of adhesion showed mixed correlation with published starch/polyester mech. properties, indicating that factors other than interfacial properties might be dominant in detg. the mech. properties of some starch/polyester blends.
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    Suresh, B.; Maruthamuthu, S.; Kannan, M.; Chandramohan, A. Mechanical and Surface Properties of Low-Density Polyethylene Film Modified by Photo-Oxidation. Polym. J. 2011, 43 (4), 398– 406,  DOI: 10.1038/pj.2010.147
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    Mechanical and surface properties of low-density polyethylene film modified by photo-oxidation
    Suresh, Balasubramanian; Maruthamuthu, Sundaram; Kannan, Murugasamy; Chandramohan, Angannan
    Polymer Journal (Tokyo, Japan) (2011), 43 (4), 398-406CODEN: POLJB8; ISSN:0032-3896. (NPG Nature Asia-Pacific)
    Mech. and surface properties are considered important in governing the phys. strength of polymers. A com. available oxo-biodegradable polymer additive, which has induced surface and mech. property changes during photo-oxidn. in low-d. polyethylene (LDPE) films, has been studied. LDPE films contg. the oxo-biodegradable additive were irradiated with UV-B lamps at 30±1°C for an extended time period. The changes manifested on the polymer surface and in the mech. properties were studied with respect to surface wettability, surface morphol. using scanning electron microscope, surface topol. by at. force microscopy, functional groups by Fourier transformed IR spectroscopy, absorbance spectra by UV-visible spectroscopy and elongation at break and tensile strength through mech. testing. The increase in the wettability and surface-free energy of the irradiated samples was attributed to the formation of hydrophilic groups on the polymer surface by photo-oxidn., which occurs by the exposure of PE to UV irradn. in the presence of air. The degree of redn. in the mech. strength and surface property modifications in our study are appreciable through the use of an oxo-biodegradable additive added to LDPE film samples.
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    Strapasson, R.; Amico, S. C.; Pereira, M. F. R.; Sydenstricker, T. H. D. Tensile and Impact Behavior of Polypropylene/Low Density Polyethylene Blends. Polym. Test. 2005, 24 (4), 468– 473,  DOI: 10.1016/j.polymertesting.2005.01.001
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    Tensile and impact behavior of polypropylene/low density polyethylene blends
    Strapasson, R.; Amico, S. C.; Pereira, M. F. R.; Sydenstricker, T. H. D.
    Polymer Testing (2005), 24 (4), 468-473CODEN: POTEDZ; ISSN:0142-9418. (Elsevier B.V.)
    Blends of polypropylene (PP) and low-d. polyethylene (LDPE) may contribute to make recycling more economically attractive. The aim of this work was to make PP/LDPE blends (0/100, 25/75, 50/50, 75/25 and 100/0 wt./wt.) via injection molding carried out under various injection temps. and to evaluate their tensile and impact properties. The blends yielded tensile stress-strain curves very dependent on their compn., esp. regarding elongation at break and the presence of necking. An irregular behavior for the 50/50 wt./wt. blend is reported. Nevertheless, a linear variation of the yield strength and elastic modulus with the blend compn. was obsd. The behavior of the blend was also very dependent on processing temp. Addn. of 25% of LDPE to the PP may result in similar degrdn. of its mech. properties to that caused by a 10 °C processing temp. increase. Statistical analyses proved valuable when reporting results concerning blends.
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    M, Z.; S, M. Z. H. Biodegradability and Tensile Properties of Compatibilized Polyethylene/Rice Bran Film. Chem. Eng. Trans. 2017, 919– 924,  DOI: 10.3303/CET1756154
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    Li, Y.; Chu, Z.; Li, X.; Ding, X.; Guo, M.; Zhao, H.; Yao, J.; Wang, L.; Cai, Q.; Fan, Y. The Effect of Mechanical Loads on the Degradation of Aliphatic Biodegradable Polyesters. Regen. Biomater. 2017, 4 (3), 179– 190,  DOI: 10.1093/rb/rbx009
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    The effect of mechanical loads on the degradation of aliphatic biodegradable polyesters
    Li, Ying; Chu, Zhaowei; Li, Xiaoming; Ding, Xili; Guo, Meng; Zhao, Haoran; Yao, Jie; Wang, Lizhen; Cai, Qiang; Fan, Yubo
    Regenerative Biomaterials (2017), 4 (3), 179-190CODEN: RBEIC4; ISSN:2056-3426. (Oxford University Press)
    Aliph. biodegradable polyesters have been the most widely used synthetic polymers for developing biodegradable devices as alternatives for the currently used permanent medical devices. The performances during biodegrdn. process play crucial roles for final realization of their functions. Because physiol. and biochem. environment in vivo significantly affects biodegrdn. process, large nos. of studies on effects of mech. loads on the degrdn. of aliph. biodegradable polyesters have been launched during last decades. In this review article, we discussed the mechanism of biodegrdn. and several different mech. loads that have been reported to affect the biodegrdn. process. Other physiol. and biochem. factors related to mech. loads were also discussed. The mech. load could change the conformational strain energy and morphol. to weaken the stability of the polymer. Besides, the load and pattern could accelerate the loss of intrinsic mech. properties of polymers. This indicated that investigations into effects of mech. loads on the degrdn. should be indispensable. More combination condition of mech. loads and multiple factors should be considered in order to keep the degrdn. rate controllable and evaluate the degrdn. process in vivo accurately. Only then can the degradable devise achieve the desired effects and further expand the special applications of aliph. biodegradable polyesters.
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    Mano, J. F.; Koniarova, D.; Reis, R. L. Thermal Properties of Thermoplastic Starch/Synthetic Polymer Blends with Potential Biomedical Applicability. J. Mater. Sci.: Mater. Med. 2003, 14 (2), 127– 135,  DOI: 10.1023/A:1022015712170
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    Thermal properties of thermoplastic starch/synthetic polymer blends with potential biomedical applicability
    Mano, J. F.; Koniarova, D.; Reis, R. L.
    Journal of Materials Science: Materials in Medicine (2003), 14 (2), 127-135CODEN: JSMMEL; ISSN:0957-4530. (Kluwer Academic Publishers)
    Previous studies shown that thermoplastic blends of corn starch with some biodegradable synthetic polymers(poly(ε-caprolactone), cellulose acetate, poly(lactic acid) and ethylene-vinyl alc. copolymer) have good potential to be used in a series of biomedical applications. In this work the thermal behavior of these structurally complex materials is investigated by differential scanning calorimetry (DSC) and by thermogravimetric anal. (TGA). In addn., Fourier-transform IR (FTIR) spectroscopy was used to investigate the chem. interactions between the different components. The endothermic gelatinization process (or water evapn.) obsd. by DSC in starch is also obsd. in the blends. Special attention was paid to the structural relaxation that can occur in the blends with poly(lactic acid) at body temp. that may change the phys. properties of the material during its application as a biomaterial. At least three degrdn. mechanisms were identified in the blends by means of using TGA, being assigned to the mass loss due to the plasticizer leaching, and to the degrdn. of the starch and the synthetic polymer fractions. The non-isothermal kinetics of the decompn. processes was analyzed using two different integral methods. The anal. included the calcn. of the activation energy of the correspondent reactions.
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    Nanda, P. K.; Lochan Nayak, P.; Krishna Rao, K. Thermal Degradation Analysis of Biodegradable Plastics from Urea-Modified Soy Protein Isolate. Polym.-Plast. Technol. Eng. 2007, 46 (3), 207– 211,  DOI: 10.1080/03602550601152713
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    Thermal degradation analysis of biodegradable plastics from urea-modified soy protein isolate
    Nanda, Prativa Kumari; Nayak, Padma Lochan; Rao, K. Krishna
    Polymer-Plastics Technology and Engineering (2007), 46 (3), 207-211CODEN: PPTEC7; ISSN:0360-2559. (Taylor & Francis, Inc.)
    Environmental pollution caused due to petroleum-based plastics is growing worldwide. Soy protein isolate, a potential alternative to some petrochem. polymers, is cheap and available in plenty. This natural biopolymer is chem. modified with urea at 5, 10, and 20% (wt./wt.) and 2M (molar) for better processing conditions. The FTIR spectra of the compds. have been studied to know the structure of biopolymers. The differential scanning calorimetry and thermogravimetric anal. of these samples have been monitored. TGA of the modified material has been followed using a computer anal. method, LOTUS package, developed by us, for assigning the degrdn. mechanism and evaluating the kinetic parameters using a no. of equations. The thermal degrdn. mechanism of this biopolymer is explained on the basis of the kinetic parameters.
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    Priselac, D.; Tomašegović, T.; Mahović Poljaček, S.; Cigula, T.; Leskovac, M. Thermal, Surface and Mechanical Properties of PCL/PLA Composites with Coconut Fibres as an Alternative Material to Photopolymer Printing Plates. Teh. Glas. 2017, 11 (3), 111– 116
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    Raghavan, D.; Torma, A. E. DSC and FTIR Characterization of Biodegradation of Polyethylene. Polym. Eng. Sci. 1992, 32 (6), 438– 442,  DOI: 10.1002/pen.760320609
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    DSC and FTIR characterization of biodegradation of polyethylene
    Raghavan, D.; Torma, A. E.
    Polymer Engineering and Science (1992), 32 (6), 438-42CODEN: PYESAZ; ISSN:0032-3888.
    aspergillus niger, A fungus, was used in the degrdn. of com. available thermoplastic polyethylene (I) films. Quant. calorimetric measurements performed on as-received, abiotic, and biotic treated I samples, revealed that the amorphousness of the sample decreases during biodegrdn. The external substrates (sucrose) in the growth medium influenced the biodegrdn. process of I. Furthermore, the crystallinity data on different biotreated samples indicated that the adapted microorganisms were able to metabolize a small portion of I. The significance of the FTIR results of I samples were discussed.
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    Odusanya, S. A.; Nkwogu, J. V.; Alu, N.; Etuk Udo, G. A.; Ajao, J. A.; Osinkolu, G. A.; Uzomah, A. C. Preliminary Studies on Microbial Degradation of Plastics Used in Packaging Potable Water in Nigeria. Niger. Food J. 2013, 31 (2), 63– 72,  DOI: 10.1016/S0189-7241(15)30078-3
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    Leroy, V.; Cancellieri, D.; Leoni, E. Thermal Degradation of Ligno-Cellulosic Fuels: DSC and TGA Studies. Thermochim. Acta 2006, 451 (1–2), 131– 138,  DOI: 10.1016/j.tca.2006.09.017
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    Thermal degradation of ligno-cellulosic fuels: DSC and TGA studies
    Leroy, V.; Cancellieri, D.; Leoni, E.
    Thermochimica Acta (2006), 451 (1-2), 131-138CODEN: THACAS; ISSN:0040-6031. (Elsevier B.V.)
    The scope of this work was to show the utility of thermal anal. and calorimetric expts. to study the thermal oxidative degrdn. of Mediterranean scrubs. We investigated the thermal degrdn. of four species; DSC and TGA were used under air sweeping to record oxidative reactions in dynamic conditions. Heat released and mass loss are important data to be measured for wildland fires modeling purpose and fire hazard studies on lignocellulosic fuels. Around 638 and 778 K, two dominating and overlapped exothermic peaks were recorded in DSC and individualized using a exptl. and numerical sepn. This stage allowed obtaining the enthalpy variation of each exothermic phenomenon. As an application, we propose to classify the fuels according to the heat released and the rate const. of each reaction. TGA expts. showed under air two successive mass loss around 638 and 778 K. Both techniques are useful in order to measure ignitability, combustibility and sustainability of forest fuels.
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    Vieyra, H.; Aguilar-Méndez, M. A.; San Martín-Martínez, E. Study of Biodegradation Evolution during Composting of Polyethylene-Starch Blends Using Scanning Electron Microscopy. J. Appl. Polym. Sci. 2013, 127 (2), 845– 853,  DOI: 10.1002/app.37818
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    Study of biodegradation evolution during composting of polyethylene-starch blends using scanning electron microscopy
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    Journal of Applied Polymer Science (2013), 127 (2), 845-853CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
    The end product of low-d. polyethylene-starch was manufd. by injection molding process. Four starch concns. (10, 25, 40, and 50%) were used for blend prepns., which were injected into the mold of a 250 mL com. cup. A control sample of neat polyethylene (PE) was also included. Square coupons (4 cm × 4 cm) of each blend were buried in the middle of a 50 cm pile of compost. Samples were recovered, washed, dried, and weighed after 25, 50, 75, 100, and 125 days beneath the compost. SEM (SEM) anal. was performed on the samples to track the biodegradability evolution. A SEM scandium analyzer was used to measure the size and no. of pores and the eroded area. Wt. loss measurements were conducted to validate the SEM observations. Total biodegrdn. time was detd. by math. anal. and graphical extrapolation. SEM anal. revealed the formation of pores, cavities, discontinuities, and cracks resulting from the time beneath the compost. Pore measurements revealed that the specimen composed of 40% starch and submerged for 125 days experienced up to 25% eroded area. Pure PE remained practically unchanged for the 125-day period. Fourier transform IR spectroscopy studies also demonstrated the biodegrdn. of PE in PE-starch blends. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012.
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    Adamcová, D.; Radziemska, M.; Zloch, J.; Dvořáčková, H.; Elbl, J.; Kynický, J.; Brtnický, M.; Vaverková, M. D. SEM Analysis and Degradation Behavior of Conventional and Bio-Based Plastics During Composting. Acta Univ. Agric. Silvic. Mendelianae Brun. 2018, 66 (2), 349– 356,  DOI: 10.11118/actaun201866020349
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    Araújo, M. A.; Cunha, A. M.; Mota, M. Changes on Surface Morphology of Corn Starch Blend Films. J. Biomed. Mater. Res., Part A 2010, 94, 720– 729,  DOI: 10.1002/jbm.a.32725
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    Journal of Biomedical Materials Research, Part A (2010), 94A (3), 720-729CODEN: JBMRCH; ISSN:1549-3296. (John Wiley & Sons, Inc.)
    This study aims at evaluating the influence of enzymic degrdn. soln. on the surface morphol. and thermal properties of a poly(ethylene-vinyl alc.) copolymer-corn starch thermoplastic blend (SEVA-C), as a function of immersion time. To perform this study, three different batches were assessed using SEVA-C samples of different thicknesses and a fixed wt. of 1.6 g, immersed in α-amylase (50 u/L) up to 90 days at 37°C. TGA, contact angle measurements, SEM and at. force microscopy (AFM) techniques were used. Three degrdn. mechanisms are considered in these systems: namely, mass loss due to plasticizer leaching (glycerol), starch enzymic cleavage, and synthetic polymer fractions degrdn. Enzymic hydrolysis of the starch fraction and subsequent leaching from the internal bulk structure led to an increase in surface porosity, pore size, roughness, and to the development of small pits throughout the surface, as obsd. by SEM and AFM. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2010.
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    Muthukumar, T.; Aravinthana, A.; Dineshram, R.; Venkatesan, R.; Doble, M. Biodegradation of Starch Blended High Density Polyethylene Using Marine Bacteria Associated with Biofilm Formation and Its Isolation Characterization. J. Microb. Biochem. Technol. 2014, 06 (03), 116– 122,  DOI: 10.4172/1948-5948.1000131
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    Biodegradation of starch blended high density polyethylene using marine bacteria associated with biofilm formation and its isolation characterization
    Muthukumar, Thangavelu; Aravinthana, Adithan; Dineshram, R.; Venkatesan, Ramasamy; Doble, Mukesh
    Journal of Microbial & Biochemical Technology (2014), 6 (3), 116-122, 7 pp.CODEN: JMBTA9; ISSN:1948-5948. (OMICS Publishing Group)
    The biofouling and biodegrdn. of starch blended high d. polyethylene (HDPE) was studied by immersing it in Bay of Bengal (India) for a period of six months. A pos. correlation was obsd. amongst the various constituents in the biofilm. FTIR spectrum showed the formation of C-O stretching band and decrease in ester and keto carbonyl bands indicating biodegrdn. 17% wt. loss was obsd., while the polymer surface turned hydrophilic. Twenty two bacterial strains were isolated from the biofilm and biochem. characterized. 16sRNA sequence anal. was performed for three strains. In vitro biodegrdn. of the polymer exposed to sunlight for 150 days incubated with the isolated pure strain (Exiguobacterium) and combination of two strains (Exiguobacterium and B. subtilis) for 75 days, showed a gravimetric wt. loss of 4.7 and 12.1 % resp. indicating synergy between the two organisms. The current study indicated, the isolated microorganisms could degrade starch blended HDPE.
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    Lambert, S.; Wagner, M. Formation of Microscopic Particles during the Degradation of Different Polymers. Chemosphere 2016, 161, 510– 517,  DOI: 10.1016/j.chemosphere.2016.07.042
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    Lambert, Scott; Wagner, Martin
    Chemosphere (2016), 161 (), 510-517CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)
    This study investigated the formation and size distribution of microscopic plastic particles during the degrdn. of different plastic materials. Particle no. concns. in the size range 30 nm-60μm were measured by nanoparticle tracking anal. (NTA) and Coulter Counter techniques. Each of the plastics used exhibited a measureable increase in the release of particles into the surrounding soln., with polystyrene (PS) and polylactic acid (PLA) generating the highest particle concns. After 112 d, particle concns. ranged from 2147 particles ml-1 in the control (C) to 92,465 particles ml-1 for PS in the 2-60μm size class; 1.2 × 105 particles ml-1 (C) to 11.6 × 106 for PLA in the 0.6-18μm size class; and 0.2 × 108 particles ml-1 (C) to 6.4 × 108 particles ml-1 for PS in the 30-2000 nm size class (84 d). A classification of samples based on principal component anal. showed a sepn. between the different plastic types, with PLA clustering individually in each of the three size classes. In addn., particle size distribution models were used to examine more closely the size distribution data generated by NTA. Overall, the results indicate that at the beginning of plastic weathering processes chain scission at the polymer surface causes many very small particles to be released into the surrounding soln. and those concns. may vary between plastic types.
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    Matuchová, M.; Nýavlt, J. Determination of Linear Growth Rates of Crystals (I). Calculation of Linear Growth Rates of Individual Crystal Faces from Overall Rates. Krist. Tech. 1976, 11 (2), 149– 161,  DOI: 10.1002/crat.19760110206
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    Determination of linear growth rates of crystals. (I). Calculation of linear growth rates of individual crystal faces from overall rates
    Matuchova, Marie; Nyvlt, J.
    Kristall und Technik (1976), 11 (2), 149-61CODEN: KRTEAW; ISSN:0023-4753.
    The basic methods for measuring the kinetics of crystal growth are described. The method of calcg. linear growth rates of individual crystal faces is based on the anal. of the time dependence of the vol. of a growing crystal. The relation between the linear growth rates of individual crystal faces and the overall crystal growth rate is presented and a method for assessing the linear growth rates of individual crystal faces from overall growth rate data, which can be measured readily, is suggested.
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    Tosin, M.; Weber, M.; Siotto, M.; Lott, C.; Degli-Innocenti, F. Laboratory Test Methods to Determine the Degradation of Plastics in Marine Environmental Conditions. Front. Microbiol. 2012, 3, 225,  DOI: 10.3389/fmicb.2012.00225
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    Laboratory test methods to determine the degradation of plastics in marine environmental conditions
    Tosin Maurizio; Weber Miriam; Siotto Michela; Lott Christian; Degli Innocenti Francesco
    Frontiers in microbiology (2012), 3 (), 225 ISSN:.
    In this technology report, three test methods were developed to characterize the degradation of plastic in marine environment. The aim was to outline a test methodology to measure the physical and biological degradation in different habitats where plastic waste can deposit when littered in the sea. Previously, research has focused mainly on the conditions encountered by plastic items when floating in the sea water (pelagic domain). However, this is just one of the possible habitats that plastic waste can be exposed to. Waves and tides tend to wash up plastic waste on the shoreline, which is also a relevant habitat to be studied. Therefore, the degradation of plastic items buried under sand kept wet with sea water has been followed by verifying the disintegration (visual disappearing) as a simulation of the tidal zone. Most biodegradable plastics have higher densities than water and also as a consequence of fouling, they tend to sink and lay on the sea floor. Therefore, the fate of plastic items lying on the sediment has been followed by monitoring the oxygen consumption (biodegradation). Also the effect of a prolonged exposure to the sea water, to simulate the pelagic domain, has been tested by measuring the decay of mechanical properties. The test material (Mater-Bi) was shown to degrade (total disintegration achieved in less than 9 months) when buried in wet sand (simulation test of the tidal zone), to lose mechanical properties but still maintain integrity (tensile strength at break = -66% in 2 years) when exposed to sea water in an aquarium (simulation of pelagic domain), and substantially biodegrade (69% in 236 days; biodegradation relative to paper: 88%) when located at the sediment/sea water interface (simulation of benthic domain). This study is not conclusive as the methodological approach must be completed by also determining degradation occurring in the supralittoral zone, on the deep sea floor, and in the anoxic sediment.
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    Yoshida, S.; Hiraga, K.; Takehana, T.; Taniguchi, I.; Yamaji, H.; Maeda, Y.; Toyohara, K.; Miyamoto, K.; Kimura, Y.; Oda, K. A Bacterium That Degrades and Assimilates Poly(Ethylene Terephthalate). Science 2016, 351 (6278), 1196– 1199,  DOI: 10.1126/science.aad6359
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    A bacterium that degrades and assimilates poly(ethylene terephthalate)
    Yoshida, Shosuke; Hiraga, Kazumi; Takehana, Toshihiko; Taniguchi, Ikuo; Yamaji, Hironao; Maeda, Yasuhito; Toyohara, Kiyotsuna; Miyamoto, Kenji; Kimura, Yoshiharu; Oda, Kohei
    Science (Washington, DC, United States) (2016), 351 (6278), 1196-1199CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Poly(ethylene terephthalate) (PET) is used extensively worldwide in plastic products, and its accumulation in the environment has become a global concern. Because the ability to enzymically degrade PET has been thought to be limited to a few fungal species, biodegrdn. is not yet a viable remediation or recycling strategy. By screening natural microbial communities exposed to PET in the environment, the authors isolated a novel bacterium, Ideonella sakaiensis 201-F6, that is able to use PET as its major energy and carbon source. When grown on PET, this strain produces two enzymes capable of hydrolyzing PET and the reaction intermediate, mono(2-hydroxyethyl) terephthalic acid. Both enzymes are required to enzymically convert PET efficiently into its two environmentally benign monomers, terephthalic acid and ethylene glycol.
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    Muthukumar, T.; Aravinthan, A.; Lakshmi, K.; Venkatesan, R.; Vedaprakash, L.; Doble, M. Fouling and Stability of Polymers and Composites in Marine Environment. Int. Biodeterior. Biodegrad. 2011, 65 (2), 276– 284,  DOI: 10.1016/j.ibiod.2010.11.012
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    Fouling and stability of polymers and composites in marine environment
    Muthukumar, Thangavelu; Aravinthan, Adithan; Lakshmi, Karunamoorthy; Venkatesan, Ramasamy; Vedaprakash, Loganathan; Doble, Mukesh
    International Biodeterioration & Biodegradation (2011), 65 (2), 276-284CODEN: IBBIES; ISSN:0964-8305. (Elsevier Ltd.)
    Effect of biofouling on various polymers and composites such as, Polyurethane (PU), Silicone rubber (SR), Polyester (PET), Glass Fiber Reinforced Polymer (GFRP), Carbon fiber Reinforced Plastic (CFRP) and Syntactic foams (SF) deployed for a period of one year in marine waters at a depth of 1 m was studied. These materials find wide marine applications. SR with lowest surface energy was the least fouled. Maximum barnacle attachment was seen on hard surface (GFRP) and min. on flexible surface (SR). Attachment of barnacles and polychaetes are pos. correlated with surface energy. Fouling load is pos. correlated with Surface energy and hardness. The surface energy, hardness and tensile strength reduced while surface roughness considerably increased during this period. Maximum gravimetric wt. loss was seen in PET (7.49%) followed by PU (4.25%) and min. in CFRP (0.45%). Maximum thermogravimetric wt. loss was obsd. in PET (73.5% at 400 °C) followed by PU (71.1%) and least in SR (2.4%). Fourier Transform IR spectrum revealed that carbonyl/oxidn. indexes decreased for PET, GFRP, CFRP, and SR indicating biotic degrdn. The same index increased for PU indicating abiotic oxidn.
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    Arkatkar, A.; Arutchelvi, J.; Bhaduri, S.; Uppara, P. V.; Doble, M. Degradation of Unpretreated and Thermally Pretreated Polypropylene by Soil Consortia. Int. Biodeterior. Biodegrad. 2009, 63 (1), 106– 111,  DOI: 10.1016/j.ibiod.2008.06.005
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    Degradation of unpretreated and thermally pretreated polypropylene by soil consortia
    Arkatkar, Ambika; Arutchelvi, J.; Bhaduri, Sumit; Uppara, Parasu Veera; Doble, Mukesh
    International Biodeterioration & Biodegradation (2009), 63 (1), 106-111CODEN: IBBIES; ISSN:0964-8305. (Elsevier B.V.)
    Unpretreated (PP-UT) and thermally pretreated (at 80 °C for 10 days) polypropylene (PP-TT) films of 0.05 mm thickness were subjected to in vitro biodegrdn. in minimal medium with mixed soil culture for 12 mo. In this period 10.7 and 0.4% wt. loss was obsd. with PP-TT and PP-UT, resp. The tensile strength decreased by 51.8 and 28.3%, the crystallinity increased by 28 and 33% and isotacticity increased by 3 and 9%, resp., over the same time period. The ester carbonyl index in PP-TT increased up to 9 mo and later decreased indicating abiotic followed by biotic process. No such changes were obsd. with PP-UT. Me group index decreased in both the cases indicating oxidn. at the primary carbon. Increase in surface energy indicated that the polymer became hydrophilic. Surface changes were obsd. by SEM and AFM. A single culture was isolated at the end of 12 mo and it was identified as Bacillus flexus. The morphol. of the organism was rods in a chain and it was present in the form of an endospore.
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    Rutkowska, M.; Heimowska, A.; Krasowska, K.; Janik, H. Biodegradability of Polyethylene Starch Blends in Sea Water. Polym. J. Environ. Stud. 2002, 11 (3), 267– 271
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    Biodegradability of polyethylene starch blends in sea water
    Rutkowska, M.; Heimowska, A.; Krasowska, K.; Janik, H.
    Polish Journal of Environmental Studies (2002), 11 (3), 267-271CODEN: PJESE2; ISSN:1230-1485. (HARD Publishing Co.)
    The subject of this work is the degrdn. of pure polyethylene and modified polyethylene films contg. 5% and 8% starch, and polyethylene with pro-degrdn. additives in the form of "master batch" in amts. of 20%. The degrdn. of polymer samples was studied under marine exposure conditions in the Baltic Sea. The expt. was also performed in lab. at the ambient temp., in a liq. medium contg. sea water with sodium azide (NaN3) to evaluate the resistance of polyethylene against hydrolysis. The incubation of polyethylene samples took 20 mo. The characteristic parameters of environment were measured during the period of degrdn. and their influence on degrdn. of polyethylene was discussed. Changes in wt., tensile strength and morphol. of polymer samples were tested during the expt. performed.
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    Muthukumar, T.; Aravinthan, A.; Mukesh, D. Effect of Environment on the Degradation of Starch and Pro-Oxidant Blended Polyolefins. Polym. Degrad. Stab. 2010, 95 (10), 1988– 1993,  DOI: 10.1016/j.polymdegradstab.2010.07.017
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    Effect of environment on the degradation of starch and pro-oxidant blended polyolefins
    Muthukumar, Thangavelu; Aravinthan, Adithan; Mukesh, Doble
    Polymer Degradation and Stability (2010), 95 (10), 1988-1993CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    The aim of this study was to understand the rate of degrdn. of com. pro-oxidant blended and starch blended high-d. polyethylene (HDPE), pro-oxidant blended low-d. polyethylene (LDPE), and starch blended polypropylene in 3 different environments, namely under direct sunlight, buried in soil, and immersed in marine waters for a period of 150 days. The bio-fouling parameters were also monitored in the case of polymers deployed in sea water. Exposure to sunlight showed highest wt. loss (>10%) and samples buried in soil showed the lowest (∼1%). Pro-oxidant blended HDPE showed higher wt. loss when compared to starch blended (22.7 as against 11%). SEM revealed surface deterioration and decrease in contact angle indicated redn. in surface hydrophobicity. Increase in the carbonyl and hydroxyl groups in the infra-red spectrum of the exposed samples suggested abiotic degrdn. Starch blended PP exposed to sunlight showed the highest thermo gravimetric wt. loss (63.8%) followed by the same polymer buried in soil (46.1%).
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    Borghei, M.; Karbassi, A.; Khoramnejadian, S.; Oromiehie, A.; Javid, A. H. Microbial Biodegradable Potato Starch Based Low Density Polyethylene. Afr. J. Biotechnol. 2010, 9 (26), 4075– 4080
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    Microbial biodegradable potato starch based low density polyethylene
    Borghei, Mehdi; Karbassi, Abdolreza; Khoramnejadian, Shahrzad; Oromiehie, Abdolrasoul; Javid, Amir hossein
    African Journal of Biotechnology (2010), 9 (26), 4075-4080CODEN: AJBFAH; ISSN:1684-5315. (Academic Journals)
    Plastic materials remain in the nature for decades. Slow degrdn. of plastics in the environment caused a public trend to biodegradable polymers. The aim of this research was to produce the microbial biodegradable low d. polyethylene with potato starch. Degrdn. of potato starch based low d. polyethylene (LDPE) was investigated in soil rich in microorganisms for 8 mo. Wt. differences of polymeric samples before and after degrdn. in soil indicated soil biodegrdn. Fourier transform spectroscopy (FTIR) approved the result. Scanning electron microscope (SEM) and wt. change after 84 days' exposure to Pseudomonas aeruginosa confirmed degrdn. by microorganisms. In addn., potato starch based LDPE was exposed to 8 different kinds of fungi and the degrdn. was studied visually. Result confirmed the microbial biodegradability of potato starch based LDPE blend in natural and lab. condition.
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    Syranidou, E.; Karkanorachaki, K.; Amorotti, F.; Franchini, M.; Repouskou, E.; Kaliva, M.; Vamvakaki, M.; Kolvenbach, B.; Fava, F.; Corvini, P. F.-X. Biodegradation of Weathered Polystyrene Films in Seawater Microcosms. Sci. Rep. 2017, 7 (1), 17991,  DOI: 10.1038/s41598-017-18366-y
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    Biodegradation of weathered polystyrene films in seawater microcosms
    Syranidou Evdokia; Karkanorachaki Katerina; Amorotti Filippo; Franchini Martina; Kalogerakis Nicolas; Amorotti Filippo; Fava Fabio; Repouskou Eftychia; Kaliva Maria; Vamvakaki Maria; Kolvenbach Boris; Corvini Philippe F-X
    Scientific reports (2017), 7 (1), 17991 ISSN:.
    A microcosm experiment was conducted at two phases in order to investigate the ability of indigenous consortia alone or bioaugmented to degrade weathered polystyrene (PS) films under simulated marine conditions. Viable populations were developed on PS surfaces in a time dependent way towards convergent biofilm communities, enriched with hydrocarbon and xenobiotics degradation genes. Members of Alphaproteobacteria and Gammaproteobacteria were highly enriched in the acclimated plastic associated assemblages while the abundance of plastic associated genera was significantly increased in the acclimated indigenous communities. Both tailored consortia efficiently reduced the weight of PS films. Concerning the molecular weight distribution, a decrease in the number-average molecular weight of films subjected to microbial treatment was observed. Moreover, alteration in the intensity of functional groups was noticed with Fourier transform infrared spectrophotometry (FTIR) along with signs of bio-erosion on the PS surface. The results suggest that acclimated marine populations are capable of degrading weathered PS pieces.
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    Sudhakar, M.; Doble, M.; Murthy, P. S.; Venkatesan, R. Marine Microbe-Mediated Biodegradation of Low- and High-Density Polyethylenes. Int. Biodeterior. Biodegrad. 2008, 61 (3), 203– 213,  DOI: 10.1016/j.ibiod.2007.07.011
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    Marine microbe-mediated biodegradation of low- and high-density polyethylenes
    Sudhakar, M.; Doble, Mukesh; Murthy, P. Sriyutha; Venkatesan, R.
    International Biodeterioration & Biodegradation (2008), 61 (3), 203-213CODEN: IBBIES; ISSN:0964-8305. (Elsevier B.V.)
    Unpretreated and thermally pretreated low- and high-d. polyethylenes (LDPE and HDPE) and unpretreated starch-blended LDPE were subjected to in vitro biodegrdn. In this study two marine micro-organisms were selected, specifically Bacillus sphericus GC subgroup IV and Bacillus cereus subgroup A, for a duration of 1 yr, at pH 7.5 and temp. 30 °C with the polymer as the sole carbon source. FTIR spectrum showed that initially carbonyl index increased, probably due to oxidn. by dissolved oxygen (abiotic factor). Prolonged exposure to organisms led to decrease in carbonyl index due to biodegrdn. (biotic) through Norrish-type mechanism or through the formation of ester. The wt. loss of the thermally treated LDPE and HDPE samples were about 19% and 9% resp., and unpretreated samples were 10% and 3.5% resp. with B. sphericus in 1 yr. Wt. loss of unpretreated starch-blended LDPE was 25% with B. cereus. Tensile strength of thermally pretreated LDPE and HDPE and unpretreated starch-blended LDPE decreased by 27%, 14.8% and 30.5%, resp., with B. sphericus and the corresponding decrease in crystallinity was 8%, 2.2% and 8.5%, resp. Decrease in contact angle indicated that the surfaces turned more hydrophilic after exposure. Surface morphol. changes of the biol.-treated samples were obsd. by at. force microscopy.
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    Luzi, F.; Fortunati, E.; Puglia, D.; Petrucci, R.; Kenny, J. M.; Torre, L. Study of Disintegrability in Compost and Enzymatic Degradation of PLA and PLA Nanocomposites Reinforced with Cellulose Nanocrystals Extracted from Posidonia oceanica. Polym. Degrad. Stab. 2015, 121, 105– 115,  DOI: 10.1016/j.polymdegradstab.2015.08.016
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    Study of disintegrability in compost and enzymatic degradation of PLA and PLA nanocomposites reinforced with cellulose nanocrystals extracted from Posidonia oceanica
    Luzi, F.; Fortunati, E.; Puglia, D.; Petrucci, R.; Kenny, J. M.; Torre, L.
    Polymer Degradation and Stability (2015), 121 (), 105-115CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    Nanocomposite films based on poly(lactic acid) (PLA) reinforced with cellulose nanocrystals extd. from Posidonia oceanica plant were prepd. by solvent casting method contg. 1 or 3% wt. of cellulose nanocrystals unmodified (CNC) and modified using a com. surfactant (s-CNC). The modification improves the dispersion of CNC into the matrix. Enzymic degrdn. using efficient enzyme proteinase K and disintegrability in composting conditions were considered to gain insights into the post-use degrdn. processes of the produced formulations. Results of visual, morphol. and thermal anal. of enzymic degrdn. studies confirmed that the selected enzyme preferentially degraded amorphous regions with respect of cryst. ones, while the crystallinity degree of the nanocomposite films increased during enzymic degrdn., as a consequence of enzyme action. The disintegration in compositing conditions of different formulations was also studied by visual and morphol. anal. The disintegrability in compost conditions showed that the formulations disintegrated in <14 days, in addn. it has been proved that CNC modified with surfactant were able to promote the disintegration behavior. The prodn. of PLA based nanocomposites incorporating cellulose ext. from marine wastes suggested the potential application of the proposed material for short-term food packaging with low environmental impact.
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  137. 137
    Pelegrini, K.; Donazzolo, I.; Brambilla, V.; Grisa, A. M. C.; Piazza, D.; Zattera, A. J.; Brandalise, R. N. Degradation of PLA and PLA in Composites with Triacetin and Buriti Fiber after 600 Days in a Simulated Marine Environment. J. Appl. Polym. Sci. 2016, 133 (15), na,  DOI: 10.1002/app.43290
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    Karamanlioglu, M.; Robson, G. D. The Influence of Biotic and Abiotic Factors on the Rate of Degradation of Poly(Lactic) Acid (PLA) Coupons Buried in Compost and Soil. Polym. Degrad. Stab. 2013, 98 (10), 2063– 2071,  DOI: 10.1016/j.polymdegradstab.2013.07.004
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    138
    The influence of biotic and abiotic factors on the rate of degradation of poly(lactic) acid (PLA) coupons buried in compost and soil
    Karamanlioglu, Mehlika; Robson, Geoffrey D.
    Polymer Degradation and Stability (2013), 98 (10), 2063-2071CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    Poly(lactic) acid (PLA) is a compostable biopolymer and has been commercialized for the for the manuf. of short-shelf life products. As a result, increasing amts. of PLA are entering waste management systems and the environment; however, the degrdn. mechanism is unclear. While hydrolysis of the polymer occurs abiotically at elevated temp. in the presence of water, potential catalytic role for microbes in this process is yet to be established. We examd. the degrdn. of PLA coupons from com. packaging at 25°, 37°, 45°, 50° and 55° in soil and compost and compared with the degrdn. rates in sterile aq. conditions by measuring loss of tensile strength and mol. wt. (Mw). In order to assess the possible effect of abiotic sol. factors in compost and soil on degrdn. of PLA, degrdn. rates in microorganism-rich compost and soil were compared with sterile compost and soil ext. at 50°. Temp. was the key parameter in PLA degrdn. and degrdn. rates in microorganism-rich compost and soil were faster than in sterile water at 45° and 50° detd. by tensile strength and Mw loss. All tensile strength was lost faster after 30 and 36 days in microorganism-rich compost and soil, resp., than in sterile compost and soil ext., 57 and 54 days, resp. at 50°. Significantly more Mw, 68 and 64%, was lost in compost and soil, resp. than in compost ext., Mw, 53%; and in soil ext., 57%. Therefore, degrdn. rates were faster in microorganism-rich compost and soil than in sterile compost and soil ext., which contained the abiotic sol. factors of compost and soil at 50°. These comparative studies support a direct role for microorganisms in PLA degrdn. at elevated temps. in humid environments. No change in tensile strength or Mw was obsd. either 25° or 37° after 1 yr suggesting that accumulation of PLA in the environment may cause future pollution issues.
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    O’Brine, T.; Thompson, R. C. Degradation of Plastic Carrier Bags in the Marine Environment. Mar. Pollut. Bull. 2010, 60 (12), 2279– 2283,  DOI: 10.1016/j.marpolbul.2010.08.005
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    Degradation of plastic carrier bags in the marine environment
    O'Brine, Tim; Thompson, Richard C.
    Marine Pollution Bulletin (2010), 60 (12), 2279-2283CODEN: MPNBAZ; ISSN:0025-326X. (Elsevier Ltd.)
    There is considerable concern about the hazards that plastic debris presents to wildlife. Use of polymers that degrade more quickly than conventional plastics presents a possible soln. to this problem. Here we investigate breakdown of two oxo-biodegradable plastics, compostable plastic and std. polyethylene in the marine environment. Tensile strength of all materials decreased during exposure, but at different rates. Compostable plastic disappeared from our test rig between 16 and 24 wk whereas approx. 98% of the other plastics remained after 40 wk. Some plastics require UV light to degrade. Transmittance of UV through oxo-biodegradable and std. polyethylene decreased as a consequence of fouling such that these materials received ∼90% less UV light after 40 wk. Our data indicate that compostable plastics may degrade relatively quickly compared to oxo-biodegradable and conventional plastics. While degradable polymers offer waste management solns., there are limitations to their effectiveness in reducing hazards assocd. with plastic debris.
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    Abou-Zeid, D.-M.; Müller, R.-J.; Deckwer, W.-D. Degradation of Natural and Synthetic Polyesters under Anaerobic Conditions. J. Biotechnol. 2001, 86 (2), 113– 126,  DOI: 10.1016/S0168-1656(00)00406-5
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    140
    Degradation of natural and synthetic polyesters under anaerobic conditions
    Abou-Zeid, D.-M.; Muller, R.-J.; Deckwer, W.-D.
    Journal of Biotechnology (2001), 86 (2), 113-126CODEN: JBITD4; ISSN:0168-1656. (Elsevier Science Ltd.)
    Often, degradability under anaerobic conditions is desirable for plastics claimed to be biodegradable, e.g., in anaerobic biowaste treatment plants, landfills, and natural anaerobic sediments. The biodegrdn. of the natural polyesters poly(β-hydroxybutyrate) (PHB), poly(β-hydroxybutyrate-co-11.6%-β-hydroxyvalerate) (PHBV), and the synthetic polyester poly(.vepsiln.-caprolactone) (PCL) was studied in two anaerobic sludges, and individual polyester-degrading anaerobic strains were isolated, characterized, and used for degrdn. expts. under controlled lab. conditions. Incubation of PHB and PHBV films in two anaerobic sludges exhibited significant degrdn. in a time scale of 6-10 wk, monitored by wt. loss and biogas formation. In contrast to aerobic conditions, PHB was degraded anaerobically more rapidly than the copolyester PHBV, when tested with either mixed cultures or a single strained isolate. PCL tends to degrade slower than the natural polyesters PHB and PHBV. Four PHB- and PCL-degrading isolates were taxonomically identified and are obviously new species belonging to the genus Clostridium group I. The depolymg. enzyme systems of PHB- and PCL-degrading isolates are supposed to be different. Using one isolated strain in an optimized lab. degrdn. test with PHB powder, the degrdn. time was drastically reduced as compared to the degrdn. in sludges (2 days vs. 6-10 wk).
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    Ishigaki, T.; Sugano, W.; Nakanishi, A.; Tateda, M.; Ike, M.; Fujita, M. The Degradability of Biodegradable Plastics in Aerobic and Anaerobic Waste Landfill Model Reactors. Chemosphere 2004, 54 (3), 225– 233,  DOI: 10.1016/S0045-6535(03)00750-1
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    The degradability of biodegradable plastics in aerobic and anaerobic waste landfill model reactors
    Ishigaki Tomonori; Sugano Wataru; Nakanishi Akane; Tateda Masafumi; Ike Michihiko; Fujita Masanori
    Chemosphere (2004), 54 (3), 225-33 ISSN:0045-6535.
    Degradabilities of four kinds of commercial biodegradable plastics (BPs), polyhydroxybutyrate and hydroxyvalerate (PHBV) plastic, polycaprolactone plastic (PCL), blend of starch and polyvinyl alcohol (SPVA) plastic and cellulose acetate (CA) plastic were investigated in waste landfill model reactors that were operated as anaerobically and aerobically. The application of forced aeration to the landfill reactor for supplying aerobic condition could potentially stimulate polymer-degrading microorganisms. However, the individual degradation behavior of BPs under the aerobic condition was completely different. PCL, a chemically synthesized BP, showed film breakage under the both conditions, which may have contributed to a reduction in the waste volume regardless of aerobic or anaerobic conditions. Effective degradation of PHBV plastic was observed in the aerobic condition, though insufficient degradation was observed in the anaerobic condition. But the aeration did not contribute much to accelerate the volume reduction of SPVA plastic and CA plastic. It could be said that the recalcitrant portions of the plastics such as polyvinyl alcohol in SPVA plastic and the highly substituted CA in CA plastic prevented the BP from degradation. These results indicated existence of the great variations in the degradability of BPs in aerobic and anaerobic waste landfills, and suggest that suitable technologies for managing the waste landfill must be combined with utilization of BPs in order to enhance the reduction of waste volume in landfill sites.
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    Luo, S.; Netravali, A. N. A Study of Physical and Mechanical Properties of Poly(Hydroxybutyrate-co-hydroxyvalerate) during Composting. Polym. Degrad. Stab. 2003, 80 (1), 59– 66,  DOI: 10.1016/S0141-3910(02)00383-X
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    A study of physical and mechanical properties of poly(hydroxybutyrate-co-hydroxyvalerate) during composting
    Luo, S.; Netravali, A. N.
    Polymer Degradation and Stability (2003), 80 (1), 59-66CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Science Ltd.)
    Changes in phys. and mech. properties of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) during degrdn. in a composting medium were studied. Effects of composting of up to 50 days were studied. Specimen wt. loss, SEM, capillary viscometry, Fourier-transform IR spectroscopy with accessory for attenuated total reflectance (FTIR-ATR), differential scanning calorimetry (DSC), and tensile testing were performed to characterize the changes in the phys. and mech. properties of PHBV during its degrdn. in the composting medium. The results from the anal. of wt. loss, SEM, mol. wt., FTIR, DSC, and tensile testing, particularly the phys. and mech. properties, suggest that the degrdn. of PHBV in compost is enzymic rather than hydrolytic and occurs from surface and the degraded material leaches out.
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    Witt, U.; Müller, R. J.; Deckwer, W.-D. Biodegradation of Polyester Copolymers Containing Aromatic Compounds. J. Macromol. Sci., Part A: Pure Appl.Chem. 1995, 32 (4), 851– 856,  DOI: 10.1080/10601329508010296
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    Singh, G.; Kaur, N.; Bhunia, H.; Bajpai, P. K.; Mandal, U. K. Degradation Behaviors of Linear Low-Density Polyethylene and Poly(L-Lactic Acid) Blends. J. Appl. Polym. Sci. 2012, 124 (3), 1993– 1998,  DOI: 10.1002/app.35216
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    Degradation behaviors of linear low-density polyethylene and poly(L-lactic acid) blends
    Singh, Gursewak; Kaur, Navleen; Bhunia, Haripada; Bajpai, Pramod K.; Mandal, Uttam K.
    Journal of Applied Polymer Science (2012), 124 (3), 1993-1998CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
    In this study, the degradability of linear low-d. polyethylene (LLDPE) and poly(L-lactic acid) (PLLA) blend films under controlled composting conditions was studied according to modified ASTM D 5338 (2003). Differential scanning calorimetry, x-ray diffraction, and Fourier transform IR spectroscopy were used to det. the thermal and morphol. properties of the plastic films. LLDPE 80 (80% LLDPE and 20% PLLA) degraded faster than grafted low-d. polyethylene-maleic anhydride (M-g-L) 80/4 (80% LLDPE, 20% PLLA, and 4 phr compatibilizer) and pure LLDPE (LLDPE 100). The mech. properties and wt. changes were detd. after composting. The tensile strength of LLDPE 100, LLDPE 80, and M-g-L 80/4 decreased by 20, 54, and 35%, resp. The films, as a result of degrdn., exhibited a decrease in their mass. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.
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    Sharon, C.; Sharon, M. Studies on Biodegradation of Polyethylene Terephthalate: A Synthetic Polymer. J. Microbiol. Biotechnol. Res. 2017, 2 (2), 248– 257
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    Müller, R.-J.; Schrader, H.; Profe, J.; Dresler, K.; Deckwer, W.-D. Enzymatic Degradation of Poly(Ethylene Terephthalate): Rapid Hydrolyse Using a Hydrolase from T. fusca. Macromol. Rapid Commun. 2005, 26 (17), 1400– 1405,  DOI: 10.1002/marc.200500410
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    Enzymatic degradation of poly(ethylene terephthalate): Rapid hydrolyse using a hydrolase from T. fusca
    Mueller, Rolf-Joachim; Schrader, Hedwig; Profe, Joern; Dresler, Karolin; Deckwer, Wolf-Dieter
    Macromolecular Rapid Communications (2005), 26 (17), 1400-1405CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    It is demonstrated that PET, which is usually regarded as 'non-biodegradable', can effectively be depolymd. by a hydrolase from the actinomycete Thermobifida fusca. Erosion rates of 8 to 17 μm per wk were obtained upon incubation at 55°. Lipases from Pseudomonas sp. and Candida antarctica did not degrade PET under comparable conditions. The influences of crystallinity, m.p., and glass transition temp. on the enzymic attack on PET, PBT, and PHB are discussed.
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    Sivan, A.; Szanto, M.; Pavlov, V. Biofilm Development of the Polyethylene-Degrading Bacterium Rhodococcus ruber. Appl. Microbiol. Biotechnol. 2006, 72 (2), 346– 352,  DOI: 10.1007/s00253-005-0259-4
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    Biofilm development of the polyethylene-degrading bacterium Rhodococcus ruber
    Sivan, A.; Szanto, M.; Pavlov, V.
    Applied Microbiology and Biotechnology (2006), 72 (2), 346-352CODEN: AMBIDG; ISSN:0175-7598. (Springer)
    We have recently isolated a biofilm-producing strain (C208) of Rhodococcus ruber that degraded polyethylene at a rate of 0.86% per wk (r 2=0.98). Strain C208 adheres to polyethylene immediately upon exposure to the polyolefin. This initial biofilm differentiates (in a stepwise process that lasts about 20 h) into cell-aggregation-forming microcolonies. Further organization yields "mushroom-like" three-dimensional structures on the mature biofilm. The ratio between the population densities of the biofilm and the planktonic C208 cells after 10 days of incubation was about 60:1, indicating a high preference for the biofilm mode of growth. Anal. of extracellular polymeric substances (EPS) in the biofilm of C208 revealed that the polysaccharides level was up to 2.5 folds higher than that of the protein. The biofilm showed a high viability even after 60 days of incubation, apparently due to polyethylene biodegrdn.
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    Otake, Y.; Kobayashi, T.; Asabe, H.; Murakami, N.; Ono, K. Biodegradation of Low-Density Polyethylene, Polystyrene, Polyvinyl Chloride, and Urea Formaldehyde Resin Buried under Soil for over 32 Years. J. Appl. Polym. Sci. 1995, 56 (13), 1789– 1796,  DOI: 10.1002/app.1995.070561309
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    Biodegradation of low-density polyethylene, polystyrene, polyvinyl chloride, and urea formaldehyde resin buried under soil for over 32 years
    Otake, Yoshito; Kobayashk, Tomoko; Asabe, Hitoshi; Murakami, Nobunao; Ono, Katsumichi
    Journal of Applied Polymer Science (1995), 56 (13), 1789-96CODEN: JAPNAB; ISSN:0021-8995. (Wiley)
    The biodegrdn. of several polymers that had been buried under soil for over 32 yr was examd. No evidence of biodegrdn. was found for polystyrene, polyvinyl chloride, and urea formaldehyde resin. A remarkable degrdn. was indicated for low d. polyethylene thin films which were directly in contact with soil. Severely degraded parts of the film is characterized by whitening. May small holes were recognized on the surface of the whitened part. The whitened part is specific for the growth of hyphae. FT-IR spectra of the whitened part showed a characteristic band in the vicinity of 1640 cm-1 which was assigned to the stretching vibration of C=C bond. Although the part which was not in contact with soil was clear, it also showed evidence of degrdn. from the presence of carbonyl band in TF-IR. It was suggested that the degrdn. of the clear part is due to the usual thermo-oxidative process, while the degrdn. of the whitened part is due to the biotic process.
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    Chandra, R.; Rustgi, R. Biodegradation of Maleated Linear Low-Density Polyethylene and Starch Blends. Polym. Degrad. Stab. 1997, 56 (2), 185– 202,  DOI: 10.1016/S0141-3910(96)00212-1
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    Biodegradation of maleated linear low-density polyethylene and starch blends
    Chandra, R.; Rustgi, Renu
    Polymer Degradation and Stability (1997), 56 (2), 185-202CODEN: PDSTDW; ISSN:0141-3910. (Elsevier)
    Environmental threats restrict the use of nondegradable polymers and encourage the development and use of degradable plastics. In order to obtain a cost-effective biodegradable plastic, starch-filled polyethylene (PE) is still the best alternative. Starch and PE blend is incompatible at the mol. level and often leads to poor performance. In order to overcome this drawback, either PE or starch should be modified. The aim of this study was to modified linear low-d. polyethylene (LLDPE) and blend it with starch. Maleic anhydride (MA) was grafted onto LLDPE in xylene using dicumyl peroxide (DCP) as an initiator. Corn starch in varying concns. (between 10 and 60%) was blended with MA-g-LLDPE in a torque rheometer. The same blend compns. of nonfunctional LLDPE with the starch were prepd. for comparative studies. The torque and totalized torque generated during blending are reported as a function of starch content. Torque decreased with increasing starch content for the compns. from 10 to 50% and increased for 60% starch content. Work energy decreased for all the compns. of blends except for 60% starch content. Tensile strength and modulus increased and percentage elongation decreased as the starch content increased in the blends. Water absorption of the blends increased with an increase in starch content. The biodegradability of MA-g-LLDPE/starch blends has been studied in two biotic environments: (1) soil environment over a period of 6 mo; (2) mixed fungi inoculum (Aspergillus niger, Penicillium funiculosum, Chaetomium globosum, Gliocladium virens and Pullularia pullulans) for 28 days. The samples contg. more than 30% starch content supported heavy fungus growth. Blends exposed to a soil environment degraded more than in fungi alone. Any changes in the various properties of the MA-g-LLDPE/starch before and after degrdn. were monitored using FTIR spectroscopy, wt. loss, a scanning electron microscope (SEM) for surface morphol., DSC for crystallinity and a thermogravimetric analyzer (TGA) for rapid detn. of starch content. Percentage crystallinity decreased as the starch content increased; the biodegrdn. resulted in an increase of crystallinity in MA-g-LLDPE/starch blends.
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    Arvanitoyannis, I.; Biliaderis, C. G.; Ogawa, H.; Kawasaki, N. Biodegradable Films Made from Low-Density Polyethylene (LDPE), Rice Starch and Potato Starch for Food Packaging Applications: Part 1. Carbohydr. Polym. 1998, 36 (2), 89– 104,  DOI: 10.1016/S0144-8617(98)00016-2
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    Biodegradable films made from low-density polyethylene (LDPE), rice starch and potato starch for food packaging applications: Part 1
    Arvanitoyannis, Ioannis; Biliaderis, Costas G.; Ogawa, Hiromasa; Kawasaki, Norioki
    Carbohydrate Polymers (1998), 36 (2/3), 89-104CODEN: CAPOD8; ISSN:0144-8617. (Elsevier Science Ltd.)
    Blends of LDPE and rice or potato starch were extruded in the presence of varying amts. of water, hot pressed and studied with regard to their mech. properties and their gas/water permeability and biodegradability before and after storage. The presence of high starch contents (>30%, wt./wt.) had an adverse effect on the mech. properties of LDPE/starch blends. Gas permeability and water-vapor transmission rate increased proportionally to the starch content in the blend. Several theor. and semiempirical calcns. for mech. properties and gas permeability were carried out and possible interpretations were provided for the occasionally obsd. deviations between the exptl. and the theor. values. The biodegradability rate of the blends was enhanced when the starch content exceeded 10% (wt./wt.).
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    Wool, R. P. The Science and Engineering of Polymer Composite Degradation. In Degradable Polymers: Principles and Applications; Scott, G., Gilead, D., Eds.; Springer Netherlands: Dordrecht, 1995; pp 138– 152.  DOI: 10.1007/978-94-011-0571-2_7 .
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    Hao, Z.; Sun, M.; Ducoste, J. J.; Benson, C. H.; Luettich, S.; Castaldi, M. J.; Barlaz, M. A. Heat Generation and Accumulation in Municipal Solid Waste Landfills. Environ. Sci. Technol. 2017, 51 (21), 12434– 12442,  DOI: 10.1021/acs.est.7b01844
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    Heat Generation and Accumulation in Municipal Solid Waste Landfills
    Hao, Zisu; Sun, Mei; Ducoste, Joel J.; Benson, Craig H.; Luettich, Scott; Castaldi, Marco J.; Barlaz, Morton A.
    Environmental Science & Technology (2017), 51 (21), 12434-12442CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    There have been reports of North American landfills that are experiencing temps. in excess of 80-100°. However, the processes causing elevated temps. are not well understood. The objectives were to develop a model to describe the generation, consumption and release of heat from landfills, to predict landfill temps., and to understand the relative importance of factors that contribute to heat generation and accumulation. Modeled heat sources include energy from aerobic and anaerobic biodegrdn., anaerobic metal corrosion, ash hydration and carbonation, and acid-base neutralization. Heat removal processes include landfill gas convection, infiltration, leachate collection, and evapn. The landfill was treated as a perfectly mixed batch reactor. Model predictions indicate that both anaerobic metal corrosion and ash hydration/carbonation contribute to landfill temps. above those estd. from biol. reactions alone. Exothermic pyrolysis of refuse, which is hypothesized to be initiated due to a local accumulation of heat, was modeled empirically to illustrate its potential impact on heat generation.
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    Edge, M.; Hayes, M.; Mohammadian, M.; Allen, N. S.; Jewitt, T. S.; Brems, K.; Jones, K. Aspects of Poly(Ethylene Terephthalate) Degradation for Archival Life and Environmental Degradation. Polym. Degrad. Stab. 1991, 32 (2), 131– 153,  DOI: 10.1016/0141-3910(91)90047-U
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    153
    Aspects of poly(ethylene terephthalate) degradation for archival life and environmental degradation
    Edge, M.; Hayes, M.; Mohammadian, M.; Allen, N. S.; Jewitt, T. S.; Brems, K.; Jones, K.
    Polymer Degradation and Stability (1991), 32 (2), 131-53CODEN: PDSTDW; ISSN:0141-3910.
    The degrdn. of poly(ethylene terephthalate) videotape, motion picture film, sheet, and bottles was studied in terms of archival storage using both accelerated thermal and photo-ageing methods. The accelerated ageing studies indicated that breakdown of the film was negligible at 60° and relatively unaffected by variations in humidity of the surrounding environment, over the time period studied (300 days), due to its high crystallinity (55%). At 70 and 80° the film exhibited signs of crosslinking rather than degrdn. due to the high crystallinity and emulsion inhibiting the diffusion of O into the polymer. The presence of Fe from a film container had an accelerating effect on the degrdn. rate of motion picture film material, but only at >90°. In contrast, normal amorphous polyester sheet and oriented bottles degraded due to their much lower crystallinity (1 and 30%, resp.), and at higher temps. (70-90°) broke down, enhanced by increasing temp., increasing relative humidity and UV irradn. The bottles were more stable than sheet due to a greater degree of orientation in the former case and hence higher degree of crystallinity. Both soil (in the case of amorphous sheet and bottles) and metal storage can (in the case of motion picture film) had significant effects on stability. At temps. above the glass transition (80°) differences in rates of degrdn. at ≤45% relative humidity were not significant. Videotapes of various archival histories were also studied using high resoln. light microscopy. White cryst. deposits and surface conglomerates were obsd. with increasing age and these appeared to be consistent with artificial aging expts.
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    Bernstein, R.; Derzon, D. K.; Gillen, K. T. Nylon 6.6 Accelerated Aging Studies: Thermal–Oxidative Degradation and Its Interaction with Hydrolysis. Polym. Degrad. Stab. 2005, 88 (3), 480– 488,  DOI: 10.1016/j.polymdegradstab.2004.11.020
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    Polymer Degradation and Stability (2005), 88 (3), 480-488CODEN: PDSTDW; ISSN:0141-3910. (Elsevier B.V.)
    Accelerated aging of nylon 66 fibers used in parachutes was conducted by following the tensile strength loss under both thermal-oxidative and 100% relative humidity conditions. Thermal-oxidative studies (air circulating ovens) were performed for time periods of weeks to years at temps. ranging from 37° to 138°. Accelerated aging humidity expts. (100% RH) were performed under both an argon atm. to examine the pure' hydrolysis pathway, and under an oxygen atm. (oxygen partial pressure close to that occurring in air) to mimic true aging conditions. Degrdn. caused by humidity is much more important than thermal-oxidative degrdn. Surprisingly when both oxygen and humidity were present the rate of degrdn. was dramatically enhanced relative to humidity aging in the absence of oxygen. This significant and previously unknown phenomena underscores the importance of careful accelerated aging that truly mimics real world storage conditions.
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    Gillen, K. T.; Celina, M.; Clough, R. L.; Wise, J. Extrapolation of Accelerated Aging Data - Arrhenius or Erroneous?. Trends Polym. Sci. 1997, 8 (5), 250– 257
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    Deroiné, M.; Le Duigou, A.; Corre, Y.-M.; Le Gac, P.-Y.; Davies, P.; César, G.; Bruzaud, S. Accelerated Ageing and Lifetime Prediction of Poly(3-Hydroxybutyrate-co-3-hydroxyvalerate) in Distilled Water. Polym. Test. 2014, 39, 70– 78,  DOI: 10.1016/j.polymertesting.2014.07.018
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    Deroine, Morgan; Le Duigou, Antoine; Corre, Yves-Marie; Le Gac, Pierre-Yves; Davies, Peter; Cesar, Guy; Bruzaud, Stephane
    Polymer Testing (2014), 39 (), 70-78CODEN: POTEDZ; ISSN:0142-9418. (Elsevier Ltd.)
    Accelerated aging was performed in distd. water at different temps. (25, 30, 40 and 50°C) on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), which is a biodegradable biopolymer, in order to est. its lifetime in aq. environment. In a first part, degrdn. mechanisms were followed by gravimetry, tensile tests and steric exclusion chromatog. Both immersion and relative humidity have been examd. In a second part, the strain at break was used as an indicator for lifetime prediction with an Arrhenius extrapolation. The study revealed the presence of only one irreversible degrdn. mechanism, i.e. hydrolytic degrdn., which is temp. dependant. So, within the approach assumptions, the lifetime in distd. water of PHBV following Arrhenius behavior can be predicted.
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    Two methods for obtaining more reliable rapid estimates of the useful life of a plastic are reported. These are measurement of phys. and chem. changes, such as weight loss, stabilizer loss, density increase, dyeability increase at the temp. of interest; and thermal development of the prefailure oxidative damage initiated at the same temp.
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    Macromolecules (1970), 3 (2), 262-4CODEN: MAMOBX; ISSN:0024-9297.
    Induction periods of unstabilized polypropylene films at 1 atm O were detd. at 50-150° by measuring the O absorption. Ir spectra showed that oxidn. took place predominantly on the surface of the film. Oxidn. at <110° was initiated by foreign metal particles.
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    Gillen, K. T.; Bernstein, R.; Celina, M. Non-Arrhenius Behavior for Oxidative Degradation of Chlorosulfonated Polyethylene Materials. Polym. Degrad. Stab. 2005, 87 (2), 335– 346,  DOI: 10.1016/j.polymdegradstab.2004.09.004
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    Non-Arrhenius behavior for oxidative degradation of chlorosulfonated polyethylene materials
    Gillen, Kenneth T.; Bernstein, Robert; Celina, Mathew
    Polymer Degradation and Stability (2005), 87 (2), 335-346CODEN: PDSTDW; ISSN:0141-3910. (Elsevier B.V.)
    We have carried out oven aging studies on eight different com. chlorosulfonated polyethylene cable jacket materials at temps. ranging from 80 °C to 150 °C utilizing ultimate tensile elongation as the degrdn. parameter. For each material, the elongation results were time-temp. superposed at the lowest aging temp. When the resulting empirical shift factors were tested for Arrhenius behavior, it was found that the eight materials were Arrhenius at ∼100 °C and higher with very similar activation energies averaging ∼107 kJ/mol. Longer-term aging results at temps. lower than 100 °C for three of the materials provided evidence for curvature to lower activation energies. For one of these materials, we conducted oxidn. rate measurements at six temps. ranging from 37 °C to 108 °C. The results offered further evidence for a small drop in activation energy below 100 °C. Chem. evidence supporting this change in activation energy was derived from anal. of the prodn. rates of CO2 during oxidn. As the temp. was lowered, the amt. of CO2 produced relative to the O2 consumed dropped substantially, implying that the chem. leading to CO2 becomes less important at lower temps.
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    Celina, M.; Gillen, K. T.; Assink, R. A. Accelerated Aging and Lifetime Prediction: Review of Non-Arrhenius Behaviour Due to Two Competing Processes. Polym. Degrad. Stab. 2005, 90 (3), 395– 404,  DOI: 10.1016/j.polymdegradstab.2005.05.004
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    Accelerated aging and lifetime prediction: Review of non-Arrhenius behaviour due to two competing processes
    Celina, M.; Gillen, K. T.; Assink, R. A.
    Polymer Degradation and Stability (2005), 90 (3), 395-404CODEN: PDSTDW; ISSN:0141-3910. (Elsevier B.V.)
    A review. Lifetime prediction of polymeric materials often requires extrapolation of accelerated aging data with the suitability and confidence in such approaches being subject to ongoing discussions. This paper reviews the evidence of non-Arrhenius behavior (curvature) instead of linear extrapolations in polymer degrdn. studies. Several studies have emphasized mechanistic variations in the degrdn. mechanism and demonstrated changes in activation energies but often data have not been fully quantified. To improve predictive capabilities a simple approach for dealing with curvature in Arrhenius plots is examd. on a basis of two competing reactions. This allows for excellent fitting of exptl. data as shown for some elastomers, does not require complex kinetic modeling, and individual activation energies are easily detd. Reviewing literature data for the thermal degrdn. of polypropylene a crossover temp. (temp. at which the two processes equally contribute) of ∼83 °C was detd., with the high temp. process having a considerably higher activation energy (107-156 kJ/mol) than the low temp. process (35-50 kJ/mol). Since low activation energy processes can dominate at low temps. and longer extrapolations result in larger uncertainties in lifetime predictions, expts. focused on estg. E a values at the lowest possible temp. instead of assuming straight line extrapolations will lead to more confident lifetime ests.
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    Albertsson, A.-C.; Karlsson, S. The Three Stages in Degradation of Polymers—Polyethylene as a Model Substance. J. Appl. Polym. Sci. 1988, 35 (5), 1289– 1302,  DOI: 10.1002/app.1988.070350515
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    The degrdn. of low-d. polyethylene film in contact with soil for 10 yr is characterized by three stages: (I) a const. degrdn. rate, (II) a parabolic decline in the rate of degrdn., and (III) a subsequent final increase in the rate of degrdn. The first step (I) is probably dependent on the environment. The material changes rapidly until some kind of equil. with the environment has been achieved. CO2 is evolved, O uptake is rapid, and a rapid change in mech. properties is also obsd. The second step (II) is characterized by low O uptake, a low evolution of CO2 and slow changes in the mech. properties, crystallinity, and mol. wt. Step III, finally, is a rapid deterioration of the structure.
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    Blamey, J.; Zhao, M.; Manovic, V.; Anthony, E. J.; Dugwell, D. R.; Fennell, P. S. A Shrinking Core Model for Steam Hydration of CaO-Based Sorbents Cycled for CO2 Capture. Chem. Eng. J. 2016, 291, 298– 305,  DOI: 10.1016/j.cej.2016.01.086
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    A shrinking core model for steam hydration of CaO-based sorbents cycled for CO2 capture
    Blamey, John; Zhao, Ming; Manovic, Vasilije; Anthony, Edward J.; Dugwell, Denis R.; Fennell, Paul S.
    Chemical Engineering Journal (Amsterdam, Netherlands) (2016), 291 (), 298-305CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
    Ca looping is a developing CO2 capture technol. based on the reversible carbonation of CaO sorbent, which becomes less reactive upon cycling. One method to increase the reactivity of un-reactive sorbent is by hydration in the calcined (CaO) form. In this work, a sorbent was subjected to repeated carbonation/calcination cycles in a small, fluidized bed reactor. Cycle nos. 0 (i.e., 1 calcination), 2, 6, and 13 were studied to generate sorbents which have been deactivated to different extents. Subsequently, the generated sorbent was subjected to steam hydration tests in a thermogravimetric analyzer at hydration temps. of 473, 573, and 673°K. Sorbents which were cycled less prior to hydration hydrated rapidly; however, the more cycled sorbents exhibited behavior where the hydration conversion tended toward an asymptotic value, likely assocd. with pore blockage. This asymptotic value tended to be lower at higher hydration temps.; however, the max. rate of hydration increased with increasing hydration temp. A shrinking core model was developed and applied to the data. It fits exptl. data which did not exhibit extensive pore blockage well, but fit exptl. data which exhibited pore blockage less well.
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    Keith, M. J.; Leeke, G. A.; Khan, P.; Ingram, A. Catalytic Degradation of a Carbon Fibre Reinforced Polymer for Recycling Applications. Polym. Degrad. Stab. 2019, 166, 188– 201,  DOI: 10.1016/j.polymdegradstab.2019.05.020
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    Catalytic degradation of a carbon fiber reinforced polymer for recycling applications
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    Polymer Degradation and Stability (2019), 166 (), 188-201CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    A range of alk. and weak Lewis acid solns. were used in conjunction with an acetone / water solvent system in order to decomp. a carbon fiber reinforced epoxy resin. The initial concn. of the additives in the mixt. was varied between 0.01 to 0.40 M at temps. and pressures of 280 to 320 °C and 13 to 20 MPa. Under these conditions and a reaction time of 1 h, KOH and NaOH did not accelerate the decompn. of the matrix relative to the neat solvent, however, 0.05 M solns. of ZnCl2 and MgCl2 and a 0.005 M soln. of AlCl3 facilitated the recovery of clean fibers at 300 °C. Under these conditions, the degrdn. achieved with acetone / water alone was just 33 wt%. By changing the process temp. and reaction time, the min. necessary conditions for complete degrdn. were identified as 290 °C, 1.5 h or 300 °C, 45 min for all metal chlorides investigated. This represents a redn. in temp. of 40 °C when compared to a neat acetone / water solvent mixt. The reaction kinetics were studied through the application of a first order rate equation and a shrinking core model with the results demonstrating that 0.05 M ZnCl2 reduces the activation energy of the reaction by 30%. Anal. of the org. liq. fraction using IR spectroscopy suggests that this is due to the cleavage of the C=N bonds in the epoxy resin by the metal ions. Gas chromatog. with mass spectrometry identified the presence of cyclic compds. and low concns. of amine derivs.
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    Okajima, I.; Sako, T. Recycling Fiber-Reinforced Plastic Using Supercritical Acetone. Polym. Degrad. Stab. 2019, 163, 1– 6,  DOI: 10.1016/j.polymdegradstab.2019.02.018
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    Recycling fiber-reinforced plastic using supercritical acetone
    Okajima, Idzumi; Sako, Takeshi
    Polymer Degradation and Stability (2019), 163 (), 1-6CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    Carbon fiber-reinforced plastic (CFRP) can be difficult to recycle owing to the presence of thermosetting plastics such as epoxy resin. Therefore, it is important to develop more efficient methods for recycling CFRP. Herein, we investigated the chem. recycling of CFRP contg. an epoxy matrix resin via a process involving superheated and supercrit. acetone. The decompn. efficiency of the epoxy resin in the CFRP at 2-14 MPa and 350 °C increased with increasing reaction time over the first 60 min, but then decreased over longer reaction times because the decompn. products carbonized. Furthermore, the decompn. efficiency increased with increasing reaction pressure and acetone d., to a max. of 95.6% at 350 °C, 60 min, and a d. of 4.35 mol/L (14 MPa). The decompn. rate of the epoxy resin in CFRP using superheated and supercrit. acetone is rationalized by a surface-reaction and shrinking-core model, with large neg. activation vols.
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    Andrady, A. L. The Plastic in Microplastics: A Review. Mar. Pollut. Bull. 2017, 119 (1), 12– 22,  DOI: 10.1016/j.marpolbul.2017.01.082
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    Marine Pollution Bulletin (2017), 119 (1), 12-22CODEN: MPNBAZ; ISSN:0025-326X. (Elsevier Ltd.)
    Microplastics [MPs], now a ubiquitous pollutant in the oceans, pose a serious potential threat to marine ecol. and has justifiably encouraged focused biol. and ecol. research attention. But, their generation, fate, fragmentation and their propensity to sorb/release persistent org. pollutants (POPs) are detd. by the characteristics of the polymers that constitutes them. Yet, physico-chem. characteristics of the polymers making up the MPs have not received detailed attention in published work. This review assesses the relevance of selected characteristics of plastics that composes the microplastics, to their role as a pollutant with potentially serious ecol. impacts. Fragmentation leading to secondary microplastics is also discussed underlining the likelihood of a surface-ablation mechanism that can lead to preferential formation of smaller sized MPs.
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    The release of plastics into the environment has been identified as an important issue for some time. Recent publications have suggested that the degrdn. of plastic materials will result in the release of nano-sized plastic particles to the environment. Nanoparticle tracking anal. was applied to characterize the formation of nanoplastics during the degrdn. of a polystyrene (PS) disposable coffee cup lid. The results clearly show an increase in the formation of nanoplastics over time. After 56 days' exposure the concn. of nanoplastics in the PS sample was 1.26 × 108 particles/mL (av. particles size 224 nm) compared to 0.41 × 108 particles/mL in the control.
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    Polymer Degradation and Stability (1994), 45 (2), 165-72CODEN: PDSTDW; ISSN:0141-3910. (Elsevier)
    Two accelerated degrdn. systems are described for the marine and soil exposures of polymer films. The systems were designed to provide controlled environments in which rates of degrdn. could be accelerated. The goal in developing these systems was to provide a standardized basis for comparing degrdn. kinetics of the films. Polymer film degrdn. kinetics are illustrated with two bacterial polyester copolymer (8% valerate and 24% valerate in butyrate-co-valerate polyester polymers) and cellophane. Initial data on wt. loss per surface area, changes in mol. wt., and changes in mech. properties of the films are described. The long-term goals are to correlate this type of data to environmental exposure conditions and to polymer morphol. and chem.
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    Polymer Degradation and Stability (1989), 26 (4), 333-45CODEN: PDSTDW; ISSN:0141-3910.
    Several types of thermoplastic and latex rubber materials commonly encountered in marine plastic debris were weathered in air and while floating in sea water, under North Carolina climatic conditions. The degrdn. of the different samples was monitored by tensile property detn. In general, the various materials tested tended to weather at a slower rate when exposed in sea water compared to that in air. This retardation of weathering is probably a result of lack of heat build-up in samples exposed at sea.
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    Marine Pollution Bulletin (2007), 54 (6), 771-778CODEN: MPNBAZ; ISSN:0025-326X. (Elsevier B.V.)
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    Ye, S.; Andrady, A. L. Fouling of Floating Plastic Debris under Biscayne Bay Exposure Conditions. Mar. Pollut. Bull. 1991, 22 (12), 608– 613,  DOI: 10.1016/0025-326X(91)90249-R
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  • Abstract

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    Figure 1

    Figure 1. Common products in the thermal- and photo-oxidative degradation pathways for polyethylene (R, R′, and R′′ are polymer chains of variable length).

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    Figure 2

    Figure 2. Photo-oxidative degradation of PE containing carbonyl impurities, via (a) a Norrish type I mechanism or (b) a Norrish type II mechanism. (c) Radical recombination to form cross-linked chains. (38) R, R′, and R′′ are polymer chains of variable length.

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    Figure 3

    Figure 3. Small molecule products of the three common degradation routes in the environmental degradation of polyethylene terephthalate. R and R′ are polymer chains of variable length.

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    Figure 4

    Figure 4. Common products in the hydrolytic and photo-oxidative degradation pathways of polylactic acid (R and R′ are polymer chains of variable length).

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    Figure 5

    Figure 5. Mechanism of PLA degradation by chain-end scission in acidic environments. Adapted from de Jong et al., 2001. (58)

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    Figure 6

    Figure 6. Representative structures for (a) a section of a flat produce bag with total thickness h and (b) a sphere of radius r. The specific surface degradation rate (SSDR) is defined as the volume of material lost by removal of a layer of thickness Δd in a specified time.

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    Figure 7

    Figure 7. Comparison of predicted degradation profiles for HDPE pieces with the same mass, density, and SSDR but different shapes (thin film, fiber, and bead). The dashed lines correspond to extrapolations assuming constant surface area; the solid lines correspond to a model which assumes the radius, and therefore the surface area, decrease over time.

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    Figure 8

    Figure 8. Specific surface degradation rates for various plastics, in μm year–1. Vertical columns represent different environmental conditions (L, landfill/compost/soil; M, marine; B, biological; S, sunlight) and plastics types (represented by their resin identification codes). Plastics type 7, “others”, corresponds to various nominally biodegradable plastics. The range and average value for plastics types 1–6 are shown on the right as lines and squares, respectively, as well as for biodegradable “others”. Data points representing degradation rates that were unmeasurably slow are shown on the x-axis. Gray columns represent combinations for which no data were found.

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    Ali Chamas

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    Ali Chamas is completing his Ph.D. in Chemistry at the University of California, Santa Barbara. He received his B.S. in biochemistry also from the University of California, Santa Barbara. His research focuses on kinetic and mechanistic studies of catalytic lignin depolymerization and recently plastic waste upcycling. Ali has been the recipient of several awards and fellowships, including the U.S. Department of Energy, Office of Science Graduate Student Research Program for in-residence research at the Pacific Northwest National Laboratory. The UC Santa Barbara Crossroads Fellowship has allowed him to work in a multidisciplinary team on understanding plastic waste degradation.

    Hyunjin Moon

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    Hyunjin Moon is currently a Ph.D. student in chemical engineering at the University of California, Santa Barbara. He received his M.S. in mechanical engineering (2016) at Seoul National University, Korea. His Master’s thesis focused on electrochemical synthesis of metal/polymer-based nanomaterials for energy storage devices. Currently, his Ph.D. research investigates valorizing lignocellulosic biomass by controlling polarities at solid–liquid interfaces. During his graduate career, he has been recognized with several fellowships including the Global Ph.D. fellowship and UC-RWTH IRES fellowship. His expertise lies in synthesis of nanoscale and microscale materials for efficient catalytic conversions and their characterization through physicochemical methods.

    Jiajia Zheng

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    Jiajia Zheng is currently a Ph.D. student at the Bren School of Environmental Science and Management at the University of California, Santa Barbara. She obtained her Master’s degree in environmental engineering from Fudan University, China. Jiajia’s research focuses on the assessment of technological opportunities for carbon mitigation. As part of the research, her recent publication in Nature Climate Change addresses the strategies to reduce the global carbon footprint of plastics. (9)

    Yang Qiu

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    Yang Qiu is a Ph.D. student at the Bren School of Environmental Science and Management at the University of California, Santa Barbara. Yang has been working in the field of industrial ecology for his Ph.D., and his research focuses on understanding the economic and environmental trade-offs of low-carbon transitions in the energy system. Additionally, he is also interested in understanding the implication of technology development on consumption and circularity of critical metals.

    Tarnuma Tabassum

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    Tarnuma Tabassum is currently a Ph.D. candidate in the Department of Chemistry and Biochemistry at the University of California, Santa Barbara. Her research interests lie in the surface characterization of supported catalytic materials using magnetic resonance spectroscopy. Specifically, she is working towards using electron paramagnetic resonance to investigate the spatial distribution of hydroxyl groups on silica and applying solid state nuclear magnetic resonance in combination with dynamic nuclear polarization to elucidate the structural characteristics of P-modified zeolites and alumina-supported vanadia. As an IRES and Chateaubriand Fellow, she has had the opportunity to conduct research as a visiting student at RWTH Aachen (Germany) and the University of Lille (France), respectively. The Crossroads Fellowship Program allowed her to broaden her scope of knowledge by offering an interdisciplinary platform that merges chemistry, chemical engineering, and environmental sciences, such that she could explore an area different from her primary research investigation.

    Jun Hee Jang

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    Jun Hee Jang is currently a Ph.D. candidate in chemical engineering at the University of California, Santa Barbara (UCSB). Prior to joining UCSB, he received a M.S. at Seoul National University with a research project focused on the microscale- and nanoscale-patterned membranes for wastewater treatment. In the Abu-Omar research group at UCSB, his research project aims at developing renewable materials for energy and environmental applications. His research areas include the synthesis of inorganic heterogeneous catalysts (metal and metal oxide catalysts), materials characterization with a variety of analytical techniques, biomass valorization, optimization of catalytic reactions, and polymer degradation.

    Mahdi Abu-Omar

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    Mahdi Abu-Omar holds the Duncan and Suzanne Mellichamp Chair in Green Chemistry at the University of California, Santa Barbara. His research accomplishments include selective conversion of biomass lignin to biophenols and the creation of renewable plastics based on lignin. He has authored/coauthored nearly 200 original research articles in peer-reviewed scientific journals, supervised more than 40 Ph.D. students, and held faculty appointments at Purdue University and the University of California, Los Angeles (UCLA). Mahdi is the founder of Spero Renewables, a clean tech company that provides cost-effective and renewable substitutes to petrochemicals (sperorenewables.com/). Mahdi was elected Fellow of the American Association for Advancement of Science (AAAS) in 2012 and was a Senior Fulbright Fellow at the Weismann Institute in 2008. Dr. Abu-Omar completed a Ph.D. from Iowa State University (1996) and a postdoc from Caltech.

    Susannah L. Scott

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    Susannah L. Scott holds the Duncan and Suzanne Mellichamp Chair in Sustainable Catalysis at the University of California, Santa Barbara, and is jointly appointed as a Distinguished Professor in both the Departments of Chemical Engineering and Chemistry and Biochemistry. She earned a B.S. in chemistry from the University of Alberta (Canada) and a Ph.D. in inorganic chemistry from Iowa State University. Her research interests include the design of heterogeneous catalysts with well-defined active sites for the efficient conversion of conventional and emerging feedstocks, as well as environmental catalysts to promote air and water quality. At the University of California, Santa Barbara, she founded the interdisciplinary Mellichamp Academic Initiative in Sustainable Manufacturing and Product Design.

    Sangwon Suh

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    Sangwon Suh is a Professor at the Bren School of Environmental Science and Management at the University of California, Santa Barbara, where he also serves as the director of the Chemical Life Cycle Collaborative (CLiCC) that developed an online tool for sustainability assessment of chemicals (clicc.net). He earned a B.E. in civil and environmental engineering and an M.E. in environmental engineering from Ajou University (South Korea) and a Ph.D. in industrial ecology from Leiden University (The Netherlands). His research focuses on the interface between technologies and the environment. In particular, his work concerns the sustainability of human–nature complexity through understanding the materials and energy exchanges between them.

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