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Tunable and Degradable Dynamic Thermosets from Compatibilized Polyhydroxyalkanoate Blends
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  • Chen Ling
    Chen Ling
    Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
    Agile BioFoundry, Emeryville, California 94608, United States
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    Ryan W. Clarke
    Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
    BOTTLE Consortium, Golden, Colorado 80401, United States
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    Gloria Rosetto
    Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
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  • Shu Xu
    Shu Xu
    Applied Materials Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
    Northwestern Argonne Institute of Science & Engineering, Evanston, Illinois 60208, United States
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    Orcidhttps://orcid.org/0000-0002-2713-7897
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    Robin M. Cywar
    Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
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    Dong Hyun Kim
    Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
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    Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
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    Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
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    William E. Michener
    Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
    Agile BioFoundry, Emeryville, California 94608, United States
    BOTTLE Consortium, Golden, Colorado 80401, United States
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    Sean P. Woodworth
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  • Kelsey J. Ramirez
    Kelsey J. Ramirez
    Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
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    BOTTLE Consortium, Golden, Colorado 80401, United States
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    Meltem Urgun-Demirtas
    Applied Materials Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
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  • Davinia Salvachúa
    Davinia Salvachúa
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    Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
    Agile BioFoundry, Emeryville, California 94608, United States
    BOTTLE Consortium, Golden, Colorado 80401, United States
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ACS Sustainable Chemistry & Engineering

Cite this: ACS Sustainable Chem. Eng. 2025, 13, 9, 3817–3829
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https://doi.org/10.1021/acssuschemeng.5c00943
Published February 27, 2025

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Abstract

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Polyhydroxyalkanoates (PHAs) are versatile, biobased polyesters that are often targeted for use as degradable thermoplastic replacements for polyolefins. Given the substantial chemical diversity of PHA, their potential as cross-linked polymers could also enable similar platforms for reversible, degradable thermosets. In this work, we genetically engineered Pseudomonas putida KT2440 to synthesize poly(3-hydroxybutyrate-co-3-hydroxyundecenoate) (PHBU), which contains both 3-hydroxybutyrate and unsaturated 3-hydroxyundecenoate components. To reduce the brittleness of this polymer, we physically blended PHBU with the soft copolymer poly(3-hydroxydecanonate-co-3-hydroxyundecenoate) in mass ratios of 1:3, 1:1, and 3:1. Upon observing varying degrees of immiscibility by scanning electron microscopy, we installed dynamic boronic ester cross-links via thiol–ene click chemistry, which resulted in compatibilized dynamic thermoset blends ranging in hard, medium, and soft rubber or elastomer thermomechanical profiles. These dynamic thermoset blends were subjected to controlled biological degradation experiments in freshwater conditions, achieving timely mass loss despite the cross-linked architectures. Overall, this work highlights a two-component platform for the production of degradable and reprocessable dynamic thermoset blends suitable for several classes of cross-linked polymer technologies from tailored, biological PHA copolymers.

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Synopsis

Microbially produced polymers are cross-linked to form rubber-like materials. These biobased materials can be reprocessed and are biodegradable.

Introduction

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The global pollution crisis stemming from plastic waste accumulation in the natural environment is prompting demand for a circular material economy that relies on sustainable alternatives to conventional fossil carbon-based plastics. (1−4) As a promising option, polyhydroxyalkanoates (PHAs) are a class of biodegradable polyesters that can be sourced from microbial synthesis using renewable feedstocks. (5−10) PHA side chains are highly tunable via biological and chemical approaches, and this versatility has been leveraged to obtain thermoplastics with enhanced thermal stability, polyolefin-like properties, and catalytic depolymerization to monomers. (2,11−17) Generally, short-chain-length (scl) PHAs consisting of pendent groups of 1–2 carbon atoms are rigid, medium-chain-length (mcl) PHAs with pendent 3–11 carbon atoms are often soft materials exhibiting elastomeric tensile profiles, (18,19) and longer chain length PHAs (pendent groups >11 carbon atoms) are less common but generally softer. (7)
To date, advances in designer-PHA materials have been primarily directed toward thermoplastics. While thermoplastics encompass the majority of plastic production, thermosets (cross-linked polymers) comprise 18% of the annual polymer manufacture and often present a greater challenge for enabling end-of-life (EoL) technologies. (20−22) PHAs are of interest in this space as biobased alternatives to synthetic elastomeric materials, and importantly, it has been shown that cross-links in PHA do not affect biodegradability. (23−25) Microbially produced PHA copolymers with unsaturated pendent groups (denoted usPHAs) can be efficiently cross-linked with high energy irradiation, (23) UV, (26) thiol–ene click chemistry, (27−29) or peroxides (Figure 1A). (30,31) The resulting cross-linked products can serve as rubber materials, (32) pressure-sensitive adhesives, (33) and shape memory composites. (34) However, the lack of melt processability, solubility, and thermomechanical reconfiguration upon cross-linking consequently precludes typical recycling approaches at EoL. (23,28,35) Covalent adaptable networks (CANs) and vitrimers present an ideal alternative in this space, as thermally triggered dynamic bond exchange across cross-links allows for sufficient chain mobility for melt reprocessability at elevated temperatures while retaining thermoset performance at ambient temperatures. We recently reported an example involving an mcl-PHA, specifically poly(3-hydroxydecanonate-co-3-hydroxyundecenoate) (PHDU), chemically cross-linked with dynamic-covalent boronic ester linkages, resulting in the creation of elastomers that were both reprocessable and biodegradable in freshwater conditions (PHDU-BE-X, Figure 1B). (36) The optimum properties for the copolymer were found to be at lower cross-linking densities (∼6%), which resulted in a soft elastomer. With additional design effort, dynamic cross-linked PHAs could serve as an entire materials platform, allowing a wider range of properties to be accessed.

Figure 1

Figure 1. Overview of past efforts in PHA thermoset materials and advances in this work. (A, B) Previously reported strategies to enhance PHA thermal and mechanical performance, and (C) herein-reported strategy to obtain tunable, degradable thermoset materials. PHA, polyhydroxyalkanoates; PHDU, poly(3-hydroxydecanoate-co-3-hydroxyundecenoate); BE-X, boronic ester cross-linker 2,2-(1,4-phenylene)-bis[4-thioethyl-1,3,2-dioxaborolane]; and PHBU, poly(3-hydroxybutyrate-co-3-hydroxyundecenoate).

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Another route to improving the performance of PHAs is blending with other biopolymers, such as poly(ε-caprolactone), polysaccharides, natural rubber, (37,38) and other PHAs (Figure 1A). (39) A common complication is compatibility of the blends, which influences material performance, in turn requiring compatibilizers to facilitate miscibility and prevent phase separation over time. Nevertheless, melt mixing of poly(3-hydroxybutyrate-co-3-valerate) (PHBV) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) at different ratios resulted in homogeneous blends, although the properties were largely dominated by PHBV and remained brittle, despite the addition of a more ductile PHA. (40) A similar example between poly-3-hydroxybutyrate (P3HB) and mcl-PHA blends showed that improvements in material properties were only observed when nanocellulose was added to the matrix. (41) More generally, dynamic cross-linking has been demonstrated as a means to upcycle a broad range of immiscible plastic waste mixtures to dynamic thermoset blends with full compatibility. (42) Considering these examples, here, we posited that PHAs with different thermomechanical profiles could also be blended and compatibilized via dynamic cross-links to yield favorable performance and EoL biodegradability.
In this work, we replaced the native mcl-specific PHA synthases in Pseudomonas putida KT2440 (hereafter P. putida) with a heterologous synthase, (43,44) allowing the engineered strain to produce scl-co-mcl PHA copolymers, thus expanding the range of mechanical properties compared to mcl PHAs alone. We subsequently demonstrated that through the physical blending of scl-co-mcl and mcl-co-mcl usPHAs, along with the promotion of compatibilization via dynamic boronic ester cross-linking at the pendent alkenes, it is possible to achieve a high degree of control over the modulus and extensibility of the resulting network polymers. EoL options were investigated by subjecting each of the substrates to biodegradability experiments in freshwater conditions, highlighting retained biodegradation properties despite the incorporation of cross-links. Thus, this work affords a straightforward platform to obtain several classes of sustainable thermoset materials by variation of the blend composition.

Results

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Introduction of PhaC61-3-S325T/Q481K to P. putida for scl-co-mcl PHA Production from Structurally Related Fatty Acids

To produce scl-co-mcl PHAs in P. putida, we pursued two primary goals. First, we aimed to replace the native mcl-specific PHA synthases with a more versatile variant capable of polymerizing both the mcl and scl precursors. Second, we sought to attenuate fatty acid degradation by selectively deleting genes within the β-oxidation pathway, thus ensuring the preservation of fatty acid substrates that were ultimately provided to the engineered strain for tailored PHA production. Consequently, the supplied fatty acid substrates─sodium butyrate and 10-undecenoic acid─were directed toward forming mcl and scl blocks in the PHA product, and an alternative carbon source (here, a nutritionally rich medium or glucose) was required for energy and cell growth. The strain engineering approach of deleting gene phaG to separate product synthesis from carbon and energy supply is illustrated in Figure 2.

Figure 2

Figure 2. Pathway of cellular metabolism (left) and PHBU production (right) in P. putida LC059. Several genes in the β-oxidation pathway were deleted to prevent degradation of trans 2-enoyl-CoA. The gene phaG was knocked out to prevent the flux from FAB to PHA synthesis. Glucose was supplemented to supply energy and biomass formation. The native type II PHA synthases, PhaC1 and PhaC2, were replaced with PhaC61-3-S325T/Q481K to accept a broader range of 3-hydroxyacyl-CoA as substrates to produce the desired PHA copolymers. The gene encoding native PHA depolymerase, phaZ, was knocked out to prevent the degradation of PHBU.

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As a starting point, we began with the engineered strain LC039 (Table 1) that is engineered to produce PHDU. (36) Strain LC039 harbors deletion of several genes associated with fatty acid degradation (fadAB, fabAx, fabBx1x2, PP_2134–2135, PP_2218, and PP_2047–2051) to prevent degradation of exogenously provided fatty acid substrates. Additionally, the gene encoding PhaG was deleted to block the endogenous generation of 3-hydroxyacyl-CoAs via fatty acid biosynthesis (FAB), which could otherwise be incorporated into PHAs. Subsequently, we deleted the native phaC1-phaZ-phaC2 operon encoding two mcl-specific synthases, PhaC1 and PhaC2, and the PHA depolymerase PhaZ. (45) Subsquently, we replaced this operon with a gene encoding a PHA synthase PhaC61-3-S325T/Q481K that is capable of polymerizing both mcl and scl units. (43,44) The resultant strain LC059 (Table 1 and Figure 2) was utilized in the subsequent 500 mL and 2.8 L shake flask and 3 L bioreactor experiments to produce PHBU. Sodium butyrate and 10-undecenoic acid served as the substrates for PHBU synthesis, while a rich medium LB or mineral medium supplemented with glucose was employed to facilitate cell growth and energy consumption (Figure 2).
Table 1. Genotypes of the Primary Strains Used in This Study
straingenotypereference or source
LC039P. putida KT2440 ΔfadAB ΔPP_2134–2135 ΔfadBx1 ΔfadAx ΔfadBx2 ΔPP_2218 ΔphaG ΔPP_2047-PP_2051 (36)
LC059LC039 ΔphaC1phaZphaC2::Ptac:phaC61–3-S325T/Q481K-codon optimizedthis study

Shake Flask and Bioreactor Cultivation for PHBU Production

To verify the functionality of PhaC61-3-S325T/Q481K in P. putida LC059, we first conducted shake flask experiments in Miller’s lysogeny broth (LB), a nutritionally rich medium, supplemented with 10-undecenoic acid and sodium butyrate as substrates to test the production of PHBU. Following the shake flask cultivations, the cells were subjected to centrifugation, washing, and lyophilization. The resulting dry cell mass was subjected to acidic methanolysis, converting the PHA product to 3-hydroxy acid methyl esters (HAMEs) for analysis. The resulting HAMEs were quantified using gas chromatography–mass spectrometry (GC/MS) to ascertain the monomer composition of the PHA copolymers. (45)
In general, 3HB (HAME-4 in the ester form) constituted the main component of PHA accumulated by the strain LC059 across all six conditions, varying the concentrations of sodium butyrate and 10-undecenoic acid (Figure 3A). The fraction of 3-hydroxyundecenoate (HAME-11 in the ester form) increased as the ratio of 10-undecenoic acid to sodium butyrate increased, as expected (Figure 3A). Surprisingly, a small fraction of HAME-10 and HAME-12 was detected, each with a mass ratio of less than 2% (Figure 3A), which may be associated with unidentified fatty acid degradation and/or synthesis mechanisms. (36) To determine the molar ratio of 3-hydroxyundecenoate (% U) in PHBU, the material was first extracted and purified to form a PHBU film, and the % U in these PHBU films was subsequently determined by 1H NMR spectroscopy (Figure S4), revealing a linear correlation with the mol % undecanoic acid fed as a substrate (Figure 3B). Notably, at the highest sodium butyrate concentration tested (4 g L–1), the total sodium butyrate utilization and cell dry weight (CDW) were the lowest (Figures 3A and S1A). We thus hypothesized that sodium butyrate might become toxic at approximately 4 g L–1. To examine this, we evaluated the cell growth of LC059 on a modified mineral (M9) medium supplemented with different concentrations of sodium butyrate. Our results showed that higher concentrations of sodium butyrate generally impair cell growth, with a notable decline observed between 3 and 4 g L–1, and no growth at 5 g L–1 (Figure 3C). These findings suggest that 4 g L–1 may represent a critical toxicity threshold (Figure 3C). Therefore, to avoid any growth inhibition by sodium butyrate, we chose to maintain its concentration at or below 2 g L–1 in subsequent experiments. In addition, incomplete consumption of 10-undecenoic acid and a lower utilization of sodium butyrate were observed when 1.37 g L–1 10-undecenoic acid was supplemented (Figure S1A), suggesting that excess 10-undecenoic acid may also negatively affect sodium butyrate utilization. The conversion extent of 10-undecenoic acid to PHBU reached 40–45%, while sodium butyrate achieved nearly 100% (Figure S1B). The absence of C9 or other odd-numbered units suggests no β-oxidation degradation, with the low conversion efficiency of 10-undecenoic acid likely being attributed to its limited solubility or alternative oxidation pathways in P. putida.

Figure 3

Figure 3. PHBU production in shake flask and bioreactor cultivations. (A) CDW and HAME profiles in shake flask cultivation samples. HAME profiles were analyzed by using GC/MS. C4 represents sodium butyrate, and usC11 represents 10-undecenoic acid. The concentrations of usC11 were calculated based on the density value of 0.912 g mL–1 at 25 °C, considering volume concentrations of 0, 0.25, 0.5, 0.75, 1.00, and 1.50 mL L–1. Error bars represent the standard deviation calculated from biological triplicates. The GC/MS plots for the analysis of HAME profiles have been incorporated in Figure S1C,D. (B) Quantification of the mol % U in PHBU using 1H NMR spectroscopy (Figure S4). The mol % values of feeding 10-undecenoic acid were corrected using the density value 0.912 g mL–1 at 25 °C. Error bars represent the standard deviation calculated from biological triplicates. (C) Growth curves of LC059 on M9 medium supplemented with 50 mM glucose, and in the absence or the presence of different sodium butyrate concentrations (1, 2.5, 5 g L–1). Error bars represent the standard deviation calculated from biological triplicates. (D) Optical density (OD600) and production of PHBU in 3 L bioreactors in the dissolved oxygen (DO)-stat fed-batch mode using modified M9 medium and glucose. We note that optical density does not necessarily correlate with growth due to PHA accumulation. (46) The results are the average of two biological replicates, and the error bars represent the absolute difference between replicates. Black arrows indicate the time at which sodium butyrate (2 g L–1) and 10-undecenoic acid (0.16 g L–1) were added in the bioreactors.

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We previously observed increased brittleness in PHDU materials when cross-linking exceeded 6 mol %, (36) prompting us to target approximately 5 mol % unsaturation in our subsequent efforts producing PHBU. To assess the scalability of our system, we conducted PHBU production in 2.8 L shake flasks containing 500 mL of rich medium. The CDW remained consistent with our previous results on a smaller scale with 500 mL flasks containing 100 mL of medium, each producing ∼2–3 g L–1 (Figures S2 and 3A). We then combined the dry cells from six 2.8 L flasks (3 L cell culture in total) and extracted the materials, obtaining 6.40 g of purified scl-co-mcl PHAs (Figure S2).
To generate larger quantities of material for subsequent characterization, we conducted 3 L bioreactor cultivations using a DO-stat fed-batch strategy with the minimal M9 medium instead of a rich medium (see the Supporting Information). This feeding strategy allows the continuous and automatic addition of glucose─the sole carbon source─in the bioreactor while avoiding its accumulation and the generation of byproducts. (47) Sodium butyrate and 10-undecenoic acid were manually added to the bioreactors at two different time points during the cultivations, at concentrations of 2 and 0.16 g L–1, respectively. Based on DO and agitation profiles (Figure S3), it is evident that the glucose uptake rate decreased after each pulse of butyrate and 10-undecenoic acid. This reflects a deceleration of metabolism due to the toxicity effect of these compounds and/or because of the accumulation of PHBU. We anticipate that future bioprocess optimization, involving pulsing substrates at lower concentrations over a longer duration, could reduce substrate toxicity and thereby increase the PHBU content (currently 55% CDW). 6.32 g of PHBU material extracted from the two bioreactors was combined with 6.40 g of materials extracted from the 2.8 L shake flasks, resulting in a pooled material with a mol % U of 5%, designated PHBU-5 (Figure S5).

Characterization of PHBU-5 and PHBU-blend-PHDU Dynamic Thermoset Blends

Recovered scl-co-mcl PHBU-5 was analyzed by 1H and 13C NMR and FTIR spectroscopies (Figures S5–S7), revealing that the polymer was of high purity as evidenced by the absence of the C4 and unsaturated C11 substrates. Additionally, gel permeation chromatography in CHCl3 returned a high molar mass product (Mn = 1.24 × 105 kg mol–1, Đ = 2.2) (Figure S8). When subjected to tensile testing, PHBU-5 yielded similar qualities to that of the structurally similar homopolymer P3HB, namely, a brittle response with low elongations at break (εB = 2–5%). (36) Otherwise, PHBU-5 exhibited a modest tensile strength (σB = ∼20 MPa) and Young’s modulus (E = 833 MPa) by tensile testing (Figures 4A and S9A, Table S5), along with high crystallinity reflected in the enthalpy of fusion (ΔHf) of 60 J g–1 at the melting temperature (Tm) of 150 °C (Figure 4B). Crystallinity is limited by slow crystallization kinetics as indicated by the cold-crystallization peak (Tc ∼ 50 °C, Figure S10A), which could be overcome by thermal annealing. In addition, temperature-ramp frequency sweep thermograms by dynamic mechanical analysis (DMA) of PHBU agreed with thermal transitions measured by DSC, reflecting film failure approaching the Tm (∼145 °C), while also exhibiting storage modulus (E’) values of 8.1 GPa at −75 °C (E′max) and 2.3 GPa at ∼23 °C (E′RT) (−75 to 150 °C, 3 °C min–1, 30 μm, 1 Hz, Figures 4C and S11A). Lastly, thermogravimetric analysis (TGA) revealed a decomposition temperature (Td,5%) of 246 °C, in agreement with traditional PHA susceptibility to thermal degradation (Figure S12A). (10)

Figure 4

Figure 4. Preparation, compatibility, and mechanical analysis of hard-PHBU-5 and soft-PHDU-6 dynamic thermoset blends. (A) Representative tensile stress/strain tests (5 mm min–1, ∼23 °C) for PHBU-5 (black) and dynamically cross-linked PHBU-blend-PHDU at composition ratios by mass of 3:1 (blue), 1:1 (orange), and 1:3 (purple) (see Figure S9 for complete data and Table S5 for values). (B) Normalized DSC heat flow (10 °C min–1, exoup, first heating cycle) traces (see Figure S10 for individual plots and Table S6 for values). (C) DMA temperature-ramp frequency sweep thermograms (−75 to 200 °C, 3 °C min–1, 30 μm, 1 Hz) (see Figure S11 for individual thermographs and Table S7 for values), and (D) general scheme for the simultaneous blending and blend compatibilization by dynamic cross-linking of scl-co-mcl and mcl-co-mcl usPHAs to produce homogenized copolymer networks. (E) SEM cross-sectional imaging of virgin (top) and dynamic cross-link compatibilized (bottom) PHBU3-blend-PHDU1, PHBU1-blend-PHDU1, and PHBU1-blend-PHDU3 usPHA blends (scale bar = 15 μm) (see Figures S15–S17 for additional images and Figures S18–S20 for droplet diameters).

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Recognizing that cross-linking PHBU would impart higher stiffness to the brittle parent polymer, we considered strategies to enhance the mechanical performance while retaining the vitrimer dichotomy of melt processability and thermoset behavior. Conceivably, introducing the recently reported unsaturated mcl-co-mcl PHDU-6, (36) a soft and amorphous elastomer (Figure 4D and Table S4, Figures S13, S14 for polymer characterization data), during the cross-linking stage presents the means for a two-component polymer system that could yield dynamic thermoset blends with a high degree of tunability in thermal and mechanical profiles. We posited that such a system could access a broad range of rubber-like performance profiles by utilizing unsaturated PHA materials with diverse properties, produced using our engineered P. putida strains through the feeding of various fatty acids. To this end, we conducted physical blending of the hard PHBU-5 with soft PHDU-6 at varying mass ratios of 3:1, 1:1, and 1:3, followed by cross-linking with dynamic boronic ester linkages. Initial analysis by scanning electron microscopy (SEM) at the cryo-fractured cross-section revealed a pool of phase-separated PHBU-5 and PHDU-6 in the typical form of droplet-style domains with average diameters between 0.6 and 13.9 μm buried in the host-polymer matrix (Figures 4E and S15–S17). Notably, a trend in reduced blend compatibility was observed with an increase in the PHDU-6 loading, likely caused by incompatibility with highly crystalline PHBU-5. Specifically, droplet size analysis revealed that increasing the PHDU-6 content from 25 to 50 to 75 wt % paralleled an increasing average droplet diameter of 1.7, 2.2, and 5.9 μm, respectively (Figures 4E and S18–S20).
It is well understood that the presence and corresponding size of droplets is a direct metric for blend performance as the low interfacial adhesion (high interfacial tension) between the two immiscible polymers sabotages interdomain entanglement. (48) Specifically, larger droplets reflect poor compatibility and greater phase separation, while smaller droplets indicate a higher degree of compatibility. With this in mind, we used the usPHA pendent functionality to install dynamic cross-links as a compatibilization strategy. To this end, UV-photoinitiated thiol–ene click chemistry was performed on 3 g scales for the 3:1, 1:1, and 1:3 w/w usPHA blends in solution to covalently link the unsaturated pendent groups on both PHBU-5 and PHDU-6 with the dynamic boronic ester cross-linker, 2,2-(1,4-phenylene)-bis[4-thioethyl-1,3,2-dioxaborolane] (BE-X), capable of boronic ester metathesis for network reconfiguration (Figure 4D). The cross-linked blends are identified as PHBU3-blend-PHDU1, PHBU1-blend-PHDU1, and PHBU1-blend-PHBU3, where subscripts denote blend ratios by weight. Upon revisiting the dynamic thermoset blends with SEM, cross-sectional interfaces revealed homogenized surfaces in the complete absence of differentiable microdomains, signaling compatibilization (Figures 4E and S15–S20).
The resulting materials exhibited a gradient of thermal properties from semicrystalline (3:1 and 1:1) to fully amorphous (1:3) (Figures 4B and S10B–D). Successful installation of the dynamic cross-links was supported by DMA thermograms for each of the three blends, revealing extended thermomechanical performance windows in the rubbery plateau (ΔE′ ∼ 0) region beyond the ∼145 °C melt-failure of the virgin PHBU-5 parent polymer due to the associative nature of the boronic ester exchange retaining a constant cross-link density during metathesis events (−75 to 200 °C, 3 °C min–1, 30 μm, 1 Hz, Figures 4C and S11B–D).
More exciting, tensile stress/strain (5 mm min–1, ∼23 °C) revealed a wide range of thermoset performances dramatically outperforming the brittle parent PHBU-5 (Figure S9B–D). Specifically, we obtain a high modulus and stiff rubber (σB = 15.1 MPa, εB = 22%, E = 665 MPa) from the compatibilized 3:1 blend, a ductile polymer with intermediate modulus (σB = 6.6 MPa, εB = 94%, E = 70 MPa) from the 1:1 blend, and a soft elastomer (σB = 2.0 MPa, εB = 187%, E = 5.7 MPa) from the 1:3 blend (PHBU-5:PHDU-6) (Figure 4A and Table S5). Similar observations were made through the DMA thermograms for the 3:1, 1:1, and 1:3 blends, where a clear trend in decreasing E′max of 4887, 3135, and 2941 MPa, respectively, is observed with decreasing loading of the more crystalline PHBU-5 (Figure 4C and Table S7).

Dynamic Cross-Link Orthogonality by Elastic Recovery and Reprocessability

The value of dynamic thermosets lies in the thermoset-like performance during operating conditions and thermoplastic-like melt reprocessability during reprocessing conditions. To demonstrate this, we first subjected each of the dynamic thermoset blends to a reprocessing cycle at sufficient temperatures (165 °C and 15 min) for full blend melting and thermal activation of dynamic boronic ester metathesis. As expected, scraps from the initial round of tensile analysis were reformed into homogeneous films from which renewed tensile bars were obtained and analyzed (Figures S21, S22 and Table S5). The reprocessed hard rubber PHBU3-blend-PHDU1 demonstrated a similar tensile profile to the original set in σB (15.1 MPa vs 15.8 MPa), εB (22 vs 26%), and E (665 vs 647 MPa) (Figure 5A). Performance retention was also observed in the reprocessed PHBU1-blend-PHDU1 sample, which overlays nearly identical to the virgin counterpart (Figure 5A). Surprisingly, we found that the soft elastomer PHBU1-blend-PHDU3 demonstrated significantly higher (+80%) average εB while exhibiting almost 2× reduction in ultimate σB, indicating a possible change in the network architecture (Figure 5A, Table S5). The deviation in tensile performance may be accredited to boronic ester ambient hydrolysis susceptibility, thoroughly investigated in our previous PHA vitrimer systems relying on this specific boronic ester linkage. (36) Due to the reduced crystallinity in these samples, water permeability may be higher, increasing the rate of hydrolysis. A higher rate of hydrolysis would thus lead to a reduction in the cross-link density and consequently the tensile toughness.

Figure 5

Figure 5. Elasticity and melt processability by dynamic cross-linking. (A) Representative averaged tensile stress/strain (5 mm min–1, ∼23 °C) overlays between virgin and reprocessed dynamic thermoset blends (see Figure S22 for complete data and Table S5 for values). (B) Normalized stress relaxation traces for PHBU1-blend-PHDU3 by shear rheology (115 to 165 °C, 5 °C increments, 5%, 1000 s, 0.1 s rise time). (C) Arrhenius relationships between temperature and relaxation time for PHBU1-blend-PHDU3 (purple) and PHBU3-blend-PHDU1 (blue), the latter of which demonstrates a deviation in slope upon crystallization. (D) Cyclic deformation experiments with firm plastic-like (PHBU1-blend-PHDU1), (E) hard rubber (PHBU3-blend-PHDU1), and (F) soft elastomer (PHBU1-blend-PHDU3) (50 mm min–1 up-ramp, 50 mm min–1 down-ramp, ×5, ∼23 °C).

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Thermoset melt reprocessability is afforded by the boronic ester’s ability to undergo thermally induced dynamic bond exchange. The thermodynamics of the exchange can be evaluated by stress relaxation experiments, where an activation energy (Ea) for the exchange can be extracted as well as used to gauge implications for network healing. We conducted oscillatory rheology stress relaxation experiments on PHBU1-blend-PHDU3 and PHBU3-blend-PHDU1 to understand the impact of blend composition on these behaviors (Figures 5B and S23). In both cases, the dynamic blends exhibited stress relaxation times decreasing with higher temperatures. Interestingly, we found that despite the higher modulus of PHBU3-blend-PHDU1, the elastomeric PHBU1-blend-PHDU3 demonstrated a slower relaxation profile. We surmise that this may be due to the alkyl substituent length, where PHBU1-blend-PHDU3 has a significantly higher composition of sterically hindering dodecyl pendent chains. Conversely, transforming the stress relaxation to an Arrhenius plot (Figure 5C) yields an even more intriguing result where PHBU1-blend-PHDU3 has a lower Ea (63.7 kJ mol–1) for bond exchange than PHBU3-blend-PHDU1 (77.0 kJ mol–1), despite slower network relaxation times. This suggests that there is a valuable relationship between PHBU and PHDU pendant group sterics, Tg, and dynamic bond exchange wherein ideal vitrimers with fast relaxation times and higher Ea barriers are obtained.
To examine elasticity, we subjected each blend to elastomer hysteresis analysis to observe the deformation recovery following cyclic stress loadings. Notably, the strain for deformation was varied between 5 and 50% in accordance with the ultimate strain obtained from initial tensile pulling tests. Following five load–unload cyclic ramps, the ultimate stress was retained at 89, 80, and 81% of the initial first cycle value on the 3:1 hard, 1:1 firm, and 1:3 soft cross-linked blends, respectively, highlighting moderate elasticity following rapid extension events (50 mm min–1 up-/down-ramp rate) (Figure 5D–F). Notably, we still observe some compounding loss in ultimate stress during terminal-end strain loadings as a result of crystalline region disruption. Overall, we credit the high tunability of these thermomechanical profiles to the thermal properties, where higher crystallinity lends itself to higher strength, lower ductility, and increased consequences for elastic recovery.

Biodegradability of Virgin and Cross-Linked Materials

To assess the biodegradability of the cross-linked PHA copolymer films in comparison with non-cross-linked PHBU-5, biodegradation studies of the 1:3 and 3:1 blends in a freshwater environment were conducted, adhering to the ISO 14851 standard test. (49) In this context, PHBU-5, PHBU1-blend-PHDU3, and PHBU3-blend-PHDU1 reached 23.8 ± 3.4, 20.6 ± 3.7, and 24.3 ± 0.6% biodegradation levels, respectively, in 107 days (Figure 6). To estimate the lifetime of these films in freshwater environments, we applied first-order kinetics, which suggests that PHBU-5 and its cross-linked blends are expected to achieve 90% biodegradation between approximately 1000 and 1300 days (Table S9). Statistical analysis revealed no significant difference in their biodegradation rates in this freshwater environment (p > 0.05), suggesting that the cross-linking using BE does not affect the biodegradability of materials. Notably, all three films exhibit a dual-stage degradation pattern, with accelerated biodegradation observed around day 20 and another spike around day 80. This feature is likely related to the degradation of different segments (e.g., amorphous vs crystalline, short chain vs long chain) or individual components (e.g., PHBU or PHDU) of the blends. Further evidence for partial biodegradation is the reduction in molar mass of the linear parent polymer PHBU-5 before and after the biodegradation experiment, which decreased by 15%, from 124 to 107 kg mol–1 (Figure S24). In summary, these findings show that the cross-linked blends have similar degradation profiles compared to the parent polymers.

Figure 6

Figure 6. Biodegradability evaluation in freshwater biodegradation experiment. Freshwater biodegradation of PHBU-5, PHBU1-blend-PHDU3, and PHBU3-blend-PHDU1 in freshwater environments. Results over a 107-day period of aerobic freshwater degradation (ISO 14851) (49) for PHA dynamic thermoset blends relative to a microcrystalline cellulose (MCC) and a glucose control.

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Discussion

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In this report, we demonstrated a feasible, two-component platform for dynamic thermoset blend production encompassing a broad range of thermal and mechanical profiles from biologically produced PHAs. The unsaturated units in PHBU and PHDU were derived from 10-undecenoic acid, primarily synthesized via the pyrolysis of ricinoleic acid, the main fatty acid in castor oil. Notably, PHA containing other unsaturated monomer units, such as 3-hydroxy-5-dodecenoate (3H5DD), has been produced in P. putida grown on unrelated carbon sources like glucose (50) and gluconate (51) via the FAB pathway. In our study, the FAB pathway was deliberately blocked to prevent its contribution to PHA synthesis (Figure 2), enabling the precise control of PHA composition for material characterization. Interestingly, the presence of unsaturated units, such as 3H5DD, may have been overlooked for decades due to limitations in conventional GC/MS and NMR spectroscopy workflows. (51) Recent advancements, such as thiomethyl pretreatment, now facilitate easier detection of these units. (51) Investigating the in vivo generation of unsaturated fatty acids remains a promising direction for future research.
Blending scl- and mcl-PHAs has been explored to mitigate the brittle nature of ubiquitous P3HB and other scl-PHAs. For example, blending elastomeric mcl-PHA poly(3-hydroxy-octanoate) with P3HB led to enhanced mechanical performance when the P3HB loading <20%, obtaining ductility values of ∼200%, which is similar to our thermoset PHBU1-blend-PHDU3. (52) However, these polymers showed high immiscibility accredited to stark differences in crystallinity and Tm at all ranges of P3HB incorporations. Thus, compatibility between an scl and mcl PHA during blending is highly dependent on the ability to cocrystallize, which is challenging due to the large difference in Tm values (Tm scl PHA ≪ Tm mcl PHA). (53) In agreement, the scl-PHA in this study, PHBU-5, which is similar in brittleness to P3HB, also displays a lack of inherent compatibility with amorphous PHDU-6. This is highlighted in Figure 4E and is a result of the differences in crystallinity between the polymers, wherein increased loadings of PHDU yield increased immiscibility. These cocrystallization considerations are no longer an impedance upon installment of dynamic cross-links, as evidenced by the compatibilization across all PHBU-blend-PHDU compositions. Furthermore, thermoplastic blends have performance limitations when it comes to elasticity. In Figure 5D–F, the hysteresis curves revealed moderate elastic recovery (80–90% stress), notably beyond the capacity for thermoplastic materials, which lose most of the performance following the yield point. Crystallinity can be reduced or ultimately eliminated by increasing the loading of PHDU or the boronic ester cross-linker to obtain elastomer properties, as it is well-known that installing cross-linkers effectively reduces crystalline domain formation by disrupting the chain packaging capability. (54,55)
To the best of our knowledge, there are no examples of PHA-based blends that can serve as thermosets and meet the same degree of tunability and reprocessability at the EoL as with thermoplastics. As a result of the scarcity of literature reports on similar material design, we compare our PHA-based blends’ performance to those of existing commercial thermosets. We find that our most elastic substrate, PHBU1-blend-PHDU3, offers similar performance in tensile strength in Figure 4A for a recyclable replacement to untreated (nonvulcanized) nitrile (acrylonitrile-co-butadiene, NBR), styrene–butadiene (SBR), and natural (isoprene) rubber, although increasing PHDU loading is likely required to achieve analogous (200–600%) ductility. Conversely, vulcanized rubbers exhibit tensile moduli similar to that of our more crystalline dynamic thermoset PHBU3-blend-PHDU1 (σB = 15.1 MPa). Through compatibilizing thermoset blends with distinctly dynamic linkages, we demonstrate the ability to access tensile profiles from elastomeric to high-modulus thermoset responses with simple changes in the blend ratio. Although examples of solution-based processes for rubbers exist at large scales, such as anionic polymerization of SBR, (56) in future, we aim to accomplish blending and compatibilization under a single melt processing step.
Finally, biodegradation tests are imperative for new materials as they indicate whether a material will persist if it ends up in the natural environment. When ultimately formulating PHA-based thermosets for specific applications, it is important that additives and modifiers do not compromise the biodegradability. An example of microbially produced mcl-PHA blended with thermoset materials such as natural, butadiene, and nitrile rubbers demonstrated, perhaps unsurprisingly, that biodegradability is only achieved in the PHA component. (38) Another report found that the biodegradation rate of peroxide-mediated cross-linked PHA was reduced by half, convincingly as a result of irreversible C–C cross-linking and structural disordering. (24) Contrarily, by constructing blends based only on PHAs, over 20% biodegradation is achieved at 107 days (Figure 6) and is projected to fully decompose in under 4 years. Despite the cross-linked architecture, biodegradability of the PHBU-blend-PHDU systems is equivalent to the PHBU-5 parent polymer. We suspect that this may be due to a range of factors including similar film surfaces and hydrolytic instability of boronic esters.
Our study suggests future research in producing PHA thermosets with customized profiles. Notably, the broad substrate polymerization capabilities of PhaC61-3-S325T, Q481K, covering precursors C4, C10, C11, and C12 (Figure 3A), suggest the potential use of strain LC059 as a platform to produce a diversity of scl-co-mcl PHA copolymers comprising multiple monomers through the feeding of related fatty acids. Future designs for PHA thermosets could exploit different reversible chemistries through the alkene functionality, such as epoxy-acid chemistry, to yield polyester CANs. All-PHA dynamic thermoset blends are thus a promising solution to compatible, tunable rubbers while preserving biodegradability and reprocessability at the EoL.

Conclusions

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We present a two-component platform for renewable and biodegradable dynamic thermoset blends with a high degree of thermomechanical tunability from the simple dialing of otherwise immiscible microbially produced polymer ratios. We characterized the biosynthesis of the targeted PHA materials, showcasing their predictability, reproducibility, and scalability across different production means, from shake flasks to bioreactors. Physical blends of various microbial-produced PHA copolymers can be compatibilized through chemical cross-linking via the thiol–ene click reaction using dithiol boronic ester, producing hard, medium, and soft rubber-like materials. Furthermore, our biodegradability tests confirm that our modifications did not significantly compromise the biodegradability of PHA copolymers. Overall, the strategy of bioproduction, followed by blending and chemical modification, offers a promising approach for producing a wide range of sustainable thermoset materials based on PHAs.

Experimental Section

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Strain Engineering

Plasmid pLC007 was transformed into strain LC039 via electroporation. The electroporation method was modified from a previous study. (57) Strain LC039 was inoculated from a glycerol stock into 14 mL culturing tubes with 5 mL of LB medium and were incubated overnight in an incubator at 30 °C and 225 rpm. To prepare for electroporation, 1 mL of the overnight culture was harvested by centrifugation at 6000 rpm for 1 min in an Eppendorf 5424R benchtop centrifuge. The supernatants were carefully removed, and the cell pellets were subjected to two successive washes: first with 1 mL of 300 mM sucrose and then with 500 μL of 300 mM sucrose. After washing, the cell pellets were resuspended in 50 μL of 300 mM sucrose, resulting in a final resuspended cell volume of approximately 100 μL, taking into account any residual sucrose in the pellets. Next, 1 μg of plasmid DNA was gently mixed with the resuspended cells. This cell–plasmid mixture was then transferred into a 0.1 cm electroporation cuvette (BioRad) and subjected to electroporation using the following parameters: 1.6 kV, 25 μF, 200 ohms. Immediately after electroporation, 950 μL of LB medium was added to the cuvette. The LB medium containing the electroporated cells was then transferred into a 1.5 mL Eppendorf tube, which was securely attached to the surface of an incubator. The culture was shaken at 30 °C for 2 h. Following the incubation, the cells were centrifuged in an Eppendorf 5424R benchtop centrifuge at 6000 rpm for 1 min. Most of the medium was removed, leaving approximately 100 μL behind. The remaining culture was resuspended and spread onto LB agar plates containing 50 μg mL–1 kanamycin (LB-Kan plates). Transformants were then restreaked on a separate LB-Kan plate to isolate single colonies. These single colonies were utilized in the subsequent SacB counter-selection process. (57)

Shake Flask Experiments

The seed train for strain LC059 was conducted as follows. Strain LC059 was inoculated from glycerol stock into 14 mL culturing tubes containing 5 mL of LB medium and incubated overnight at 30 °C and 225 rpm (initial seed cultures). The initial seed cultures were then inoculated into 125 mL baffled flasks containing 25 mL of LB medium, with 1% inoculating volume (second seed cultures). The second seed cultures were incubated at 30 °C and 225 rpm for around 8 h, reaching an OD600 around 4. To prepare the medium for PHBU production in shake flask experiments, LB broth (Miller) powder was first added into 2.8 L flasks, followed by the addition of appropriate amounts of sodium butyrate and 10-undecenoic acid. Finally, 4 g L–1 Brij-35 detergent was added to the mixtures (to enhance the solubility of the fatty acids) and the entire content was thoroughly mixed and subsequently autoclaved. In the case of the shake flask experiments using 500 mL flasks, 100 mL of the autoclaved medium was transferred from the 2.8 L flasks into each of the 500 mL flasks. The second seed cultures mentioned above were then inoculated into either 500 mL baffled flasks with 100 mL of the prepared medium or 2.8 L baffled flasks with 500 mL of the prepared medium to an initial OD600 of 0.05. All shake flask experiments were run for around 66 h. After completion of the experiments, the final cell cultures were subjected to centrifugation at 10,000 rpm for 10 min. The supernatants were discarded, and the cell pellets were washed with equal volumes of Milli-Q water and 70% ethanol, separately. These washed cell pellets were then placed in a −80 °C freezer for a minimum of 3 h, followed by freeze-drying for at least 24 h.

Sodium Butyrate Toxicity Test

The seed culture was prepared as follows. P. putida LC059 was scrapped from a glycerol stock, inoculated in 250 mL baffled flasks containing 50 mL of the LB-Miller medium, and incubated overnight (16 h) at 30 °C and 225 rpm. The cells were harvested by centrifugation at 5000 rpm for 10 min and then resuspended in a modified M9 medium. This medium consisted of 13.56 g L–1 Na2HPO4, 6 g L–1 KH2PO4, 1 g L–1 NaCl, 2 g L–1 (NH4)2SO4, 2 mL L–1 of 1 M MgSO4, 0.1 mL of 1 M CaCl2, and 1 mL L–1 of 1 mM FeSO4. M9 was supplemented with glucose (9 g L–1 = 50 mM). The resuspended cells were then inoculated in 96-well plates containing modified M9 media (200 μL) with different concentrations of sodium butyrate (1, 2.5, and 5 g L–1) at an initial OD600 of 0.2. The plates were incubated at 30 °C in the high-speed mode for 48 h using LogPhase 600 (BioTek, Inc.). Assays at the different sodium butyrate concentrations were conducted in triplicate.

PHBU Production in Bioreactors

The strain utilized for PHBU production in bioreactors was P. putida strain LC059. The preparation of the seed culture was conducted as follows. The surface of the bacterial glycerol stock was scrapped and inoculated in 250 mL baffled flasks containing 50 mL of LB-Miller media. The seed was incubated for 16 h at 30 °C and 225 rpm (initial seed culture). Then, the cells were inoculated in 1 L baffled flasks containing 200 mL of LB-Miller media at an initial OD600 of 0.2 (second seed culture). Once the cells reached an OD600 of 2, the cells were harvested by centrifugation at 5000 rpm for 10 min and resuspended in 5 mL of modified M9 medium for further inoculation in 3 L bioreactors (Applikon) at an initial OD600 of 0.2. PHBU production in bioreactors was conducted using a modified minimal M9 medium in the fed-batch mode. The volume of the media in the batch phase was 1.2 L, and the modified M9 medium consisted of 13.56 g L–1 Na2HPO4, 6 g L–1 KH2PO4, 1 g L–1 NaCl, 2 g L–1 (NH4)2SO4, 2 mL L–1 of 1 M MgSO4, 0.1 mL L–1 of 1 M CaCl2, 1 mL L–1 of 18 mM FeSO4, and 3 g L–1 glucose. The bioreactors were controlled at 30 °C and pH 7 with an airflow rate of 1 vvm. The pH was automatically controlled by the addition of 4 N NaOH. The initial agitation was set at 350 rpm, and the initial DO was 100%. When the DO decreased to 30%, the DO was automatically controlled by changes in the agitation speed. The fed-batch phase initiated when glucose was depleted from the batch medium, and the DO level increased up to 75%. Three independent feeding solutions were prepared: (1) a solution with 500 g L–1 glucose and 100 g L–1 (NH4)2SO4 adjusted to pH 7 with 4 N NaOH, (2) a solution of 100 g L–1 sodium butyrate, and (3) a solution of 10-undecenoic acid (98% purity, Sigma). Solution (1) was added following a DO-stat fed-batch strategy. This recipe was programmed to add 1 mM glucose every time the DO reached a level of 75%, and agitation was manually controlled. Solutions (2) and (3) were manually added to the bioreactors at different times during the cultivations to achieve a sodium butyrate concentration of 2 g L–1 and a 10-undecenoic acid concentration of 0.16 g L–1. Antifoam 204 (Sigma-Aldrich) was added as necessary. Samples were collected during cultivation in bioreactors to measure the optical density at 600 nm (OD600), glucose, and butyrate. It is worth noting that OD600 is not an indicator of bacterial growth because the accumulation of PHBU also increases the value of the optical density. Glucose was analyzed in a glucose analyzer (YSI 2500 Biochemistry Analyzer). At the end of the cultivation, cells were collected from three independent bioreactors by centrifugation (5000 rpm, 10 min), washed twice with water, and utilized for CDW quantification and for downstream product purification and quantification. 1278 mL was the final volume in the bioreactors.

Chromatographic Analysis

The methodologies employed for the chromatographic analysis of PHA samples and fatty acids remained consistent with our prior investigation, (36) except for butyric acid. In the case of butyric acid, analysis utilized an Agilent Technologies 1260 series high-performance liquid chromatography system with a refractive index detector (RID) used for analyte detection and an Aminex HPX-87H (300 × 7.8 mm, Biorad Laboratories) column. Samples and standards were injected on the column at a volume of 6 μL. The column compartment and RID were maintained at 55 °C, and chromatographic separation was achieved using a mobile phase of 0.01 N sulfuric acid with an isocratic flow rate of 0.6 mL min–1 for a runtime of 27 min. The calibration curve for butyric acid was assessed at concentrations from 0.5 to 30.0 g L–1 with a minimum of five calibration standards used, resulting in a curve with an R2 coefficient of 0.995 or better. A calibration verification standard was analyzed every 10–15 samples to ensure the integrity of the initial calibration throughout the analysis run.

Polymer Isolation and Purification

Lyophilized biomass was stirred vigorously in CHCl3 for 24 h. The mixture was filtered through a Chemrus disposable 10 μm pore size filter funnel and then through a 0.2 μm PTFE filter frit. The polymer solution was concentrated on the rotary evaporator until viscous and then precipitated from cold ethanol. The polymer was recovered by filtration and dried in a vacuum oven at 40 °C for 24 h.

Blending and Thiol–Ene Click Cross-Linking Compatibilization

A 250 mL round-bottom flask was charged with PHBU-5, PHDU-6, and Bis-BE-SH (5 equiv of SH:alkene) in a glovebox. DMPA (0.5 wt % relative to polymer) and degassed, anhydrous, inhibitor-free DCM (150 mL) were added under a positive flow of nitrogen on a Schlenk line. The flask was placed in an air-cooled photoreactor (365 nm LED light) and irradiated for 2 h. After the reaction, most of the DCM was removed in vacuo, and the mixture was precipitated in anhydrous methanol. The polymer was collected and dried in a vacuum oven at 40 °C for 24 h.

Biodegradation Testing

CHN elemental analysis was conducted to quantify the total organic carbon and hydrogen in the samples employed for biodegradation assessment (Table S8). The biodegradability of polymer samples in a freshwater environment was assessed following the ISO 14851 methodology. Polymer film samples, including PHBU-5, PHBU1-blend-PHDU3, and PHBU3-blend-PHDU1 (approximately 4 mm × 3 mm × 1 mm in size), were tested in triplicates within 300 mL biological oxygen demand (BOD) glass bottles (VWR International). In each BOD bottle, activated sludge from a wastewater treatment plant (Lemont, IL, USA) was combined with 200 mL of aqueous medium, which was composed of the following components (in mg L–1): KH2PO4, 85; K2HPO4, 217.5; Na2HPO4, 334; NH4Cl, 15; MgSO4·7H2O, 22.5; CaCl2·2H2O, 36.4; and FeCl3·6H2O, 0.25. The total solid from the sludge was 60 mg L–1. For each of the triplicate test bottles of polymer samples, PHBU-5, PHBU1-blend-PHDU3, and PHBU3-blend-PHDU1 film samples (approximately 4 mm × 3 mm × 1 mm size) were added to the BOD bottles. The total organic carbon from polymer samples (PHBU-5, PHBU1-blend-PHDU3, and PHBU3-blend-PHDU1) added to every test bottle was 9.0 mg. Three blank test bottles with no additional carbon content other than the aqueous medium and three positive control bottles with 9.0 mg of total organic carbon content from d-glucose (Fisher Scientific, granular powder) and cellulose (microcrystalline, particle size 0.05 mm, Acros Organics) were also set up as positive controls. All bottles were incubated in a New Brunswick Scientific incubator shaker (Eppendorf, model I-24) at 25 °C and 150 rpm. BOD was determined by measuring oxygen consumption using a pH/RDO/DO meter (Thermo Fisher Scientific, model Orion Star A216) based on the conditions listed in the ISO 14851 standard method. The percentage biodegradability of the sample was calculated as
%Biodegradation=BODsample−BODblankc×ThOD×100%
(1)
The observed values of BODsample and BODblank were recorded for the sample and the blank bioreactor, respectively. The amount of sample added, denoted as “c”, was carefully measured. ThOD, representing the theoretical oxygen demand value of the sample, was calculated based on the chemical formula, assuming complete oxidation of the polymer sample. It was required by the protocol that the positive control (glucose) reach a biodegradation level of 60% at the conclusion of the test and that the standard deviation of each sample be less than 20% of the mean.

Estimation of End of Lifetime

A first-order kinetic model was employed to calculate the biodegradation rate and predict the lifespan of the polymer samples in a freshwater environment.
%Biodegradation=1−e(−kt+C)
(2)
Equation 2 was utilized to create a plot of percentage biodegradation against time. Within the equation, k represents the rate constant, t denotes the reaction time, and C is a constant from the plot. Table S9 provides a summary of the rate constants and estimated times to reach 90% biodegradation in a freshwater environment, and R2 values indicate the fitness of the model.
See the Supporting Information for materials and polymer characterization instrumentation and methods.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acssuschemeng.5c00943.

  • Source data for each figure, where applicable (XLSX)

  • Materials, NMR spectra, tensile data, DSC and TGA graphs, DMA data, SEM images (PDF)

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Author Information

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  • Corresponding Authors
    • Nicholas A. Rorrer - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  BOTTLE Consortium, Golden, Colorado 80401, United States;  Orcidhttps://orcid.org/0000-0001-9134-5853;  Email: [email protected]
    • Gregg T. Beckham - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  Agile BioFoundry, Emeryville, California 94608, United States;  BOTTLE Consortium, Golden, Colorado 80401, United States;  Orcidhttps://orcid.org/0000-0002-3480-212X;  Email: [email protected]
  • Authors
    • Chen Ling - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  Agile BioFoundry, Emeryville, California 94608, United States;  Present Address: State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiamen, Fujian 361102, China
    • Ryan W. Clarke - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  BOTTLE Consortium, Golden, Colorado 80401, United States;  Orcidhttps://orcid.org/0000-0002-1083-3618
    • Gloria Rosetto - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
    • Shu Xu - Applied Materials Division, Argonne National Laboratory, Lemont, Illinois 60439, United States;  Northwestern Argonne Institute of Science & Engineering, Evanston, Illinois 60208, United States;  Orcidhttps://orcid.org/0000-0002-2713-7897
    • Robin M. Cywar - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
    • Dong Hyun Kim - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
    • Levi J. Hamernik - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
    • Stefan J. Haugen - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  BOTTLE Consortium, Golden, Colorado 80401, United States
    • William E. Michener - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  Agile BioFoundry, Emeryville, California 94608, United States;  BOTTLE Consortium, Golden, Colorado 80401, United States
    • Sean P. Woodworth - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  BOTTLE Consortium, Golden, Colorado 80401, United States;  Orcidhttps://orcid.org/0000-0003-3792-9553
    • Torrey M. Lind - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  Agile BioFoundry, Emeryville, California 94608, United States
    • Kelsey J. Ramirez - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  Agile BioFoundry, Emeryville, California 94608, United States;  BOTTLE Consortium, Golden, Colorado 80401, United States
    • Meltem Urgun-Demirtas - Applied Materials Division, Argonne National Laboratory, Lemont, Illinois 60439, United States;  Orcidhttps://orcid.org/0000-0003-1581-1554
    • Davinia Salvachúa - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  Agile BioFoundry, Emeryville, California 94608, United States;  Orcidhttps://orcid.org/0000-0003-0799-061X
    • Christopher W. Johnson - Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States;  Agile BioFoundry, Emeryville, California 94608, United States;  Orcidhttps://orcid.org/0000-0002-2979-4751
  • Author Contributions

    C.L., R.W.C., G.R., R.M.C., G.T.B., and N.A.R. conceptualized the project. C.L., R.W.C., G.R., S.X., R.M.C., D.H.K., S.J.H., W.E.M., S.P.W., T.M.L., K.J.R., and M.U.D. developed the methodology. C.L., R.W.C., G.R., S.X., R.M.C., D.H.K., and D.S. ran the experiments. M.U.D., D.S., C.W.J., N.A.R., and G.T.B. supervised the project. C.L., R.W.C., and G.R. wrote the initial draft. All authors reviewed and edited the manuscript. C.L., R.W.C., and G.R. contributed equally to this work.

  • Notes
    The authors declare the following competing financial interest(s): RWC, GR, RMC, NAR, and GTB are listed as co-inventors on a US provisional patent application.

    R.W.C., G.R., R.M.C., N.A.R., and G.T.B. are listed as coinventors on US patent application US20240239956A1.

Acknowledgments

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This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding for C.L., D.Y.K., C.M.K., T.M.L., D.S., C.W.J., and G.T.B. was provided by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office (BETO) for the Agile BioFoundry. Funding was provided to G.R., N.A.R., and G.T.B. by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office (BETO) through the Performance-Advantaged Bioproducts program. Funding was provided to R.W.C., S.X., M.U.D., S.P.W., N.A.R., C.J.T., R.D.A., E.Y.X.C., and G.T.B. by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Materials and Manufacturing Technologies Office (AMMTO) and Bioenergy Technologies Office (BETO). This work was performed as part of the BOTTLE Consortium and was supported by AMMTO and BETO under contract no. DE-AC36-08GO28308 with the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, and with Argonne National Laboratory under contract DE-AC02-06CH11357. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

References

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This article references 57 other publications.

  1. 1
    Zhu, Y.; Romain, C.; Williams, C. K. Sustainable polymers from renewable resources. Nature 2016, 540 (7633), 354– 362,  DOI: 10.1038/nature21001
    Google Scholar
    1
    Sustainable polymers from renewable resources
    Zhu, Yunqing; Romain, Charles; Williams, Charlotte K.
    Nature (London, United Kingdom) (2016), 540 (7633), 354-362CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    Renewable resources are used increasingly in the prodn. of polymers. In particular, monomers such as carbon dioxide, terpenes, vegetable oils and carbohydrates can be used as feedstocks for the manuf. of a variety of sustainable materials and products, including elastomers, plastics, hydrogels, flexible electronics, resins, engineering polymers and composites. Efficient catalysis is required to produce monomers, to facilitate selective polymns. and to enable recycling or upcycling of waste materials. There are opportunities to use such sustainable polymers in both high-value areas and in basic applications such as packaging. Life-cycle assessment can be used to quantify the environmental benefits of sustainable polymers.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVyru7%252FP&md5=1a3419dd9b1a7e1643b4671cdf42553f
  2. 2
    Cywar, R. M.; Rorrer, N. A.; Hoyt, C. B.; Beckham, G. T.; Chen, E. Y. X. Bio-based polymers with performance-advantaged properties. Nature Reviews Materials 2022, 7 (2), 83– 103,  DOI: 10.1038/s41578-021-00363-3
    Google Scholar
    2
    Bio-based polymers with performance-advantaged properties
    Cywar, Robin M.; Rorrer, Nicholas A.; Hoyt, Caroline B.; Beckham, Gregg T.; Chen, Eugene Y.-X.
    Nature Reviews Materials (2022), 7 (2), 83-103CODEN: NRMADL; ISSN:2058-8437. (Nature Portfolio)
    A review Bio-based compds. with unique chem. functionality can be obtained through selective transformations of plant and other non-fossil, biogenic feedstocks for the development of new polymers to displace those produced from fossil carbon feedstocks. Although substantial efforts have been invested to produce bio-based polymers that are chem. identical to and directly replace those from petroleum, a long-pursued goal is to synthesize new, sustainable, bio-based polymers that either functionally replace or exhibit performance advantages relative to incumbent polymers. Owing to anthropogenic climate change and the environmental consequences of global plastics pollution, the need to realize a bio-based materials economy at scale is crit. To that end, in this Review we describe the concept of performance-advantaged, bio-based polymers (PBPs), highlighting examples wherein superior performance is facilitated by the inherent chem. functionality of bio-based feedstocks. We focus on PBPs with C-O and C-N inter-unit chem. bonds, as these are often readily accessible from bio-based feedstocks, which are heteroatom-rich relative to petroleum-derived feedstocks. Finally, we outline guiding principles and challenges to aid progress in the development of PBPs.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXitF2ksrrM&md5=55f4470fa36fcea2204592aaacfc44c5
  3. 3
    Law, K. L.; Narayan, R. Reducing environmental plastic pollution by designing polymer materials for managed end-of-life. Nature Reviews Materials 2022, 7 (2), 104– 116,  DOI: 10.1038/s41578-021-00382-0
    Google Scholar
    3
    Reducing environmental plastic pollution by designing polymer materials for managed end-of-life
    Law, Kara Lavender; Narayan, Ramani
    Nature Reviews Materials (2022), 7 (2), 104-116CODEN: NRMADL; ISSN:2058-8437. (Nature Portfolio)
    Abstr.: Plastics are a ubiquitous class of synthetic polymer materials used in virtually all com. and industrial sectors. The majority of global plastics consists of polymers with carbon-carbon backbones, whose environmental persistence and low cost have resulted in a massive reservoir of plastic waste that resides in landfills and the environment. Although plastic debris contaminating the ocean has been documented for decades, details about plastic debris compn., distribution, impact and ultimate fate in the environment remain elusive. In this Review, we present an overview of environmental plastic contamination and discuss the origin (feedstock) and degrdn. behavior of plastics to help inform material design principles addressing end-of-life management. We argue that designing materials to be 'marine biodegradable' or universally biodegradable is not, in itself, a soln. to plastic pollution. Instead, material and product design principles must include a feasible plan for recovery and treatment based upon existing (or, possibly, simultaneously developed) systems.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXit1Kms7jO&md5=1f3d0bbeef65ea8ff9f079de45dfd7cf
  4. 4
    Shi, C.; Reilly, L. T.; Kumar, V. S. P.; Coile, M. W.; Nicholson, S. R.; Broadbelt, L. J.; Beckham, G. T.; Chen, E. Y.-X. Design principles for intrinsically circular polymers with tunable properties. Chem. 2021, 7 (11), 2896– 2912,  DOI: 10.1016/j.chempr.2021.10.004
    Google Scholar
    4
    Design principles for intrinsically circular polymers with tunable properties
    Shi, Changxia; Reilly, Liam T.; Phani Kumar, V. Sai; Coile, Matthew W.; Nicholson, Scott R.; Broadbelt, Linda J.; Beckham, Gregg T.; Chen, Eugene Y.-X.
    Chem (2021), 7 (11), 2896-2912CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)
    A review. This perspective discusses a set of design principles for next-generation kinetically trapped, intrinsically circular polymers (iCPs) that are inherently, selectively, and expediently depolymerizable to their monomer state once their kinetic barriers of deconstruction are overcome, thereby enabling not only the ideal shortest chem. circularity but also tunable performance properties. After describing four elements of the design principles-thermodn. and kinetics, strategies to overcome trade-offs and unify conflicting properties, predictive modeling, and supply-chain life-cycle assessment and techno-economic anal., which are illustrated with state-of-the-art examples-it concludes with presenting key challenges and opportunities for sustainable development of iCPs.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXisFaju7zE&md5=46bec1e371e2b5fe904af4c39701d09f
  5. 5
    Narancic, T.; Verstichel, S.; Reddy Chaganti, S.; Morales-Gamez, L.; Kenny, S. T.; De Wilde, B.; Babu Padamati, R.; O’Connor, K. E. Biodegradable plastic blends create new possibilities for end-of-life management of plastics but they are not a panacea for plastic pollution. Environ. Sci. Technol. 2018, 52 (18), 10441– 10452,  DOI: 10.1021/acs.est.8b02963
    Google Scholar
    5
    Biodegradable Plastic Blends Create New Possibilities for End-of-Life Management of Plastics but They Are Not a Panacea for Plastic Pollution
    Narancic, Tanja; Verstichel, Steven; Reddy Chaganti, Srinivasa; Morales-Gamez, Laura; Kenny, Shane T.; De Wilde, Bruno; Babu Padamati, Ramesh; O'Connor, Kevin E.
    Environmental Science & Technology (2018), 52 (18), 10441-10452CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Plastic waste pollution is a global environmental problem which could be addressed by biodegradable plastics. The latter are blended together to achieve com. functional properties, but the environmental fate of these blends is unknown. We have tested neat polymers, polylactic acid (PLA), polyhydroxybutyrate, polyhydroxyoctanoate, poly(butylene succinate), thermoplastic starch, polycaprolactone (PCL), and blends thereof for biodegrdn. across seven managed and unmanaged environments. PLA is one of the world's best-selling biodegradable plastics, but it is not home compostable. We show here that PLA when blended with PCL becomes home compostable. We also demonstrate that the majority of the tested bioplastics and their blends degrade by thermophilic anaerobic digestion with high biogas output, but degrdn. times are 3-6 times longer than the retention times in com. plants. While some polymers and their blends showed good biodegrdn. in soil and water, the majority of polymers and their blends tested in this study failed to achieve ISO and ASTM biodegrdn. stds., and some failed to show any biodegrdn. Thus, biodegradable plastic blends need careful postconsumer management, and further design to allow more rapid biodegrdn. in multiple environments is needed as their release into the environment can cause plastic pollution.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsF2nsLjF&md5=0812c55b4ea95a33a9f0a4ef87198871
  6. 6
    Tang, X.; Westlie, A. H.; Watson, E. M.; Chen, E. Y.-X. Stereosequenced crystalline polyhydroxyalkanoates from diastereomeric monomer mixtures. Science 2019, 366 (6466), 754– 758,  DOI: 10.1126/science.aax8466
    Google Scholar
    6
    Stereosequenced crystalline polyhydroxyalkanoates from diastereomeric monomer mixtures
    Tang, Xiaoyan; Westlie, Andrea H.; Watson, Eli M.; Chen, Eugene Y.-X.
    Science (Washington, DC, United States) (2019), 366 (6466), 754-758CODEN: SCIEAS; ISSN:1095-9203. (American Association for the Advancement of Science)
    A review. Stereoselective polymn. of chiral or prochiral monomers is a powerful method to produce high-performance stereoregular cryst. polymeric materials. However, for monomers with two stereogenic centers, it is generally necessary to sep. diastereomers before polymn., resulting in substantial material loss and added energy cost assocd. with the sepn. and purifn. process. Here we report a diastereoselective polymn. methodol. enabled by catalysts that directly polymerize mixts. of eight-membered diolide (8DL) monomers with varying starting ratios of chiral racemic (rac) and achiral meso diastereomers into stereosequenced cryst. polyhydroxyalkanoates with isotactic and syndiotactic stereodiblock or stereotapered block microstructures. These polymers show enhanced ductility and toughness relative to polymers of pure rac-8DL, subject to tuning by variation of the diastereomeric ratio and structure of the 8DL monomers.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitFaksbzM&md5=77d5393285825bc53339b92088dc1c56
  7. 7
    Choi, S. Y.; Cho, I. J.; Lee, Y.; Kim, Y.-J.; Kim, K.-J.; Lee, S. Y. Microbial polyhydroxyalkanoates and nonnatural polyesters. Adv. Mater. 2020, 32 (35), 1907138  DOI: 10.1002/adma.201907138
    Google Scholar
    7
    Microbial Polyhydroxyalkanoates and Nonnatural Polyesters
    Choi, So Young; Cho, In Jin; Lee, Youngjoon; Kim, Yeo-Jin; Kim, Kyung-Jin; Lee, Sang Yup
    Advanced Materials (Weinheim, Germany) (2020), 32 (35), 1907138CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Microorganisms produce diverse polymers for various purposes such as storing genetic information, energy, and reducing power, and serving as structural materials and scaffolds. Among these polymers, polyhydroxyalkanoates (PHAs) are microbial polyesters synthesized and accumulated intracellularly as a storage material of carbon, energy, and reducing power under unfavorable growth conditions in the presence of excess carbon source. PHAs have attracted considerable attention for their wide range of applications in industrial and medical fields. Since the first discovery of PHA accumulating bacteria about 100 years ago, remarkable advances have been made in the understanding of PHA biosynthesis and metabolic engineering of microorganisms toward developing efficient PHA producers. Recently, nonnatural polyesters have also been synthesized by metabolically engineered microorganisms, which opened a new avenue toward sustainable prodn. of more diverse plastics. Herein, the current state of PHAs and nonnatural polyesters is reviewed, covering mechanisms of microbial polyester biosynthesis, metabolic pathways, and enzymes involved in biosynthesis of short-chain-length PHAs, medium-chain-length PHAs, and nonnatural polyesters, esp. 2-hydroxyacid-contg. polyesters, metabolic engineering strategies to produce novel polymers and enhance prodn. capabilities and fermn., and downstream processing strategies for cost-effective prodn. of these microbial polyesters. In addn., the applications of PHAs and prospects are discussed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXmsVSnurY%253D&md5=b04d4cfcc486ff1c97114d002c79d2c2
  8. 8
    Mezzina, M. P.; Manoli, M. T.; Prieto, M. A.; Nikel, P. I. Engineering native and synthetic pathways in Pseudomonas putida for the production of tailored polyhydroxyalkanoates. Biotechnol. J. 2021, 16 (3), 2000165  DOI: 10.1002/biot.202000165
    Google Scholar
    8
    Engineering Native and Synthetic Pathways in Pseudomonas putida for the Production of Tailored Polyhydroxyalkanoates
    Mezzina, Mariela P.; Manoli, Maria Tsampika; Prieto, M. Auxiliadora; Nikel, Pablo I.
    Biotechnology Journal (2021), 16 (3), 2000165CODEN: BJIOAM; ISSN:1860-6768. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Growing environmental concern sparks renewed interest in the sustainable prodn. of (bio)materials that can replace oil-derived goods. Polyhydroxyalkanoates (PHAs) are isotactic polymers that play a crit. role in the central metab. of producer bacteria, as they act as dynamic reservoirs of carbon and reducing equiv. PHAs continue to attract industrial attention as a starting point toward renewable, biodegradable, biocompatible, and versatile thermoplastic and elastomeric materials. Pseudomonas species have been known for long as efficient biopolymer producers, esp. for medium-chain-length PHAs. The surge of synthetic biol. and metabolic engineering approaches in recent years offers the possibility of exploiting the untapped potential of Pseudomonas cell factories for the prodn. of tailored PHAs. In this article, an overview of the metabolic and regulatory circuits that rule PHA accumulation in Pseudomonas putida is provided, and approaches leading to the biosynthesis of novel polymers (e.g., PHAs including nonbiol. chem. elements in their structures) are discussed. The potential of novel PHAs to disrupt existing and future market segments is closer to realization than ever before. The review is concluded by pinpointing challenges that currently hinder the wide adoption of bio-based PHAs, and strategies toward programmable polymer biosynthesis from alternative substrates in engineered P. putida strains are proposed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXit1KhsbnK&md5=f35780bd7754cbefd28ccb36ff26e7c9
  9. 9
    Tan, D.; Wang, Y.; Tong, Y.; Chen, G. Q. Grand challenges for industrializing polyhydroxyalkanoates (PHAs). Trends Biotechnol 2021, 39 (9), 953– 963,  DOI: 10.1016/j.tibtech.2020.11.010
    Google Scholar
    9
    Grand Challenges for Industrializing Polyhydroxyalkanoates (PHAs)
    Tan, Dan; Wang, Ying; Tong, Yi; Chen, Guo-Qiang
    Trends in Biotechnology (2021), 39 (9), 953-963CODEN: TRBIDM; ISSN:0167-7799. (Elsevier Ltd.)
    Polyhydroxyalkanoates (PHAs) are a diverse family of sustainable bioplastics synthesized by various bacteria, but their high prodn. cost and unstable material properties make them challenging to use in com. applications. Current industrial biotechnol. (CIB) employs conventional microbial chassis, leading to high prodn. costs. However, next-generation industrial biotechnol. (NGIB) approaches, based on fast-growing and contamination-resistant extremophilic Halomonas spp., allow stable continuous processing and thus economical prodn. of PHAs with stable properties. Halomonas spp. designed and constructed using synthetic biol. not only produce low-cost intracellular PHAs but also secrete extracellular sol. products for improved process economics. Next-generation industrial biotechnol. is expected to reduce the bioprodn. cost and process complexity, leading to successful com. prodn. of PHAs.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisFSgsLnE&md5=f91c9c556958150eff0d35075687e7c4
  10. 10
    Zhou, L.; Zhang, Z.; Shi, C.; Scoti, M.; Barange, D. K.; Gowda, R. R.; Chen, E. Y.-X. Chemically circular, mechanically tough, and melt-processable polyhydroxyalkanoates. Science 2023, 380 (6640), 64– 69,  DOI: 10.1126/science.adg4520
    Google Scholar
    10
    Chemically circular, mechanically tough, and melt-processable polyhydroxyalkanoates
    Zhou, Li; Zhang, Zhen; Shi, Changxia; Scoti, Miriam; Barange, Deepak K.; Gowda, Ravikumar R.; Chen, Eugene Y.-X.
    Science (Washington, DC, United States) (2023), 380 (6640), 64-69CODEN: SCIEAS; ISSN:1095-9203. (American Association for the Advancement of Science)
    Polyhydroxyalkanoates (PHAs) have attracted increasing interest as sustainable plastics because of their bio-renewability and biodegradability in the ambient environment. However, current semicryst. PHAs face three long-standing challenges to broad com. implementation and application: lack of melt processability, mech. brittleness, and unrealized recyclability, the last of which is essential for achieving a circular plastics economy. Here we report a synthetic PHA platform that addresses the origin of thermal instability by eliminating α-hydrogens in the PHA repeat units and thus precluding facile cis-elimination during thermal degrdn. This simple α,α-di-substitution in PHAs enhances the thermal stability so substantially that the PHAs become melt-processable. Synergistically, this structural modification also endows the PHAs with the mech. toughness, intrinsic crystallinity, and closed-loop chem. recyclability.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3sXns1Oku78%253D&md5=72a96cae0db8e361bec627d1024ef928
  11. 11
    Linger, J. G.; Vardon, D. R.; Guarnieri, M. T.; Karp, E. M.; Hunsinger, G. B.; Franden, M. A.; Johnson, C. W.; Chupka, G.; Strathmann, T. J.; Pienkos, P. T. Lignin valorization through integrated biological funneling and chemical catalysis. Proc. Natl. Acad. Sci. U. S. A. 2014, 111 (33), 12013– 12018,  DOI: 10.1073/pnas.1410657111
    Google Scholar
    11
    Lignin valorization through integrated biological funneling and chemical catalysis
    Linger, Jeffrey G.; Vardon, Derek R.; Guarnieri, Michael T.; Karp, Eric M.; Hunsinger, Glendon B.; Franden, Mary Ann; Johnson, Christopher W.; Chupka, Gina; Strathmann, Timothy J.; Pienkos, Philip T.; Beckham, Gregg T.
    Proceedings of the National Academy of Sciences of the United States of America (2014), 111 (33), 12013-12018CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    Lignin is an energy-dense, heterogeneous polymer comprised of phenylpropanoid monomers used by plants for structure, water transport, and defense, and it is the second most abundant biopolymer on Earth after cellulose. In prodn. of fuels and chems. from biomass, lignin is typically underused as a feedstock and burned for process heat because its inherent heterogeneity and recalcitrance make it difficult to selectively valorize. In nature, however, some organisms have evolved metabolic pathways that enable the utilization of lignin-derived arom. mols. as carbon sources. Arom. catabolism typically occurs via upper pathways that act as a "biol. funnel" to convert heterogeneous substrates to central intermediates, such as protocatechuate or catechol. These intermediates undergo ring cleavage and are further converted via the β-ketoadipate pathway to central carbon metab. Here, we use a natural arom.-catabolizing organism, Pseudomonas putida KT2440, to demonstrate that these arom. metabolic pathways can be used to convert both arom. model compds. and heterogeneous, lignin-enriched streams derived from pilot-scale biomass pretreatment into medium chain-length polyhydroxyalkanoates (mcl-PHAs). mcl-PHAs were then isolated from the cells and demonstrated to be similar in physicochem. properties to conventional carbohydrate-derived mcl-PHAs, which have applications as bioplastics. In a further demonstration of their utility, mcl-PHAs were catalytically converted to both chem. precursors and fuel-range hydrocarbons. Overall, this work demonstrates that the use of arom. catabolic pathways enables an approach to valorize lignin by overcoming its inherent heterogeneity to produce fuels, chems., and materials.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1GqtLnJ&md5=cfc41188e1879a545da121e6df144959
  12. 12
    Tang, X.; Westlie, A. H.; Caporaso, L.; Cavallo, L.; Falivene, L.; Chen, E. Y.-X. Biodegradable polyhydroxyalkanoates by stereoselective copolymerization of racemic diolides: stereocontrol and polyolefin-like properties. Angew. Chem., Int. Ed. 2020, 59 (20), 7881– 7890,  DOI: 10.1002/anie.201916415
    Google Scholar
    12
    Biodegradable Polyhydroxyalkanoates by Stereoselective Copolymerization of Racemic Diolides: Stereocontrol and Polyolefin-Like Properties
    Tang, Xiaoyan; Westlie, Andrea H.; Caporaso, Lucia; Cavallo, Luigi; Falivene, Laura; Chen, Eugene Y.-X.
    Angewandte Chemie, International Edition (2020), 59 (20), 7881-7890CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Bacterial polyhydroxyalkanoates (PHAs) are a unique class of biodegradable polymers because of their biodegradability in ambient environments and structural diversity enabled by side-chain groups. However, the biosynthesis of PHAs is slow and expensive, limiting their broader applications as commodity plastics. To overcome such limitation, the catalyzed chem. synthesis of bacterial PHAs has been developed, using the metal-catalyzed stereoselective ring-opening (co)polymn. of racemic cyclic diolides (rac-8DLR, R=alkyl group). In this combined exptl. and computational study, polymn. kinetics, stereocontrol, copolymn. characteristics, and the properties of the resulting PHAs have been examd. Most notably, stereoselective copolymns. of rac-8DLMe with rac-8DLR (R=Et, Bu) have yielded high-mol.-wt., cryst. isotactic PHA copolymers that are hard, ductile, and tough plastics, and exhibit polyolefin-like thermal and mech. properties.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXksVKjt7o%253D&md5=106c89f1765f0498dbb54ab51637bf30
  13. 13
    Li, M.; Ma, Y.; Zhang, X.; Zhang, L.; Chen, X.; Ye, J. W.; Chen, G. Q. Tailor-made polyhydroxyalkanoates by reconstructing Pseudomonas entomophila. Adv. Mater. 2021, 33 (41), e2102766  DOI: 10.1002/adma.202102766
    Google Scholar
    There is no corresponding record for this reference.
  14. 14
    Bruckmoser, J.; Pongratz, S.; Stieglitz, L.; Rieger, B. Highly isoselective ring-opening polymerization of rac-β-butyrolactone: access to synthetic poly(3-hydroxybutyrate) with polyolefin-like material properties. J. Am. Chem. Soc. 2023, 145 (21), 11494– 11498,  DOI: 10.1021/jacs.3c02348
    Google Scholar
    There is no corresponding record for this reference.
  15. 15
    Quinn, E. C.; Knauer, K. M.; Beckham, G. T.; Chen, E. Y. X. Mono-material product design with bio-based, circular, and biodegradable polymers. One Earth 2023, 6 (6), 582– 586,  DOI: 10.1016/j.oneear.2023.05.019
    Google Scholar
    There is no corresponding record for this reference.
  16. 16
    Yang, J.-C.; Yang, J.; Zhang, T.-Y.; Li, X.-J.; Lu, X.-B.; Liu, Y. Toughening poly(3-hydroxybutyrate) by using catalytic carbonylative terpolymerization of epoxides. Macromolecules 2023, 56 (2), 510– 517,  DOI: 10.1021/acs.macromol.2c02438
    Google Scholar
    There is no corresponding record for this reference.
  17. 17
    Zhou, Z.; LaPointe, A. M.; Shaffer, T. D.; Coates, G. W. Nature-inspired methylated polyhydroxybutyrates from C1 and C4 feedstocks. Nat. Chem. 2023, 15 (6), 856– 861,  DOI: 10.1038/s41557-023-01187-0
    Google Scholar
    There is no corresponding record for this reference.
  18. 18
    Rai, R.; Keshavarz, T.; Roether, J. A.; Boccaccini, A. R.; Roy, I. Medium chain length polyhydroxyalkanoates, promising new biomedical materials for the future. Materials Science and Engineering: R: Reports 2011, 72 (3), 29– 47,  DOI: 10.1016/j.mser.2010.11.002
    Google Scholar
    18
    Medium chain length polyhydroxyalkanoates, promising new biomedical materials for the future
    Rai, R.; Keshavarz, T.; Roether, J. A.; Boccaccini, A. R.; Roy, I.
    Materials Science & Engineering, R: Reports (2011), R72 (3), 29-47CODEN: MIGIEA; ISSN:0927-796X. (Elsevier B.V.)
    A review. Medium chain length polyhydroxyalkanoates, mcl-PHAs (C6-C14 carbon atoms), are polyesters of hydroxyalkanoates produced mainly by fluorescent Pseudomonads under unbalanced growth conditions. These mcl-PHAs which can be produced using renewable resources are biocompatible, biodegradable and thermoprocessable. They have low crystallinity, low glass transition temp., low tensile strength and high elongation to break, making them elastomeric polymers. Mcl-PHAs and their copolymers are suitable for a range of biomedical applications where flexible biomaterials are required, such as heart valves and other cardiovascular applications as well as matrixes for controlled drug delivery. Mcl-PHAs are more structurally diverse than short chain length PHAs and hence can be more readily tailored for specific applications. Composites have also been fabricated using mcl-PHAs and their copolymers, such as poly (3-hydroxyoctanoate) [P(3HO)] combined with single walled carbon nanotubes and poly(3-hydroxbutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] combined with hydroxyapatite. Because of these attractive properties of biodegradability, biocompatibility and tailorability, Mcl-PHAs and their composites are being increasingly used for biomedical applications. However, studies remain limited mainly to P(3HO) and the copolymer P(3HB-co-3HHx), which are the only mcl-PHAs available in large quantities. In this review we have consolidated current knowledge on the properties and biomedical applications of these elastomeric mcl-PHAs, their copolymers and their composites.
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  19. 19
    Muthuraj, R.; Valerio, O.; Mekonnen, T. H. Recent developments in short- and medium-chain- length polyhydroxyalkanoates: Production, properties, and applications. Int. J. Biol. Macromol. 2021, 187, 422– 440,  DOI: 10.1016/j.ijbiomac.2021.07.143
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    There is no corresponding record for this reference.
  20. 20
    Fortman, D. J.; Brutman, J. P.; De Hoe, G. X.; Snyder, R. L.; Dichtel, W. R.; Hillmyer, M. A. Approaches to sustainable and continually recyclable cross-linked polymers. ACS Sustainable Chem. Eng. 2018, 6 (9), 11145– 11159,  DOI: 10.1021/acssuschemeng.8b02355
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    20
    Approaches to Sustainable and Continually Recyclable Cross-Linked Polymers
    Fortman, David J.; Brutman, Jacob P.; De Hoe, Guilhem X.; Snyder, Rachel L.; Dichtel, William R.; Hillmyer, Marc A.
    ACS Sustainable Chemistry & Engineering (2018), 6 (9), 11145-11159CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
    A review. Crosslinked polymers are ubiquitous in daily life, finding applications as tires, insulation, adhesives, automotive parts, and countless other products. The covalent crosslinks in these materials render them mech. robust, chem. resistant, and thermally stable, but they also prevent recycling these materials into similar-value goods. Furthermore, crosslinked polymers are typically produced from petroleum-based feedstocks, and their hydrocarbon backbones render them non-degradable, making them unsustainable in the long-term. In recent years, much effort has focused on the development of recycling strategies for crosslinked polymeric materials. In the following Perspective, we discuss many of these approaches, and highlight efforts to sustainably produce recyclable crosslinked polymers. We present our thoughts on future challenges that must be overcome to enable widespread, viable, and more sustainable and practical implementation of these materials, including the sustainable sourcing of feedstocks, long-term environmental stability of inherently dynamic polymers, and moving toward industrially viable synthesis and reprocessing methods.
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  21. 21
    Ma, S.; Webster, D. C. Degradable thermosets based on labile bonds or linkages: A review. Prog. Polym. Sci. 2018, 76, 65– 110,  DOI: 10.1016/j.progpolymsci.2017.07.008
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    21
    Degradable thermosets based on labile bonds or linkages: A review
    Ma, Songqi; Webster, Dean C.
    Progress in Polymer Science (2018), 76 (), 65-110CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    A review. Compared with thermoplastic polymers, thermoset polymers are difficult to recycle because they can not be remolded once cured and often do not decomp. under mild conditions. Thermosets designed to be degradable afford a useful route to obtain thermoset recyclability and enable the recycling of valuable components that may be encapsulated in thermoset materials. In this review, the need for degradable thermosets as well as a summary of research progress is presented. Degradable thermosets are divided into different categories based on the different labile bonds or linkages studied such as esters, sulfur contg. linkages (disulfide, sulfonate, 5-membered cyclic dithiocarbonate, trithiocarbonate, sulfite), nitrogen contg. structures (acylhydrazone, alkoxyamine, azlactones, Schiff base, hindered ureas, aminal, carbamate), orthoester structures, carbonates, acetals, hemiacetals, olefinic bonds, D-A addn. structures, vicinal tricarbonyl structures, peroxide bonds, phosphorus contg. structures, tertiary ether bonds, and so on. The synthetic route, recycling methods, degrdn. mechanisms and progress in research of each approach to degradable thermosets is described. The efforts of the applicability of some degradable thermosets are also summarized. Finally, conclusions and trends of future work are highlighted.
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  22. 22
    Morici, E.; Dintcheva, N. T. Recycling of thermoset materials and thermoset-based composites: Challenge and opportunity. Polymers 2022, 14 (19), 4153,  DOI: 10.3390/polym14194153
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    22
    Recycling of Thermoset Materials and Thermoset-Based Composites: Challenge and Opportunity
    Morici, Elisabetta; Dintcheva, Nadka Tz.
    Polymers (Basel, Switzerland) (2022), 14 (19), 4153CODEN: POLYCK; ISSN:2073-4360. (MDPI AG)
    A review. Thermoset materials and their composites are characterized by a long life cycle with their main applications in aircrafts, wind turbines and constructions as insulating materials. The thermoset materials and their composites, to be successfully recovered and valorized, must degrade their three-dimensional structures and recover the mono-oligomers and/or fillers. The thermoset materials could successfully degrade through thermal treatment at different temps. (for example, above 1000°C for incineration, ca. 500°C for oxidn./combustion of org. constituents,), chem. degrdn. by catalyst, irradn. with or without the presence of water, alc., etc., and mech. recycling, obtaining fine particles that are useful as filler and/or reinforcement additives. Among these recycling methods, this mini-review focuses on the formulation and recovery method of innovative thermoset with in-build recyclability. The aim of this review is to get an overview of the state of the art in thermoset recycling and of the most commonly used thermoset composites, recovering valuable reinforcing fibers. Addnl., in this work, we also report not only known recycling routes for thermoset and thermoset-based composites, but also new and novel formulating strategies for producing thermosets with built-in recyclability, i.e., contg. chem.-triggered on-demand links. This mini-review is also a valuable guide for educational purposes for students and specialized technicians in polymer prodn. and recycling.
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  23. 23
    de Koning, G. J. M.; van Bilsen, H. M. M.; Lemstra, P. J.; Hazenberg, W.; Witholt, B.; Preusting, H.; van der Galiën, J. G.; Schirmer, A.; Jendrossek, D. A biodegradable rubber by crosslinking poly(hydroxyalkanoate) from Pseudomonas oleovorans. Polymer 1994, 35 (10), 2090– 2097,  DOI: 10.1016/0032-3861(94)90233-X
    Google Scholar
    There is no corresponding record for this reference.
  24. 24
    Scherer, T. M.; Fuller, R. C.; Lenz, R. W. Characterization and enzymatic degradation of a cross-linked bacterial polyester. J. Environ. Polym. Degrad. 1994, 2 (4), 263– 269,  DOI: 10.1007/BF02071974
    Google Scholar
    There is no corresponding record for this reference.
  25. 25
    S̨ucu, T.; Shaver, M. P. Inherently degradable cross-linked polyesters and polycarbonates: resins to be cheerful. Polym. Chem. 2020, 11 (40), 6397– 6412,  DOI: 10.1039/D0PY01226B
    Google Scholar
    There is no corresponding record for this reference.
  26. 26
    Valentin, H. E.; Berger, P. A.; Gruys, K. J.; de Andrade, Filomena; Rodrigues, M.; Steinbüchel, A.; Tran, M.; Asrar, J. Biosynthesis and characterization of poly(3-hydroxy-4-pentenoic acid). Macromolecules 1999, 32 (22), 7389– 7395,  DOI: 10.1021/ma9905167
    Google Scholar
    26
    Biosynthesis and characterization of poly(3-hydroxy-4-pentenoic acid)
    Valentin, Henry E.; Berger, Pierre A.; Gruys, Kenneth J.; de Rodrigues, Maria Filomena; Steinbuechel, Alexander; Tran, Minhtien; Asrar, Jawed
    Macromolecules (1999), 32 (22), 7389-7395CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Burkholderia sp. was grown on sucrose-contg. mineral salts medium with phosphate limitation to induce poly(hydroxyalkanoate) (PHA) accumulation. Under these conditions the cultures accumulated 3-hydroxybutyric acid (3HB) and 3-hydroxy-4-pentenoic acid (3HPE) contg. polyesters. Solvent fractionation of the purified polyester indicated the presence of two homopolymers, poly(3HB) and poly(3HPE), rather than a co-polyester with random monomer distribution as has been reported previously. The simultaneous accumulation of two homopolyesters by Burkholderia sp. was confirmed by NMR spectroscopic anal. Therefore, this is the first report on accumulation of a poly(3HPE) homopolyester and its accumulation from structurally unrelated carbon sources. Purified poly(3HPE) was cross-linked by UV radiation and subjected to epoxidn. using 3-chloroperoxybenzoic acid. Introduction of epoxides into the 3HPE homopolyester was found to increase the glass transition temp.
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  27. 27
    Ishida, K.; Hortensius, R.; Luo, X.; Mather, P. T. Soft bacterial polyester-based shape memory nanocomposites featuring reconfigurable nanostructure. J. Polym. Sci., Part B: Polym. Phys. 2012, 50 (6), 387– 393,  DOI: 10.1002/polb.23021
    Google Scholar
    There is no corresponding record for this reference.
  28. 28
    Levine, A. C.; Sparano, A.; Twigg, F. F.; Numata, K.; Nomura, C. T. Influence of cross-linking on the physical properties and cytotoxicity of polyhydroxyalkanoate (PHA) scaffolds for tissue engineering. ACS Biomaterials Science & Engineering 2015, 1 (7), 567– 576,  DOI: 10.1021/acsbiomaterials.5b00052
    Google Scholar
    There is no corresponding record for this reference.
  29. 29
    Levine, A. C.; Heberlig, G. W.; Nomura, C. T. Use of thiol-ene click chemistry to modify mechanical and thermal properties of polyhydroxyalkanoates (PHAs). Int. J. Biol. Macromol. 2016, 83, 358– 365,  DOI: 10.1016/j.ijbiomac.2015.11.048
    Google Scholar
    29
    Use of thiol-ene click chemistry to modify mechanical and thermal properties of polyhydroxyalkanoates (PHAs)
    Levine, Alex C.; Heberlig, Graham W.; Nomura, Christopher T.
    International Journal of Biological Macromolecules (2016), 83 (), 358-365CODEN: IJBMDR; ISSN:0141-8130. (Elsevier B.V.)
    In order to diversify the no. of applications for poly[(R)-3-hydroxyalkanoates] (PHAs), methods must be developed to alter their phys. properties so they are not limited to aliph. polyesters. Recently we developed Escherichia coli LSBJ as a living biocatalyst with the ability to control the repeating unit compn. of PHA polymers, including the ability to incorporate unsatd. repeating units into the PHA polymer at specific ratios. The incorporation of repeating units with terminal alkenes in the side chain of the polymer allowed for the prodn. of random PHA copolymers with defined repeating unit ratios that can be chem. modified for the purpose of tailoring the phys. properties of these materials beyond what are available in current PHAs. In this study, unsatd. PHA copolymers were chem. modified via thiol-ene click chem. to contain an assortment of new functional groups, and the mech. and thermal properties of these materials were measured. Results showed that crosslinking the copolymer resulted in a unique combination of improved strength and pliability and that the addn. of polar functional groups increased the tensile strength, Young's modulus, and hydrophilic profile of the materials. This work demonstrates that unsatd. PHAs can be chem. modified to extend their phys. properties to distinguish them from currently available PHA polymers.
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  30. 30
    Gagnon, K. D.; Lenz, R. W.; Farris, R. J.; Fuller, R. C. Chemical modification of bacterial elastomers: 1. Peroxide crosslinking. Polymer 1994, 35 (20), 4358– 4367,  DOI: 10.1016/0032-3861(94)90093-0
    Google Scholar
    There is no corresponding record for this reference.
  31. 31
    Mangeon, C.; Renard, E.; Thevenieau, F.; Langlois, V. Networks based on biodegradable polyesters: An overview of the chemical ways of crosslinking. Materials Science and Engineering: C 2017, 80, 760– 770,  DOI: 10.1016/j.msec.2017.07.020
    Google Scholar
    There is no corresponding record for this reference.
  32. 32
    Steinbüchel, A. Production of rubber-like polymers by microorganisms. Curr. Opin. Microbiol. 2003, 6 (3), 261– 270,  DOI: 10.1016/S1369-5274(03)00061-4
    Google Scholar
    There is no corresponding record for this reference.
  33. 33
    Vendamme, R.; Schüwer, N.; Eevers, W. Recent synthetic approaches and emerging bio-inspired strategies for the development of sustainable pressure-sensitive adhesives derived from renewable building blocks. J. Appl. Polym. Sci. 2014, 131 (17), e40669  DOI: 10.1002/app.40669
    Google Scholar
    There is no corresponding record for this reference.
  34. 34
    Wang, C.; Wang, H.; Zou, F.; Chen, S.; Wang, Y. Development of polyhydroxyalkanoate-based polyurethane with water-thermal response shape-memory behavior as new 3D elastomers scaffolds. Polymers 2019, 11 (6), 1030,  DOI: 10.3390/polym11061030
    Google Scholar
    There is no corresponding record for this reference.
  35. 35
    Oyama, T.; Kobayashi, S.; Okura, T.; Sato, S.; Tajima, K.; Isono, T.; Satoh, T. Biodegradable compatibilizers for poly(hydroxyalkanoate)/poly(ε-caprolactone) blends through click reactions with end-functionalized microbial poly(hydroxyalkanoate)s. ACS Sustainable Chem. Eng. 2019, 7 (8), 7969– 7978,  DOI: 10.1021/acssuschemeng.9b00897
    Google Scholar
    There is no corresponding record for this reference.
  36. 36
    Cywar, R. M.; Ling, C.; Clarke, R. W.; Kim, D. H.; Kneucker, C. M.; Salvachúa, D.; Addison, B.; Hesse, S. A.; Takacs, C. J.; Xu, S. Elastomeric vitrimers from designer polyhydroxyalkanoates with recyclability and biodegradability. Sci. Adv. 2023, 9 (47), eadi1735  DOI: 10.1126/sciadv.adi1735
    Google Scholar
    There is no corresponding record for this reference.
  37. 37
    Han, C. C.; Ismail, J.; Kammer, H.-W. Melt reaction in blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and epoxidized natural rubber. Polym. Degrad. Stab. 2004, 85 (3), 947– 955,  DOI: 10.1016/j.polymdegradstab.2003.11.020
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    37
    Melt reaction in blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and epoxidized natural rubber
    Han, Chan Chin; Ismail, Jamil; Kammer, Hans-Werner
    Polymer Degradation and Stability (2004), 85 (3), 947-955CODEN: PDSTDW; ISSN:0141-3910. (Elsevier B.V.)
    Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with hydroxyvalerate content of 12 mol% is a natural aliph. polyester. At temps. above its m.p., thermal decompn. occurs leading to shorter chains with carboxyl end groups. In blends with epoxidized natural rubber (ENR), 50% epoxidn. level, these carboxyl chain ends may trigger reactions between the constituents since the epoxidized groups provide reactive sites. Glass transition temp. studies reveal immiscibility of the polymers over the entire compn. range. Hence, any reaction between the constituents is restricted to the interfacial region between the components. We report here on studies on melt reactions between the components at elevated temps. DSC traces display an exothermic peak when the blends are annealed at temps. ranging from 220 up to 234°. The kinetics of the reaction are discussed in terms of a serial reaction scheme. It turns out that the reaction rate increases with annealing temp. (Ta) and with descending PHBV content in the blends when PHBV is the minor component. Morphol. studies by optical microscopy reveal that PHBV is still capable of crystg. at 50° after melt reaction at 234°. Either ring-banded or fibrillar spherulites can be seen in blends with PHBV in excess, however, the rate of crystn. is dramatically reduced after melt reaction at Ta=234°.
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  38. 38
    Bhatt, R.; Shah, D.; Patel, K. C.; Trivedi, U. PHA–rubber blends: Synthesis, characterization and biodegradation. Bioresour. Technol. 2008, 99 (11), 4615– 4620,  DOI: 10.1016/j.biortech.2007.06.054
    Google Scholar
    38
    PHA-rubber blends: Synthesis, characterization and biodegradation
    Bhatt, Rachana; Shah, Dishma; Patel, K. C.; Trivedi, Ujjval
    Bioresource Technology (2008), 99 (11), 4615-4620CODEN: BIRTEB; ISSN:0960-8524. (Elsevier Ltd.)
    Medium chain length polyhydroxyalkanoates (mcl-PHA) and different rubbers; namely natural rubber, nitrile rubber and butadiene rubber were blended at room temp. using soln. blending technique. Blends constituted 5%, 10% and 15% of mcl-PHA in different rubbers. Thermogravimetric anal. of mcl-PHA showed the melting temp. of the polymer around 50 °C. Thermal properties of the synthesized blend were studied by Differential Scanning Calorimetry which confirmed effective blending between the polymers. Blending of mcl-PHA with natural rubber led to the synthesis of a different polymer having the m.p. of 90 °C. Degrdn. studies of the blends were carried out using a soil isolate, Pseudomonas sp. 202 for 30 days. Extracellular protein concn. as well as OD660 due to the growth of Pseudomonas sp. 202 was studied. The degrdn. of blended plastic material, as evidenced by %wt. loss after degrdn. and increase in the growth of organism correlated with the amt. of mcl-PHA present in the sample. Growth of Pseudomonas sp. 202 resulted in 14.63%, 16.12% and 3.84% wt. loss of PHA:rubber blends (natural, nitrile and butadiene rubber). Scanning electron microscopic studies after 30 days of incubation further confirmed biodegrdn. of the films.
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  39. 39
    Popa, M. S.; Frone, A. N.; Panaitescu, D. M. Polyhydroxybutyrate blends: A solution for biodegradable packaging?. Int. J. Biol. Macromol. 2022, 207, 263– 277,  DOI: 10.1016/j.ijbiomac.2022.02.185
    Google Scholar
    There is no corresponding record for this reference.
  40. 40
    Feijoo, P.; Samaniego-Aguilar, K.; Sánchez-Safont, E.; Torres-Giner, S.; Lagaron, J. M.; Gamez-Perez, J.; Cabedo, L. Development and characterization of fully renewable and biodegradable polyhydroxyalkanoate blends with improved thermoformability. Polymers 2022, 14 (13), 2527,  DOI: 10.3390/polym14132527
    Google Scholar
    40
    Development and Characterization of Fully Renewable and Biodegradable Polyhydroxyalkanoate Blends with Improved Thermoformability
    Feijoo, Patricia; Samaniego-Aguilar, Kerly; Sanchez-Safont, Estefania; Torres-Giner, Sergio; Lagaron, Jose M.; Gamez-Perez, Jose; Cabedo, Luis
    Polymers (Basel, Switzerland) (2022), 14 (13), 2527CODEN: POLYCK; ISSN:2073-4360. (MDPI AG)
    Poly(3-hydroxybutyrate-co-3-valerate) (PHBV), being one of the most studied and com. available polyhydroxyalkanoates (PHAs), presents an intrinsic brittleness and narrow processing window that currently hinders its use in several plastic applications. The aim of this study was to develop a biodegradable PHA-based blend by combining PHBV with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), another copolyester of the PHA family that shows a more ductile behavior. Blends of PHBV with 20% wt., 30% wt., and 40% wt. of PHBH were obtained by melt mixing, processed by cast extrusion in the form of films, and characterized in terms of their morphol., crystn. behavior, thermal stability, mech. properties, and thermoformability. Full miscibility of both biopolymers was obsd. in the amorphous phase due to the presence of a single delta peak, ranging from 4.5°C to 13.7°C. Moreover, the incorporation of PHBH hindered the crystn. process of PHBV by decreasing the spherulite growth rate from 1.0μm/min to 0.3μm/min. However, for the entire compn. range studied, the high brittleness of the resulting materials remained since the presence of PHBH did not prevent the PHBV cryst. phase from governing the mech. behavior of the blend. Interestingly, the addn. of PHBH greatly improved the thermoformability by widening the processing window of PHBV by 7 s, as a result of the increase in the melt strength of the blends even for the lowest PHBH content.
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  41. 41
    Panaitescu, D. M.; Frone, A. N.; Nicolae, C.-A.; Gabor, A. R.; Miu, D. M.; Soare, M.-G.; Vasile, B. S.; Lupescu, I. Poly(3-hydroxybutyrate) nanocomposites modified with even and odd chain length polyhydroxyalkanoates. Int. J. Biol. Macromol. 2023, 244, 125324  DOI: 10.1016/j.ijbiomac.2023.125324
    Google Scholar
    There is no corresponding record for this reference.
  42. 42
    Clarke, R. W.; Sandmeier, T.; Franklin, K. A.; Reich, D.; Zhang, X.; Vengallur, N.; Patra, T. K.; Tannenbaum, R. J.; Adhikari, S.; Kumar, S. K. Dynamic crosslinking compatibilizes immiscible mixed plastics. Nature 2023, 616 (7958), 731– 739,  DOI: 10.1038/s41586-023-05858-3
    Google Scholar
    42
    Dynamic crosslinking compatibilizes immiscible mixed plastics
    Clarke, Ryan W.; Sandmeier, Tobias; Franklin, Kevin A.; Reich, Dominik; Zhang, Xiao; Vengallur, Nayan; Patra, Tarak K.; Tannenbaum, Robert J.; Adhikari, Sabin; Kumar, Sanat K.; Rovis, Tomislav; Chen, Eugene Y.-X.
    Nature (London, United Kingdom) (2023), 616 (7958), 731-739CODEN: NATUAS; ISSN:1476-4687. (Nature Portfolio)
    The global plastics problem is a trifecta, greatly affecting environment, energy and climate1-4. Many innovative closed/open-loop plastics recycling or upcycling strategies have been proposed or developed5-16, addressing various aspects of the issues underpinning the achievement of a circular economy17-19. In this context, reusing mixed-plastics waste presents a particular challenge with no current effective closed-loop soln.20. This is because such mixed plastics, esp. polar/apolar polymer mixts., are typically incompatible and phase sep., leading to materials with substantially inferior properties. To address this key barrier, here we introduce a new compatibilization strategy that installs dynamic crosslinkers into several classes of binary, ternary and postconsumer immiscible polymer mixts. in situ. Our combined exptl. and modeling studies show that specifically designed classes of dynamic crosslinker can reactivate mixed-plastics chains, represented here by apolar polyolefins and polar polyesters, by compatibilizing them via dynamic formation of graft multiblock copolymers. The resulting in-situ-generated dynamic thermosets exhibit intrinsic reprocessability and enhanced tensile strength and creep resistance relative to virgin plastics. This approach avoids the need for de/reconstruction and thus potentially provides an alternative, facile route towards the recovery of the endowed energy and materials value of individual plastics.
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  43. 43
    Takase, K.; Taguchi, S.; Doi, Y. Enhanced synthesis of poly(3-hydroxybutyrate) in recombinant Escherichia coli by means of error-prone PCR mutagenesis, saturation mutagenesis, and in vitro recombination of the type II polyhydroxyalkanoate synthase gene. Journal of Biochemistry 2003, 133 (1), 139– 145,  DOI: 10.1093/jb/mvg015
    Google Scholar
    There is no corresponding record for this reference.
  44. 44
    Li, M.; Chen, X.; Che, X.; Zhang, H.; Wu, L. P.; Du, H.; Chen, G. Q. Engineering Pseudomonas entomophila for synthesis of copolymers with defined fractions of 3-hydroxybutyrate and medium-chain-length 3-hydroxyalkanoates. Metab Eng. 2019, 52, 253– 262,  DOI: 10.1016/j.ymben.2018.12.007
    Google Scholar
    There is no corresponding record for this reference.
  45. 45
    Salvachúa, D.; Rydzak, T.; Auwae, R.; De Capite, A.; Black, B. A.; Bouvier, J. T.; Cleveland, N. S.; Elmore, J. R.; Furches, A.; Huenemann, J. D. Metabolic engineering of Pseudomonas putida for increased polyhydroxyalkanoate production from lignin. Microbial Biotechnology 2020, 13 (1), 290– 298,  DOI: 10.1111/1751-7915.13481
    Google Scholar
    There is no corresponding record for this reference.
  46. 46
    Ye, J.; Huang, W.; Wang, D.; Chen, F.; Yin, J.; Li, T.; Zhang, H.; Chen, G. Q. Pilot scale-up of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) production by Halomonas bluephagenesis via cell growth adapted optimization process. Biotechnol. J. 2018, 13 (5), e1800074  DOI: 10.1002/biot.201800074
    Google Scholar
    There is no corresponding record for this reference.
  47. 47
    Johnson, C. W.; Salvachúa, D.; Rorrer, N. A.; Black, B. A.; Vardon, D. R.; St John, P. C.; Cleveland, N. S.; Dominick, G.; Elmore, J. R.; Grundl, N. Innovative chemicals and materials from bacterial aromatic catabolic pathways. Joule 2019, 3 (6), 1523– 1537,  DOI: 10.1016/j.joule.2019.05.011
    Google Scholar
    47
    Innovative Chemicals and Materials from Bacterial Aromatic Catabolic Pathways
    Johnson, Christopher W.; Salvachua, Davinia; Rorrer, Nicholas A.; Black, Brenna A.; Vardon, Derek R.; St. John, Peter C.; Cleveland, Nicholas S.; Dominick, Graham; Elmore, Joshua R.; Grundl, Nicholas; Khanna, Payal; Martinez, Chelsea R.; Michener, William E.; Peterson, Darren J.; Ramirez, Kelsey J.; Singh, Priyanka; VanderWall, Todd A.; Wilson, A. Nolan; Yi, Xiunan; Biddy, Mary J.; Bomble, Yannick J.; Guss, Adam M.; Beckham, Gregg T.
    Joule (2019), 3 (6), 1523-1537CODEN: JOULBR; ISSN:2542-4351. (Cell Press)
    To drive innovation in chem. and material applications beyond what has been afforded by the mature petrochem. industry, new mols. that possess diverse chem. functionality are needed. One source of such mols. lies in the varied metabolic pathways that soil microbes utilize to catabolize arom. compds. generated during plant decompn. Here, we have engineered Pseudomonas putida KT2440 to convert these arom. compds. to 15 catabolic intermediates that exhibit substantial chem. diversity. Bioreactor cultivations, anal. methods, and bench-scale sepns. were developed to enable prodn. (up to 58 g/L), detection, and purifn. of each target mol. We further engineered strains for prodn. of a subset of these mols. from glucose, achieving a 41% molar yield of muconic acid. Finally, we produce materials from three compds. to illustrate the potential for realizing performance-advantaged properties relative to petroleum-derived analogs.
    >> More from SciFinder ®
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  48. 48
    Self, J. L.; Zervoudakis, A. J.; Peng, X.; Lenart, W. R.; Macosko, C. W.; Ellison, C. J. Linear, graft, and beyond: Multiblock copolymers as next-generation compatibilizers. JACS Au 2022, 2 (2), 310– 321,  DOI: 10.1021/jacsau.1c00500
    Google Scholar
    48
    Review of Linear, Graft, and Beyond, Multiblock Copolymers as Next-Generation Compatibilizers
    Self, Jeffrey L.; Zervoudakis, Aristotle J.; Peng, Xiayu; Lenart, William R.; Macosko, Christopher W.; Ellison, Christopher J.
    JACS Au (2022), 2 (2), 310-321CODEN: JAAUCR; ISSN:2691-3704. (American Chemical Society)
    A review. Properly addressing the global issue of unsustainable plastic waste generation and accumulation will require a confluence of technol. breakthroughs on various fronts. Mech. recycling of plastic waste into polymer blends is one method expected to contribute to a soln. Due to phase sepn. of individual components, mech. recycling of mixed polymer waste streams generally results in an unsuitable material with substantially reduced performance. However, when an appropriately designed compatibilizer is used, the recycled blend can have competitive properties to virgin materials. In its current state, polymer blend compatibilization is usually not cost-effective compared to traditional waste management, but further tech. development and optimization will be essential for driving future cost competitiveness. Historically, effective compatibilizers have been diblock copolymers or in situ generated graft copolymers, but recent progress shows there is great potential for multiblock copolymer compatibilizers. In this perspective, we lay out recent advances in synthesis and understanding for two types of multiblock copolymers currently being developed as blend compatibilizers: linear and graft. Importantly, studies of appropriately designed copolymers have shown them to efficiently compatibilize model binary blends at concns. as low as ∼0.2 wt %. These investigations pave the way for studies on more complex (ternary or higher) mixed waste streams that will require novel compatibilizer architectures. Given the progress outlined here, we believe that multiblock copolymers offer a practical and promising soln. to help close the loop on plastic waste. While a complete discussion of the implementation of this technol. would entail infrastructural, policy and social developments, they are outside the scope of this perspective which instead focuses on material design considerations and the tech. advancements of block copolymer compatibilizers.
    >> More from SciFinder ®
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  49. 49
    ISO Standards. Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium. ISO 14851:2019, 2019.
    Google Scholar
    There is no corresponding record for this reference.
  50. 50
    Huijberts, G. N.; Eggink, G.; de Waard, P.; Huisman, G. W.; Witholt, B. Pseudomonas putida KT2442 cultivated on glucose accumulates poly(3-hydroxyalkanoates) consisting of saturated and unsaturated monomers. Appl. Environ. Microbiol. 1992, 58 (2), 536– 544,  DOI: 10.1128/aem.58.2.536-544.1992
    Google Scholar
    50
    Pseudomonas putida KT2442 cultivated on glucose accumulates poly(3-hydroxyalkanoates) consisting of saturated and unsaturated monomers
    Huijberts, Gern N. M.; Eggink, Gerrit; De Waard, Pieter; Huisman, Gjalt W.; Witholt, Bernard
    Applied and Environmental Microbiology (1992), 58 (2), 536-44CODEN: AEMIDF; ISSN:0099-2240.
    The biosynthesis of poly(3-hydroxyalkanoates) (PHAs) by P. putida KT2442 during growth on carbohydrates was studied. PHAs isolated from P. putida cultivated on glucose, fructose, and glycerol were found to have a very similar monomer compn. In addn. to the major constituent 3-hydroxydecanoate, six other monomers were found to be preset: 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydodecanoate, 3-hydroxydodecenoate, 3-hydroxytetradecanoate, and 3-hydroxytetradecenoate. The identity of all seven 3-hydroxy fatty acids was established by gas chromatog.-mass spectrometry, one-dimensional 1H NMR, and two-dimensional double-quantum filtered correlation spectroscopy 1H NMR. The chem. structures of the monomer units are identical to the structure of the acyl moiety of the 3-hydroxyacyl-acyl carrier protein intermediates of de novo fatty acid biosynthesis. Furthermore, the degree of unsatn. of PHA and membrane lipids is similarly influenced by shifts in the cultivation temp. These results strongly indicate that, during growth on nonrelated substrates, PHA monomers are derived from intermediates of de novo fatty acid biosynthesis. Anal. of a P. putida pha mutant and complementation of this mutant with the cloned pha locus revealed that the PHA polymerase genes necessary for PHA synthesis from octanoate are also responsible for PHA formation from glucose.
    >> More from SciFinder ®
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  51. 51
    Huang, P.; Okoshi, T.; Mizuno, S.; Hiroe, A.; Tsuge, T. Gas chromatography-mass spectrometry-based monomer composition analysis of medium-chain-length polyhydroxyalkanoates biosynthesized by Pseudomonas spp. Biosci Biotechnol Biochem 2018, 82 (9), 1615– 1623,  DOI: 10.1080/09168451.2018.1473027
    Google Scholar
    There is no corresponding record for this reference.
  52. 52
    Dufresne, A.; Vincendon, M. Poly(3-hydroxybutyrate) and poly(3-hydroxyoctanoate) blends: Morphology and mechanical behavior. Macromolecules 2000, 33 (8), 2998– 3008,  DOI: 10.1021/ma991854a
    Google Scholar
    52
    Poly(3-hydroxybutyrate) and Poly(3-hydroxyoctanoate) Blends: Morphology and Mechanical Behavior
    Dufresne, Alain; Vincendon, Marc
    Macromolecules (2000), 33 (8), 2998-3008CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Blends of bacterial poly(hydroxybutyrate) (PHB) with poly(hydroxyoctanoate) (PHO) were prepd. by co-dissolving the two polyesters in chloroform and casting the mixt. To probe the question of blend miscibility, SEM observations and differential scanning calorimetry (DSC) spectra were collected for the blends and blend components. PHB shows no miscibility with PHO, resulting in two-phase systems in which the nature of the continuous phase is compn.-dependent. Dynamic mech. anal. and tensile properties of these materials were also investigated. The morphol. of the blend strongly influences the mech. behavior. The mech. properties of these materials have been predicted from a model involving the percolation concept. It takes both linear and nonlinear mech. behaviors into account and allows for the effect of the lack of adhesion between material domains and/or breakage of one of the component.
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  53. 53
    Li, Z.; Yang, J.; Loh, X. J. Polyhydroxyalkanoates: opening doors for a sustainable future. NPG Asia Materials 2016, 8 (4), e265  DOI: 10.1038/am.2016.48
    Google Scholar
    53
    Polyhydroxyalkanoates: opening doors for a sustainable future
    Li, Zibiao; Yang, Jing; Loh, Xian Jun
    NPG Asia Materials (2016), 8 (4), e265CODEN: NAMPCE; ISSN:1884-4057. (Nature Publishing Group)
    Polyhydroxyalkanoates (PHAs) comprise a group of natural biodegradable polyesters that are synthesized by microorganisms. However, several disadvantages limit their competition with traditional synthetic plastics or their application as ideal biomaterials. These disadvantages include their poor mech. properties, high prodn. cost, limited functionalities, incompatibility with conventional thermal processing techniques and susceptibility to thermal degrdn. To circumvent these drawbacks, PHAs need to be modified to ensure improved performance in specific applications. In this review, well-established modification methods of PHAs are summarized and discussed. The improved properties of PHA that blends with natural raw materials or other biodegradable polymers, including starch, cellulose derivs., lignin, poly(lactic acid), polycaprolactone and different PHA-type blends, are summarized. The functionalization of PHAs by chem. modification is described with respect to two important synthesis approaches: block copolymn. and graft copolymn. The expanded utilization of the modified PHAs as engineering materials and the biomedical significance in different areas are also addressed.
    >> More from SciFinder ®
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  54. 54
    Montoya-Ospina, M. C.; Verhoogt, H.; Ordner, M.; Tan, X.; Osswald, T. A. Effect of cross-linking on the mechanical properties, degree of crystallinity and thermal stability of polyethylene vitrimers. Polym. Eng. Sci. 2022, 62 (12), 4203– 4213,  DOI: 10.1002/pen.26178
    Google Scholar
    54
    Effect of cross-linking on the mechanical properties, degree of crystallinity and thermal stability of polyethylene vitrimers
    Montoya-Ospina, Maria Camila; Verhoogt, Henk; Ordner, Mark; Tan, Xiao; Osswald, Tim A.
    Polymer Engineering & Science (2022), 62 (12), 4203-4213CODEN: PYESAZ; ISSN:0032-3888. (John Wiley & Sons, Inc.)
    Maleic anhydride-grafted-polyethylene was dynamically cross-linked via reactive melt blending with 4,4'-dithiodianiline. Thermal and mech. properties of polyethylene vitrimers with different crosslinking d. were investigated. The results indicate that the degree of crystallinity decreased with increasing crosslinking d. This behavior was directly related to short-term and long-term mech. properties: vitrimers showed a decrease in yield strength and creep performance. The yield strength of PE vitrimers decreased linearly in relation to the degree of crystallinity. Polarized optical microscopy revealed that the cross-links inhibit the growth of spherulites structure in polyethylene vitrimers. Thermogravimetric anal. indicated an increase in the onset degrdn. temp. and decompn. rate for vitrimers with increased crosslinking d. The stiffness of the vitrimers decreased with increasing crosslinking d. which led to higher damping properties. Finally, it was demonstrated that reprocessing of polyethylene vitrimer was possible without significant impact in mech. properties.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38Xis12mur%252FN&md5=fc568eed52ed8e0823f82ca73b989b98
  55. 55
    Wang, Y.-X.; Wang, C.-C.; Shi, Y.; Liu, L.-Z.; Bai, N.; Song, L.-F. Effects of Dynamic Crosslinking on Crystallization, Structure and Mechanical Property of Ethylene-Octene Elastomer/EPDM Blends. Polymers 2022, 14 (1), 139,  DOI: 10.3390/polym14010139
    Google Scholar
    There is no corresponding record for this reference.
  56. 56
    Sisanth, K. S.; Thomas, M. G.; Abraham, J.; Thomas, S. 1 - General introduction to rubber compounding. In Progress in Rubber Nanocomposites; Thomas, S.; Maria, H. J., Eds.; Woodhead Publishing, 2017; pp 1– 39.
    Google Scholar
    There is no corresponding record for this reference.
  57. 57
    Johnson, C. W.; Beckham, G. T. Aromatic catabolic pathway selection for optimal production of pyruvate and lactate from lignin. Metab Eng. 2015, 28, 240– 247,  DOI: 10.1016/j.ymben.2015.01.005
    Google Scholar
    57
    Aromatic catabolic pathway selection for optimal production of pyruvate and lactate from lignin
    Johnson, Christopher W.; Beckham, Gregg T.
    Metabolic Engineering (2015), 28 (), 240-247CODEN: MEENFM; ISSN:1096-7176. (Elsevier B. V.)
    Lignin represents an untapped feedstock for the prodn. of fuels and chems., but its intrinsic heterogeneity makes lignin valorization a significant challenge. In nature, many aerobic organisms degrade lignin-derived arom. mols. through conserved central intermediates including catechol and protocatechuate. Harnessing this microbial approach offers potential for lignin upgrading in modern biorefineries, but significant tech. development is needed to achieve this end. Catechol and protocatechuate are subjected to arom. ring cleavage by dioxygenase enzymes that, depending on the position, ortho or meta relative to adjacent hydroxyl groups, result in different products that are metabolized through parallel pathways for entry into the TCA cycle. These degrdn. pathways differ in the combination of succinate, acetyl-CoA, and pyruvate produced, the reducing equiv. regenerated, and the amt. of carbon emitted as CO2-factors that will ultimately impact the yield of the targeted product. As shown here, the ring-cleavage pathways can be interchanged with one another, and such substitutions have a predictable and substantial impact on product yield. We demonstrate that replacement of the catechol ortho degrdn. pathway endogenous to Pseudomonas putida KT2440 with an exogenous meta-cleavage pathway from P. putida mt-2 increases yields of pyruvate produced from arom. mols. in engineered strains. Even more dramatically, replacing the endogenous protocatechuate ortho pathway with a meta-cleavage pathway from Sphingobium sp. SYK-6 results in a nearly five-fold increase in pyruvate prodn. We further demonstrate the aerobic conversion of pyruvate to L-lactate with a yield of 41.1±2.6% (wt/wt). Overall, this study illustrates how arom. degrdn. pathways can be tuned to optimize the yield of a desired product in biol. lignin upgrading.
    >> More from SciFinder ®
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  • Abstract

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    Figure 1

    Figure 1. Overview of past efforts in PHA thermoset materials and advances in this work. (A, B) Previously reported strategies to enhance PHA thermal and mechanical performance, and (C) herein-reported strategy to obtain tunable, degradable thermoset materials. PHA, polyhydroxyalkanoates; PHDU, poly(3-hydroxydecanoate-co-3-hydroxyundecenoate); BE-X, boronic ester cross-linker 2,2-(1,4-phenylene)-bis[4-thioethyl-1,3,2-dioxaborolane]; and PHBU, poly(3-hydroxybutyrate-co-3-hydroxyundecenoate).

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    Figure 2

    Figure 2. Pathway of cellular metabolism (left) and PHBU production (right) in P. putida LC059. Several genes in the β-oxidation pathway were deleted to prevent degradation of trans 2-enoyl-CoA. The gene phaG was knocked out to prevent the flux from FAB to PHA synthesis. Glucose was supplemented to supply energy and biomass formation. The native type II PHA synthases, PhaC1 and PhaC2, were replaced with PhaC61-3-S325T/Q481K to accept a broader range of 3-hydroxyacyl-CoA as substrates to produce the desired PHA copolymers. The gene encoding native PHA depolymerase, phaZ, was knocked out to prevent the degradation of PHBU.

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    Figure 3

    Figure 3. PHBU production in shake flask and bioreactor cultivations. (A) CDW and HAME profiles in shake flask cultivation samples. HAME profiles were analyzed by using GC/MS. C4 represents sodium butyrate, and usC11 represents 10-undecenoic acid. The concentrations of usC11 were calculated based on the density value of 0.912 g mL–1 at 25 °C, considering volume concentrations of 0, 0.25, 0.5, 0.75, 1.00, and 1.50 mL L–1. Error bars represent the standard deviation calculated from biological triplicates. The GC/MS plots for the analysis of HAME profiles have been incorporated in Figure S1C,D. (B) Quantification of the mol % U in PHBU using 1H NMR spectroscopy (Figure S4). The mol % values of feeding 10-undecenoic acid were corrected using the density value 0.912 g mL–1 at 25 °C. Error bars represent the standard deviation calculated from biological triplicates. (C) Growth curves of LC059 on M9 medium supplemented with 50 mM glucose, and in the absence or the presence of different sodium butyrate concentrations (1, 2.5, 5 g L–1). Error bars represent the standard deviation calculated from biological triplicates. (D) Optical density (OD600) and production of PHBU in 3 L bioreactors in the dissolved oxygen (DO)-stat fed-batch mode using modified M9 medium and glucose. We note that optical density does not necessarily correlate with growth due to PHA accumulation. (46) The results are the average of two biological replicates, and the error bars represent the absolute difference between replicates. Black arrows indicate the time at which sodium butyrate (2 g L–1) and 10-undecenoic acid (0.16 g L–1) were added in the bioreactors.

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    Figure 4

    Figure 4. Preparation, compatibility, and mechanical analysis of hard-PHBU-5 and soft-PHDU-6 dynamic thermoset blends. (A) Representative tensile stress/strain tests (5 mm min–1, ∼23 °C) for PHBU-5 (black) and dynamically cross-linked PHBU-blend-PHDU at composition ratios by mass of 3:1 (blue), 1:1 (orange), and 1:3 (purple) (see Figure S9 for complete data and Table S5 for values). (B) Normalized DSC heat flow (10 °C min–1, exoup, first heating cycle) traces (see Figure S10 for individual plots and Table S6 for values). (C) DMA temperature-ramp frequency sweep thermograms (−75 to 200 °C, 3 °C min–1, 30 μm, 1 Hz) (see Figure S11 for individual thermographs and Table S7 for values), and (D) general scheme for the simultaneous blending and blend compatibilization by dynamic cross-linking of scl-co-mcl and mcl-co-mcl usPHAs to produce homogenized copolymer networks. (E) SEM cross-sectional imaging of virgin (top) and dynamic cross-link compatibilized (bottom) PHBU3-blend-PHDU1, PHBU1-blend-PHDU1, and PHBU1-blend-PHDU3 usPHA blends (scale bar = 15 μm) (see Figures S15–S17 for additional images and Figures S18–S20 for droplet diameters).

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    Figure 5

    Figure 5. Elasticity and melt processability by dynamic cross-linking. (A) Representative averaged tensile stress/strain (5 mm min–1, ∼23 °C) overlays between virgin and reprocessed dynamic thermoset blends (see Figure S22 for complete data and Table S5 for values). (B) Normalized stress relaxation traces for PHBU1-blend-PHDU3 by shear rheology (115 to 165 °C, 5 °C increments, 5%, 1000 s, 0.1 s rise time). (C) Arrhenius relationships between temperature and relaxation time for PHBU1-blend-PHDU3 (purple) and PHBU3-blend-PHDU1 (blue), the latter of which demonstrates a deviation in slope upon crystallization. (D) Cyclic deformation experiments with firm plastic-like (PHBU1-blend-PHDU1), (E) hard rubber (PHBU3-blend-PHDU1), and (F) soft elastomer (PHBU1-blend-PHDU3) (50 mm min–1 up-ramp, 50 mm min–1 down-ramp, ×5, ∼23 °C).

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    Figure 6

    Figure 6. Biodegradability evaluation in freshwater biodegradation experiment. Freshwater biodegradation of PHBU-5, PHBU1-blend-PHDU3, and PHBU3-blend-PHDU1 in freshwater environments. Results over a 107-day period of aerobic freshwater degradation (ISO 14851) (49) for PHA dynamic thermoset blends relative to a microcrystalline cellulose (MCC) and a glucose control.

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  • References

    This article references 57 other publications.

    1. 1
      Zhu, Y.; Romain, C.; Williams, C. K. Sustainable polymers from renewable resources. Nature 2016, 540 (7633), 354– 362,  DOI: 10.1038/nature21001
      1
      Sustainable polymers from renewable resources
      Zhu, Yunqing; Romain, Charles; Williams, Charlotte K.
      Nature (London, United Kingdom) (2016), 540 (7633), 354-362CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Renewable resources are used increasingly in the prodn. of polymers. In particular, monomers such as carbon dioxide, terpenes, vegetable oils and carbohydrates can be used as feedstocks for the manuf. of a variety of sustainable materials and products, including elastomers, plastics, hydrogels, flexible electronics, resins, engineering polymers and composites. Efficient catalysis is required to produce monomers, to facilitate selective polymns. and to enable recycling or upcycling of waste materials. There are opportunities to use such sustainable polymers in both high-value areas and in basic applications such as packaging. Life-cycle assessment can be used to quantify the environmental benefits of sustainable polymers.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVyru7%252FP&md5=1a3419dd9b1a7e1643b4671cdf42553f
    2. 2
      Cywar, R. M.; Rorrer, N. A.; Hoyt, C. B.; Beckham, G. T.; Chen, E. Y. X. Bio-based polymers with performance-advantaged properties. Nature Reviews Materials 2022, 7 (2), 83– 103,  DOI: 10.1038/s41578-021-00363-3
      2
      Bio-based polymers with performance-advantaged properties
      Cywar, Robin M.; Rorrer, Nicholas A.; Hoyt, Caroline B.; Beckham, Gregg T.; Chen, Eugene Y.-X.
      Nature Reviews Materials (2022), 7 (2), 83-103CODEN: NRMADL; ISSN:2058-8437. (Nature Portfolio)
      A review Bio-based compds. with unique chem. functionality can be obtained through selective transformations of plant and other non-fossil, biogenic feedstocks for the development of new polymers to displace those produced from fossil carbon feedstocks. Although substantial efforts have been invested to produce bio-based polymers that are chem. identical to and directly replace those from petroleum, a long-pursued goal is to synthesize new, sustainable, bio-based polymers that either functionally replace or exhibit performance advantages relative to incumbent polymers. Owing to anthropogenic climate change and the environmental consequences of global plastics pollution, the need to realize a bio-based materials economy at scale is crit. To that end, in this Review we describe the concept of performance-advantaged, bio-based polymers (PBPs), highlighting examples wherein superior performance is facilitated by the inherent chem. functionality of bio-based feedstocks. We focus on PBPs with C-O and C-N inter-unit chem. bonds, as these are often readily accessible from bio-based feedstocks, which are heteroatom-rich relative to petroleum-derived feedstocks. Finally, we outline guiding principles and challenges to aid progress in the development of PBPs.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXitF2ksrrM&md5=55f4470fa36fcea2204592aaacfc44c5
    3. 3
      Law, K. L.; Narayan, R. Reducing environmental plastic pollution by designing polymer materials for managed end-of-life. Nature Reviews Materials 2022, 7 (2), 104– 116,  DOI: 10.1038/s41578-021-00382-0
      3
      Reducing environmental plastic pollution by designing polymer materials for managed end-of-life
      Law, Kara Lavender; Narayan, Ramani
      Nature Reviews Materials (2022), 7 (2), 104-116CODEN: NRMADL; ISSN:2058-8437. (Nature Portfolio)
      Abstr.: Plastics are a ubiquitous class of synthetic polymer materials used in virtually all com. and industrial sectors. The majority of global plastics consists of polymers with carbon-carbon backbones, whose environmental persistence and low cost have resulted in a massive reservoir of plastic waste that resides in landfills and the environment. Although plastic debris contaminating the ocean has been documented for decades, details about plastic debris compn., distribution, impact and ultimate fate in the environment remain elusive. In this Review, we present an overview of environmental plastic contamination and discuss the origin (feedstock) and degrdn. behavior of plastics to help inform material design principles addressing end-of-life management. We argue that designing materials to be 'marine biodegradable' or universally biodegradable is not, in itself, a soln. to plastic pollution. Instead, material and product design principles must include a feasible plan for recovery and treatment based upon existing (or, possibly, simultaneously developed) systems.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXit1Kms7jO&md5=1f3d0bbeef65ea8ff9f079de45dfd7cf
    4. 4
      Shi, C.; Reilly, L. T.; Kumar, V. S. P.; Coile, M. W.; Nicholson, S. R.; Broadbelt, L. J.; Beckham, G. T.; Chen, E. Y.-X. Design principles for intrinsically circular polymers with tunable properties. Chem. 2021, 7 (11), 2896– 2912,  DOI: 10.1016/j.chempr.2021.10.004
      4
      Design principles for intrinsically circular polymers with tunable properties
      Shi, Changxia; Reilly, Liam T.; Phani Kumar, V. Sai; Coile, Matthew W.; Nicholson, Scott R.; Broadbelt, Linda J.; Beckham, Gregg T.; Chen, Eugene Y.-X.
      Chem (2021), 7 (11), 2896-2912CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)
      A review. This perspective discusses a set of design principles for next-generation kinetically trapped, intrinsically circular polymers (iCPs) that are inherently, selectively, and expediently depolymerizable to their monomer state once their kinetic barriers of deconstruction are overcome, thereby enabling not only the ideal shortest chem. circularity but also tunable performance properties. After describing four elements of the design principles-thermodn. and kinetics, strategies to overcome trade-offs and unify conflicting properties, predictive modeling, and supply-chain life-cycle assessment and techno-economic anal., which are illustrated with state-of-the-art examples-it concludes with presenting key challenges and opportunities for sustainable development of iCPs.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXisFaju7zE&md5=46bec1e371e2b5fe904af4c39701d09f
    5. 5
      Narancic, T.; Verstichel, S.; Reddy Chaganti, S.; Morales-Gamez, L.; Kenny, S. T.; De Wilde, B.; Babu Padamati, R.; O’Connor, K. E. Biodegradable plastic blends create new possibilities for end-of-life management of plastics but they are not a panacea for plastic pollution. Environ. Sci. Technol. 2018, 52 (18), 10441– 10452,  DOI: 10.1021/acs.est.8b02963
      5
      Biodegradable Plastic Blends Create New Possibilities for End-of-Life Management of Plastics but They Are Not a Panacea for Plastic Pollution
      Narancic, Tanja; Verstichel, Steven; Reddy Chaganti, Srinivasa; Morales-Gamez, Laura; Kenny, Shane T.; De Wilde, Bruno; Babu Padamati, Ramesh; O'Connor, Kevin E.
      Environmental Science & Technology (2018), 52 (18), 10441-10452CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Plastic waste pollution is a global environmental problem which could be addressed by biodegradable plastics. The latter are blended together to achieve com. functional properties, but the environmental fate of these blends is unknown. We have tested neat polymers, polylactic acid (PLA), polyhydroxybutyrate, polyhydroxyoctanoate, poly(butylene succinate), thermoplastic starch, polycaprolactone (PCL), and blends thereof for biodegrdn. across seven managed and unmanaged environments. PLA is one of the world's best-selling biodegradable plastics, but it is not home compostable. We show here that PLA when blended with PCL becomes home compostable. We also demonstrate that the majority of the tested bioplastics and their blends degrade by thermophilic anaerobic digestion with high biogas output, but degrdn. times are 3-6 times longer than the retention times in com. plants. While some polymers and their blends showed good biodegrdn. in soil and water, the majority of polymers and their blends tested in this study failed to achieve ISO and ASTM biodegrdn. stds., and some failed to show any biodegrdn. Thus, biodegradable plastic blends need careful postconsumer management, and further design to allow more rapid biodegrdn. in multiple environments is needed as their release into the environment can cause plastic pollution.
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    6. 6
      Tang, X.; Westlie, A. H.; Watson, E. M.; Chen, E. Y.-X. Stereosequenced crystalline polyhydroxyalkanoates from diastereomeric monomer mixtures. Science 2019, 366 (6466), 754– 758,  DOI: 10.1126/science.aax8466
      6
      Stereosequenced crystalline polyhydroxyalkanoates from diastereomeric monomer mixtures
      Tang, Xiaoyan; Westlie, Andrea H.; Watson, Eli M.; Chen, Eugene Y.-X.
      Science (Washington, DC, United States) (2019), 366 (6466), 754-758CODEN: SCIEAS; ISSN:1095-9203. (American Association for the Advancement of Science)
      A review. Stereoselective polymn. of chiral or prochiral monomers is a powerful method to produce high-performance stereoregular cryst. polymeric materials. However, for monomers with two stereogenic centers, it is generally necessary to sep. diastereomers before polymn., resulting in substantial material loss and added energy cost assocd. with the sepn. and purifn. process. Here we report a diastereoselective polymn. methodol. enabled by catalysts that directly polymerize mixts. of eight-membered diolide (8DL) monomers with varying starting ratios of chiral racemic (rac) and achiral meso diastereomers into stereosequenced cryst. polyhydroxyalkanoates with isotactic and syndiotactic stereodiblock or stereotapered block microstructures. These polymers show enhanced ductility and toughness relative to polymers of pure rac-8DL, subject to tuning by variation of the diastereomeric ratio and structure of the 8DL monomers.
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    7. 7
      Choi, S. Y.; Cho, I. J.; Lee, Y.; Kim, Y.-J.; Kim, K.-J.; Lee, S. Y. Microbial polyhydroxyalkanoates and nonnatural polyesters. Adv. Mater. 2020, 32 (35), 1907138  DOI: 10.1002/adma.201907138
      7
      Microbial Polyhydroxyalkanoates and Nonnatural Polyesters
      Choi, So Young; Cho, In Jin; Lee, Youngjoon; Kim, Yeo-Jin; Kim, Kyung-Jin; Lee, Sang Yup
      Advanced Materials (Weinheim, Germany) (2020), 32 (35), 1907138CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Microorganisms produce diverse polymers for various purposes such as storing genetic information, energy, and reducing power, and serving as structural materials and scaffolds. Among these polymers, polyhydroxyalkanoates (PHAs) are microbial polyesters synthesized and accumulated intracellularly as a storage material of carbon, energy, and reducing power under unfavorable growth conditions in the presence of excess carbon source. PHAs have attracted considerable attention for their wide range of applications in industrial and medical fields. Since the first discovery of PHA accumulating bacteria about 100 years ago, remarkable advances have been made in the understanding of PHA biosynthesis and metabolic engineering of microorganisms toward developing efficient PHA producers. Recently, nonnatural polyesters have also been synthesized by metabolically engineered microorganisms, which opened a new avenue toward sustainable prodn. of more diverse plastics. Herein, the current state of PHAs and nonnatural polyesters is reviewed, covering mechanisms of microbial polyester biosynthesis, metabolic pathways, and enzymes involved in biosynthesis of short-chain-length PHAs, medium-chain-length PHAs, and nonnatural polyesters, esp. 2-hydroxyacid-contg. polyesters, metabolic engineering strategies to produce novel polymers and enhance prodn. capabilities and fermn., and downstream processing strategies for cost-effective prodn. of these microbial polyesters. In addn., the applications of PHAs and prospects are discussed.
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    8. 8
      Mezzina, M. P.; Manoli, M. T.; Prieto, M. A.; Nikel, P. I. Engineering native and synthetic pathways in Pseudomonas putida for the production of tailored polyhydroxyalkanoates. Biotechnol. J. 2021, 16 (3), 2000165  DOI: 10.1002/biot.202000165
      8
      Engineering Native and Synthetic Pathways in Pseudomonas putida for the Production of Tailored Polyhydroxyalkanoates
      Mezzina, Mariela P.; Manoli, Maria Tsampika; Prieto, M. Auxiliadora; Nikel, Pablo I.
      Biotechnology Journal (2021), 16 (3), 2000165CODEN: BJIOAM; ISSN:1860-6768. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Growing environmental concern sparks renewed interest in the sustainable prodn. of (bio)materials that can replace oil-derived goods. Polyhydroxyalkanoates (PHAs) are isotactic polymers that play a crit. role in the central metab. of producer bacteria, as they act as dynamic reservoirs of carbon and reducing equiv. PHAs continue to attract industrial attention as a starting point toward renewable, biodegradable, biocompatible, and versatile thermoplastic and elastomeric materials. Pseudomonas species have been known for long as efficient biopolymer producers, esp. for medium-chain-length PHAs. The surge of synthetic biol. and metabolic engineering approaches in recent years offers the possibility of exploiting the untapped potential of Pseudomonas cell factories for the prodn. of tailored PHAs. In this article, an overview of the metabolic and regulatory circuits that rule PHA accumulation in Pseudomonas putida is provided, and approaches leading to the biosynthesis of novel polymers (e.g., PHAs including nonbiol. chem. elements in their structures) are discussed. The potential of novel PHAs to disrupt existing and future market segments is closer to realization than ever before. The review is concluded by pinpointing challenges that currently hinder the wide adoption of bio-based PHAs, and strategies toward programmable polymer biosynthesis from alternative substrates in engineered P. putida strains are proposed.
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    9. 9
      Tan, D.; Wang, Y.; Tong, Y.; Chen, G. Q. Grand challenges for industrializing polyhydroxyalkanoates (PHAs). Trends Biotechnol 2021, 39 (9), 953– 963,  DOI: 10.1016/j.tibtech.2020.11.010
      9
      Grand Challenges for Industrializing Polyhydroxyalkanoates (PHAs)
      Tan, Dan; Wang, Ying; Tong, Yi; Chen, Guo-Qiang
      Trends in Biotechnology (2021), 39 (9), 953-963CODEN: TRBIDM; ISSN:0167-7799. (Elsevier Ltd.)
      Polyhydroxyalkanoates (PHAs) are a diverse family of sustainable bioplastics synthesized by various bacteria, but their high prodn. cost and unstable material properties make them challenging to use in com. applications. Current industrial biotechnol. (CIB) employs conventional microbial chassis, leading to high prodn. costs. However, next-generation industrial biotechnol. (NGIB) approaches, based on fast-growing and contamination-resistant extremophilic Halomonas spp., allow stable continuous processing and thus economical prodn. of PHAs with stable properties. Halomonas spp. designed and constructed using synthetic biol. not only produce low-cost intracellular PHAs but also secrete extracellular sol. products for improved process economics. Next-generation industrial biotechnol. is expected to reduce the bioprodn. cost and process complexity, leading to successful com. prodn. of PHAs.
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    10. 10
      Zhou, L.; Zhang, Z.; Shi, C.; Scoti, M.; Barange, D. K.; Gowda, R. R.; Chen, E. Y.-X. Chemically circular, mechanically tough, and melt-processable polyhydroxyalkanoates. Science 2023, 380 (6640), 64– 69,  DOI: 10.1126/science.adg4520
      10
      Chemically circular, mechanically tough, and melt-processable polyhydroxyalkanoates
      Zhou, Li; Zhang, Zhen; Shi, Changxia; Scoti, Miriam; Barange, Deepak K.; Gowda, Ravikumar R.; Chen, Eugene Y.-X.
      Science (Washington, DC, United States) (2023), 380 (6640), 64-69CODEN: SCIEAS; ISSN:1095-9203. (American Association for the Advancement of Science)
      Polyhydroxyalkanoates (PHAs) have attracted increasing interest as sustainable plastics because of their bio-renewability and biodegradability in the ambient environment. However, current semicryst. PHAs face three long-standing challenges to broad com. implementation and application: lack of melt processability, mech. brittleness, and unrealized recyclability, the last of which is essential for achieving a circular plastics economy. Here we report a synthetic PHA platform that addresses the origin of thermal instability by eliminating α-hydrogens in the PHA repeat units and thus precluding facile cis-elimination during thermal degrdn. This simple α,α-di-substitution in PHAs enhances the thermal stability so substantially that the PHAs become melt-processable. Synergistically, this structural modification also endows the PHAs with the mech. toughness, intrinsic crystallinity, and closed-loop chem. recyclability.
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    11. 11
      Linger, J. G.; Vardon, D. R.; Guarnieri, M. T.; Karp, E. M.; Hunsinger, G. B.; Franden, M. A.; Johnson, C. W.; Chupka, G.; Strathmann, T. J.; Pienkos, P. T. Lignin valorization through integrated biological funneling and chemical catalysis. Proc. Natl. Acad. Sci. U. S. A. 2014, 111 (33), 12013– 12018,  DOI: 10.1073/pnas.1410657111
      11
      Lignin valorization through integrated biological funneling and chemical catalysis
      Linger, Jeffrey G.; Vardon, Derek R.; Guarnieri, Michael T.; Karp, Eric M.; Hunsinger, Glendon B.; Franden, Mary Ann; Johnson, Christopher W.; Chupka, Gina; Strathmann, Timothy J.; Pienkos, Philip T.; Beckham, Gregg T.
      Proceedings of the National Academy of Sciences of the United States of America (2014), 111 (33), 12013-12018CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      Lignin is an energy-dense, heterogeneous polymer comprised of phenylpropanoid monomers used by plants for structure, water transport, and defense, and it is the second most abundant biopolymer on Earth after cellulose. In prodn. of fuels and chems. from biomass, lignin is typically underused as a feedstock and burned for process heat because its inherent heterogeneity and recalcitrance make it difficult to selectively valorize. In nature, however, some organisms have evolved metabolic pathways that enable the utilization of lignin-derived arom. mols. as carbon sources. Arom. catabolism typically occurs via upper pathways that act as a "biol. funnel" to convert heterogeneous substrates to central intermediates, such as protocatechuate or catechol. These intermediates undergo ring cleavage and are further converted via the β-ketoadipate pathway to central carbon metab. Here, we use a natural arom.-catabolizing organism, Pseudomonas putida KT2440, to demonstrate that these arom. metabolic pathways can be used to convert both arom. model compds. and heterogeneous, lignin-enriched streams derived from pilot-scale biomass pretreatment into medium chain-length polyhydroxyalkanoates (mcl-PHAs). mcl-PHAs were then isolated from the cells and demonstrated to be similar in physicochem. properties to conventional carbohydrate-derived mcl-PHAs, which have applications as bioplastics. In a further demonstration of their utility, mcl-PHAs were catalytically converted to both chem. precursors and fuel-range hydrocarbons. Overall, this work demonstrates that the use of arom. catabolic pathways enables an approach to valorize lignin by overcoming its inherent heterogeneity to produce fuels, chems., and materials.
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    12. 12
      Tang, X.; Westlie, A. H.; Caporaso, L.; Cavallo, L.; Falivene, L.; Chen, E. Y.-X. Biodegradable polyhydroxyalkanoates by stereoselective copolymerization of racemic diolides: stereocontrol and polyolefin-like properties. Angew. Chem., Int. Ed. 2020, 59 (20), 7881– 7890,  DOI: 10.1002/anie.201916415
      12
      Biodegradable Polyhydroxyalkanoates by Stereoselective Copolymerization of Racemic Diolides: Stereocontrol and Polyolefin-Like Properties
      Tang, Xiaoyan; Westlie, Andrea H.; Caporaso, Lucia; Cavallo, Luigi; Falivene, Laura; Chen, Eugene Y.-X.
      Angewandte Chemie, International Edition (2020), 59 (20), 7881-7890CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Bacterial polyhydroxyalkanoates (PHAs) are a unique class of biodegradable polymers because of their biodegradability in ambient environments and structural diversity enabled by side-chain groups. However, the biosynthesis of PHAs is slow and expensive, limiting their broader applications as commodity plastics. To overcome such limitation, the catalyzed chem. synthesis of bacterial PHAs has been developed, using the metal-catalyzed stereoselective ring-opening (co)polymn. of racemic cyclic diolides (rac-8DLR, R=alkyl group). In this combined exptl. and computational study, polymn. kinetics, stereocontrol, copolymn. characteristics, and the properties of the resulting PHAs have been examd. Most notably, stereoselective copolymns. of rac-8DLMe with rac-8DLR (R=Et, Bu) have yielded high-mol.-wt., cryst. isotactic PHA copolymers that are hard, ductile, and tough plastics, and exhibit polyolefin-like thermal and mech. properties.
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    13. 13
      Li, M.; Ma, Y.; Zhang, X.; Zhang, L.; Chen, X.; Ye, J. W.; Chen, G. Q. Tailor-made polyhydroxyalkanoates by reconstructing Pseudomonas entomophila. Adv. Mater. 2021, 33 (41), e2102766  DOI: 10.1002/adma.202102766
      There is no corresponding record for this reference.
    14. 14
      Bruckmoser, J.; Pongratz, S.; Stieglitz, L.; Rieger, B. Highly isoselective ring-opening polymerization of rac-β-butyrolactone: access to synthetic poly(3-hydroxybutyrate) with polyolefin-like material properties. J. Am. Chem. Soc. 2023, 145 (21), 11494– 11498,  DOI: 10.1021/jacs.3c02348
      There is no corresponding record for this reference.
    15. 15
      Quinn, E. C.; Knauer, K. M.; Beckham, G. T.; Chen, E. Y. X. Mono-material product design with bio-based, circular, and biodegradable polymers. One Earth 2023, 6 (6), 582– 586,  DOI: 10.1016/j.oneear.2023.05.019
      There is no corresponding record for this reference.
    16. 16
      Yang, J.-C.; Yang, J.; Zhang, T.-Y.; Li, X.-J.; Lu, X.-B.; Liu, Y. Toughening poly(3-hydroxybutyrate) by using catalytic carbonylative terpolymerization of epoxides. Macromolecules 2023, 56 (2), 510– 517,  DOI: 10.1021/acs.macromol.2c02438
      There is no corresponding record for this reference.
    17. 17
      Zhou, Z.; LaPointe, A. M.; Shaffer, T. D.; Coates, G. W. Nature-inspired methylated polyhydroxybutyrates from C1 and C4 feedstocks. Nat. Chem. 2023, 15 (6), 856– 861,  DOI: 10.1038/s41557-023-01187-0
      There is no corresponding record for this reference.
    18. 18
      Rai, R.; Keshavarz, T.; Roether, J. A.; Boccaccini, A. R.; Roy, I. Medium chain length polyhydroxyalkanoates, promising new biomedical materials for the future. Materials Science and Engineering: R: Reports 2011, 72 (3), 29– 47,  DOI: 10.1016/j.mser.2010.11.002
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      Medium chain length polyhydroxyalkanoates, promising new biomedical materials for the future
      Rai, R.; Keshavarz, T.; Roether, J. A.; Boccaccini, A. R.; Roy, I.
      Materials Science & Engineering, R: Reports (2011), R72 (3), 29-47CODEN: MIGIEA; ISSN:0927-796X. (Elsevier B.V.)
      A review. Medium chain length polyhydroxyalkanoates, mcl-PHAs (C6-C14 carbon atoms), are polyesters of hydroxyalkanoates produced mainly by fluorescent Pseudomonads under unbalanced growth conditions. These mcl-PHAs which can be produced using renewable resources are biocompatible, biodegradable and thermoprocessable. They have low crystallinity, low glass transition temp., low tensile strength and high elongation to break, making them elastomeric polymers. Mcl-PHAs and their copolymers are suitable for a range of biomedical applications where flexible biomaterials are required, such as heart valves and other cardiovascular applications as well as matrixes for controlled drug delivery. Mcl-PHAs are more structurally diverse than short chain length PHAs and hence can be more readily tailored for specific applications. Composites have also been fabricated using mcl-PHAs and their copolymers, such as poly (3-hydroxyoctanoate) [P(3HO)] combined with single walled carbon nanotubes and poly(3-hydroxbutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] combined with hydroxyapatite. Because of these attractive properties of biodegradability, biocompatibility and tailorability, Mcl-PHAs and their composites are being increasingly used for biomedical applications. However, studies remain limited mainly to P(3HO) and the copolymer P(3HB-co-3HHx), which are the only mcl-PHAs available in large quantities. In this review we have consolidated current knowledge on the properties and biomedical applications of these elastomeric mcl-PHAs, their copolymers and their composites.
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    19. 19
      Muthuraj, R.; Valerio, O.; Mekonnen, T. H. Recent developments in short- and medium-chain- length polyhydroxyalkanoates: Production, properties, and applications. Int. J. Biol. Macromol. 2021, 187, 422– 440,  DOI: 10.1016/j.ijbiomac.2021.07.143
      There is no corresponding record for this reference.
    20. 20
      Fortman, D. J.; Brutman, J. P.; De Hoe, G. X.; Snyder, R. L.; Dichtel, W. R.; Hillmyer, M. A. Approaches to sustainable and continually recyclable cross-linked polymers. ACS Sustainable Chem. Eng. 2018, 6 (9), 11145– 11159,  DOI: 10.1021/acssuschemeng.8b02355
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      Approaches to Sustainable and Continually Recyclable Cross-Linked Polymers
      Fortman, David J.; Brutman, Jacob P.; De Hoe, Guilhem X.; Snyder, Rachel L.; Dichtel, William R.; Hillmyer, Marc A.
      ACS Sustainable Chemistry & Engineering (2018), 6 (9), 11145-11159CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
      A review. Crosslinked polymers are ubiquitous in daily life, finding applications as tires, insulation, adhesives, automotive parts, and countless other products. The covalent crosslinks in these materials render them mech. robust, chem. resistant, and thermally stable, but they also prevent recycling these materials into similar-value goods. Furthermore, crosslinked polymers are typically produced from petroleum-based feedstocks, and their hydrocarbon backbones render them non-degradable, making them unsustainable in the long-term. In recent years, much effort has focused on the development of recycling strategies for crosslinked polymeric materials. In the following Perspective, we discuss many of these approaches, and highlight efforts to sustainably produce recyclable crosslinked polymers. We present our thoughts on future challenges that must be overcome to enable widespread, viable, and more sustainable and practical implementation of these materials, including the sustainable sourcing of feedstocks, long-term environmental stability of inherently dynamic polymers, and moving toward industrially viable synthesis and reprocessing methods.
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    21. 21
      Ma, S.; Webster, D. C. Degradable thermosets based on labile bonds or linkages: A review. Prog. Polym. Sci. 2018, 76, 65– 110,  DOI: 10.1016/j.progpolymsci.2017.07.008
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      Degradable thermosets based on labile bonds or linkages: A review
      Ma, Songqi; Webster, Dean C.
      Progress in Polymer Science (2018), 76 (), 65-110CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
      A review. Compared with thermoplastic polymers, thermoset polymers are difficult to recycle because they can not be remolded once cured and often do not decomp. under mild conditions. Thermosets designed to be degradable afford a useful route to obtain thermoset recyclability and enable the recycling of valuable components that may be encapsulated in thermoset materials. In this review, the need for degradable thermosets as well as a summary of research progress is presented. Degradable thermosets are divided into different categories based on the different labile bonds or linkages studied such as esters, sulfur contg. linkages (disulfide, sulfonate, 5-membered cyclic dithiocarbonate, trithiocarbonate, sulfite), nitrogen contg. structures (acylhydrazone, alkoxyamine, azlactones, Schiff base, hindered ureas, aminal, carbamate), orthoester structures, carbonates, acetals, hemiacetals, olefinic bonds, D-A addn. structures, vicinal tricarbonyl structures, peroxide bonds, phosphorus contg. structures, tertiary ether bonds, and so on. The synthetic route, recycling methods, degrdn. mechanisms and progress in research of each approach to degradable thermosets is described. The efforts of the applicability of some degradable thermosets are also summarized. Finally, conclusions and trends of future work are highlighted.
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    22. 22
      Morici, E.; Dintcheva, N. T. Recycling of thermoset materials and thermoset-based composites: Challenge and opportunity. Polymers 2022, 14 (19), 4153,  DOI: 10.3390/polym14194153
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      Recycling of Thermoset Materials and Thermoset-Based Composites: Challenge and Opportunity
      Morici, Elisabetta; Dintcheva, Nadka Tz.
      Polymers (Basel, Switzerland) (2022), 14 (19), 4153CODEN: POLYCK; ISSN:2073-4360. (MDPI AG)
      A review. Thermoset materials and their composites are characterized by a long life cycle with their main applications in aircrafts, wind turbines and constructions as insulating materials. The thermoset materials and their composites, to be successfully recovered and valorized, must degrade their three-dimensional structures and recover the mono-oligomers and/or fillers. The thermoset materials could successfully degrade through thermal treatment at different temps. (for example, above 1000°C for incineration, ca. 500°C for oxidn./combustion of org. constituents,), chem. degrdn. by catalyst, irradn. with or without the presence of water, alc., etc., and mech. recycling, obtaining fine particles that are useful as filler and/or reinforcement additives. Among these recycling methods, this mini-review focuses on the formulation and recovery method of innovative thermoset with in-build recyclability. The aim of this review is to get an overview of the state of the art in thermoset recycling and of the most commonly used thermoset composites, recovering valuable reinforcing fibers. Addnl., in this work, we also report not only known recycling routes for thermoset and thermoset-based composites, but also new and novel formulating strategies for producing thermosets with built-in recyclability, i.e., contg. chem.-triggered on-demand links. This mini-review is also a valuable guide for educational purposes for students and specialized technicians in polymer prodn. and recycling.
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    23. 23
      de Koning, G. J. M.; van Bilsen, H. M. M.; Lemstra, P. J.; Hazenberg, W.; Witholt, B.; Preusting, H.; van der Galiën, J. G.; Schirmer, A.; Jendrossek, D. A biodegradable rubber by crosslinking poly(hydroxyalkanoate) from Pseudomonas oleovorans. Polymer 1994, 35 (10), 2090– 2097,  DOI: 10.1016/0032-3861(94)90233-X
      There is no corresponding record for this reference.
    24. 24
      Scherer, T. M.; Fuller, R. C.; Lenz, R. W. Characterization and enzymatic degradation of a cross-linked bacterial polyester. J. Environ. Polym. Degrad. 1994, 2 (4), 263– 269,  DOI: 10.1007/BF02071974
      There is no corresponding record for this reference.
    25. 25
      S̨ucu, T.; Shaver, M. P. Inherently degradable cross-linked polyesters and polycarbonates: resins to be cheerful. Polym. Chem. 2020, 11 (40), 6397– 6412,  DOI: 10.1039/D0PY01226B
      There is no corresponding record for this reference.
    26. 26
      Valentin, H. E.; Berger, P. A.; Gruys, K. J.; de Andrade, Filomena; Rodrigues, M.; Steinbüchel, A.; Tran, M.; Asrar, J. Biosynthesis and characterization of poly(3-hydroxy-4-pentenoic acid). Macromolecules 1999, 32 (22), 7389– 7395,  DOI: 10.1021/ma9905167
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      Biosynthesis and characterization of poly(3-hydroxy-4-pentenoic acid)
      Valentin, Henry E.; Berger, Pierre A.; Gruys, Kenneth J.; de Rodrigues, Maria Filomena; Steinbuechel, Alexander; Tran, Minhtien; Asrar, Jawed
      Macromolecules (1999), 32 (22), 7389-7395CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Burkholderia sp. was grown on sucrose-contg. mineral salts medium with phosphate limitation to induce poly(hydroxyalkanoate) (PHA) accumulation. Under these conditions the cultures accumulated 3-hydroxybutyric acid (3HB) and 3-hydroxy-4-pentenoic acid (3HPE) contg. polyesters. Solvent fractionation of the purified polyester indicated the presence of two homopolymers, poly(3HB) and poly(3HPE), rather than a co-polyester with random monomer distribution as has been reported previously. The simultaneous accumulation of two homopolyesters by Burkholderia sp. was confirmed by NMR spectroscopic anal. Therefore, this is the first report on accumulation of a poly(3HPE) homopolyester and its accumulation from structurally unrelated carbon sources. Purified poly(3HPE) was cross-linked by UV radiation and subjected to epoxidn. using 3-chloroperoxybenzoic acid. Introduction of epoxides into the 3HPE homopolyester was found to increase the glass transition temp.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXmsV2ms7Y%253D&md5=d8301a93815ae12969ecf54d4b2b903f
    27. 27
      Ishida, K.; Hortensius, R.; Luo, X.; Mather, P. T. Soft bacterial polyester-based shape memory nanocomposites featuring reconfigurable nanostructure. J. Polym. Sci., Part B: Polym. Phys. 2012, 50 (6), 387– 393,  DOI: 10.1002/polb.23021
      There is no corresponding record for this reference.
    28. 28
      Levine, A. C.; Sparano, A.; Twigg, F. F.; Numata, K.; Nomura, C. T. Influence of cross-linking on the physical properties and cytotoxicity of polyhydroxyalkanoate (PHA) scaffolds for tissue engineering. ACS Biomaterials Science & Engineering 2015, 1 (7), 567– 576,  DOI: 10.1021/acsbiomaterials.5b00052
      There is no corresponding record for this reference.
    29. 29
      Levine, A. C.; Heberlig, G. W.; Nomura, C. T. Use of thiol-ene click chemistry to modify mechanical and thermal properties of polyhydroxyalkanoates (PHAs). Int. J. Biol. Macromol. 2016, 83, 358– 365,  DOI: 10.1016/j.ijbiomac.2015.11.048
      29
      Use of thiol-ene click chemistry to modify mechanical and thermal properties of polyhydroxyalkanoates (PHAs)
      Levine, Alex C.; Heberlig, Graham W.; Nomura, Christopher T.
      International Journal of Biological Macromolecules (2016), 83 (), 358-365CODEN: IJBMDR; ISSN:0141-8130. (Elsevier B.V.)
      In order to diversify the no. of applications for poly[(R)-3-hydroxyalkanoates] (PHAs), methods must be developed to alter their phys. properties so they are not limited to aliph. polyesters. Recently we developed Escherichia coli LSBJ as a living biocatalyst with the ability to control the repeating unit compn. of PHA polymers, including the ability to incorporate unsatd. repeating units into the PHA polymer at specific ratios. The incorporation of repeating units with terminal alkenes in the side chain of the polymer allowed for the prodn. of random PHA copolymers with defined repeating unit ratios that can be chem. modified for the purpose of tailoring the phys. properties of these materials beyond what are available in current PHAs. In this study, unsatd. PHA copolymers were chem. modified via thiol-ene click chem. to contain an assortment of new functional groups, and the mech. and thermal properties of these materials were measured. Results showed that crosslinking the copolymer resulted in a unique combination of improved strength and pliability and that the addn. of polar functional groups increased the tensile strength, Young's modulus, and hydrophilic profile of the materials. This work demonstrates that unsatd. PHAs can be chem. modified to extend their phys. properties to distinguish them from currently available PHA polymers.
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    30. 30
      Gagnon, K. D.; Lenz, R. W.; Farris, R. J.; Fuller, R. C. Chemical modification of bacterial elastomers: 1. Peroxide crosslinking. Polymer 1994, 35 (20), 4358– 4367,  DOI: 10.1016/0032-3861(94)90093-0
      There is no corresponding record for this reference.
    31. 31
      Mangeon, C.; Renard, E.; Thevenieau, F.; Langlois, V. Networks based on biodegradable polyesters: An overview of the chemical ways of crosslinking. Materials Science and Engineering: C 2017, 80, 760– 770,  DOI: 10.1016/j.msec.2017.07.020
      There is no corresponding record for this reference.
    32. 32
      Steinbüchel, A. Production of rubber-like polymers by microorganisms. Curr. Opin. Microbiol. 2003, 6 (3), 261– 270,  DOI: 10.1016/S1369-5274(03)00061-4
      There is no corresponding record for this reference.
    33. 33
      Vendamme, R.; Schüwer, N.; Eevers, W. Recent synthetic approaches and emerging bio-inspired strategies for the development of sustainable pressure-sensitive adhesives derived from renewable building blocks. J. Appl. Polym. Sci. 2014, 131 (17), e40669  DOI: 10.1002/app.40669
      There is no corresponding record for this reference.
    34. 34
      Wang, C.; Wang, H.; Zou, F.; Chen, S.; Wang, Y. Development of polyhydroxyalkanoate-based polyurethane with water-thermal response shape-memory behavior as new 3D elastomers scaffolds. Polymers 2019, 11 (6), 1030,  DOI: 10.3390/polym11061030
      There is no corresponding record for this reference.
    35. 35
      Oyama, T.; Kobayashi, S.; Okura, T.; Sato, S.; Tajima, K.; Isono, T.; Satoh, T. Biodegradable compatibilizers for poly(hydroxyalkanoate)/poly(ε-caprolactone) blends through click reactions with end-functionalized microbial poly(hydroxyalkanoate)s. ACS Sustainable Chem. Eng. 2019, 7 (8), 7969– 7978,  DOI: 10.1021/acssuschemeng.9b00897
      There is no corresponding record for this reference.
    36. 36
      Cywar, R. M.; Ling, C.; Clarke, R. W.; Kim, D. H.; Kneucker, C. M.; Salvachúa, D.; Addison, B.; Hesse, S. A.; Takacs, C. J.; Xu, S. Elastomeric vitrimers from designer polyhydroxyalkanoates with recyclability and biodegradability. Sci. Adv. 2023, 9 (47), eadi1735  DOI: 10.1126/sciadv.adi1735
      There is no corresponding record for this reference.
    37. 37
      Han, C. C.; Ismail, J.; Kammer, H.-W. Melt reaction in blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and epoxidized natural rubber. Polym. Degrad. Stab. 2004, 85 (3), 947– 955,  DOI: 10.1016/j.polymdegradstab.2003.11.020
      37
      Melt reaction in blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and epoxidized natural rubber
      Han, Chan Chin; Ismail, Jamil; Kammer, Hans-Werner
      Polymer Degradation and Stability (2004), 85 (3), 947-955CODEN: PDSTDW; ISSN:0141-3910. (Elsevier B.V.)
      Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with hydroxyvalerate content of 12 mol% is a natural aliph. polyester. At temps. above its m.p., thermal decompn. occurs leading to shorter chains with carboxyl end groups. In blends with epoxidized natural rubber (ENR), 50% epoxidn. level, these carboxyl chain ends may trigger reactions between the constituents since the epoxidized groups provide reactive sites. Glass transition temp. studies reveal immiscibility of the polymers over the entire compn. range. Hence, any reaction between the constituents is restricted to the interfacial region between the components. We report here on studies on melt reactions between the components at elevated temps. DSC traces display an exothermic peak when the blends are annealed at temps. ranging from 220 up to 234°. The kinetics of the reaction are discussed in terms of a serial reaction scheme. It turns out that the reaction rate increases with annealing temp. (Ta) and with descending PHBV content in the blends when PHBV is the minor component. Morphol. studies by optical microscopy reveal that PHBV is still capable of crystg. at 50° after melt reaction at 234°. Either ring-banded or fibrillar spherulites can be seen in blends with PHBV in excess, however, the rate of crystn. is dramatically reduced after melt reaction at Ta=234°.
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    38. 38
      Bhatt, R.; Shah, D.; Patel, K. C.; Trivedi, U. PHA–rubber blends: Synthesis, characterization and biodegradation. Bioresour. Technol. 2008, 99 (11), 4615– 4620,  DOI: 10.1016/j.biortech.2007.06.054
      38
      PHA-rubber blends: Synthesis, characterization and biodegradation
      Bhatt, Rachana; Shah, Dishma; Patel, K. C.; Trivedi, Ujjval
      Bioresource Technology (2008), 99 (11), 4615-4620CODEN: BIRTEB; ISSN:0960-8524. (Elsevier Ltd.)
      Medium chain length polyhydroxyalkanoates (mcl-PHA) and different rubbers; namely natural rubber, nitrile rubber and butadiene rubber were blended at room temp. using soln. blending technique. Blends constituted 5%, 10% and 15% of mcl-PHA in different rubbers. Thermogravimetric anal. of mcl-PHA showed the melting temp. of the polymer around 50 °C. Thermal properties of the synthesized blend were studied by Differential Scanning Calorimetry which confirmed effective blending between the polymers. Blending of mcl-PHA with natural rubber led to the synthesis of a different polymer having the m.p. of 90 °C. Degrdn. studies of the blends were carried out using a soil isolate, Pseudomonas sp. 202 for 30 days. Extracellular protein concn. as well as OD660 due to the growth of Pseudomonas sp. 202 was studied. The degrdn. of blended plastic material, as evidenced by %wt. loss after degrdn. and increase in the growth of organism correlated with the amt. of mcl-PHA present in the sample. Growth of Pseudomonas sp. 202 resulted in 14.63%, 16.12% and 3.84% wt. loss of PHA:rubber blends (natural, nitrile and butadiene rubber). Scanning electron microscopic studies after 30 days of incubation further confirmed biodegrdn. of the films.
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    39. 39
      Popa, M. S.; Frone, A. N.; Panaitescu, D. M. Polyhydroxybutyrate blends: A solution for biodegradable packaging?. Int. J. Biol. Macromol. 2022, 207, 263– 277,  DOI: 10.1016/j.ijbiomac.2022.02.185
      There is no corresponding record for this reference.
    40. 40
      Feijoo, P.; Samaniego-Aguilar, K.; Sánchez-Safont, E.; Torres-Giner, S.; Lagaron, J. M.; Gamez-Perez, J.; Cabedo, L. Development and characterization of fully renewable and biodegradable polyhydroxyalkanoate blends with improved thermoformability. Polymers 2022, 14 (13), 2527,  DOI: 10.3390/polym14132527
      40
      Development and Characterization of Fully Renewable and Biodegradable Polyhydroxyalkanoate Blends with Improved Thermoformability
      Feijoo, Patricia; Samaniego-Aguilar, Kerly; Sanchez-Safont, Estefania; Torres-Giner, Sergio; Lagaron, Jose M.; Gamez-Perez, Jose; Cabedo, Luis
      Polymers (Basel, Switzerland) (2022), 14 (13), 2527CODEN: POLYCK; ISSN:2073-4360. (MDPI AG)
      Poly(3-hydroxybutyrate-co-3-valerate) (PHBV), being one of the most studied and com. available polyhydroxyalkanoates (PHAs), presents an intrinsic brittleness and narrow processing window that currently hinders its use in several plastic applications. The aim of this study was to develop a biodegradable PHA-based blend by combining PHBV with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), another copolyester of the PHA family that shows a more ductile behavior. Blends of PHBV with 20% wt., 30% wt., and 40% wt. of PHBH were obtained by melt mixing, processed by cast extrusion in the form of films, and characterized in terms of their morphol., crystn. behavior, thermal stability, mech. properties, and thermoformability. Full miscibility of both biopolymers was obsd. in the amorphous phase due to the presence of a single delta peak, ranging from 4.5°C to 13.7°C. Moreover, the incorporation of PHBH hindered the crystn. process of PHBV by decreasing the spherulite growth rate from 1.0μm/min to 0.3μm/min. However, for the entire compn. range studied, the high brittleness of the resulting materials remained since the presence of PHBH did not prevent the PHBV cryst. phase from governing the mech. behavior of the blend. Interestingly, the addn. of PHBH greatly improved the thermoformability by widening the processing window of PHBV by 7 s, as a result of the increase in the melt strength of the blends even for the lowest PHBH content.
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    41. 41
      Panaitescu, D. M.; Frone, A. N.; Nicolae, C.-A.; Gabor, A. R.; Miu, D. M.; Soare, M.-G.; Vasile, B. S.; Lupescu, I. Poly(3-hydroxybutyrate) nanocomposites modified with even and odd chain length polyhydroxyalkanoates. Int. J. Biol. Macromol. 2023, 244, 125324  DOI: 10.1016/j.ijbiomac.2023.125324
      There is no corresponding record for this reference.
    42. 42
      Clarke, R. W.; Sandmeier, T.; Franklin, K. A.; Reich, D.; Zhang, X.; Vengallur, N.; Patra, T. K.; Tannenbaum, R. J.; Adhikari, S.; Kumar, S. K. Dynamic crosslinking compatibilizes immiscible mixed plastics. Nature 2023, 616 (7958), 731– 739,  DOI: 10.1038/s41586-023-05858-3
      42
      Dynamic crosslinking compatibilizes immiscible mixed plastics
      Clarke, Ryan W.; Sandmeier, Tobias; Franklin, Kevin A.; Reich, Dominik; Zhang, Xiao; Vengallur, Nayan; Patra, Tarak K.; Tannenbaum, Robert J.; Adhikari, Sabin; Kumar, Sanat K.; Rovis, Tomislav; Chen, Eugene Y.-X.
      Nature (London, United Kingdom) (2023), 616 (7958), 731-739CODEN: NATUAS; ISSN:1476-4687. (Nature Portfolio)
      The global plastics problem is a trifecta, greatly affecting environment, energy and climate1-4. Many innovative closed/open-loop plastics recycling or upcycling strategies have been proposed or developed5-16, addressing various aspects of the issues underpinning the achievement of a circular economy17-19. In this context, reusing mixed-plastics waste presents a particular challenge with no current effective closed-loop soln.20. This is because such mixed plastics, esp. polar/apolar polymer mixts., are typically incompatible and phase sep., leading to materials with substantially inferior properties. To address this key barrier, here we introduce a new compatibilization strategy that installs dynamic crosslinkers into several classes of binary, ternary and postconsumer immiscible polymer mixts. in situ. Our combined exptl. and modeling studies show that specifically designed classes of dynamic crosslinker can reactivate mixed-plastics chains, represented here by apolar polyolefins and polar polyesters, by compatibilizing them via dynamic formation of graft multiblock copolymers. The resulting in-situ-generated dynamic thermosets exhibit intrinsic reprocessability and enhanced tensile strength and creep resistance relative to virgin plastics. This approach avoids the need for de/reconstruction and thus potentially provides an alternative, facile route towards the recovery of the endowed energy and materials value of individual plastics.
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    43. 43
      Takase, K.; Taguchi, S.; Doi, Y. Enhanced synthesis of poly(3-hydroxybutyrate) in recombinant Escherichia coli by means of error-prone PCR mutagenesis, saturation mutagenesis, and in vitro recombination of the type II polyhydroxyalkanoate synthase gene. Journal of Biochemistry 2003, 133 (1), 139– 145,  DOI: 10.1093/jb/mvg015
      There is no corresponding record for this reference.
    44. 44
      Li, M.; Chen, X.; Che, X.; Zhang, H.; Wu, L. P.; Du, H.; Chen, G. Q. Engineering Pseudomonas entomophila for synthesis of copolymers with defined fractions of 3-hydroxybutyrate and medium-chain-length 3-hydroxyalkanoates. Metab Eng. 2019, 52, 253– 262,  DOI: 10.1016/j.ymben.2018.12.007
      There is no corresponding record for this reference.
    45. 45
      Salvachúa, D.; Rydzak, T.; Auwae, R.; De Capite, A.; Black, B. A.; Bouvier, J. T.; Cleveland, N. S.; Elmore, J. R.; Furches, A.; Huenemann, J. D. Metabolic engineering of Pseudomonas putida for increased polyhydroxyalkanoate production from lignin. Microbial Biotechnology 2020, 13 (1), 290– 298,  DOI: 10.1111/1751-7915.13481
      There is no corresponding record for this reference.
    46. 46
      Ye, J.; Huang, W.; Wang, D.; Chen, F.; Yin, J.; Li, T.; Zhang, H.; Chen, G. Q. Pilot scale-up of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) production by Halomonas bluephagenesis via cell growth adapted optimization process. Biotechnol. J. 2018, 13 (5), e1800074  DOI: 10.1002/biot.201800074
      There is no corresponding record for this reference.
    47. 47
      Johnson, C. W.; Salvachúa, D.; Rorrer, N. A.; Black, B. A.; Vardon, D. R.; St John, P. C.; Cleveland, N. S.; Dominick, G.; Elmore, J. R.; Grundl, N. Innovative chemicals and materials from bacterial aromatic catabolic pathways. Joule 2019, 3 (6), 1523– 1537,  DOI: 10.1016/j.joule.2019.05.011
      47
      Innovative Chemicals and Materials from Bacterial Aromatic Catabolic Pathways
      Johnson, Christopher W.; Salvachua, Davinia; Rorrer, Nicholas A.; Black, Brenna A.; Vardon, Derek R.; St. John, Peter C.; Cleveland, Nicholas S.; Dominick, Graham; Elmore, Joshua R.; Grundl, Nicholas; Khanna, Payal; Martinez, Chelsea R.; Michener, William E.; Peterson, Darren J.; Ramirez, Kelsey J.; Singh, Priyanka; VanderWall, Todd A.; Wilson, A. Nolan; Yi, Xiunan; Biddy, Mary J.; Bomble, Yannick J.; Guss, Adam M.; Beckham, Gregg T.
      Joule (2019), 3 (6), 1523-1537CODEN: JOULBR; ISSN:2542-4351. (Cell Press)
      To drive innovation in chem. and material applications beyond what has been afforded by the mature petrochem. industry, new mols. that possess diverse chem. functionality are needed. One source of such mols. lies in the varied metabolic pathways that soil microbes utilize to catabolize arom. compds. generated during plant decompn. Here, we have engineered Pseudomonas putida KT2440 to convert these arom. compds. to 15 catabolic intermediates that exhibit substantial chem. diversity. Bioreactor cultivations, anal. methods, and bench-scale sepns. were developed to enable prodn. (up to 58 g/L), detection, and purifn. of each target mol. We further engineered strains for prodn. of a subset of these mols. from glucose, achieving a 41% molar yield of muconic acid. Finally, we produce materials from three compds. to illustrate the potential for realizing performance-advantaged properties relative to petroleum-derived analogs.
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    48. 48
      Self, J. L.; Zervoudakis, A. J.; Peng, X.; Lenart, W. R.; Macosko, C. W.; Ellison, C. J. Linear, graft, and beyond: Multiblock copolymers as next-generation compatibilizers. JACS Au 2022, 2 (2), 310– 321,  DOI: 10.1021/jacsau.1c00500
      48
      Review of Linear, Graft, and Beyond, Multiblock Copolymers as Next-Generation Compatibilizers
      Self, Jeffrey L.; Zervoudakis, Aristotle J.; Peng, Xiayu; Lenart, William R.; Macosko, Christopher W.; Ellison, Christopher J.
      JACS Au (2022), 2 (2), 310-321CODEN: JAAUCR; ISSN:2691-3704. (American Chemical Society)
      A review. Properly addressing the global issue of unsustainable plastic waste generation and accumulation will require a confluence of technol. breakthroughs on various fronts. Mech. recycling of plastic waste into polymer blends is one method expected to contribute to a soln. Due to phase sepn. of individual components, mech. recycling of mixed polymer waste streams generally results in an unsuitable material with substantially reduced performance. However, when an appropriately designed compatibilizer is used, the recycled blend can have competitive properties to virgin materials. In its current state, polymer blend compatibilization is usually not cost-effective compared to traditional waste management, but further tech. development and optimization will be essential for driving future cost competitiveness. Historically, effective compatibilizers have been diblock copolymers or in situ generated graft copolymers, but recent progress shows there is great potential for multiblock copolymer compatibilizers. In this perspective, we lay out recent advances in synthesis and understanding for two types of multiblock copolymers currently being developed as blend compatibilizers: linear and graft. Importantly, studies of appropriately designed copolymers have shown them to efficiently compatibilize model binary blends at concns. as low as ∼0.2 wt %. These investigations pave the way for studies on more complex (ternary or higher) mixed waste streams that will require novel compatibilizer architectures. Given the progress outlined here, we believe that multiblock copolymers offer a practical and promising soln. to help close the loop on plastic waste. While a complete discussion of the implementation of this technol. would entail infrastructural, policy and social developments, they are outside the scope of this perspective which instead focuses on material design considerations and the tech. advancements of block copolymer compatibilizers.
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    49. 49
      ISO Standards. Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium. ISO 14851:2019, 2019.
      There is no corresponding record for this reference.
    50. 50
      Huijberts, G. N.; Eggink, G.; de Waard, P.; Huisman, G. W.; Witholt, B. Pseudomonas putida KT2442 cultivated on glucose accumulates poly(3-hydroxyalkanoates) consisting of saturated and unsaturated monomers. Appl. Environ. Microbiol. 1992, 58 (2), 536– 544,  DOI: 10.1128/aem.58.2.536-544.1992
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      Pseudomonas putida KT2442 cultivated on glucose accumulates poly(3-hydroxyalkanoates) consisting of saturated and unsaturated monomers
      Huijberts, Gern N. M.; Eggink, Gerrit; De Waard, Pieter; Huisman, Gjalt W.; Witholt, Bernard
      Applied and Environmental Microbiology (1992), 58 (2), 536-44CODEN: AEMIDF; ISSN:0099-2240.
      The biosynthesis of poly(3-hydroxyalkanoates) (PHAs) by P. putida KT2442 during growth on carbohydrates was studied. PHAs isolated from P. putida cultivated on glucose, fructose, and glycerol were found to have a very similar monomer compn. In addn. to the major constituent 3-hydroxydecanoate, six other monomers were found to be preset: 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydodecanoate, 3-hydroxydodecenoate, 3-hydroxytetradecanoate, and 3-hydroxytetradecenoate. The identity of all seven 3-hydroxy fatty acids was established by gas chromatog.-mass spectrometry, one-dimensional 1H NMR, and two-dimensional double-quantum filtered correlation spectroscopy 1H NMR. The chem. structures of the monomer units are identical to the structure of the acyl moiety of the 3-hydroxyacyl-acyl carrier protein intermediates of de novo fatty acid biosynthesis. Furthermore, the degree of unsatn. of PHA and membrane lipids is similarly influenced by shifts in the cultivation temp. These results strongly indicate that, during growth on nonrelated substrates, PHA monomers are derived from intermediates of de novo fatty acid biosynthesis. Anal. of a P. putida pha mutant and complementation of this mutant with the cloned pha locus revealed that the PHA polymerase genes necessary for PHA synthesis from octanoate are also responsible for PHA formation from glucose.
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    51. 51
      Huang, P.; Okoshi, T.; Mizuno, S.; Hiroe, A.; Tsuge, T. Gas chromatography-mass spectrometry-based monomer composition analysis of medium-chain-length polyhydroxyalkanoates biosynthesized by Pseudomonas spp. Biosci Biotechnol Biochem 2018, 82 (9), 1615– 1623,  DOI: 10.1080/09168451.2018.1473027
      There is no corresponding record for this reference.
    52. 52
      Dufresne, A.; Vincendon, M. Poly(3-hydroxybutyrate) and poly(3-hydroxyoctanoate) blends: Morphology and mechanical behavior. Macromolecules 2000, 33 (8), 2998– 3008,  DOI: 10.1021/ma991854a
      52
      Poly(3-hydroxybutyrate) and Poly(3-hydroxyoctanoate) Blends: Morphology and Mechanical Behavior
      Dufresne, Alain; Vincendon, Marc
      Macromolecules (2000), 33 (8), 2998-3008CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Blends of bacterial poly(hydroxybutyrate) (PHB) with poly(hydroxyoctanoate) (PHO) were prepd. by co-dissolving the two polyesters in chloroform and casting the mixt. To probe the question of blend miscibility, SEM observations and differential scanning calorimetry (DSC) spectra were collected for the blends and blend components. PHB shows no miscibility with PHO, resulting in two-phase systems in which the nature of the continuous phase is compn.-dependent. Dynamic mech. anal. and tensile properties of these materials were also investigated. The morphol. of the blend strongly influences the mech. behavior. The mech. properties of these materials have been predicted from a model involving the percolation concept. It takes both linear and nonlinear mech. behaviors into account and allows for the effect of the lack of adhesion between material domains and/or breakage of one of the component.
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    53. 53
      Li, Z.; Yang, J.; Loh, X. J. Polyhydroxyalkanoates: opening doors for a sustainable future. NPG Asia Materials 2016, 8 (4), e265  DOI: 10.1038/am.2016.48
      53
      Polyhydroxyalkanoates: opening doors for a sustainable future
      Li, Zibiao; Yang, Jing; Loh, Xian Jun
      NPG Asia Materials (2016), 8 (4), e265CODEN: NAMPCE; ISSN:1884-4057. (Nature Publishing Group)
      Polyhydroxyalkanoates (PHAs) comprise a group of natural biodegradable polyesters that are synthesized by microorganisms. However, several disadvantages limit their competition with traditional synthetic plastics or their application as ideal biomaterials. These disadvantages include their poor mech. properties, high prodn. cost, limited functionalities, incompatibility with conventional thermal processing techniques and susceptibility to thermal degrdn. To circumvent these drawbacks, PHAs need to be modified to ensure improved performance in specific applications. In this review, well-established modification methods of PHAs are summarized and discussed. The improved properties of PHA that blends with natural raw materials or other biodegradable polymers, including starch, cellulose derivs., lignin, poly(lactic acid), polycaprolactone and different PHA-type blends, are summarized. The functionalization of PHAs by chem. modification is described with respect to two important synthesis approaches: block copolymn. and graft copolymn. The expanded utilization of the modified PHAs as engineering materials and the biomedical significance in different areas are also addressed.
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    54. 54
      Montoya-Ospina, M. C.; Verhoogt, H.; Ordner, M.; Tan, X.; Osswald, T. A. Effect of cross-linking on the mechanical properties, degree of crystallinity and thermal stability of polyethylene vitrimers. Polym. Eng. Sci. 2022, 62 (12), 4203– 4213,  DOI: 10.1002/pen.26178
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      Effect of cross-linking on the mechanical properties, degree of crystallinity and thermal stability of polyethylene vitrimers
      Montoya-Ospina, Maria Camila; Verhoogt, Henk; Ordner, Mark; Tan, Xiao; Osswald, Tim A.
      Polymer Engineering & Science (2022), 62 (12), 4203-4213CODEN: PYESAZ; ISSN:0032-3888. (John Wiley & Sons, Inc.)
      Maleic anhydride-grafted-polyethylene was dynamically cross-linked via reactive melt blending with 4,4'-dithiodianiline. Thermal and mech. properties of polyethylene vitrimers with different crosslinking d. were investigated. The results indicate that the degree of crystallinity decreased with increasing crosslinking d. This behavior was directly related to short-term and long-term mech. properties: vitrimers showed a decrease in yield strength and creep performance. The yield strength of PE vitrimers decreased linearly in relation to the degree of crystallinity. Polarized optical microscopy revealed that the cross-links inhibit the growth of spherulites structure in polyethylene vitrimers. Thermogravimetric anal. indicated an increase in the onset degrdn. temp. and decompn. rate for vitrimers with increased crosslinking d. The stiffness of the vitrimers decreased with increasing crosslinking d. which led to higher damping properties. Finally, it was demonstrated that reprocessing of polyethylene vitrimer was possible without significant impact in mech. properties.
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    55. 55
      Wang, Y.-X.; Wang, C.-C.; Shi, Y.; Liu, L.-Z.; Bai, N.; Song, L.-F. Effects of Dynamic Crosslinking on Crystallization, Structure and Mechanical Property of Ethylene-Octene Elastomer/EPDM Blends. Polymers 2022, 14 (1), 139,  DOI: 10.3390/polym14010139
      There is no corresponding record for this reference.
    56. 56
      Sisanth, K. S.; Thomas, M. G.; Abraham, J.; Thomas, S. 1 - General introduction to rubber compounding. In Progress in Rubber Nanocomposites; Thomas, S.; Maria, H. J., Eds.; Woodhead Publishing, 2017; pp 1– 39.
      There is no corresponding record for this reference.
    57. 57
      Johnson, C. W.; Beckham, G. T. Aromatic catabolic pathway selection for optimal production of pyruvate and lactate from lignin. Metab Eng. 2015, 28, 240– 247,  DOI: 10.1016/j.ymben.2015.01.005
      57
      Aromatic catabolic pathway selection for optimal production of pyruvate and lactate from lignin
      Johnson, Christopher W.; Beckham, Gregg T.
      Metabolic Engineering (2015), 28 (), 240-247CODEN: MEENFM; ISSN:1096-7176. (Elsevier B. V.)
      Lignin represents an untapped feedstock for the prodn. of fuels and chems., but its intrinsic heterogeneity makes lignin valorization a significant challenge. In nature, many aerobic organisms degrade lignin-derived arom. mols. through conserved central intermediates including catechol and protocatechuate. Harnessing this microbial approach offers potential for lignin upgrading in modern biorefineries, but significant tech. development is needed to achieve this end. Catechol and protocatechuate are subjected to arom. ring cleavage by dioxygenase enzymes that, depending on the position, ortho or meta relative to adjacent hydroxyl groups, result in different products that are metabolized through parallel pathways for entry into the TCA cycle. These degrdn. pathways differ in the combination of succinate, acetyl-CoA, and pyruvate produced, the reducing equiv. regenerated, and the amt. of carbon emitted as CO2-factors that will ultimately impact the yield of the targeted product. As shown here, the ring-cleavage pathways can be interchanged with one another, and such substitutions have a predictable and substantial impact on product yield. We demonstrate that replacement of the catechol ortho degrdn. pathway endogenous to Pseudomonas putida KT2440 with an exogenous meta-cleavage pathway from P. putida mt-2 increases yields of pyruvate produced from arom. mols. in engineered strains. Even more dramatically, replacing the endogenous protocatechuate ortho pathway with a meta-cleavage pathway from Sphingobium sp. SYK-6 results in a nearly five-fold increase in pyruvate prodn. We further demonstrate the aerobic conversion of pyruvate to L-lactate with a yield of 41.1±2.6% (wt/wt). Overall, this study illustrates how arom. degrdn. pathways can be tuned to optimize the yield of a desired product in biol. lignin upgrading.
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