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Interphase Design of Cellulose Nanocrystals/Poly(hydroxybutyrate-ran-valerate) Bionanocomposites for Mechanical and Thermal Properties Tuning
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  • Chiara Magnani
    Chiara Magnani
    Laboratory of Polymeric and Composite Materials (LPCM), Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons (UMONS), 23 Place du Parc, B-7000 Mons, Belgium
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    Orcidhttp://orcid.org/0000-0003-0858-6264
  • Alexander Idström
    Alexander Idström
    Department of Chemistry and Chemical Engineering, Division of Applied Chemistry, Chalmers University of Technology, Kemivägen 4, SE-412 96 Göteborg, Sweden
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    Orcidhttp://orcid.org/0000-0003-4765-8224
  • Lars Nordstierna
    Lars Nordstierna
    Department of Chemistry and Chemical Engineering, Division of Applied Chemistry, Chalmers University of Technology, Kemivägen 4, SE-412 96 Göteborg, Sweden
    Wallenberg Wood Science Center (WWSC), KTH Royal Institute of Technology, Teknikringen 56, SE-100 44 Stockholm, Sweden
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    Orcidhttp://orcid.org/0000-0002-6580-0610
  • Alejandro J. Müller
    Alejandro J. Müller
    POLYMAT and Polymer Science and Technology Department, Faculty of Chemistry, University of the Basque Country UPV/EHU, San Sebastián 20018, Spain
    IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
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    Orcidhttp://orcid.org/0000-0001-7009-7715
  • Philippe Dubois
    Philippe Dubois
    Laboratory of Polymeric and Composite Materials (LPCM), Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons (UMONS), 23 Place du Parc, B-7000 Mons, Belgium
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    Orcidhttp://orcid.org/0000-0003-1534-1564
  • Jean-Marie Raquez
    Jean-Marie Raquez
    Laboratory of Polymeric and Composite Materials (LPCM), Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons (UMONS), 23 Place du Parc, B-7000 Mons, Belgium
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    Orcidhttp://orcid.org/0000-0003-1940-7129
  • Giada Lo Re*
    Giada Lo Re
    Department of Industrial and Materials Science, Division of Engineering Materials, Chalmers University of Technology, Hörsalsvägen 7A, SE-412 96 Göteborg, Sweden
    *E-mail: [email protected]
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    Orcidhttp://orcid.org/0000-0001-8840-1172
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Biomacromolecules

Cite this: Biomacromolecules 2020, 21, 5, 1892–1901
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https://doi.org/10.1021/acs.biomac.9b01760
Published February 20, 2020

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Abstract

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Poly[(3-hydroxybutyrate)-ran-(3-hydroxyvalerate)] (PHBV) is a bacterial polyester with a strong potential as a substitute for oil-based thermoplastics due to its biodegradability and renewability. However, its inherent slow crystallization rate limits its thermomechanical properties and therefore its applications. In this work, surface-modified cellulose nanocrystals (CNCs) have been investigated as green and biosourced nucleating and reinforcing agent for PHBV matrix. Different ester moieties from the CNCs were thereby produced through a green one-pot hydrolysis/Fisher esterification. Beyond the improved dispersion, the CNCs surface esterification affected the thermal and thermomechanical properties of PHBV. The results demonstrate that butyrate-modified CNCs, mimicking the PHBV chemical structure, brought a considerable improvement toward the CNCs/matrix interface, leading to an enhancement of the PHBV thermomechanical properties via a more efficient stress transfer, especially above its glass transition.

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SPECIAL ISSUE

This article is part of the Anselme Payen Award Special Issue special issue.

Introduction

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The problem concerning the environmental impact of plastic pollution and waste management (1,2) can no longer be neglected. As a consequence, single-use plastics have been recently banned (3) in Europe, and the replacement of traditional not biodegradable oil-based polymers is becoming urgent. Thus, the interest in biosourced and particularly biodegradable materials is being increased, especially for their potential in packaging and disposable items, (4) bringing them to the attention of benchmark commodity suppliers. Among other commercially available emerging polyesters, poly(3-hydroxybutyrate-ran-3-hydroxyvalerate) (PHBV) is a semicrystalline biosourced poly hydroxyalkanoate naturally produced by bacteria. (5) Beyond its renewability (6) and biodegradability, (7−9) PHBV has many advantages compared to the well-known homopolymer poly(3-hydroxybutyrate) (PHB). Its mechanical and thermal properties can be readily tuned up by varying the relative percentage of the comonomer 3-hydroxyvalerate (HV). (10) In this approach, a higher content of HV as comonomer is used to overcome the inherent brittleness of PHB, although progressively lowering its crystallization rate. Commercially available grades of PHBV generally contain low HV content (<12 wt %). Therefore, PHBV application is limited because of its low ductility, high cost, (11,12) and low thermal stability, (13) as well as slow crystallization rate. (14) Different approaches have been explored to overcome PHBV drawbacks, beyond the HV comonomer content, as blending with other polymers, (15−17) addition of plasticizers, (18−20) or nucleating agents. (21) The use of nucleating agents is an economically viable approach already demonstrated for improving other commercialy available PHAs. (22)
Cellulose nanocrystals (CNCs) are of interest as emerging nucleating agents because of their natural origin and good mechanical properties exploitable to efficiently reinforce a polymer matrix. (23) A few studies have reported a positive effect of CNCs, obtained from sulfuric or hydrochloric acid hydrolysis, as a nucleating agent for PHBV, leading to an amelioration of its mechanical properties, even at low nanofiller content. (24−29)
An efficient reinforcement and a faster crystallization require a high level of dispersibility and individualization of CNCs, which remain a challenge. (30,31) Their inherent high hydrophilic surface adversely interacts with the generally more hydrophobic polymer matrices, leading to agglomerate formation and depletion at the interphase, (32) as already seen for CNCs in PHBV matrix by Malmir et al. (26) Therefore, surface modification has been the most exploited strategy to tackle this challenge. (33,34) However, the main drawback associated with this approach lies in the addition of cost and time-consuming steps, which often require the use of not sustainable organic solvents and harmful chemicals. (35,36)
Braun et al. (37) introduced a one-pot acid hydrolysis/Fischer esterification in water dispersion. This approach allowed for the CNCs preparation and their simultaneous surface esterification in a green and fast process, with high potential for scaling up. This method was found to be efficient with many acids. (25,31,38,39) Yu et al. used this method to graft organic acids carrying different content of hydroxyl functionalities and studied the influence of hydrogen bonds at the PHBV/CNCs interphase on mechanical properties of PHBV. (31) Their results demonstrated in the case of PHBV bionanocomposites at 10 wt % CNCs that the higher the hydrogen bonding content, the higher the Young’s modulus. They also demonstrated a favorable effect on thermal stability of hydrogen bonds formed between the surface polyol moieties of CNCs and PHBV carboxyl groups. (25)
To our knowledge, no other studies have investigated the influence of different CNCs surface moieties on the PHBV thermal and dynamical-mechanical properties. In the current study, organic moieties with chemical structure similar to PHBV were selected to decorate the CNCs surface in order to improve the interaction with the polyester in a selective manner. This approach has been considered under the statement that an improved interface CNCs/PHBV would promote the adhesion of the polyester to the CNCs surface leading to a more efficient stress transfer. (40) This approach was found successful in the case of polylactide matrix by Spinella et al. (38) In this study, lactate decorated CNCs mimicking the backbone structure of polylactide significantly improved the thermal stability of the cellulose nanocrystals and the final performance of the bionanocomposite.
Green one-pot acid hydrolysis/Fischer esterification has herein been chosen to produce CNCs decorated with lactate and butyrate surface moieties. The reasons behind the choice of these two moieties lie on the assessment of the synergic or competitive effect of an improved thermal stability (provided by lactate moieties) and a mimicking of the PHBV molecular structure (with butyrate moieties). The present work focuses on the CNC/PHBV interface and its effect on mechanical and thermal properties. The rationale behind the bionanocomposite preparation method intended to limit the variables under investigation only to the surface chemistry at the interface. Aware of the substantial impact on the “green” aspect of the work, the bionanocomposites were therefore prepared through solvent casting for the sake of achieving a near-perfect dispersion. (41,42) Indeed, this method prevents the CNCs aggregation, taking advantage of the mobility of the polymer chains dissolved in an organic solvent, while avoiding possible thermal degradation during melt processing.
The results highlighted that different modifications of CNCs affect the thermal behavior of PHBV and that butyrate moieties from the nanocellulose mimicking the polyester backbone lead to an improved CNCs/PHBV interphase and a more efficient stress transfer.

Experimental Section

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Materials

PHBV (Enmat Y1000, Mw = 2.6 × 105 g/mol) was produced by Tianan Biologic Material Co. Ltd. (Ningbo, China) and supplied by helianPolymer. Hydroxyvalerate (HV) content was indicated to be around 2.56 mol %. We calculated it as 0.8% from 1H NMR. Ramie cellulose fibers were purchased from the Woolery (http://www.woolery.com/) and purified according to the protocol below. Butyric acid, lactic acid, hydrochloric acid (37%), NaOH, chloroform, and tetrachloroethane were obtained from VWR and used as received.

Cellulose Fibers Purification

NaOH treatment: 80 g of Ramie cellulose fibers were purified from impurities and residual hemicellulose through basic treatment. Briefly, fibers were soaked twice in a NaOH solution (4 wt %), first at 80 °C for 2 h and then at 60 °C overnight, under mechanical agitation, washing them with deionized water between the two treatments. Bleached fibers were then rinsed with deionized water until a neutral pH and dried under vacuum at 30 °C.

Cellulose Nanocrystal Preparation and Functionalization: One-Pot Acid Hydrolysis/Fischer Esterification

A total of 10 g of fibers were soaked overnight in the organic acid chosen (lactic or butyric acid). The preparation was carried out at 105 °C under mechanical stirring, adding in a row of water and HCl (Figure 1). HCl concentration was 0.05 M for CNCs_butyrate and 0.07 M for CNCs_lactate. The final solution contained 90 wt % of acid compared to water. The reaction was quenched after 9 h, reaching pH = 5 through water rinses (centrifuge 4000 rpm, 5 min, 10 °C). To recover cellulose nanocrystals, the suspension was mixed for 20 min with an immersion mixer, and subsequently, the opalescent supernatants containing nanocrystals were collected from the following centrifugations and combined to obtain the final water suspension (STEM). Depending on the characterization, a certain amount of suspension was freeze-dried (FT-IR, XRD, TGA, as specified in the Characterization section).

Figure 1

Figure 1. One-pot acid hydrolysis/Fischer esterification method (upper left image); FTIR spectra (upper right graph) and STEM micrographs of unmodified (CNCs_HCl) and modified nanocrystals with different ester moieties (CNCs_butyrate, CNCs_lactate, CNCs_but_lact, bottom image). A similar aspect ratio (13.5 ± 1.5) was calculated for the different CNCs from the morphological analysis on 100 different individualized CNCs. Samples observed in the STEM were directly obtained after the purification step following the synthesis (in water suspention ≈ 1.5 wt %).

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Control Nanocrystals

A total of 10 g of bleached fibers have been soaked in water for one night. The temperature has been increased to 105 °C under reflux and mechanical stirring. Then, HCl 37% has been added slowly to reach a concentration of 2.5 M, and the hydrolysis has been quenched after 1 h by adding DI ice cubes and with the help of an ice bath. The rest of the protocol was the same as for functionalized nanocrystals.

Bionanocomposites Solvent Casting

To boost CNCs dispersion (after the synthesis in water) in the polymer matrix, preventing the irreversible hydrogen bonds formation upon drying (so their aggregation) and degradation during melt processing, CNCs were transferred from water to chloroform through solvent exchange, gently increasing the hydrophobicity of the solvent. In particular, the solvent sequence was water, ethanol, acetone, and finally, chloroform, and their stability was assessed (Supporting Information). PHBV was dissolved in a mixture of chloroform and tetrachloroethane (50:50) for at least 3 h at 70 °C. For each composite, the desired amount of CNCs suspension in chloroform was added to a PHBV solution. The mix was then homogenized through mechanical stirring and sonication. Then it was poured in a glass Petri dish, and a casted film was obtained in an oven at 50 °C, controlling the decreasing of the pressure until 0 mbar to avoid bubble formation. Films were then dried at 50 °C for one night. CNCs wt % was evaluated considering negligible the weight changes due to the surface modification.

Samples for Mechanical Tests

Bars with an average dimension of 2.5 cm × 0.5 cm × 0.45 mm were obtained from the casted films through compression molding at 180 °C.

Characterization

Attenuated total reflectance Fourier transform infrared spectroscopy (FT-IR) was carried out on freeze-dried CNCs using a Bruker Tensor 17 spectrometer. Ultraviolet–visible spectroscopy (UV–vis) was performed on the bionanocomposite films using a spectrophotometer Shimadzu UV-2600 in the wavelength range between 200 and 800 nm. Scanning electron microscopy (SEM) was carried out with the apparatus Hitachi SU8020. CNC morphology was observed in the transmission mode (STEM) on a water suspension of CNCs, recovered after a purification step following the synthesis, and the aspect ratio was calculated from the morphological analysis of 100 different individualized CNCs (the scattering of the data was lower than 5%). Morphological analysis of the bionanocomposites was carried out on a DMTA specimen cross-section obtained by cryofracture in liquid nitrogen. The X-ray diffractometry (XRD) was performed on freeze-dried CNCs by a Panalytical Empirean diffractometer with an area detector operating under Cu Kα (1.5418 Å) radiation (40 kV, 40 mA). The crystallinity was assessed as the areas of the crystalline diffraction peaks to the total area under the curve between 2θ = 10 and 50°. The crystallinity of CNCs and bionanocomposites were determined based on the Rietveld–Ruland approach: (43,44)
where ACR is the area for crystalline peaks and Aam is area for amorphous peaks. The crystallite sizes of 002 lattice planes were estimated by using the Scherrer equation: (24,28)
where Dhkl is the crystallite size in the direction normal to the hkl lattice planes, λ is the radiation wavelength (1.54 Å), and Bhkl is the full width at half-maximum in radians of the corresponding hkl lattice planes.
Solid-state cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C NMR) was evaluated using a single pulse direct polarization experiment on freeze-dried CNCs, and quantitative data of the modifications could be obtained. Comparing the integral of the lactic acid signal L3 at 18 ppm with the total integral of the C4 signal of the CNCs, the lactic acid modification degree of substitution, DS, could be obtained. Similarly, comparing the average integral of the butyric acid signals B2, B3, and B4, with the C4 signal of the CNCs, the butyric acid DS could be obtained. For the samples containing both lactic and butyric acid some overlap of the modification signals was inevitable. To circumvent this, similarly to above but instead only using the well resolved signals B2 and B4, the DS for the butyric acid could be obtained. No lactic acid signal could be integrated without severe overlap from other signals. However, estimating the B3 integral (overlapping with L3) as the average of the integrals for B2 and B4 and then removing this from the combined integral of B3 and L3, the L3 integral could be estimated, hence, giving the lactic acid DS. The obtained DS for all modifications could be seen in Table 1. By studying the CNCs in the wet state, NMR signals corresponding to the accessible surfaces of the CNCs can be distinguished from those on internal inaccessible surfaces. (45) The analysis provided a relative amount of accessible surface signals to be around 11% for all modified CNCs. Knowing the relative amount of accessible surface, the degree of substitution on the surface, DSsurf, could be calculated for all modified CNC samples, as seen in Table 1. Thermogravimetrical analysis was carried out on freeze-dried CNCs and casted films with a TGA Q500 apparatus from T.A. Instruments under a nitrogen flow from r.t. to 800 °C with a step of 20 °C/min. Casted films were analyzed by differential scanning calorimetry (DSC) on a DSC Q2000 apparatus, calibrated with indium from T.A. using aluminum pans and nitrogen atmosphere. Nonisothermal analysis were performed following a heat–cool–heat program from −80 to 190 °C (rate 20 °C/min), with an isotherm of 3 min at 190 °C. Isothermal analysis were performed at 120 °C after an heating ramp until 190 °C with isotherm of 3 min and cooling at 60 °C/min. The crystallinity χDSC of PHBV bionanocomposites was calculated as follows:
where the w(CNCs) is the mass content of CNCs, ΔHm is the measured fusion enthalpy, and ΔH100 is chosen as 146.6 J/g for theoretical fusion enthalpy of 100% crystalline PHBV due to low HV content of PHBV. (31)
Table 1. Crystallinity Index (χNMR) and Degree of Substitution (DS) for All Samplesa
 χNMR (%)DS (%) lactateDS (%) butyrateDSsurf (%) lactateDSsurf (%) butyrate
CNCs_HCl63    
CNCs_lactate593.3 29 
CNCs_butyrate58 1.8 15
CNCs_but_lact582.11.61613
a

For lactic acid modification, DS values were obtained comparing the integral of the lactic acid signal L3 at 18 ppm with the total integral of the C4 signal of the CNC. For the butyric acid, DS values were obtained comparing the average integral of the butyric acid signals B2, B3, and B4, at 32, 15, and 10 ppm, respectively, with the C4 signal of the CNC. The assessed relative amount of accessible surface of about 11%, enabled the estimation of the degree of substitution on the surface, DSsurf.

Half-crystallization time was calculated from isothermal analysis as the time to reach 50% of crystallization peak area. Mechanical performance ofthe bionanocomposites was evaluated by dynamic mechanical thermal analysis (DMTA) on compression molded bars using a DMTA Q800 apparatus (T.A. Instrument) equipped with a single cantilever clamp, in frequency sweep (0.1–10 Hz, 25 °C, strain 0.02%) and temperature sweep (−80 to 100 °C, 2 °C/min, 1 Hz, strain 0.02%).

Results and Discussion

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In order to elaborate PHBV-based bionanocomposites, we propose to surface-modify cellulose nanocrystals using a one-pot acid hydrolysis/Fischer esterification process from butyric acid, lactic acid, and their mixture, (25,37,38) as schematically sketched in Figure 1. For sake of comparison, nonfunctional cellulose nanocrystals were obtained from HCl-hydrolysis. In accordance with our previous studies, (38,39) the morphology of these nanocrystals was similar to a typical needle shape of an average dimension of 260 nm in length and 20 nm in width (Figure 1). The presence of peak centered at around 1730 cm–1 in the FTIR spectra, corresponding to the ester (C═O) stretching, indicates that the Fisher esterification took place simultaneously during the acid hydrolysis. X-ray analyses (Figure S1) confirmed that the typical crystalline structure of cellulose I for the unmodified and modified nanocrystals was maintained after hydrolysis upon these characteristic peaks at 14.6°, 16.3°, 20.3°, and 34°. These correspond to the respective crystalline lattices (1–10), (110), (200), and (400), confirming that the Fischer esterification represents a mild surface-modification method. (38)
The degree of surface substitution (DSsurf) compared to the bulk assessment (DS) and the crystallinity extent (χNMR) of modified and unmodified CNCs was then determined using CP/MAS 13C NMR spectroscopy (Figure 2) and the values are reported in Table 1.

Figure 2

Figure 2. CP/MAS 13C NMR spectrum of CNCs_HCl, CNCs_lactate, CNCs_butyrate, and CNCs_but_lact. Zoom-in of the spectra highlight some of the signals from the modifications. Inset shows the structural formula of the anhydroglucose unit of the CNCs as well as the lactic and butyric acid modifications, with numbered carbons.

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From the CP/MAS 13C NMR spectrum, the surface-modification from butyric and lactic acid was confirmed, following the peaks between 5 and 37 ppm (L3 and B2, B3, and B4), together with the typical peaks of cellulose nanocrystals. The carbonyl carbons, L1 and B1, are not probed effectively with the CP/MAS pulse sequence hence not visible in the spectra (region not shown). In this work, the L2 carbon in the lactate modification was not assigned due to severe overlap with the large cellulose signals; however, the signals have previously been shown to appear around 70 ppm. (46) For the CNCs_butyrate, a small signal at 37 ppm (marked with *, Figure 2) originated from a residual solvent in the sample. The additional spectral features from the wet state analysis enabled the assessment of the accessible surface (about the 11%), (45,47) so allowing to distinguish the bulk from the surface degree of substitution (DS and DSsurf, respectively), obtained using the C4 signal of the CNCs as the reference. For the CNCs_lactate nanocrystals, a degree of surface modification (DS) of 29% in lactate moieties was assessed, while a DS of 15% was estimated for the butyrate ones. The higher acidity of lactid acid could explain its higher reactivity toward the Fisher esterification, although previous studies stated that there is no evident influence of acids strength on the substitution degree. (37,39) For the simultaneous modification, the DS value of both lactic and butyric acid was of 15 and 13%, being slightly lower than the corresponding CNCs_lactate and CNCs_butyrate nanocrystals. This indicates that a certain competition between both acids can occur during the simultaneous surface decoration. The DS values calculated were in line with the relatively low degree of modification required to preserve the CNCs crystallinity, (48) in accordance with the crystallinity index, χNMR (Table 1). The χNMR was calculated by comparing the crystalline and amorphous signals of the C4 carbon in the anhydroglucose unit of CNCs (43,46) (Park, 2010). No significant changes in the crystallinity of the samples for the ester-decorated CNCs could be seen after modification, which is interesting toward reinforcing effect in cellulose-based nanocomposites. (48) The surface modification slightly disturbs the structuring of the unmodified cellulose, as already observed in other studies. (49,50) A slight decrease of the χNMR for the CNC could be seen after modifications, in line with values obtained from previous work. (46,51,52) Harsher modifications have also been shown to render larger changes in the CI values. (53,54) XRD assessment of the crystallinity of the different CNCs showed values in line with the literature (31) and confirmed the CP/MAS 13C NMR analysis while presenting a higher absolute value, as already reported elsewhere. (47)
First attempts were then carried out to see whether these as-modified cellulose nanocrystals can be readily dispersed into PHBV by solvent-casting. Practically speaking and in order to circumvent the difficulty to redisperse freeze-dried CNCs in organic solvents, (23,48) never-dried nanocrystals from solvent exchange to chloroform have been herein investigated, with the goal to obtain near-perfect bionanocomposites from solvent casting. Figure 3 illustrates the quality of the dispersion of CNCs_HCl and functionalized nanocrystals in chloroform. All the ester-modified CNCs showed a similar dispersibility (Figure S3) during the 15 min, as an overestimated time needed for the mixing of the CNCs with the polymer solution. From the visual analysis, it is clear that the ester functionalities of the modified CNCs avoid the aggregation of these nanocrystals in chloroform in contrast to the unreversible agglomeration of the unmodified ones (CNCs_HCl, Figure 3).

Figure 3

Figure 3. Dispersion in chloroform of the unmodified and modified cellulose nanocrystals after 15 min from the mechanical stirring (top image), visual aspect (central image), and UV–vis spectra (bottom image) of bionanocomposites with different amounts and types of CNCs.

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The good stability in chloroform is a key factor to obtain a good dispersion of nanocrystals in a polymer solution during solvent casting. (23,48) Therefore, a content of 2 wt % in CNCs in the bionanocomposites was chosen to evaluate their transparency as casted films (Figure 3, bottom image) as a first evaluation of the near-perfect dispersion quality expected. A 5 wt % CNCs_butyrate-based nanocomposite was also prepared for comparison. The visual aspect of the films showed good transparency and homogeneity for the bionanocomposites containing functionalized CNCs, appearing more transparent than the film made of neat PHBV. In the presence of CNCs_HCl instead, an increased opalescence can be distinguished in the corresponding bionanocomposite film that can be explained, assuming the presence of micrometric agglomerates. (25) The improved dispersion in choroform, therefore, resulted in a uniform transparency of the modified CNCs-based bionanocomposite compared with the unmodified CNCs-based ones, as further confirmed by the UV–vis spectroscopy (Figure 3). The film containing the 2 wt % of CNCs_HCl showed about a 20% decrease in transmittance compared to the neat matrix, while the modified CNCs led to an increase in transmittance of about 14%. This result is in contrast with previous works, showing that the addition into chloroform PHBV solution of 1 wt % of CNCs (modified with formic acid, eventually coupled with silver nanoparticles (25,55)) decreased the transparency of solvent-casted films.
Thermal properties of the bionanocomposites were investigated to assess the nucleating CNCs effect on PHBV (Figure S4 and Tables S3–S5). We must highlight that all modified CNCs showed an improvement in terms of the degradation temperature, especially for lactate-functionalized ones using thermogravimetric analysis under a nitrogen atmosphere (Figure S2). (38) This enhanced thermostability was even noticed in the case of PHBV composites after CNC addition into PHBV, as already observed for similar CNC-based bionanocomposites produced by solvent casting (25) (Figures S4 and S5). From Table 2, the bionanocomposites containing CNCs_butyrate showed an increased Tc (103 °C), compared to the neat PHBV and other bionanocomposites (98 and 99 °C). This is consistent with a more pronounced nucleating effect of the CNCs decorated with butyrate moieties. A more effective nucleation is suggested by the half-crystallization time calculated from the isothermal analysis at 120 °C (Table 2), in the presence of CNCs_butyrate, followed by the other modified CNCs. Indeed, neat PHBV τ1/2 was reduced by more than half in the presence of functionalized nanocrystals, and it was even lower in the case of CNCs_butyrate. These results can be explained by an improved interface and/or an improved dispersion of ester modified CNCs into the PHBV matrix. (56) On the contrary, CNCs_HCl seemed not to have any nucleating effect.
Table 2. Thermal Results of Neat PHBV and Bionanocomposites at 2 wt % of Different CNCsa
 ΔHm (J/g)χDSCb (%)Tc (°C)t1/2@120°Cb (min)χXRDb (%)D121d (nm)D002d (nm)
PHBV88479911568.55.5
PHBV + 2% CNCs_butyrate99501034567.74.3
PHBV + 2% CNCs_lactate8846985468.75.9
PHBV + 2% CNCs_but_lact10251985548.04.9
PHBV + 2% CNCs_HCl83449912538.05.1
a

From the second heating of non-isothermal DSC analysis was assessed ΔHm, χDSC, and Tc, corresponding, respectively, to melting enthalpy, crystallization temperature, and crystallinity. The half-crystallization time t1/2(120°C) has been estimated from the isothermal crystallization at 120 °C. Crystallinity χXRD and the dimension on the direction perpendicular to (121) and (002) crystal faces, D121 and D002, respectively, are calculated from XRD diffractogram.

b

Crystallinity calculated from DSC nonisothermal analysis.

c

Crystallization half-time (t1/2@120°C) calculated from isothermal crystallization at 120 °C.

d

D002 and D121 calculated with Scherrer equation.

The bionanocomposites diffractograms present a typical crystalline peak pattern corresponding to PHBV lattice, (57) further confirming that neither the crystalline characteristics of PHBV nor its average degree of crystallinity were affected by the surface modification (Figure 4 and Table 2). Interestingly, the presence of CNCs and their different surface chemistry seems to affect the crystal dimensions in the case of PHBV. The approximate dimensions were calculated in the direction perpendicular to two different crystalline lattice planes, (121) and (002), applying the Scherrer equation (24,28) (Table 2).

Figure 4

Figure 4. XRD diffractograms of neat PHBV and bionanocomposites at a content of 2 wt % of CNCs with different surface chemistry (left); example of deconvolution of XRD spectra with PeakFit (bionanocomposites containing CNCs_butyrate, right).

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To unravel the effect of the different surface esterification on the structure of PHBV crystals, X-ray diffraction was used.
Further crystallization kinetics studies are under investigation for deeper comprehension about the crystallization and nucleation phenomena occurring in these bionanocomposites, but they are beyond the scope of the current study.
Dynamical mechanical analysis (Figure 5) were carried out to further investigate an eventual correlation between the different surface features related with the different CNCs/PHBV interface and their efficiency toward stress transfer.

Figure 5

Figure 5. Dynamical-thermomechanical properties obtained from DMTA analysis of neat PHBV and bionanocomposites with CNCs with different surface chemistry; (a) Storage moduli and (b) tan δ in temperature sweep analysis (2 °C/min, 1 Hz, 0.02% strain); (c) tan δ in frequency sweep (25 °C, 0.02% strain).

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Before the glass transition (T < Tg), the storage moduli increase for all the bionanocomposites, as a consequence of CNCs addition (Figure 5 a). The highest moduli at lower temperature are shown by the bionanocomposites with CNCs_HCl and CNCs_butyrate. The importance of the interphase came out across the Tg and over, that is the region where the reinforcing effect is more evident since an increasing mobility of the matrix is expected. In particular, across and after the glass transition dynamical mechanical behavior of CNCs_butyrate-based bionanocomposite exhibits a peculiar slow decreasing in the modulus. At −80 °C, its flexural storage modulus is 17% higher than the one of the neat PHBV. At room temperature, its modulus is still the 26% higher than the corresponding modulus of the neat PHBV. Moreover, among the bionanocomposites, this is the only one presenting a shift of Tg from 12 to 17 °C. This is consistent with a more pronounced damping (Figure 5b and Table 3) that indicates a hindered molecular mobility of the matrix at the molecular level, while the Tg values of all the other bionanocomposites are decreasing.
Table 3. Average DMTA Results of Neat PHBV and Bionanocomposites at 2 wt % of Different CNC Typesa
 G′@–80°C (MPa)G′@25°C (MPa)Tgb (°C)Tαb (°C)DFc
PHBV6504381212140.044
PHBV + 2% CNCs_butyrate7612478817190.035
PHBV + 2% CNCs_lactate706732838130.063
PHBV + 2% CNCs_but_lact730934966100.059
PHBV + 2% CNCs_HCl755034075100.060
a

Scattering of the data below 3%.

b

Glass transition, Tg, was calculated from the Loss Modulus peak maximum obtained by a temperature sweep.

c

Damping factor, DF, was calculated as tan δ peak maximum, obtained by a temperature sweep.

A weak interphase can explain this effect, and the tan δ curves obtained from a frequency sweep (Figure 5c) supported this hypothesis: the damping decreased from CNCs_lactate to CNCs_butyrate, demonstrating a reduced mobility of polymer chains caused by the CNCs/PHBV interface and corroborating a depleting interface in the case of the lactate moieties, making the stress transfer detrimental.
Finally, cryofractured samples of the bionanocomposites were observed with a SEM microscope (Figure 6). SEM analysis provided direct evidence to the morphological changes of CNCs/PHBV upon the different CNCs surface chemistry. The morphology of bionanocomposites containing esterified CNCs do not present any evidence of CNCs agglomeration (lower magnification micrographs in Figure 6), in agreement with the higher transmittance recorded by UV–vis spectroscopy, as well as their thermal and mechanical analyses. In contrast, aggregates are clearly visible in the presence of CNCs_HCl (Figure 6b), with micrometric debonding all along the agglomerate/matrix interface, consistent with a worse dispersion already demonstrated and a poor adhesion with the matrix (Figure 6b′).

Figure 6

Figure 6. SEM micrographs after cryofracture of PHBV (a, a′) and of the bionanocomposites at 2 wt % content of differently surface decorated CNCs (b–e′) at two different magnifications (bars 10 μm, left micrographs, and 1 μm, right micrographs).

High Resolution Image
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PHBV showed a typical morphology of a brittle semicrystalline polymer (Figure 6a), with the peculiar presence of micrometric holes (Figure 6a′), as previously observed. (27) In the case of CNCs_butyrate, it is difficult to distinguish individualized CNCs from the matrix (Figure 6c). At higher magnification the interphase CNCs_butyrate/PHBV appear smooth, no pull-out is visible, and bridges connecting the matrix to the nanocrystals are noteworthy remarkable (Figure 6c′), confirming their very good interaction with PHBV. A depleting interface with the PHBV is presented instead by the lactate decorated CNCs. Although well dispersed, this bionanocomposite showed cavities at the interfacial area surrounding the nanocrystals and CNCs pull-outs (Figure 6e′), which indicate a relatively poor interfacial adhesion caused by a lack of interactions like the unmodified CNCs. Interestingly, CNCs_but_lact brought to an intermediate interface morphology, where adhesion and debonding areas are coexisting around nanocrystals. This feature is in line with a patchy functionalized surface.

Conclusions

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Modified CNCs have been successfully obtained through one-pot acid hydrolysis/Fischer esterification approach, without significant changes in the aspect ratio nor affecting the crystallinity of the nanocrystals. Successful unprecedented cofunctionalization has been carried out while synthesizing the CNCs in the presence of two different organic acids that enable the decoration of the CNCs’ surface with two functional moieties.
Bionanocomposites with the different surface-modified nanocrystals were casted from a chloroform/tetrachloroethane mixture to ensure the highest level of CNCs dispersion in the polymer matrix and, thus, to investigate the CNCs/PHBV interface effect on the crystallization behavior of PHBV and on the efficiency of the stress transfer. The optical properties of the bionanocomposites reflected the different degrees of dispersion of modified and unmodified CNCs, already visible in the organic solvent. Surprisingly, modified-CNCs improved PHBV films transparency, a highly important property for future applications.
Thermal and morphological analyses confirmed that CNCs surface modification impacts on PHBV crystallization behavior and on its mechanical properties. The greater effect on the bionanocomposites containing butyrate-modified CNCs, indicated the decoration of the CNCs surface with butyrate moieties as the more suitable for the use of cellulose nanocrystals as nucleating agent for the poly(3-hydroxybutyrate)-co-(3-hydroxyvaleriate).
An improved interphase between butyrate-modified nanocellulose and PHBV, is confirmed by dynamical mechanical analysis. Increased glass transition and dumping highlighted a more efficient stress transfer for this bionanocomposite, even at room temperature. These results show that the suitable surface decoration of the CNCs can hinder the PHBV mobility at the molecular scale so improving the mechanical properties of the bionanocomposite, even at very low CNCs content (2 wt %). Our results show that green chemical modification of nanostructured cellulose is a suitable way to pave the way for broadening the applicability of PHBV bionanocomposites.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.biomac.9b01760.

  • List of acronyms and compositions of prepared bionanocomposites, XRD spectrum, deconvolution of XRD spectrum and crystallinity index (χXRD) of modified and unmodified CNCs, CNCs average length (L) and diameter (D), and related aspect ratio (L/D), TGA and relative derivative DTG curves of modified and unmodified CNCs, evolution during time of functionalized CNCs suspension in chloroform, TGA and relative DTG curves of neat PHBV and composites with 2 and 5 wt % of CNCs_butyrate, thermal properties of neat PHBV and bionanocomposites at 2 and 5 wt % of different type of CNCs, TGA and relative derivative DTG curves of neat PHBV and bionanocomposites with 2 wt % of modified and unmodified CNCs, Flexural storage modulus and glass transition temperature, Tg, obtained from DMTA results (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Chiara Magnani - Laboratory of Polymeric and Composite Materials (LPCM), Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons (UMONS), 23 Place du Parc, B-7000 Mons, Belgium;  Orcidhttp://orcid.org/0000-0003-0858-6264
    • Alexander Idström - Department of Chemistry and Chemical Engineering, Division of Applied Chemistry, Chalmers University of Technology, Kemivägen 4, SE-412 96 Göteborg, Sweden;  Orcidhttp://orcid.org/0000-0003-4765-8224
    • Lars Nordstierna - Department of Chemistry and Chemical Engineering, Division of Applied Chemistry, Chalmers University of Technology, Kemivägen 4, SE-412 96 Göteborg, Sweden;  Wallenberg Wood Science Center (WWSC), KTH Royal Institute of Technology, Teknikringen 56, SE-100 44 Stockholm, Sweden;  Orcidhttp://orcid.org/0000-0002-6580-0610
    • Alejandro J. Müller - POLYMAT and Polymer Science and Technology Department, Faculty of Chemistry, University of the Basque Country UPV/EHU, San Sebastián 20018, Spain;  IKERBASQUE, Basque Foundation for Science, Bilbao, Spain;  Orcidhttp://orcid.org/0000-0001-7009-7715
    • Philippe Dubois - Laboratory of Polymeric and Composite Materials (LPCM), Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons (UMONS), 23 Place du Parc, B-7000 Mons, Belgium;  Orcidhttp://orcid.org/0000-0003-1534-1564
    • Jean-Marie Raquez - Laboratory of Polymeric and Composite Materials (LPCM), Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons (UMONS), 23 Place du Parc, B-7000 Mons, Belgium;  Orcidhttp://orcid.org/0000-0003-1940-7129
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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G.L.R. acknowledges the Chalmers Areas of Advance, Genie and KAW Biocomposites No. V-2019-0041 for financial support. Funding from the Region Wallon and European Comission in the frame of the ARC 2017–2021 Program (PHASYN Project) and from European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement No. 778092 are gratefully acknowledged. The solid state NMR experiments were carried out at the Swedish NMR Centre in Gothenburg, Sweden.

References

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    Polymer Testing (2016), 56 (), 45-53CODEN: POTEDZ; ISSN:0142-9418. (Elsevier Ltd.)
    Poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV) is a promising bio-based, biodegradable polymer for replacing synthetic polymers, but its brittleness limits its application range. With the aim of improving the mech. properties of PHBV films, different plasticizers (polyethylene glycol (PEG 200, 1000 and 4000), lauric acid (LA) and stearic acid (SA)) were incorporated into the film formulation at 10 wt%. All plasticized films showed lower melting temp. and crystn. degree than pure PHBV films. All plasticizers, except SA, reduced film stiffness and resistance to break, and increased the films' water sorption capacity and soly. as well as their water vapor permeability, but only PEG1000 yielded more extensible films. PEG1000 and PEG4000 gave rise to the most heat-resistant plasticized films, while LA and SA highly promoted the heat-sensitivity of PHBV. PEG1000 was the most effective at plasticizing PHBV films, and it was the only plasticizer that partially mitigated the ageing effects. However, a greater ratio of plasticizer would be required to adapt PHBV mech. properties to some packaging requirements.
  19. 19
    Jost, V.; Langowski, H. C. Effect of Different Plasticisers on the Mechanical and Barrier Properties of Extruded Cast PHBV Films. Eur. Polym. J. 2015, 68, 302– 312,  DOI: 10.1016/j.eurpolymj.2015.04.012
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    Effect of different plasticizers on the mechanical and barrier properties of extruded cast PHBV films
    Jost, Verena; Langowski, Horst-Christian
    European Polymer Journal (2015), 68 (), 302-312CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
    PHAs are gaining interest as biobased and biodegradable thermoplastics as an alternative for conventional polymers. However applications still struggle with the high brittleness of these polymers. In this study PHBV was plasticised by different types and concns. of plasticisers in order to improve flexibility and elongation. Thereby an evaluation of the effectiveness of the selected plasticisers, which differ in their mol. wt. and functional groups, is enabled. Those are propylene glycol, glycerol, tri-Et citrate, castor oil, epoxidised soybean oil and polyethylene glycol. The results of an increasing plasticiser concn. show a decreasing melting temp., increasing crystallinity, a decreasing Young's Modulus and tensile strength as well as an increasing elongation at break. The water vapor and oxygen permeability is increased by all plasticisers but to a different extent. Overall the effectiveness of tri-Et citrate and polyethylene glycol in PHBV showed the most promising results within thermal, mech. and permeative characterization.
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    Kelly, C. A.; Fitzgerald, A. V. L.; Jenkins, M. J. Control of the Secondary Crystallisation Process in Poly(Hydroxybutyrate-Co-Hydroxyvalerate) through the Incorporation of Poly(Ethylene Glycol). Polym. Degrad. Stab. 2018, 148, 67– 74,  DOI: 10.1016/j.polymdegradstab.2018.01.003
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    Control of the secondary crystallisation process in poly(hydroxybutyrate-co-hydroxyvalerate) through the incorporation of poly(ethylene glycol)
    Kelly, Catherine A.; Fitzgerald, Annabel V. L.; Jenkins, Mike J.
    Polymer Degradation and Stability (2018), 148 (), 67-74CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    Poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-co-HV) is a sustainable and biodegradable polymer, but as a potential packaging material, it suffers from a narrow processing window and embrittlement over time due to secondary crystn. This study aims to extend previous research by exploring the effect of the addn. of poly(ethylene glycol) (PEG), in a range of mol. wts. and compns., on the rate of embrittlement. On blending, it was apparent that there was a redn. in both the m.p. (of up to 7°C) and the melt viscosity. Furthermore, there was a redn. in both the modulus and tensile strength indicating that PEG acts as an effective plasticiser in PHB-co-HV. In terms of the secondary crystn. process, the addn. of PEG could not prevent the process from occurring, only hinder it. PEG 600 in relatively high concns. was found to be the most effective in this regard with a 53% redn. in the change in Young's modulus compared to pure PHB-co-HV. This observation, together with the m.p. redn. which extends the processing window for PHB-co-HV, makes PEG a worthwhile additive to an otherwise fundamentally brittle polymer.
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    Zhu, C.; Nomura, C. T.; Perrotta, J. A.; Stipanovic, A. J.; Nakas, J. P. The Effect of Nucleating Agents on Physical Properties of Poly-3-Hydroxybutyrate (PHB) and Poly-3-Hydroxybutyrate-Co-3-Hydroxyvalerate (PHB-Co-HV) Produced by Burkholderia Cepacia ATCC 17759. Polym. Test. 2012, 31, 579– 585,  DOI: 10.1016/j.polymertesting.2012.03.004
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    The effect of nucleating agents on physical properties of poly-3-hydroxybutyrate (PHB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHB-co-HV) produced by Burkholderia cepacia ATCC 17759
    Zhu, Chengjun; Nomura, Christopher T.; Perrotta, Joseph A.; Stipanovic, Arthur J.; Nakas, James P.
    Polymer Testing (2012), 31 (5), 579-585CODEN: POTEDZ; ISSN:0142-9418. (Elsevier Ltd.)
    In the absence of nucleating agents, polyhydroxyalkanoates (PHAs) generally exhibit slow crystn. rates which make them less favorable for injection molding purposes. The copolymer, PHB-co-HV (poly-3-hydroxybutyrate-co-3-hydroxyvalerate), exhibited increased Tc as compared to the homopolymer PHB (poly-3-hydroxybutyrate). Increasing the mol. fraction of HV monomer in the PHB-co-HV initially led to a decrease in the Tm of the copolymer from 175.4 °C to a min. of 168.5 °C, at 20 mol% of HV and, subsequently, increased in PHB-co-HV copolymers with higher fractions of HV, indicating a typical isodimorphic relationship. Two nucleating agents, heptane dicarboxylic deriv. HPN-68L and ULTRATALC 609, were tested to increase the Tc and reduce the time for crystn. necessary for injection molding. HPN-68L decreased the Tdecomp of the homopolymer and all copolymers by almost 50 °C. However, the use of ULTRATALC609 as a nucleating agent slightly enhanced the Tdecomp and had negligible effect on the Tms of all polymers. Also, PHB and PHB-co-HV with 5% (wt./wt.) talc exhibited higher Tc than polymers without ULTRATALC609. A careful comparison of Tc, Tm and Tdecomp, for PHB-co-HV with 20 mol% of HV indicated that this copolymer is the best option for injection molding, with both a high Tdecomp and more rapid crystn.
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    Whitehouse, R. S.; Padwa, A. R. Nucleating Agents for Polyhydroxyalkanoates. U.S. Patent 847023, July 16, 2013.
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    Habibi, Y.; Lucia, L. A.; Rojas, O. J. Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications. Chem. Rev. 2010, 110, 3479– 3500,  DOI: 10.1021/cr900339w
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    Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications
    Habibi, Youssef; Lucia, Lucian A.; Rojas, Orlando J.
    Chemical Reviews (Washington, DC, United States) (2010), 110 (6), 3479-3500CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review discussing chem. and phys. features of the most dominant fundamental building block in the biosphere, cellulose nanocrystals. A brief introduction to cellulose was followed by the discussion of morphol., chem., including prepn. and chem. routes for functionalization, and self-assembly in various media under various conditions, and applications in the nanocomposites.
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    Ten, E.; Turtle, J.; Bahr, D.; Jiang, L.; Wolcott, M. Thermal and Mechanical Properties of Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate)/Cellulose Nanowhiskers Composites. Polymer 2010, 51, 2652– 2660,  DOI: 10.1016/j.polymer.2010.04.007
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    Thermal and mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhiskers composites
    Ten, Elena; Turtle, Joel; Bahr, David; Jiang, Long; Wolcott, Michael
    Polymer (2010), 51 (12), 2652-2660CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    Bacterial polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was reinforced with cellulose nanowhiskers (CNW) in 1-5% concns. using a solvent casting method. The CNW was prepd. from microcryst. cellulose (MCC) using sulfuric acid hydrolysis. The influence of CNW on the PHBV crystn., thermal, dynamic mech. and mech. properties were evaluated using polarized optical microscope (POM), differential scanning calorimeter (DSC), dynamic mech. anal. (DMA), tensile and bulge tests, resp. POM test results demonstrated that CNW was an effective PHBV nucleation agent. Tensile strength, Young's modulus and toughness of PHBV increased with the increasing concn. of CNW. DMA results showed an increased tan δ peak temp. and broadened transition peak, indicating restrained PHBV mol. mobility in the vicinity of the CNW surface. Storage modulus of the PHBV also increased with the addn. of CNW, esp. at the temps. higher than the PHBV glass transition temp. These results indicated that the CNW could substantially increase the mech. properties of PHBV and this increase could be attributed to the strong interactions between these two phases.
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    Yu, H.; Yan, C.; Yao, J. Fully Biodegradable Food Packaging Materials Based on Functionalized Cellulose Nanocrystals/Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate) Nanocomposites. RSC Adv. 2014, 4, 59792– 59802,  DOI: 10.1039/C4RA12691B
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    Fully biodegradable food packaging materials based on functionalized cellulose nanocrystals/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nanocomposites
    Yu, Houyong; Yan, Chenfeng; Yao, Juming
    RSC Advances (2014), 4 (104), 59792-59802CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    Current packaging materials (mainly composed of petroleum-based synthetic polymers) face environmental and disposal issues, and as a result, developing eco-friendly and bio-based nanocomposites as alternatives have motivated academic and industrial research. We report here on our effort to develop a transparent nanocomposite-based packaging film comprised of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and functionalized cellulose nanocrystals (cellulose nanocrystal Me ester, CNC-me). The resultant CNC-me with hydrophobic ester groups are uniformly dispersed in PHBV without the aid of a compatibilizer or surfactant. Therefore, both the crystn. temp. and crystallinity of the PHBV matrix were increased due to the heterogeneous nucleating effect of CNC-me. With an increase of CNC-me concn., significant improvements in mech. performance, thermal stability, barrier and migration properties were achieved, which were ascribed to the improved interfacial interaction and increased crystallinity. Compared to neat PHBV, the tensile strength and max. decompn. temp. (Tmax) of the nanocomposites all achieved their max. values at loading levels of 20 wt% CNC-me. Meanwhile the overall migration levels in both non-polar and polar simulants were well below the limits required by the current legislative stds. for food packaging materials.
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    Malmir, S.; Montero, B.; Rico, M.; Barral, L.; Bouza, R.; Farrag, Y. PHBV/CNC Bionanocomposites Processed by Extrusion: Structural Characterization and Properties. Polym. Compos. 2019, 40, E275– E284,  DOI: 10.1002/pc.24634
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    PHBV/CNC bionanocomposites processed by extrusion: Structural characterization and properties
    Malmir, Sara; Montero, Belen; Rico, Maite; Barral, Luis; Bouza, Rebeca; Farrag, Yousof
    Polymer Composites (2019), 40 (S1), E275-E284CODEN: PCOMDI; ISSN:0272-8397. (John Wiley & Sons, Inc.)
    Bionanocomposites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with cellulose nanocrystals (CNC) were processed by extrusion. Differential scanning calorimetry showed that with increasing the amt. of CNC the overall crystn. time was reduced. Wide angle X-ray scattering showed diffraction peaks of orthorhombic α- type cryst. structure and confirmed the nucleating agent effect of CNC particles in the PHBV matrix. Small angle X-ray scattering showed that the reducing rate of long spacing was slower in the filled sample than in PHBV. Microscopy images (SEM and TEM) revealed well-dispersed morphol. in low loading of the filler while slight agglomerations appeared at higher filler concn. Statistical anal. was done by applying a one-way ANOVA (α = 0.05) to evaluate the effect of filler on mech. properties of PHBV. Water vapor, oxygen and carbon dioxide transmission rate showed that the incorporation of CNC nanocrystals led to an improvement in the barrier properties of the bionanocomposites due to higher crystallinity and more tortuosity in their morphologies.
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    Malmir, S.; Montero, B.; Rico, M.; Barral, L.; Bouza, R. Morphology, Thermal and Barrier Properties of Biodegradable Films of Poly (3-Hydroxybutyrate-Co-3-Hydroxyvalerate) Containing Cellulose Nanocrystals. Composites, Part A 2017, 93, 41– 48,  DOI: 10.1016/j.compositesa.2016.11.011
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    Morphology, thermal and barrier properties of biodegradable films of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) containing cellulose nanocrystals
    Malmir, Sara; Montero, Belen; Rico, Maite; Barral, Luis; Bouza, Rebeca
    Composites, Part A: Applied Science and Manufacturing (2017), 93 (), 41-48CODEN: CASMFJ; ISSN:1359-835X. (Elsevier Ltd.)
    Solvent casting method was used to prep. biodegradable films of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) with cellulose nanocrystals (CNC). Nucleating effect of cellulose nanoparticles was confirmed with DSC and POM tests while WAXS patterns showed that the cryst. structure of bionanocomposites was not changed. POM images showed that smaller spherulites were formed with higher rate and quantity in the samples with CNC compared to neat polymer. TEM images illustrated that CNC nanoparticles were well dispersed in the films up to 4 wt.% of CNC. SEM results exhibited significant redn. in the porosity of the matrix with addn. of CNC up to 4 wt.%. More surface roughness for bionanocomposites was obsd. in AFM images compared to unfilled matrix. Moreover, nanocomposites with 4 wt.% of CNC exhibited better barrier properties against water vapor and oxygen up to approx. four times more than neat PHBV. These biodegradable nanocomposites could be a good alternative for synthetic plastic packaging materials.
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    Yu, H. Y.; Qin, Z. Y.; Liu, L.; Yang, X. G.; Zhou, Y.; Yao, J. M. Comparison of the Reinforcing Effects for Cellulose Nanocrystals Obtained by Sulfuric and Hydrochloric Acid Hydrolysis on the Mechanical and Thermal Properties of Bacterial Polyester. Compos. Sci. Technol. 2013, 87, 22– 28,  DOI: 10.1016/j.compscitech.2013.07.024
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    28
    Comparison of the reinforcing effects for cellulose nanocrystals obtained by sulfuric and hydrochloric acid hydrolysis on the mechanical and thermal properties of bacterial polyester
    Yu, Hou-Yong; Qin, Zong-Yi; Liu, Lin; Yang, Xiao-Gang; Zhou, Ying; Yao, Ju-Ming
    Composites Science and Technology (2013), 87 (), 22-28CODEN: CSTCEH; ISSN:0266-3538. (Elsevier Ltd.)
    Two kinds of cellulose nanocrystals (CNCs) obtained by sulfuric acid hydrolysis (CNC-S) and hydrochloric acid hydrolysis under hydrothermal condition (CNC-H) were used as org. nanoreinforcment to enhance the mech. property and thermal stability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Comparison of the reinforcing effects for different CNCs on the properties of PHBV was carried out. Compared to CNC-S, CNC-H exhibited the larger aspect ratio, higher crystallinity, and esp. no residual acid groups. Moreover, better dispersion of CNC-H with larger loading contents could be introduced into PHBV matrix, which was beneficial to form more intermol. hydrogen bonding interactions, leading to the formation of refined crystal structure of PHBV although the crystn. rate was promoted due to stronger reinforcing effects of CNC-H. Therefore, at the same contents, the reinforcing effect of CNC-H was stronger than CNC-S. More importantly, compared to the neat PHBV, the tensile strength and Young's modulus of the nanocomposite with 12 wt.% CNC-H were enhanced by 175% and 300%, resp., meanwhile the initial decompn. temp. (T0) and max. decompn. temp (Tmax) were increased by 58.1 and 52.1°, resp.
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    Jun, D.; Guomin, Z.; Mingzhu, P.; Leilei, Z.; Dagang, L.; Rui, Z. Crystallization and Mechanical Properties of Reinforced PHBV Composites Using Melt Compounding: Effect of CNCs and CNFs. Carbohydr. Polym. 2017, 168, 255– 262,  DOI: 10.1016/j.carbpol.2017.03.076
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    Crystallization and mechanical properties of reinforced PHBV composites using melt compounding: Effect of CNCs and CNFs
    Jun Du; Guomin Zhao; Leilei Zhuang; Dagang Li; Mingzhu Pan; Rui Zhang
    Carbohydrate polymers (2017), 168 (), 255-262 ISSN:.
    Nanocellulose reinforced poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) composites were prepared using melt compounding. The effects of nanocellulose types (CNCs and CNFs) and nanocellulose content (1, 2, 3, 4, 5, 6 and 7wt%) on the crystallization, thermal and mechanical properties of PHBV composites were systematically compared in this study. The thermal stability of PHBV composites was improved by both CNCs and CNFs. CNFs with a higher thermal stability leaded to a higher thermal stability of PHBV composites. Both CNCs and CNFs induced a reduction in the crystalline size of PHBV spherulites. Furthermore, CNCs could act as a better nucleating agent for PHBV than did CNFs. CNCs and CNFs showed reinforcing effects in PHBV composites. At the equivalent content of nanocellulose, CNCs led to a higher tensile modulus of PHBV composites than did CNFs. 1wt% CNCs/PHBV composites exhibited the most optimum mechanical properties.
  30. 30
    Jiang, L.; Morelius, E.; Zhang, J.; Wolcott, M.; Holbery, J. Study of the Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate)/Cellulose Nanowhisker Composites Prepared by Solution Casting and Melt Processing. J. Compos. Mater. 2008, 42, 2629– 2645,  DOI: 10.1177/0021998308096327
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    Study of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhisker composites prepared by solution casting and melt processing
    Jiang, Long; Morelius, Erving; Zhang, Jinwen; Wolcott, Michael; Holbery, James
    Journal of Composite Materials (2008), 42 (24), 2629-2645CODEN: JCOMBI; ISSN:0021-9983. (Sage Publications Ltd.)
    In this study cellulose nanowhiskers (CNW) were prepd. by sulfuric acid hydrolysis from microcryst. cellulose (MCC). The biopolymer composites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/CNW, was fabricated by soln. casting using N,N-dimethylformamide (DMF) as the solvent. Homogeneous dispersion of the whiskers was achieved and the composites exhibited improved tensile strength and modulus and increased glass transition temp. The melt processing (extrusion and injection molding) of PHBV/CNW composites was also attempted. Despite using polyethylene glycol (PEG) as a compatibilizer, CNW agglomerates formed during freeze-drying could not be broken and well dispersed by the extrusion process due to the large surface area and the polar nature of CNW. As a result, the melt processed PHBV/CNW composites exhibited decreased strength and const. glass transition temp., a typical trend of microparticle filled polymer systems. MCC was also treated by high-speed mech. homogenizer to reduce its particle size down to nanoscale range. The homogenized MCC (HMCC) was blended with PHBV by melt processing with the same conditions. The obtained composites were found to have similar properties as the melt-processed PHBV/CNW composites due to poor HMCC dispersion. To the best of our knowledge, PHBV/CNW system has not been studied so far. The treatment of MCC with high-speed homogenizer has also not been reported. This study augments the research on CNW nanocomposites.
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    Yu, H. Y.; Yao, J. M. Reinforcing Properties of Bacterial Polyester with Different Cellulose Nanocrystals via Modulating Hydrogen Bonds. Compos. Sci. Technol. 2016, 136, 53– 60,  DOI: 10.1016/j.compscitech.2016.10.004
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    Reinforcing properties of bacterial polyester with different cellulose nanocrystals via modulating hydrogen bonds
    Yu, Hou-Yong; Yao, Ju-Ming
    Composites Science and Technology (2016), 136 (), 53-60CODEN: CSTCEH; ISSN:0266-3538. (Elsevier Ltd.)
    This work provides a direct evidence to investigate relationship between hydrogen bonding interactions and property enhancement of cellulose nanocrystals (CN) based bionanocomposites. Cellulose nanocrystal citrates (CN-C) with more hydroxyl (O-H) and carboxyl groups, CN and cellulose nanocrystal formates (CN-F) with less O-H groups were extd. from com. microcryst. cellulose using citric/hydrochloric acids, hydrochloric acid and formic/hydrochloric acids, resp. Then different nanocrystals were incorporated into bacterial polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) for tuning hydrogen bonding interactions and properties of PHBV nanocomposites. As expected, at the same loading contents, CN-C had stronger reinforcing capability on PHBV matrix than CN and CN-F. Compared to neat PHBV, tensile strengths of 10% CN-F/PHBV, 10% CN/PHBV and 10% CN-C/PHBV were improved by 146%, 166% and 187%, resp. Esp., the max. decompn. temp. of 10% CN-C/PHBV was increased by 48.1°C, and this nanocomposite showed superior barrier properties with a 64% redn. in water vapor permeability (WVP). Besides, the nanocomposites showed excellent biocompatibility to human MG-63 cells and lower overall migration levels. Such an outstanding reinforcement by CN-C was ascribed to improved interfacial interaction (more hydrogen bonding interactions or hydrogen bond network), and nanodispersibility in the nanocomposites.
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    Habibi, Y.; Goffin, A. L.; Schiltz, N.; Duquesne, E.; Dubois, P.; Dufresne, A. Bionanocomposites Based on Poly(ε-Caprolactone)-Grafted Cellulose Nanocrystals by Ring-Opening Polymerization. J. Mater. Chem. 2008, 18, 5002– 5010,  DOI: 10.1039/b809212e
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    Bionanocomposites based on poly(ε-caprolactone)-grafted cellulose nanocrystals by ring-opening polymerization
    Habibi, Youssef; Goffin, Anne-Lise; Schiltz, Nancy; Duquesne, Emmanuel; Dubois, Philippe; Dufresne, Alain
    Journal of Materials Chemistry (2008), 18 (41), 5002-5010CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
    A 'grafting from' approach was used to graft poly(.vepsiln.-caprolactone) (PCL) polymers to cellulose nanocrystals by Sn(Oct)2-catalyzed ring-opening polymn. (ROP). The grafting efficiency was evidenced by the long-term stability of suspension of PCL-grafted cellulose nanocrystals in toluene. These observations were confirmed by Fourier Transform IR Spectroscopy (FT-IR) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). Extd. nanohybrids were characterized by Differential Scanning Calorimetry (DSC), XPS, and contact angle measurements. The morphol. and cryst. structure of the PCL-grafted cellulose nanocrystals was examd. by transmission electron microscopy (TEM) and X-Ray diffraction, resp. Results showed that cellulose nanocrystals kept their initial morphol. integrity and their native crystallinity. Nanocomposites with high content of cellulose nanocrystals were prepd. using either neat cellulose nanocrystals or PCL-grafted cellulose nanocrystals and high mol. wt. PCL as matrix using a casting/evapn. technique. Thermo-mech. properties of processed nanocomposites were studied by DSC, dynamical mech. analyses (DMA) and tensile tests. A significant improvement in terms of Young's modulus and storage modulus was obtained.
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    Habibi, Y. Key Advances in the Chemical Modification of Nanocelluloses. Chem. Soc. Rev. 2014, 43, 1519– 1542,  DOI: 10.1039/C3CS60204D
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    Key advances in the chemical modification of nanocelluloses
    Habibi, Youssef
    Chemical Society Reviews (2014), 43 (5), 1519-1542CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Nanocelluloses, including nanocryst. cellulose, nanofibrillated cellulose and bacterial cellulose nanofibers, have become fascinating building blocks for the design of new biomaterials. Derived from the must abundant and renewable biopolymer, they are drawing a tremendous level of attention, which certainly will continue to grow in the future driven by the sustainability trend. This growing interest is related to their unsurpassed quintessential phys. and chem. properties. Yet, owing to their hydrophilic nature, their utilization is restricted to applications involving hydrophilic or polar media, which limits their exploitation. With the presence of a large no. of chem. functionalities within their structure, these building blocks provide a unique platform for significant surface modification through various chemistries. These chem. modifications are prerequisite, sometimes unavoidable, to adapt the interfacial properties of nanocellulose substrates or adjust their hydrophilic-hydrophobic balance. Therefore, various chemistries have been developed aiming to surface-modify these nano-sized substrates in order to confer to them specific properties, extending therefore their use to highly sophisticated applications. This review collocates current knowledge in the research and development of nanocelluloses and emphasizes more particularly on the chem. modification routes developed so far for their functionalization.
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    Lin, N.; Huang, J.; Chang, P. R.; Feng, J.; Yu, J. Surface Acetylation of Cellulose Nanocrystal and Its Reinforcing Function in Poly(Lactic Acid). Carbohydr. Polym. 2011, 83, 1834– 1842,  DOI: 10.1016/j.carbpol.2010.10.047
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    Surface acetylation of cellulose nanocrystal and its reinforcing function in poly(lactic acid)
    Lin, Ning; Huang, Jin; Chang, Peter R.; Feng, Jiwen; Yu, Jiahui
    Carbohydrate Polymers (2011), 83 (4), 1834-1842CODEN: CAPOD8; ISSN:0144-8617. (Elsevier Ltd.)
    A novel and facile method for surface acetylation of cellulose nanocrystals (CN) was developed by reaction with acetic anhydride and hydroxyl groups on the surface of CN. The resultant acetylated cellulose nanocrystals (ACN) exhibited improved dispersion in various org. solvents and reduced polarity as compared with unmodified CN. These ACN were subsequently introduced into a poly(lactic acid) (PLA) polymeric matrix to produce fully biodegradable nanocomposites, which showed superior mech. performance and thermal stability. This improvement was primarily attributed to uniform dispersion of the ACN and to strong interfacial adhesion between filler and matrix. This high performance and eco-friendly nanocomposite will expand the utilization of cellulose nanocrystals from renewable bioresources and the practical application of PLA-based plastic.
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    Yu, H. Y.; Qin, Z. Y.; Yan, C. F.; Yao, J. M. Green Nanocomposites Based on Functionalized Cellulose Nanocrystals: A Study on the Relationship between Interfacial Interaction and Property Enhancement. ACS Sustainable Chem. Eng. 2014, 2, 875– 886,  DOI: 10.1021/sc400499g
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    Green Nanocomposites Based on Functionalized Cellulose Nanocrystals: A Study on the Relationship between Interfacial Interaction and Property Enhancement
    Yu, Hou-Yong; Qin, Zong-Yi; Yan, Chen-Feng; Yao, Ju-Ming
    ACS Sustainable Chemistry & Engineering (2014), 2 (4), 875-886CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
    Functionalized cellulose nanocrystals (PHCNs) were synthesized by grafting poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) onto cellulose nanocrystals (CNCs). The resultant PHCNs with high loading levels were uniformly dispersed into a PHBV matrix to produce fully biodegradable nanocomposites, which showed superior mech. performance and thermal stability. Compared with those of neat PHBV, the tensile strength, Young's modulus, and elongation at break of the nanocomposites with 20 wt. % PHCNs were enhanced by 113%, 95%, and 17%, resp. Meanwhile, the initial decompn. temp. (T0), temp. at 5% wt. loss (T5%), max. decompn. temp. (Tmax), and complete decompn. temp. (Tf) increased by 29.6, 23.9, 34.7, and 37.0 °C, resp. This improvement was primarily ascribed to uniform dispersion of the PHCNs and to strong interfacial adhesion between filler and matrix due to the chain entanglements, cocrystn., and hydrogen bonding interactions. Moreover, the nanocomposites showed a wider melt-processing window than neat PHBV. Furthermore, the crystallinity and hydrophilic properties of the nanocomposites could be modulated through with the increase of the PHCN contents. In addn., the nanocomposites were nontoxic to human MG-63 cells. Such high performance bionanocomposites have great potential in expanding the utilization of CNCs from natural resources and practical application as PHBV-based bioplastic and biomedical materials.
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    Zhang, J.; Li, M.-C.; Zhang, X.; Ren, S.; Dong, L.; Lee, S.; Cheng, H. N.; Lei, T.; Wu, Q. Surface Modified Cellulose Nanocrystals for Tailoring Interfacial Miscibility and Microphase Separation of Polymer Nanocomposites. Cellulose 2019, 26, 4301– 4312,  DOI: 10.1007/s10570-019-02379-z
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    Surface modified cellulose nanocrystals for tailoring interfacial miscibility and microphase separation of polymer nanocomposites
    Zhang, Jinlong; Li, Mei-Chun; Zhang, Xiuqiang; Ren, Suxia; Dong, Lili; Lee, Sunyoung; Cheng, H. N.; Lei, Tingzhou; Wu, Qinglin
    Cellulose (Dordrecht, Netherlands) (2019), 26 (7), 4301-4312CODEN: CELLE8; ISSN:0969-0239. (Springer)
    High performance nanocomposites with good interfacial miscibility and phase sepd. morphol. have received a lot of attention. In this work, cellulose nanocrystals (CNCs) were first grafted with hydrophobic poly(Me methacrylate) (PMMA) chains to produce modified CNCs (PMCNCs) with increased thermal stability. Such surface-tailored CNCs effectively influenced the phase morphol. and improved the mech. properties of poly(Bu acrylate-co-MMA) (PBA-co-PMMA) nanocomposites. Morphol. anal. indicated the presence of microphase sepn. in PMCNCs/PBA-co-PMMA nanocomposites with PBA as the soft domain and PMMA as well as CNCs as the hard domain. The nanocomposites with 10 wt% PMCNCs/PBA-co-PMMA showed increases in Young's modulus of more than 20-fold and in tensile strength of about 3-fold compared to those of the unmodified PBA-co-PMMA copolymer. Therefore, the PMCNCs played a crucial role in controlling the interfacial miscibility and tuning the phase morphol. of the nanocomposites. It is also essential to understand the role played by microphase sepn. in achieving nano-scaled morphol. control and in fine-tuning the resultant composite properties.
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    Braun, B.; Dorgan, J. R. Single-Step Method for the Isolation and Surface Functionalization of Cellulosic Nanowhiskers. Biomacromolecules 2009, 10, 334– 341,  DOI: 10.1021/bm8011117
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    Single-Step Method for the Isolation and Surface Functionalization of Cellulosic Nanowhiskers
    Braun, Birgit; Dorgan, John R.
    Biomacromolecules (2009), 10 (2), 334-341CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)
    Surface modification of cellulosic nanowhiskers (CNW) is of great interest, esp. to facilitate their use as polymer reinforcements. Generally, alteration of the surface chem. is performed using multiple reaction steps. In contrast, this study demonstrates that the needed hydrolysis of amorphous cellulose chains can be performed simultaneously with the esterification of accessible hydroxyl groups to produce surface functionalized CNW in a single step. The reaction is carried out in an acid mixt. composed of hydrochloric and an org. acid (acetic and butyric are both demonstrated). Resulting CNW are of similar dimensions compared to those obtained by hydrochloric acid hydrolysis alone; sizes are verified by multiangle laser-light scattering and transmission electron microscopy. However, narrower diam. polydispersity indexes indicate that surface groups aid the individualization of the nanowhiskers (Px = 2.5 and 2.1 for acetic and butyric acid, Px = 3.0 for hydrochloric acid). More than half of the hydroxyl groups located on the CNW surface are substituted under the employed reaction conditions as detd. by quant. Fourier-transform IR-spectroscopy. The resulting surface modified CNW are dispersible in Et acetate and toluene indicating increased hydrophobicity and thus are presumably more compatible with hydrophobic polymers when used as a reinforcing phase.
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    Spinella, S.; Lo Re, G.; Liu, B.; Dorgan, J.; Habibi, Y.; Leclère, P.; Raquez, J. M.; Dubois, P.; Gross, R. A. Polylactide/Cellulose Nanocrystal Nanocomposites: Efficient Routes for Nanofiber Modification and Effects of Nanofiber Chemistry on PLA Reinforcement. Polymer 2015, 65, 9– 17,  DOI: 10.1016/j.polymer.2015.02.048
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    Polylactide/cellulose nanocrystal nanocomposites: Efficient routes for nanofiber modification and effects of nanofiber chemistry on PLA reinforcement
    Spinella, Stephen; Lo Re, Giada; Liu, Bo; Dorgan, John; Habibi, Youssef; Leclere, Philippe; Raquez, Jean-Marie; Dubois, Philippe; Gross, Richard A.
    Polymer (2015), 65 (), 9-17CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    To improve the Heat Deflection Temp. of polylactide (PLA), nanocomposites were prepd. with modified cellulose nanocrystals (CNCs) by melt blending. The prepn. of acetate and lactate modified CNCs (AA- and LA-CNCs) was performed by a green one-pot dual acid (org. acid and HCl) method such that acid hydrolysis and Fischer Esterification occur in tandem. The degree of substitution for AA-CNCs and LA-CNCs, detd. by FTIR, are 0.12 and 0.13, resp. Relative to unmodified CNCs, esterification of CNC surfaces with lactate and acetate moieties resulted in a 40 °C increase in thermal stability. At 5 wt% loading of CNCs, LA-CNCs gave superior reinforcement below and above the glass temp. of PLA, corresponding to a 31% and 450% increase in PLA's storage modulus compared to neat PLA. An increase in PLA's heat deflection temp. by 10 °C and 20 °C was achieved by melt-blending PLA with 5 and 20% LA-CNCs, resp. The above studies provide indirect evidence that LA-CNCs were best dispersed (lowest tendency to aggregate) in the PLA matrix. This hypothesis was confirmed through direct visualization using AFM. Thus, a simple modification strategy for CNCs was devised that enables the formation of PLA nanocomposites with high extents of nanofiber dispersion within the matrix. Furthermore, the dispersion of CNCs in PLA matrixes is profoundly influenced by relatively small changes in the modification chem., in this case, appending lactate vs. acetate groups.
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    Spinella, S.; Maiorana, A.; Qian, Q.; Dawson, N. J.; Hepworth, V.; McCallum, S. A.; Ganesh, M.; Singer, K. D.; Gross, R. A. Concurrent Cellulose Hydrolysis and Esterification to Prepare Surface-Modified Cellulose Nanocrystal Decorated with Carboxylic Acid Moieties. ACS Sustainable Chem. Eng. 2016, 4, 1538– 1550,  DOI: 10.1021/acssuschemeng.5b01489
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    Concurrent Cellulose Hydrolysis and Esterification to Prepare a Surface-Modified Cellulose Nanocrystal Decorated with Carboxylic Acid Moieties
    Spinella, Stephen; Maiorana, Anthony; Qian, Qian; Dawson, Nathan J.; Hepworth, Victoria; McCallum, Scott A.; Ganesh, Manoj; Singer, Kenneth D.; Gross, Richard A.
    ACS Sustainable Chemistry & Engineering (2016), 4 (3), 1538-1550CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
    Cellulose nanocrystals (CNCs) were modified with natural di- and tricarboxylic acids using two concurrent acid-catalyzed reactions including hydrolysis of amorphous cellulose segments and Fischer esterification, resulting in the introduction of free carboxylic acid functionality onto CNC surfaces. CNC esterification was characterized by Fourier transform IR spectroscopy, 13C solid state magic-angle spinning (MAS), and conductometric titrn. expts. Av. degree of substitution values for malonate, malate, and citrate CNCs are 0.16, 0.22, and 0.18, resp. Despite differences in org. acid pKa, optimal HCl cocatalyst concns. were similar for malonic, malic, and citric acids. After isolation of modified CNCs, residual cellulose coproducts were identified that are similar to microcryst. cellulose based on SEM and XRD anal. As proof of concept, recycling expts. were carried to increase the yield of citrate CNCs. The byproduct was then recycled by subsequent citric acid/HCl treatments that resulted in 55% total yield of citrate CNCs. The crystallinity, morphol., and substitution of citrate CNCs from recycled cellulose coproduct is similar to modified citrate CNCs formed in the first reaction cycle. Thermal stability of all modified CNCs under air and nitrogen resulted in T10% and T50% values above 256 and 323 °C, resp. Thus, they can be used for melt-processing operations performed at moderately high temps. without thermal decompn. Nanocomposites of poly(vinyl alc.) with modified CNCs (1 wt % malonate, malate, citrate, and unmodified CNCs) were prepd. An increase in the thermal decompn. temp. by almost 40 °C was obtained for PVOH-citrate-modified CNC nanocomposites.
  40. 40
    Lo Re, G.; Engström, J.; Wu, Q.; Malmström, E.; Gedde, U. W.; Olsson, R. T.; Berglund, L. Improved Cellulose Nanofibril Dispersion in Melt-Processed Polycaprolactone Nanocomposites by a Latex-Mediated Interphase and Wet Feeding as LDPE Alternative. ACS Appl. Nano Mater. 2018, 1, 2669– 2677,  DOI: 10.1021/acsanm.8b00376
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    Improved Cellulose Nanofibril Dispersion in Melt-Processed Polycaprolactone Nanocomposites by a Latex-Mediated Interphase and Wet Feeding as LDPE Alternative
    Lo Re, Giada; Engstroem, Joakim; Wu, Qiong; Malmstroem, Eva; Gedde, Ulf W.; Olsson, Richard T.; Berglund, Lars
    ACS Applied Nano Materials (2018), 1 (6), 2669-2677CODEN: AANMF6; ISSN:2574-0970. (American Chemical Society)
    This work reports the development of a sustainable and green one-step wet-feeding method to prep. tougher and stronger nanocomposites from biodegradable cellulose nanofibrils (CNF)/polycaprolactone (PCL) constituents, compatibilized with reversible addn. fragmentation chain transfer-mediated surfactant-free poly(Me methacrylate) (PMMA) latex nanoparticles. When a PMMA latex is used, a favorable electrostatic interaction between CNF and the latex is obtained, which facilitates mixing of the constituents and hinders CNF agglomeration. The improved dispersion is manifested in significant improvement of mech. properties compared with the ref. material. The tensile tests show much higher modulus (620 MPa) and strength (23 MPa) at 10 wt. % CNF content (compared to the neat PCL ref. modulus of 240 and 16 MPa strength), while maintaining high level of work to fracture the matrix (7 times higher than the ref. nanocomposite without the latex compatibilizer). Rheol. anal. showed a strongly increased viscosity as the PMMA latex was added, i.e., from a well-dispersed and strongly interacting CNF network in the PCL.
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    Dufresne, A. Cellulose Nanomaterials as Green Nanoreinforcements for Polymer Nanocomposites. Philos. Trans. R. Soc., A 2018, 376, 20170040,  DOI: 10.1098/rsta.2017.0040
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    Cellulose nanomaterials as green nanoreinforcements for polymer nanocomposites
    Dufresne, Alain
    Philosophical Transactions of the Royal Society, A: Mathematical, Physical & Engineering Sciences (2018), 376 (2112), 20170040/1-20170040/23CODEN: PTRMAD; ISSN:1364-503X. (Royal Society)
    A review. Unexpected and attractive properties can be obsd. when decreasing the size of a material down to the nanoscale. Cellulose is no exception to the rule. In addn., the highly reactive surface of cellulose resulting from the high d. of hydroxyl groups is exacerbated at this scale. Different forms of cellulose nanomaterials, resulting from a topdown deconstruction strategy (cellulose nanocrystals, cellulose nanofibrils) or bottom-up strategy (bacterial cellulose), are potentially useful for a large no. of industrial applications. These include the paper and cardboard industry, use as reinforcing filler in polymer nanocomposites, the basis for low-d. foams, additives in adhesives and paints, as well as a wide variety of filtration, electronic, food, hygiene, cosmetic andmedical products. This paper focuses on the use of cellulose nanomaterials as a filler for the prepn. of polymer nanocomposites. Impressive mech. properties can be obtained for these materials. They obviously depend on the type of nanomaterial used, but the crucial point is the processing technique. The emphasis is on the melt processing of such nanocomposite materials, which has not yet been properly resolved and remains a challenge.
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    Oksman, K.; Aitomäki, Y.; Mathew, A. P.; Siqueira, G.; Zhou, Q.; Butylina, S.; Tanpichai, S.; Zhou, X.; Hooshmand, S. Review of the Recent Developments in Cellulose Nanocomposite Processing. Composites, Part A 2016, 83, 2– 18,  DOI: 10.1016/j.compositesa.2015.10.041
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    Review of the recent developments in cellulose nanocomposite processing
    Oksman, Kristiina; Aitomaeki, Yvonne; Mathew, Aji P.; Siqueira, Gilberto; Zhou, Qi; Butylina, Svetlana; Tanpichai, Supachok; Zhou, Xiaojian; Hooshmand, Saleh
    Composites, Part A: Applied Science and Manufacturing (2016), 83 (), 2-18CODEN: CASMFJ; ISSN:1359-835X. (Elsevier Ltd.)
    A review. This review addresses the recent developments of the processing of cellulose nanocomposites, focusing on the most used techniques, including soln. casting, melt-processing of thermoplastic cellulose nanocomposites and resin impregnation of cellulose nanopapers using thermoset resins. Important techniques, such as partially dissolved cellulose nanocomposites, nanocomposite foams reinforced with nanocellulose, as well as long continuous fibers or filaments, are also addressed. It is shown how the research on cellulose nanocomposites has rapidly increased during the last 10 years, and manufg. techniques have been developed from simple casting to these more sophisticated methods. To produce cellulose nanocomposites for com. use, the processing of these materials must be developed from lab. to industrially viable methods.
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    Park, S.; Baker, J. O.; Himmel, M. E.; Parilla, P. A.; Johnson, D. K. Cellulose Crystallinity Index: Measurement Techniques and Their Impact on Interpreting Cellulase Performance. Biotechnol. Biofuels 2010, 3, 10,  DOI: 10.1186/1754-6834-3-10
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    Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance
    Park Sunkyu; Baker John O; Himmel Michael E; Parilla Philip A; Johnson David K
    Biotechnology for biofuels (2010), 3 (), 10 ISSN:.
    Although measurements of crystallinity index (CI) have a long history, it has been found that CI varies significantly depending on the choice of measurement method. In this study, four different techniques incorporating X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) were compared using eight different cellulose preparations. We found that the simplest method, which is also the most widely used, and which involves measurement of just two heights in the X-ray diffractogram, produced significantly higher crystallinity values than did the other methods. Data in the literature for the cellulose preparation used (Avicel PH-101) support this observation. We believe that the alternative X-ray diffraction (XRD) and NMR methods presented here, which consider the contributions from amorphous and crystalline cellulose to the entire XRD and NMR spectra, provide a more accurate measure of the crystallinity of cellulose. Although celluloses having a high amorphous content are usually more easily digested by enzymes, it is unclear, based on studies published in the literature, whether CI actually provides a clear indication of the digestibility of a cellulose sample. Cellulose accessibility should be affected by crystallinity, but is also likely to be affected by several other parameters, such as lignin/hemicellulose contents and distribution, porosity, and particle size. Given the methodological dependency of cellulose CI values and the complex nature of cellulase interactions with amorphous and crystalline celluloses, we caution against trying to correlate relatively small changes in CI with changes in cellulose digestibility. In addition, the prediction of cellulase performance based on low levels of cellulose conversion may not include sufficient digestion of the crystalline component to be meaningful.
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    Chen, L.; Wang, Q.; Hirth, K.; Baez, C.; Agarwal, U. P.; Zhu, J. Y. Tailoring the Yield and Characteristics of Wood Cellulose Nanocrystals (CNC) Using Concentrated Acid Hydrolysis. Cellulose 2015, 22, 1753– 1762,  DOI: 10.1007/s10570-015-0615-1
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    Tailoring the yield and characteristics of wood cellulose nanocrystals (CNC) using concentrated acid hydrolysis
    Chen, Liheng; Wang, Qianqian; Hirth, Kolby; Baez, Carlos; Agarwal, Umesh P.; Zhu, J. Y.
    Cellulose (Dordrecht, Netherlands) (2015), 22 (3), 1753-1762CODEN: CELLE8; ISSN:0969-0239. (Springer)
    Cellulose nanocrystals (CNC) have recently received much attention in the global scientific community for their unique mech. and optical properties. Here, we conducted the first detailed exploration of the basic properties of CNC, such as morphol., crystallinity, degree of sulfation and yield, as a function of prodn. condition variables. The rapid cellulose depolymn. and sulfation reactions under concd. acid concns. of around 60 wt% resulted in a very narrow operating window for CNC prodn. We found that CNC yields as high as 70 wt% from a bleached eucalyptus kraft pulp with glucan content of 78 wt% can be achieved under a tight range of reaction conditions and that a weighted av. length of over 200 nm and sulfur content (a measure of CNC surface charge) between 3 and 10 mg/g can be produced. This study provided crit. knowledge for the prodn. of CNC with characteristics tailored for different specific applications, significant to commercialization.
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    Wickholm, K.; Larsson, P. T.; Iversen, T. Assignment of Non-Crystalline Forms in Cellulose I by CP/MAS 13C NMR Spectroscopy. Carbohydr. Res. 1998, 312, 123– 129,  DOI: 10.1016/S0008-6215(98)00236-5
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    Assignment of non-crystalline forms in cellulose I by CP/MAS carbon-13 NMR spectroscopy
    Wickholm, Kristina; Larsson, Per Tomas; Iversen, Tommy
    Carbohydrate Research (1998), 312 (3), 123-129CODEN: CRBRAT; ISSN:0008-6215. (Elsevier Science Ltd.)
    Non-cryst. forms of cellulose (I) in birch pulp, cotton linters, and Cladophora species were studied by CP/MAS 13C NMR spectroscopy. New assignments were made for the NMR-signals in the lower shift part of the C-4 region (80-86 ppm). These signals were assigned to I at accessible fibril surfaces, I at inaccessible fibril surfaces, and hemicellulose. Also, further evidence was found for para-cryst. I as an "in-fibril" form, inaccessible to the surrounding solvent.
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    Gårdebjer, S.; Bergstrand, A.; Idström, A.; Börstell, C.; Naana, S.; Nordstierna, L.; Larsson, A. Solid-State NMR to Quantify Surface Coverage and Chain Length of Lactic Acid Modified Cellulose Nanocrystals, Used as Fillers in Biodegradable Composites. Compos. Sci. Technol. 2015, 107, 1– 9,  DOI: 10.1016/j.compscitech.2014.11.014
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    Park, S.; Johnson, D. K.; Ishizawa, C. I.; Parilla, P. A.; Davis, M. F. Measuring the Crystallinity Index of Cellulose by Solid State 13C Nuclear Magnetic Resonance. Cellulose 2009, 16, 641– 647,  DOI: 10.1007/s10570-009-9321-1
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    Measuring the crystallinity index of cellulose by solid state 13C nuclear magnetic resonance
    Park, Sunkyu; Johnson, David K.; Ishizawa, Claudia I.; Parilla, Philip A.; Davis, Mark F.
    Cellulose (Dordrecht, Netherlands) (2009), 16 (4), 641-647CODEN: CELLE8; ISSN:0969-0239. (Springer)
    The crystallinity index of cellulose is an important parameter to establish because of the effect this property has on the utilization of cellulose as a material and as a feedstock for biofuels prodn. However, it has been found that the crystallinity index varies significantly depending on the choice of instrument and data anal. technique applied to the measurement. We introduce in this study a simple and straightforward method to evaluate the crystallinity index of cellulose. This novel method was developed using solid state 13C NMR and subtraction of the spectrum of a std. amorphous cellulose. The crystallinity indexes of twelve different celluloses were measured and the values from this method were compared with the values obtained by other existing methods, including methods based on X-ray diffraction. An interesting observation was that the hydration of the celluloses increased their crystallinity indexes by about 5%, suggesting that addn. of water increased cellulose order for all the cellulose samples studied.
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    Eichhorn, S. J.; Dufresne, A.; Aranguren, M.; Marcovich, N. E.; Capadona, J. R.; Rowan, S. J.; Weder, C.; Thielemans, W.; Roman, M.; Renneckar, S.; Gindl, W.; Veigel, S.; Keckes, J.; Yano, H.; Abe, K.; Nogi, M.; Nakagaito, A. N.; Mangalam, A.; Simonsen, J.; Benight, A. S.; Bismarck, A.; Berglund, L. A.; Peijs, T. Review: Current International Research into Cellulose Nanofibres and Nanocomposites. J. Mater. Sci. 2010, 45, 1– 33,  DOI: 10.1007/s10853-009-3874-0
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    Review: current international research into cellulose nanofibres and nanocomposites
    Eichhorn, S. J.; Dufresne, A.; Aranguren, M.; Marcovich, N. E.; Capadona, J. R.; Rowan, S. J.; Weder, C.; Thielemans, W.; Toman, M.; Renneckar, S.; Gindl, W.; Veigel, S.; Keckes, J.; Yano, H.; Abe, K.; Nogi, M.; Nakagaito, A. N.; Mangalam, A.; Simonsen, J.; Benight, A. S.; Bismarck, A.; Berglund, L. A.; Peijs, T.
    Journal of Materials Science (2010), 45 (1), 1-33CODEN: JMTSAS; ISSN:0022-2461. (Springer)
    A review. This paper provides an overview of recent progress made in the area of cellulose nanofiber-based nanocomposites. An introduction into the methods used to isolate cellulose nanofibers (nanowhiskers, nanofibrils) is given, with details of their structure. Following this, the article is split into sections dealing with processing and characterization of cellulose nanocomposites and new developments in the area, with particular emphasis on applications. The types of cellulose nanofibers covered are those extd. from plants by acid hydrolysis (nanowhiskers), mech. treatment and those that occur naturally (tunicate nanowhiskers) or under culturing conditions (bacterial cellulose nanofibrils). Research highlighted in the article are the use of cellulose nanowhiskers for shape memory nanocomposites, anal. of the interfacial properties of cellulose nanowhisker and nanofibril-based composites using Raman spectroscopy, switchable interfaces that mimic sea cucumbers, polymn. from the surface of cellulose nanowhiskers by atom transfer radical polymn. and ring opening polymn.
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    Lo Re, G.; Spinella, S.; Boujemaoui, A.; Vilaseca, F.; Larsson, P. T.; Adås, F.; Berglund, L. A. Poly(ϵ-Caprolactone) Biocomposites Based on Acetylated Cellulose Fibers and Wet Compounding for Improved Mechanical Performance. ACS Sustainable Chem. Eng. 2018, 6, 6753– 6760,  DOI: 10.1021/acssuschemeng.8b00551
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    Poly(ε-caprolactone) Biocomposites Based on Acetylated Cellulose Fibers and Wet Compounding for Improved Mechanical Performance
    Lo Re, Giada; Spinella, Stephen; Boujemaoui, Assya; Vilaseca, Fabiola; Larsson, Per Tomas; Adaas, Fredrik; Berglund, Lars A.
    ACS Sustainable Chemistry & Engineering (2018), 6 (5), 6753-6760CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
    Poly(ε-caprolactone) (PCL) is a ductile thermoplastic, which is biodegradable in the marine environment. Limitations include low strength, petroleum-based origin, and comparably high cost. Cellulose fiber reinforcement is therefore of interest although uniform fiber dispersion is a challenge. In this study, a one-step wet compounding is proposed to validate a sustainable and feasible method to improve the dispersion of the cellulose fibers in hydrophobic polymer matrix as PCL, which showed to be insensitive to the presence of the water during the processing. A comparison between unmodified and acetylated cellulosic wood fibers is made to further assess the net effect of the wet feeding and chem. modification on the biocomposites properties, and the influence of acetylation on fiber structure is reported (ATR-FTIR, XRD). Effects of processing on nanofibrillation, shortening, and dispersion of the cellulose fibers are assessed as well as on PCL molar mass. Mech. testing, dynamic mech. thermal anal., FE-SEM, and X-ray tomog. is used to characterize composites. With the addn. of 20 wt % cellulosic fibers, the Young's modulus increased from 240 MPa (neat PCL) to 1850 MPa for the biocomposites produced by using the wet feeding strategy, compared to 690 MPa showed for the biocomposites produced using dry feeling. A wet feeding of acetylated cellulosic fibers allowed even a greater increase, with an addnl. 46% and 248% increase of the ultimate strength and Young's modulus, when compared to wet feeding of the unmodified pulp, resp.
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    Svenningsson, L.; Sparrman, T.; Bialik, E.; Bernin, D.; Nordstierna, L. Molecular Orientation Distribution of Regenerated Cellulose Fibers Investigated with Rotor Synchronized Solid State NMR Spectroscopy. Cellulose 2019, 26, 4681– 4692,  DOI: 10.1007/s10570-019-02430-z
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    Molecular orientation distribution of regenerated cellulose fibers investigated with rotor synchronized solid state NMR spectroscopy
    Svenningsson, Leo; Sparrman, Tobias; Bialik, Erik; Bernin, Diana; Nordstierna, Lars
    Cellulose (Dordrecht, Netherlands) (2019), 26 (8), 4681-4692CODEN: CELLE8; ISSN:0969-0239. (Springer)
    A regenerated cellulose fiber is, in contrast to cotton, a man-made fiber. In the fiber prodn., the cellulose polymer is subject to various processing steps, affecting the underlying mol. orientation distribution, which is a detg. factor for mech. properties of the fiber. In this work, the mol. orientation distribution was detd. in a 13C natural abundance Lyocell regenerated cellulose fiber bundle using rotor synchronized magic angle spinning NMR spectroscopy (ROSMAS) to investigate the chem. shift anisotropy (CSA). The recorded signal intensities were compared with an anal. model of the expt. to find the order parameters reflecting the orientation of the fiber. The CSA tensor was calcd. using d. functional theory for the cryst. cellulose II structure, commonly found in regenerated cellulose, and is required as an input parameter. The expected order parameter values were only found when approximating the glycosidic bond and its CSA tensor as being parallel to the mol. frame with the order parameter P2 = 0.45±0.02 compared to P2 = 0.46±0.02 obtained with wide angle x-ray scattering on a fiber bundle. To make this method accessible to the community, we distribute the Matlab script for the simulation of spectra obtained by the ROSMAS expt. at github.com/LeoSvenningsson/ROSMAS.
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    Moon, R. J.; Martini, A.; Nairn, J.; Simonsen, J.; Youngblood, J. Cellulose Nanomaterials Review: Structure, Properties and Nanocomposites. Chem. Soc. Rev. 2011, 40, 3941– 3994,  DOI: 10.1039/c0cs00108b
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    Cellulose nanomaterials review: structure, properties and nanocomposites
    Moon, Robert J.; Martini, Ashlie; Nairn, John; Simonsen, John; Youngblood, Jeff
    Chemical Society Reviews (2011), 40 (7), 3941-3994CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    This crit. review provides a processing-structure-property perspective on recent advances in cellulose nanoparticles and composites produced from them. It summarizes cellulose nanoparticles in terms of particle morphol., crystal structure, and properties. Also described are the self-assembly and rheol. properties of cellulose nanoparticle suspensions. The methodol. of composite processing and resulting properties are fully covered, with an emphasis on neat and high fraction cellulose composites. Addnl., advances in predictive modeling from mol. dynamic simulations of cryst. cellulose to the continuum modeling of composites made with such particles are reviewed (392 refs.).
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    Girouard, N. M.; Xu, S.; Schueneman, G. T.; Shofner, M. L.; Meredith, J. C. Site-Selective Modification of Cellulose Nanocrystals with Isophorone Diisocyanate and Formation of Polyurethane-CNC Composites. ACS Appl. Mater. Interfaces 2016, 8, 1458– 1467,  DOI: 10.1021/acsami.5b10723
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    Site-Selective Modification of Cellulose Nanocrystals with Isophorone Diisocyanate and Formation of Polyurethane-CNC Composites
    Girouard, Natalie M.; Xu, Shanhong; Schueneman, Gregory T.; Shofner, Meisha L.; Meredith, J. Carson
    ACS Applied Materials & Interfaces (2016), 8 (2), 1458-1467CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    The unequal reactivity of the two isocyanate groups in an isophorone diisocyanate (IPDI) monomer was exploited to yield modified cellulose nanocrystals (CNCs) with both urethane and isocyanate functionality. The chem. functionality of the modified CNCs was verified with ATR-FTIR anal. and elemental anal. The selectivity for the secondary isocyanate group using di-Bu tin dilaurate (DBTDL) as the reaction catalyst was confirmed with 13C NMR. The modified CNCs showed improvements in the onset of thermal degrdn. by 35 °C compared to the unmodified CNCs. Polyurethane composites based on IPDI and a trifunctional polyether alc. were synthesized using unmodified (um-CNC) and modified CNCs (m-CNC). The degree of nanoparticle dispersion was qual. assessed with polarized optical microscopy. It was found that the modification step facilitated superior nanoparticle dispersion compared to the um-CNCs, which resulted in increases in the tensile strength and work of fracture of over 200% compared to the neat matrix without degrdn. of elongation at break.
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    Abraham, E.; Kam, D.; Nevo, Y.; Slattegard, R.; Rivkin, A.; Lapidot, S.; Shoseyov, O. Highly Modified Cellulose Nanocrystals and Formation of Epoxy-Nanocrystalline Cellulose (CNC) Nanocomposites. ACS Appl. Mater. Interfaces 2016, 8, 28086– 28095,  DOI: 10.1021/acsami.6b09852
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    Highly Modified Cellulose Nanocrystals and Formation of Epoxy-Nanocrystalline Cellulose (CNC) Nanocomposites
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    ACS Applied Materials & Interfaces (2016), 8 (41), 28086-28095CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    This work presents an environmentally friendly, iodine-catalyzed chem. modification method to generate highly hydrophobic, optically active nanocryst. cellulose (CNC). The high degree of ester substitution (DS = 2.18), hydrophobicity, cryst. behavior, and optical activity of the generated acetylated CNC (Ac-CNC) were quantified by TEM, FTIR, solid 13C NMR, contact angle, x-ray diffraction, and POM analyses. Ac-CNC possesses substantial enhancement in thermal stability (16.8%) and forms thin films with an interlayer distance of 50-150 nm, presenting cavities suitable for entrapping nano- and microparticles. Generated Ac-CNC proved to be an effective reinforcing agent in hydrophobic polymer matrixes for fabricating high performance nanocomposites. When integrated at a low wt. percentage (0.5%) in an epoxy matrix, Ac-CNC provided for a 73% increase in tensile strength and a 98% increase in modulus, demonstrating its remarkable reinforcing potential and effective stress transfer behavior. The method of modification and the unique properties of the modified CNC (hydrophobicity, crystallinity, reinforcing ability, and optical activity) render them a novel bionanomaterial for a range of multipurpose applications.
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    Surface modification of cellulose nanocrystals with succinic anhydride
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    Polymers (Basel, Switzerland) (2019), 11 (5), 866CODEN: POLYCK; ISSN:2073-4360. (MDPI AG)
    The surface modification of cellulose nanocrystals (CNC) is a key intermediate step in the development of new functionalities and the tailoring of nanomaterial properties for specific applications. In the area of polymeric nanocomposites, apart from good interfacial adhesion, the high thermal stability of cellulose nanomaterial is vitally required for the stable processing and improvement of material properties. In this respect, the heterogeneous esterification of CNC with succinic anhydride was investigated in this work in order to obtain CNC with optimized surface and thermal properties. The influence of reaction parameters, such as time, temp., and molar ratio of reagents, on the structure, morphol. and thermal properties, were systematically studied over a wide range of values by DLS, FTIR, XPS, WAXD, SEM and TGA methods. It was found that the degree of surface substitution of CNC increased with the molar ratio of succinic anhydride to cellulose hydroxyl groups (SA:OH), as well as the reaction time, while the temp. of reaction showed a moderate effect on the degree of esterification in the range of 70-110°C. The studies on the thermal stability of modified nanoparticles indicated that there is a crit. extent of surface esterification below which only a slight decrease of the initial temp. of degrdn. was obsd. in pyrolytic and oxidative atmospheres. A significant redn. of CNC thermal stability was obsd. only for the longest reaction time (240 min) and the highest molar ratio of SA:OH. This illustrates the possibility of manufg. thermally stable, succinylated, CNC by controlling the reaction conditions and the degree of esterification.
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    Green nanocomposites contg. biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and cellulose nanocrystals/silver (CNC-Ag) nanohybrids were synthesized and their properties were investigated. It was found that homogeneously dispersed CNC-Ag could act as bifunctional reinforcements to improve the thermal, mech. and antibacterial properties of PHBV. Compared to pristine PHBV, the tensile strength and the max. decompn. temp. (Tmax) of the nanocomposite with 10 wt% CNC-Ag were enhanced by 140% and 24.2 °C, resp. The nanocomposites displayed reduced water uptake and water vapor permeability along with lower migration level in both non-polar and polar simulants compared to the neat biopolymer, which can be related to the increased crystallinity and improved interfacial adhesion. Moreover, the nanocomposites showed strong antibacterial activity against both Gram-neg. E. coli and Gram-pos. S. aureus. The results of the study indicate that the high performance nanocomposites show great potential applications in the fields of food, beverage packaging and disposable overwrap films.
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    Impact of the nature and shape of cellulosic nanoparticles on the isothermal crystallization kinetics of poly(ε-caprolactone)
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    European Polymer Journal (2011), 47 (12), 2216-2227CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
    Polycaprolactone (PCL)/cellulose nanocomposites were prepd. by mixing PCL with surface modified sisal nanowhiskers (CNW) and microfibrillated cellulose (MFC) extd. from sisal fibers. The influence of cellulosic nanoparticles on the crystn. behavior of PCL was investigated by differential scanning calorimetry. Isothermal crystn. data were modeled with Avrami's kinetics, Lauritzen-Hoffman secondary nucleation theory and equil. m.ps. were detd. with the Hoffman-Weeks method. The cellulose nanoparticles, acting as nucleating agents, drastically accelerate the crystn. of PCL while depressing its equil. melting by 9-10°. The crystn. of MFC-nanocomposites is slightly faster than that of CNW-nanocomposites, in agreement with the slightly lower bulk activation energy for crystn. and nucleation parameter in the former. The results are discussed based on the differences of sp. surface area and surface chem. of nanoparticles, as well as the confinement phenomenon.
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  • Abstract

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    Figure 1

    Figure 1. One-pot acid hydrolysis/Fischer esterification method (upper left image); FTIR spectra (upper right graph) and STEM micrographs of unmodified (CNCs_HCl) and modified nanocrystals with different ester moieties (CNCs_butyrate, CNCs_lactate, CNCs_but_lact, bottom image). A similar aspect ratio (13.5 ± 1.5) was calculated for the different CNCs from the morphological analysis on 100 different individualized CNCs. Samples observed in the STEM were directly obtained after the purification step following the synthesis (in water suspention ≈ 1.5 wt %).

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    Figure 2

    Figure 2. CP/MAS 13C NMR spectrum of CNCs_HCl, CNCs_lactate, CNCs_butyrate, and CNCs_but_lact. Zoom-in of the spectra highlight some of the signals from the modifications. Inset shows the structural formula of the anhydroglucose unit of the CNCs as well as the lactic and butyric acid modifications, with numbered carbons.

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    Figure 3

    Figure 3. Dispersion in chloroform of the unmodified and modified cellulose nanocrystals after 15 min from the mechanical stirring (top image), visual aspect (central image), and UV–vis spectra (bottom image) of bionanocomposites with different amounts and types of CNCs.

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    Figure 4

    Figure 4. XRD diffractograms of neat PHBV and bionanocomposites at a content of 2 wt % of CNCs with different surface chemistry (left); example of deconvolution of XRD spectra with PeakFit (bionanocomposites containing CNCs_butyrate, right).

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    Figure 5

    Figure 5. Dynamical-thermomechanical properties obtained from DMTA analysis of neat PHBV and bionanocomposites with CNCs with different surface chemistry; (a) Storage moduli and (b) tan δ in temperature sweep analysis (2 °C/min, 1 Hz, 0.02% strain); (c) tan δ in frequency sweep (25 °C, 0.02% strain).

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    Figure 6

    Figure 6. SEM micrographs after cryofracture of PHBV (a, a′) and of the bionanocomposites at 2 wt % content of differently surface decorated CNCs (b–e′) at two different magnifications (bars 10 μm, left micrographs, and 1 μm, right micrographs).

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      Volova, T. G.; Boyandin, A. N.; Vasiliev, A. D.; Karpov, V. A.; Prudnikova, S. V.; Mishukova, O. V.; Boyarskikh, U. A.; Filipenko, M. L.; Rudnev, V. P.; Xuan, Bui Ba; Dung, Vu Viet; Gitelson, I. I.
      Polymer Degradation and Stability (2010), 95 (12), 2350-2359CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
      Biodegradability patterns of 2 PHAs: a polymer of 3-hydroxybutyric acid (3-PHB) and a copolymer of 3-hydroxybutyric and 3-hydroxyvaleric acids (3-PHB/3-PHV) contg. 11 mol% of hydroxyvalerate, were studied in the tropical marine environment, in the South China Sea (Nha Trang, Vietnam). No significant differences were obsd. between degrdn. rates of 3-PHB and 3-PHB/3-PHV specimens; it was found that under study conditions, biodegrdn. is rather influenced by the shape of the polymer item and the prepn. technique than by the chem. compn. of the polymer. Biodegrdn. rates of polymer films in seawater were higher than those of compacted pellets. As 3-PHB and 3-PHB/3-PHV are degraded and the specimens lose their mass, mol. wt. of both polymers is decreased, i.e. polymer chains get destroyed. The polydispersity index of the PHAs grows significantly. However, the degree of crystallinity of both PHAs remains unchanged, i.e. the amorphous phase and the cryst. one are equally disintegrated. PHA-degrading microorganisms were isolated using the clear-zone technique, by inoculating the isolates onto mineral agar that contained PHA as sole C source. Based on the 16S rRNA anal., the PHA-degrading strains were identified as Enterobacter sp. (4 strains), Bacillus sp. and Gracilibacillus sp.
    9. 9
      Gilmore, D. F.; Fuller, R. C.; Schneider, B.; Lenz, R. W.; Lotti, N.; Scandola, M. Biodegradability of Blends of Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate) with Cellulose Acetate Esters in Activated Sludge. J. Environ. Polym. Degrad. 1994, 2, 49– 57,  DOI: 10.1007/BF02073486
      9
      Biodegradability of blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with cellulose acetate esters in activated sludge
      Gilmore, D. F.; Fuller, R. C.; Schneider, B.; Lenz, R. W.; Lotti, N.; Scandola, M.
      Journal of Environmental Polymer Degradation (1994), 2 (1), 49-57CODEN: JEPDED; ISSN:1064-7546.
      Blends of the bacterially produced polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with cellulose acetate esters (CAE) further substituted with propionyl or butyryl groups (degree of substitution: 2.60 propionyl and 0.36 acetyl or 2.59 butyryl and 0.36 acetyl, resp.) were exposed for 4 mo to activated sludge to det. their biodegradability. Samples of such blends made by soln.-mixing and solvent-casting had complex morphologies in which both individual components as well as a miscible blend phase were present. Addnl., the two opposite surfaces of solvent-cast films showed both phys. and chem. differences. After 2 mo, samples of pure PHBV had degraded by more than 98% (15 mg/cm2 of surface area), whereas a pure CAE sample had degraded less than 1% (<0.2 mg/cm2). Samples contg. 25% CAE lost less than 40% of their initial wts. (6 mg/cm2) over the total 4-mo period. Samples with 50% CAE lost up to 16% wt. (2 mg/cm2), whereas those contg. 75% CAE lost only slightly more wt. than corresponding sterile control samples (1 mg/cm2). NMR results confirm that wt. loss from samples contg. 25% CAE resulted only from degrdn. of PHBV and that the surface of samples became enriched in CAE. Solvent-cast film samples contg. equal amts. of PHBV and CAE degraded preferentially on the surface which formed at the polymer-air interface. SEM and attenuated total reflectance IR spectroscopy revealed this surface to have a rougher texture and a greater PHBV content.
    10. 10
      Doi, Y. Microbial Polyesters; VCH: New York, 1990.
      There is no corresponding record for this reference.
    11. 11
      Singh, A. K.; Srivastava, J. K.; Chandel, A. K.; Sharma, L.; Mallick, N.; Singh, S. P. Biomedical Applications of Microbially Engineered Polyhydroxyalkanoates: An Insight into Recent Advances, Bottlenecks, and Solutions. Appl. Microbiol. Biotechnol. 2019, 103, 2007– 2032,  DOI: 10.1007/s00253-018-09604-y
      11
      Biomedical applications of microbially engineered polyhydroxyalkanoates: an insight into recent advances, bottlenecks, and solutions
      Singh, Akhilesh Kumar; Srivastava, Janmejai Kumar; Chandel, Anuj Kumar; Sharma, Laxuman; Mallick, Nirupama; Singh, Satarudra Prakash
      Applied Microbiology and Biotechnology (2019), 103 (5), 2007-2032CODEN: AMBIDG; ISSN:0175-7598. (Springer)
      A review. Biopolymeric polyhydroxyalkanoates (PHAs) are fabricated and accumulated by microbes under unbalanced growth conditions, primarily by diverse genera of bacteria. Over the last two decades, microbially engineered PHAs gained substantial interest worldwide owing to their promising wide-range uses in biomedical field as biopolymeric biomaterials. Because of non-hazardous disintegration products, preferred surface alterations, inherent biocompatibility, modifiable mech. properties, cultivation support for cells, adhesion devoid of carcinogenic impacts, and controllable biodegradability, the PHAs like poly-3-hydroxybutyrate, 3-hydroxybutyrate and 3-hydroxyvalerate co-polymers, 3-hydroxybutyrate and 4-hydroxybutyrate co-polymers, etc., are available for various medical applications. These PHAs have been exploited to design in vivo implants like sutures as well as valves for direct tissue repairing as well as in regeneration devices like bone graft substitutes, nerve guides as well as cardiovascular patches, etc. In addn., innovative approaches like PHAs co-prodn. with other value-added products, etc., must be developed currently for economical PHA prodn. This provides an insight toward the recent advances, bottlenecks, and potential solns. for prospective biomedical applications of PHAs with conclusion that relatively little research/study has been performed presently toward the viability of PHAs as realistic biopolymeric biomaterials.
    12. 12
      Lettner, M.; Schöggl, J. P.; Stern, T. Factors Influencing the Market Diffusion of Bio-Based Plastics: Results of Four Comparative Scenario Analyses. J. Cleaner Prod. 2017, 157, 289– 298,  DOI: 10.1016/j.jclepro.2017.04.077
      There is no corresponding record for this reference.
    13. 13
      Kunioka, M.; Doi, Y. Thermal Degradation of Microbial Copolyesters: Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate) and Poly(3-Hydroxybutyrate-Co-4-Hydroxybutyrate). Macromolecules 1990, 23, 1933– 1936,  DOI: 10.1021/ma00209a009
      13
      Thermal degradation of microbial copolyesters: poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate)
      Kunioka, Masao; Doi, Yoshiharu
      Macromolecules (1990), 23 (7), 1933-6CODEN: MAMOBX; ISSN:0024-9297.
      Thermal degrdn. processes of microbial polyesters were studied at 100-200° by monitoring the time-dependent changes in mol. wts. of the melt samples. Two types of copolyesters, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (3-hydroxybutyrate = 0-71 mol%) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (4-hydroxybutyrate = 0-82 mol%) were studied. All copolyester samples used were thermally unstable at >170° and their mol. wt. decreased rapidly with time. The time-dependent changes in mol. wts. during the thermal degrdn. followed the kinetic model of random chain scission at ester groups. The rates of random chain scission were independent of the compns. of the polyesters, but were strongly dependent on temp. The copolyester samples were thermally stable at <160°. It was suggested that the microbial polyesters with m.ps. <160° were applicable to conventional plastic processing methods.
    14. 14
      Kamiya, N.; Yamamoto, Y.; Inoue, Y.; Chujo, R.; Doi, Y. Microstructure of Bacterially Synthesized Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate). Macromolecules 1989, 22, 1676– 1682,  DOI: 10.1021/ma00194a030
      14
      Microstructure of bacterially synthesized poly(3-hydroxybutyrate-co-3-hydroxyvalerate)
      Kamiya, Naoko; Yamamoto, Yasuhiko; Inoue, Yoshio; Chujo, Riichiro; Doi, Yoshiharu
      Macromolecules (1989), 22 (4), 1676-82CODEN: MAMOBX; ISSN:0024-9297.
      Bacterially synthesized (0-7):(0-93) copolyesters of 3-hydroxybutyric acid and 3-hydroxyvaleric acid were analyzed by NMR spectroscopy and DSC. The sequence distributions of some polyesters, detd. from 13C NMR spectra, were statistically random, but those of the other samples were not. The sequence distributions of the latter obeyed the model of a mixt. of two random copolymers. These samples had two or three peaks in DSC melting curves, indicating that they were mixts. of different polymers.
    15. 15
      Ferreira, B. M. P.; Zavaglia, C. A. C.; Duek, E. A. R. Films of PLLA/PHBV: Thermal, Morphological, and Mechanical Characterization. J. Appl. Polym. Sci. 2002, 86, 2898– 2906,  DOI: 10.1002/app.11334
      15
      Films of PLLA/PHBV: thermal, morphological, and mechanical characterization
      Ferreira, B. M. P.; Zavaglia, C. A. C.; Duek, E. A. R.
      Journal of Applied Polymer Science (2002), 86 (11), 2898-2906CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
      Poly(L-lactic acid) (PLLA)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) blends were prepd. in various compns. and characterized by TGA, DSC, DMA, SEM, polarized light microscopy and tensile tests. Although the blends do not present clear phase sepn., anal. by TGA, DSC, and DMA showed that the blends are immiscible. The cross-sections obsd. by SEM showed that the morphol. of the blends changes from porous to dense, due to the compn. DSC and DMA data show two distinct Tg and melting temps. However, DMA anal. related to frequency variation showed partial mol. interactions between the components.
    16. 16
      Ha, C. S.; Cho, W. J. Miscibility, Properties, and Biodegradability of Microbial Polyester Containing Blends. Prog. Polym. Sci. 2002, 27, 759– 809,  DOI: 10.1016/S0079-6700(01)00050-8
      16
      Miscibility, properties, and biodegradability of microbial polyester containing blends
      Ha, Chang-Sik; Cho, Won-Jei
      Progress in Polymer Science (2002), 27 (4), 759-809CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)
      A review. The blending of poly[(R)-3-hydroxybutyrate] [P(3HB)] or poly((R)-3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] with other synthetic polymers has attracted much interest as one approach to improve the inherent brittleness as well as to reduce the high prodn. cost of the microbial polyesters. The crystn. behavior, phys. properties, and biodegrdn. of the microbial polyester-contg. blends are significantly affected by the nature of the blend partner component depending on whether it is biodegradable or not and/or whether it is miscible with the microbial polyesters or not. Recent progress on polymer blends based on microbial polyesters is discussed.
    17. 17
      Corre, Y.-M.; Bruzaud, S.; Grohens, Y. Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate) and Poly(Propylene Carbonate) Blends: An Efficient Method to Finely Adjust Properties of Functional Materials. Macromol. Mater. Eng. 2013, 298, 1176– 1183,  DOI: 10.1002/mame.201200345
      17
      Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Poly(propylene carbonate) Blends: an Efficient Method to Finely Adjust Properties of Functional Materials
      Corre, Yves-Marie; Bruzaud, Stephane; Grohens, Yves
      Macromolecular Materials and Engineering (2013), 298 (11), 1176-1183CODEN: MMENFA; ISSN:1438-7492. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Polyhydroxyalkanoate (PHA) and poly(propylene carbonate) (PPC) are blended in order to investigate their mutual contributions in terms of functional properties. A wide range of blend compn. is processed through extrusion from dry blends. Droplet-matrix morphol. is obsd. for all samples. Thermal investigations reveal the PPC effect on the PHA crystn. process with a decrease and broadening of the crystn. temp. window and on the depression of its glass transition temp. This investigation also confirms the as yet unreported non-miscibility of this kind of blend. However, a slight phase interaction is expected since thermal behavior of PHA is impacted. The fragile behavior of PHA is balanced by the high ductility of PPC. The weak strain at break of PHA can thus be increased by up to 200% although a significant amt. of PPC is needed to start modifying this property. Stress at break and modulus are linearly decreased from pure PHA to pure PPC values. PPC also acts as an impact modifier for PHA. In terms of barrier properties, PHA brings a large contribution even at low content to the initially high oxygen and water vapor permeability of PPC.
    18. 18
      Requena, R.; Jiménez, A.; Vargas, M.; Chiralt, A. Effect of Plasticizers on Thermal and Physical Properties of Compression-Moulded Poly[(3-Hydroxybutyrate)-Co-(3-Hydroxyvalerate)] Films. Polym. Test. 2016, 56, 45– 53,  DOI: 10.1016/j.polymertesting.2016.09.022
      18
      Effect of plasticizers on thermal and physical properties of compression-moulded poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] films
      Requena, Raquel; Jimenez, Alberto; Vargas, Maria; Chiralt, Amparo
      Polymer Testing (2016), 56 (), 45-53CODEN: POTEDZ; ISSN:0142-9418. (Elsevier Ltd.)
      Poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV) is a promising bio-based, biodegradable polymer for replacing synthetic polymers, but its brittleness limits its application range. With the aim of improving the mech. properties of PHBV films, different plasticizers (polyethylene glycol (PEG 200, 1000 and 4000), lauric acid (LA) and stearic acid (SA)) were incorporated into the film formulation at 10 wt%. All plasticized films showed lower melting temp. and crystn. degree than pure PHBV films. All plasticizers, except SA, reduced film stiffness and resistance to break, and increased the films' water sorption capacity and soly. as well as their water vapor permeability, but only PEG1000 yielded more extensible films. PEG1000 and PEG4000 gave rise to the most heat-resistant plasticized films, while LA and SA highly promoted the heat-sensitivity of PHBV. PEG1000 was the most effective at plasticizing PHBV films, and it was the only plasticizer that partially mitigated the ageing effects. However, a greater ratio of plasticizer would be required to adapt PHBV mech. properties to some packaging requirements.
    19. 19
      Jost, V.; Langowski, H. C. Effect of Different Plasticisers on the Mechanical and Barrier Properties of Extruded Cast PHBV Films. Eur. Polym. J. 2015, 68, 302– 312,  DOI: 10.1016/j.eurpolymj.2015.04.012
      19
      Effect of different plasticizers on the mechanical and barrier properties of extruded cast PHBV films
      Jost, Verena; Langowski, Horst-Christian
      European Polymer Journal (2015), 68 (), 302-312CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
      PHAs are gaining interest as biobased and biodegradable thermoplastics as an alternative for conventional polymers. However applications still struggle with the high brittleness of these polymers. In this study PHBV was plasticised by different types and concns. of plasticisers in order to improve flexibility and elongation. Thereby an evaluation of the effectiveness of the selected plasticisers, which differ in their mol. wt. and functional groups, is enabled. Those are propylene glycol, glycerol, tri-Et citrate, castor oil, epoxidised soybean oil and polyethylene glycol. The results of an increasing plasticiser concn. show a decreasing melting temp., increasing crystallinity, a decreasing Young's Modulus and tensile strength as well as an increasing elongation at break. The water vapor and oxygen permeability is increased by all plasticisers but to a different extent. Overall the effectiveness of tri-Et citrate and polyethylene glycol in PHBV showed the most promising results within thermal, mech. and permeative characterization.
    20. 20
      Kelly, C. A.; Fitzgerald, A. V. L.; Jenkins, M. J. Control of the Secondary Crystallisation Process in Poly(Hydroxybutyrate-Co-Hydroxyvalerate) through the Incorporation of Poly(Ethylene Glycol). Polym. Degrad. Stab. 2018, 148, 67– 74,  DOI: 10.1016/j.polymdegradstab.2018.01.003
      20
      Control of the secondary crystallisation process in poly(hydroxybutyrate-co-hydroxyvalerate) through the incorporation of poly(ethylene glycol)
      Kelly, Catherine A.; Fitzgerald, Annabel V. L.; Jenkins, Mike J.
      Polymer Degradation and Stability (2018), 148 (), 67-74CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
      Poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-co-HV) is a sustainable and biodegradable polymer, but as a potential packaging material, it suffers from a narrow processing window and embrittlement over time due to secondary crystn. This study aims to extend previous research by exploring the effect of the addn. of poly(ethylene glycol) (PEG), in a range of mol. wts. and compns., on the rate of embrittlement. On blending, it was apparent that there was a redn. in both the m.p. (of up to 7°C) and the melt viscosity. Furthermore, there was a redn. in both the modulus and tensile strength indicating that PEG acts as an effective plasticiser in PHB-co-HV. In terms of the secondary crystn. process, the addn. of PEG could not prevent the process from occurring, only hinder it. PEG 600 in relatively high concns. was found to be the most effective in this regard with a 53% redn. in the change in Young's modulus compared to pure PHB-co-HV. This observation, together with the m.p. redn. which extends the processing window for PHB-co-HV, makes PEG a worthwhile additive to an otherwise fundamentally brittle polymer.
    21. 21
      Zhu, C.; Nomura, C. T.; Perrotta, J. A.; Stipanovic, A. J.; Nakas, J. P. The Effect of Nucleating Agents on Physical Properties of Poly-3-Hydroxybutyrate (PHB) and Poly-3-Hydroxybutyrate-Co-3-Hydroxyvalerate (PHB-Co-HV) Produced by Burkholderia Cepacia ATCC 17759. Polym. Test. 2012, 31, 579– 585,  DOI: 10.1016/j.polymertesting.2012.03.004
      21
      The effect of nucleating agents on physical properties of poly-3-hydroxybutyrate (PHB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHB-co-HV) produced by Burkholderia cepacia ATCC 17759
      Zhu, Chengjun; Nomura, Christopher T.; Perrotta, Joseph A.; Stipanovic, Arthur J.; Nakas, James P.
      Polymer Testing (2012), 31 (5), 579-585CODEN: POTEDZ; ISSN:0142-9418. (Elsevier Ltd.)
      In the absence of nucleating agents, polyhydroxyalkanoates (PHAs) generally exhibit slow crystn. rates which make them less favorable for injection molding purposes. The copolymer, PHB-co-HV (poly-3-hydroxybutyrate-co-3-hydroxyvalerate), exhibited increased Tc as compared to the homopolymer PHB (poly-3-hydroxybutyrate). Increasing the mol. fraction of HV monomer in the PHB-co-HV initially led to a decrease in the Tm of the copolymer from 175.4 °C to a min. of 168.5 °C, at 20 mol% of HV and, subsequently, increased in PHB-co-HV copolymers with higher fractions of HV, indicating a typical isodimorphic relationship. Two nucleating agents, heptane dicarboxylic deriv. HPN-68L and ULTRATALC 609, were tested to increase the Tc and reduce the time for crystn. necessary for injection molding. HPN-68L decreased the Tdecomp of the homopolymer and all copolymers by almost 50 °C. However, the use of ULTRATALC609 as a nucleating agent slightly enhanced the Tdecomp and had negligible effect on the Tms of all polymers. Also, PHB and PHB-co-HV with 5% (wt./wt.) talc exhibited higher Tc than polymers without ULTRATALC609. A careful comparison of Tc, Tm and Tdecomp, for PHB-co-HV with 20 mol% of HV indicated that this copolymer is the best option for injection molding, with both a high Tdecomp and more rapid crystn.
    22. 22
      Whitehouse, R. S.; Padwa, A. R. Nucleating Agents for Polyhydroxyalkanoates. U.S. Patent 847023, July 16, 2013.
      There is no corresponding record for this reference.
    23. 23
      Habibi, Y.; Lucia, L. A.; Rojas, O. J. Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications. Chem. Rev. 2010, 110, 3479– 3500,  DOI: 10.1021/cr900339w
      23
      Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications
      Habibi, Youssef; Lucia, Lucian A.; Rojas, Orlando J.
      Chemical Reviews (Washington, DC, United States) (2010), 110 (6), 3479-3500CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review discussing chem. and phys. features of the most dominant fundamental building block in the biosphere, cellulose nanocrystals. A brief introduction to cellulose was followed by the discussion of morphol., chem., including prepn. and chem. routes for functionalization, and self-assembly in various media under various conditions, and applications in the nanocomposites.
    24. 24
      Ten, E.; Turtle, J.; Bahr, D.; Jiang, L.; Wolcott, M. Thermal and Mechanical Properties of Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate)/Cellulose Nanowhiskers Composites. Polymer 2010, 51, 2652– 2660,  DOI: 10.1016/j.polymer.2010.04.007
      24
      Thermal and mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhiskers composites
      Ten, Elena; Turtle, Joel; Bahr, David; Jiang, Long; Wolcott, Michael
      Polymer (2010), 51 (12), 2652-2660CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      Bacterial polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was reinforced with cellulose nanowhiskers (CNW) in 1-5% concns. using a solvent casting method. The CNW was prepd. from microcryst. cellulose (MCC) using sulfuric acid hydrolysis. The influence of CNW on the PHBV crystn., thermal, dynamic mech. and mech. properties were evaluated using polarized optical microscope (POM), differential scanning calorimeter (DSC), dynamic mech. anal. (DMA), tensile and bulge tests, resp. POM test results demonstrated that CNW was an effective PHBV nucleation agent. Tensile strength, Young's modulus and toughness of PHBV increased with the increasing concn. of CNW. DMA results showed an increased tan δ peak temp. and broadened transition peak, indicating restrained PHBV mol. mobility in the vicinity of the CNW surface. Storage modulus of the PHBV also increased with the addn. of CNW, esp. at the temps. higher than the PHBV glass transition temp. These results indicated that the CNW could substantially increase the mech. properties of PHBV and this increase could be attributed to the strong interactions between these two phases.
    25. 25
      Yu, H.; Yan, C.; Yao, J. Fully Biodegradable Food Packaging Materials Based on Functionalized Cellulose Nanocrystals/Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate) Nanocomposites. RSC Adv. 2014, 4, 59792– 59802,  DOI: 10.1039/C4RA12691B
      25
      Fully biodegradable food packaging materials based on functionalized cellulose nanocrystals/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nanocomposites
      Yu, Houyong; Yan, Chenfeng; Yao, Juming
      RSC Advances (2014), 4 (104), 59792-59802CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      Current packaging materials (mainly composed of petroleum-based synthetic polymers) face environmental and disposal issues, and as a result, developing eco-friendly and bio-based nanocomposites as alternatives have motivated academic and industrial research. We report here on our effort to develop a transparent nanocomposite-based packaging film comprised of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and functionalized cellulose nanocrystals (cellulose nanocrystal Me ester, CNC-me). The resultant CNC-me with hydrophobic ester groups are uniformly dispersed in PHBV without the aid of a compatibilizer or surfactant. Therefore, both the crystn. temp. and crystallinity of the PHBV matrix were increased due to the heterogeneous nucleating effect of CNC-me. With an increase of CNC-me concn., significant improvements in mech. performance, thermal stability, barrier and migration properties were achieved, which were ascribed to the improved interfacial interaction and increased crystallinity. Compared to neat PHBV, the tensile strength and max. decompn. temp. (Tmax) of the nanocomposites all achieved their max. values at loading levels of 20 wt% CNC-me. Meanwhile the overall migration levels in both non-polar and polar simulants were well below the limits required by the current legislative stds. for food packaging materials.
    26. 26
      Malmir, S.; Montero, B.; Rico, M.; Barral, L.; Bouza, R.; Farrag, Y. PHBV/CNC Bionanocomposites Processed by Extrusion: Structural Characterization and Properties. Polym. Compos. 2019, 40, E275– E284,  DOI: 10.1002/pc.24634
      26
      PHBV/CNC bionanocomposites processed by extrusion: Structural characterization and properties
      Malmir, Sara; Montero, Belen; Rico, Maite; Barral, Luis; Bouza, Rebeca; Farrag, Yousof
      Polymer Composites (2019), 40 (S1), E275-E284CODEN: PCOMDI; ISSN:0272-8397. (John Wiley & Sons, Inc.)
      Bionanocomposites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with cellulose nanocrystals (CNC) were processed by extrusion. Differential scanning calorimetry showed that with increasing the amt. of CNC the overall crystn. time was reduced. Wide angle X-ray scattering showed diffraction peaks of orthorhombic α- type cryst. structure and confirmed the nucleating agent effect of CNC particles in the PHBV matrix. Small angle X-ray scattering showed that the reducing rate of long spacing was slower in the filled sample than in PHBV. Microscopy images (SEM and TEM) revealed well-dispersed morphol. in low loading of the filler while slight agglomerations appeared at higher filler concn. Statistical anal. was done by applying a one-way ANOVA (α = 0.05) to evaluate the effect of filler on mech. properties of PHBV. Water vapor, oxygen and carbon dioxide transmission rate showed that the incorporation of CNC nanocrystals led to an improvement in the barrier properties of the bionanocomposites due to higher crystallinity and more tortuosity in their morphologies.
    27. 27
      Malmir, S.; Montero, B.; Rico, M.; Barral, L.; Bouza, R. Morphology, Thermal and Barrier Properties of Biodegradable Films of Poly (3-Hydroxybutyrate-Co-3-Hydroxyvalerate) Containing Cellulose Nanocrystals. Composites, Part A 2017, 93, 41– 48,  DOI: 10.1016/j.compositesa.2016.11.011
      27
      Morphology, thermal and barrier properties of biodegradable films of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) containing cellulose nanocrystals
      Malmir, Sara; Montero, Belen; Rico, Maite; Barral, Luis; Bouza, Rebeca
      Composites, Part A: Applied Science and Manufacturing (2017), 93 (), 41-48CODEN: CASMFJ; ISSN:1359-835X. (Elsevier Ltd.)
      Solvent casting method was used to prep. biodegradable films of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) with cellulose nanocrystals (CNC). Nucleating effect of cellulose nanoparticles was confirmed with DSC and POM tests while WAXS patterns showed that the cryst. structure of bionanocomposites was not changed. POM images showed that smaller spherulites were formed with higher rate and quantity in the samples with CNC compared to neat polymer. TEM images illustrated that CNC nanoparticles were well dispersed in the films up to 4 wt.% of CNC. SEM results exhibited significant redn. in the porosity of the matrix with addn. of CNC up to 4 wt.%. More surface roughness for bionanocomposites was obsd. in AFM images compared to unfilled matrix. Moreover, nanocomposites with 4 wt.% of CNC exhibited better barrier properties against water vapor and oxygen up to approx. four times more than neat PHBV. These biodegradable nanocomposites could be a good alternative for synthetic plastic packaging materials.
    28. 28
      Yu, H. Y.; Qin, Z. Y.; Liu, L.; Yang, X. G.; Zhou, Y.; Yao, J. M. Comparison of the Reinforcing Effects for Cellulose Nanocrystals Obtained by Sulfuric and Hydrochloric Acid Hydrolysis on the Mechanical and Thermal Properties of Bacterial Polyester. Compos. Sci. Technol. 2013, 87, 22– 28,  DOI: 10.1016/j.compscitech.2013.07.024
      28
      Comparison of the reinforcing effects for cellulose nanocrystals obtained by sulfuric and hydrochloric acid hydrolysis on the mechanical and thermal properties of bacterial polyester
      Yu, Hou-Yong; Qin, Zong-Yi; Liu, Lin; Yang, Xiao-Gang; Zhou, Ying; Yao, Ju-Ming
      Composites Science and Technology (2013), 87 (), 22-28CODEN: CSTCEH; ISSN:0266-3538. (Elsevier Ltd.)
      Two kinds of cellulose nanocrystals (CNCs) obtained by sulfuric acid hydrolysis (CNC-S) and hydrochloric acid hydrolysis under hydrothermal condition (CNC-H) were used as org. nanoreinforcment to enhance the mech. property and thermal stability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Comparison of the reinforcing effects for different CNCs on the properties of PHBV was carried out. Compared to CNC-S, CNC-H exhibited the larger aspect ratio, higher crystallinity, and esp. no residual acid groups. Moreover, better dispersion of CNC-H with larger loading contents could be introduced into PHBV matrix, which was beneficial to form more intermol. hydrogen bonding interactions, leading to the formation of refined crystal structure of PHBV although the crystn. rate was promoted due to stronger reinforcing effects of CNC-H. Therefore, at the same contents, the reinforcing effect of CNC-H was stronger than CNC-S. More importantly, compared to the neat PHBV, the tensile strength and Young's modulus of the nanocomposite with 12 wt.% CNC-H were enhanced by 175% and 300%, resp., meanwhile the initial decompn. temp. (T0) and max. decompn. temp (Tmax) were increased by 58.1 and 52.1°, resp.
    29. 29
      Jun, D.; Guomin, Z.; Mingzhu, P.; Leilei, Z.; Dagang, L.; Rui, Z. Crystallization and Mechanical Properties of Reinforced PHBV Composites Using Melt Compounding: Effect of CNCs and CNFs. Carbohydr. Polym. 2017, 168, 255– 262,  DOI: 10.1016/j.carbpol.2017.03.076
      29
      Crystallization and mechanical properties of reinforced PHBV composites using melt compounding: Effect of CNCs and CNFs
      Jun Du; Guomin Zhao; Leilei Zhuang; Dagang Li; Mingzhu Pan; Rui Zhang
      Carbohydrate polymers (2017), 168 (), 255-262 ISSN:.
      Nanocellulose reinforced poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) composites were prepared using melt compounding. The effects of nanocellulose types (CNCs and CNFs) and nanocellulose content (1, 2, 3, 4, 5, 6 and 7wt%) on the crystallization, thermal and mechanical properties of PHBV composites were systematically compared in this study. The thermal stability of PHBV composites was improved by both CNCs and CNFs. CNFs with a higher thermal stability leaded to a higher thermal stability of PHBV composites. Both CNCs and CNFs induced a reduction in the crystalline size of PHBV spherulites. Furthermore, CNCs could act as a better nucleating agent for PHBV than did CNFs. CNCs and CNFs showed reinforcing effects in PHBV composites. At the equivalent content of nanocellulose, CNCs led to a higher tensile modulus of PHBV composites than did CNFs. 1wt% CNCs/PHBV composites exhibited the most optimum mechanical properties.
    30. 30
      Jiang, L.; Morelius, E.; Zhang, J.; Wolcott, M.; Holbery, J. Study of the Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate)/Cellulose Nanowhisker Composites Prepared by Solution Casting and Melt Processing. J. Compos. Mater. 2008, 42, 2629– 2645,  DOI: 10.1177/0021998308096327
      30
      Study of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhisker composites prepared by solution casting and melt processing
      Jiang, Long; Morelius, Erving; Zhang, Jinwen; Wolcott, Michael; Holbery, James
      Journal of Composite Materials (2008), 42 (24), 2629-2645CODEN: JCOMBI; ISSN:0021-9983. (Sage Publications Ltd.)
      In this study cellulose nanowhiskers (CNW) were prepd. by sulfuric acid hydrolysis from microcryst. cellulose (MCC). The biopolymer composites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/CNW, was fabricated by soln. casting using N,N-dimethylformamide (DMF) as the solvent. Homogeneous dispersion of the whiskers was achieved and the composites exhibited improved tensile strength and modulus and increased glass transition temp. The melt processing (extrusion and injection molding) of PHBV/CNW composites was also attempted. Despite using polyethylene glycol (PEG) as a compatibilizer, CNW agglomerates formed during freeze-drying could not be broken and well dispersed by the extrusion process due to the large surface area and the polar nature of CNW. As a result, the melt processed PHBV/CNW composites exhibited decreased strength and const. glass transition temp., a typical trend of microparticle filled polymer systems. MCC was also treated by high-speed mech. homogenizer to reduce its particle size down to nanoscale range. The homogenized MCC (HMCC) was blended with PHBV by melt processing with the same conditions. The obtained composites were found to have similar properties as the melt-processed PHBV/CNW composites due to poor HMCC dispersion. To the best of our knowledge, PHBV/CNW system has not been studied so far. The treatment of MCC with high-speed homogenizer has also not been reported. This study augments the research on CNW nanocomposites.
    31. 31
      Yu, H. Y.; Yao, J. M. Reinforcing Properties of Bacterial Polyester with Different Cellulose Nanocrystals via Modulating Hydrogen Bonds. Compos. Sci. Technol. 2016, 136, 53– 60,  DOI: 10.1016/j.compscitech.2016.10.004
      31
      Reinforcing properties of bacterial polyester with different cellulose nanocrystals via modulating hydrogen bonds
      Yu, Hou-Yong; Yao, Ju-Ming
      Composites Science and Technology (2016), 136 (), 53-60CODEN: CSTCEH; ISSN:0266-3538. (Elsevier Ltd.)
      This work provides a direct evidence to investigate relationship between hydrogen bonding interactions and property enhancement of cellulose nanocrystals (CN) based bionanocomposites. Cellulose nanocrystal citrates (CN-C) with more hydroxyl (O-H) and carboxyl groups, CN and cellulose nanocrystal formates (CN-F) with less O-H groups were extd. from com. microcryst. cellulose using citric/hydrochloric acids, hydrochloric acid and formic/hydrochloric acids, resp. Then different nanocrystals were incorporated into bacterial polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) for tuning hydrogen bonding interactions and properties of PHBV nanocomposites. As expected, at the same loading contents, CN-C had stronger reinforcing capability on PHBV matrix than CN and CN-F. Compared to neat PHBV, tensile strengths of 10% CN-F/PHBV, 10% CN/PHBV and 10% CN-C/PHBV were improved by 146%, 166% and 187%, resp. Esp., the max. decompn. temp. of 10% CN-C/PHBV was increased by 48.1°C, and this nanocomposite showed superior barrier properties with a 64% redn. in water vapor permeability (WVP). Besides, the nanocomposites showed excellent biocompatibility to human MG-63 cells and lower overall migration levels. Such an outstanding reinforcement by CN-C was ascribed to improved interfacial interaction (more hydrogen bonding interactions or hydrogen bond network), and nanodispersibility in the nanocomposites.
    32. 32
      Habibi, Y.; Goffin, A. L.; Schiltz, N.; Duquesne, E.; Dubois, P.; Dufresne, A. Bionanocomposites Based on Poly(ε-Caprolactone)-Grafted Cellulose Nanocrystals by Ring-Opening Polymerization. J. Mater. Chem. 2008, 18, 5002– 5010,  DOI: 10.1039/b809212e
      32
      Bionanocomposites based on poly(ε-caprolactone)-grafted cellulose nanocrystals by ring-opening polymerization
      Habibi, Youssef; Goffin, Anne-Lise; Schiltz, Nancy; Duquesne, Emmanuel; Dubois, Philippe; Dufresne, Alain
      Journal of Materials Chemistry (2008), 18 (41), 5002-5010CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
      A 'grafting from' approach was used to graft poly(.vepsiln.-caprolactone) (PCL) polymers to cellulose nanocrystals by Sn(Oct)2-catalyzed ring-opening polymn. (ROP). The grafting efficiency was evidenced by the long-term stability of suspension of PCL-grafted cellulose nanocrystals in toluene. These observations were confirmed by Fourier Transform IR Spectroscopy (FT-IR) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). Extd. nanohybrids were characterized by Differential Scanning Calorimetry (DSC), XPS, and contact angle measurements. The morphol. and cryst. structure of the PCL-grafted cellulose nanocrystals was examd. by transmission electron microscopy (TEM) and X-Ray diffraction, resp. Results showed that cellulose nanocrystals kept their initial morphol. integrity and their native crystallinity. Nanocomposites with high content of cellulose nanocrystals were prepd. using either neat cellulose nanocrystals or PCL-grafted cellulose nanocrystals and high mol. wt. PCL as matrix using a casting/evapn. technique. Thermo-mech. properties of processed nanocomposites were studied by DSC, dynamical mech. analyses (DMA) and tensile tests. A significant improvement in terms of Young's modulus and storage modulus was obtained.
    33. 33
      Habibi, Y. Key Advances in the Chemical Modification of Nanocelluloses. Chem. Soc. Rev. 2014, 43, 1519– 1542,  DOI: 10.1039/C3CS60204D
      33
      Key advances in the chemical modification of nanocelluloses
      Habibi, Youssef
      Chemical Society Reviews (2014), 43 (5), 1519-1542CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Nanocelluloses, including nanocryst. cellulose, nanofibrillated cellulose and bacterial cellulose nanofibers, have become fascinating building blocks for the design of new biomaterials. Derived from the must abundant and renewable biopolymer, they are drawing a tremendous level of attention, which certainly will continue to grow in the future driven by the sustainability trend. This growing interest is related to their unsurpassed quintessential phys. and chem. properties. Yet, owing to their hydrophilic nature, their utilization is restricted to applications involving hydrophilic or polar media, which limits their exploitation. With the presence of a large no. of chem. functionalities within their structure, these building blocks provide a unique platform for significant surface modification through various chemistries. These chem. modifications are prerequisite, sometimes unavoidable, to adapt the interfacial properties of nanocellulose substrates or adjust their hydrophilic-hydrophobic balance. Therefore, various chemistries have been developed aiming to surface-modify these nano-sized substrates in order to confer to them specific properties, extending therefore their use to highly sophisticated applications. This review collocates current knowledge in the research and development of nanocelluloses and emphasizes more particularly on the chem. modification routes developed so far for their functionalization.
    34. 34
      Lin, N.; Huang, J.; Chang, P. R.; Feng, J.; Yu, J. Surface Acetylation of Cellulose Nanocrystal and Its Reinforcing Function in Poly(Lactic Acid). Carbohydr. Polym. 2011, 83, 1834– 1842,  DOI: 10.1016/j.carbpol.2010.10.047
      34
      Surface acetylation of cellulose nanocrystal and its reinforcing function in poly(lactic acid)
      Lin, Ning; Huang, Jin; Chang, Peter R.; Feng, Jiwen; Yu, Jiahui
      Carbohydrate Polymers (2011), 83 (4), 1834-1842CODEN: CAPOD8; ISSN:0144-8617. (Elsevier Ltd.)
      A novel and facile method for surface acetylation of cellulose nanocrystals (CN) was developed by reaction with acetic anhydride and hydroxyl groups on the surface of CN. The resultant acetylated cellulose nanocrystals (ACN) exhibited improved dispersion in various org. solvents and reduced polarity as compared with unmodified CN. These ACN were subsequently introduced into a poly(lactic acid) (PLA) polymeric matrix to produce fully biodegradable nanocomposites, which showed superior mech. performance and thermal stability. This improvement was primarily attributed to uniform dispersion of the ACN and to strong interfacial adhesion between filler and matrix. This high performance and eco-friendly nanocomposite will expand the utilization of cellulose nanocrystals from renewable bioresources and the practical application of PLA-based plastic.
    35. 35
      Yu, H. Y.; Qin, Z. Y.; Yan, C. F.; Yao, J. M. Green Nanocomposites Based on Functionalized Cellulose Nanocrystals: A Study on the Relationship between Interfacial Interaction and Property Enhancement. ACS Sustainable Chem. Eng. 2014, 2, 875– 886,  DOI: 10.1021/sc400499g
      35
      Green Nanocomposites Based on Functionalized Cellulose Nanocrystals: A Study on the Relationship between Interfacial Interaction and Property Enhancement
      Yu, Hou-Yong; Qin, Zong-Yi; Yan, Chen-Feng; Yao, Ju-Ming
      ACS Sustainable Chemistry & Engineering (2014), 2 (4), 875-886CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
      Functionalized cellulose nanocrystals (PHCNs) were synthesized by grafting poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) onto cellulose nanocrystals (CNCs). The resultant PHCNs with high loading levels were uniformly dispersed into a PHBV matrix to produce fully biodegradable nanocomposites, which showed superior mech. performance and thermal stability. Compared with those of neat PHBV, the tensile strength, Young's modulus, and elongation at break of the nanocomposites with 20 wt. % PHCNs were enhanced by 113%, 95%, and 17%, resp. Meanwhile, the initial decompn. temp. (T0), temp. at 5% wt. loss (T5%), max. decompn. temp. (Tmax), and complete decompn. temp. (Tf) increased by 29.6, 23.9, 34.7, and 37.0 °C, resp. This improvement was primarily ascribed to uniform dispersion of the PHCNs and to strong interfacial adhesion between filler and matrix due to the chain entanglements, cocrystn., and hydrogen bonding interactions. Moreover, the nanocomposites showed a wider melt-processing window than neat PHBV. Furthermore, the crystallinity and hydrophilic properties of the nanocomposites could be modulated through with the increase of the PHCN contents. In addn., the nanocomposites were nontoxic to human MG-63 cells. Such high performance bionanocomposites have great potential in expanding the utilization of CNCs from natural resources and practical application as PHBV-based bioplastic and biomedical materials.
    36. 36
      Zhang, J.; Li, M.-C.; Zhang, X.; Ren, S.; Dong, L.; Lee, S.; Cheng, H. N.; Lei, T.; Wu, Q. Surface Modified Cellulose Nanocrystals for Tailoring Interfacial Miscibility and Microphase Separation of Polymer Nanocomposites. Cellulose 2019, 26, 4301– 4312,  DOI: 10.1007/s10570-019-02379-z
      36
      Surface modified cellulose nanocrystals for tailoring interfacial miscibility and microphase separation of polymer nanocomposites
      Zhang, Jinlong; Li, Mei-Chun; Zhang, Xiuqiang; Ren, Suxia; Dong, Lili; Lee, Sunyoung; Cheng, H. N.; Lei, Tingzhou; Wu, Qinglin
      Cellulose (Dordrecht, Netherlands) (2019), 26 (7), 4301-4312CODEN: CELLE8; ISSN:0969-0239. (Springer)
      High performance nanocomposites with good interfacial miscibility and phase sepd. morphol. have received a lot of attention. In this work, cellulose nanocrystals (CNCs) were first grafted with hydrophobic poly(Me methacrylate) (PMMA) chains to produce modified CNCs (PMCNCs) with increased thermal stability. Such surface-tailored CNCs effectively influenced the phase morphol. and improved the mech. properties of poly(Bu acrylate-co-MMA) (PBA-co-PMMA) nanocomposites. Morphol. anal. indicated the presence of microphase sepn. in PMCNCs/PBA-co-PMMA nanocomposites with PBA as the soft domain and PMMA as well as CNCs as the hard domain. The nanocomposites with 10 wt% PMCNCs/PBA-co-PMMA showed increases in Young's modulus of more than 20-fold and in tensile strength of about 3-fold compared to those of the unmodified PBA-co-PMMA copolymer. Therefore, the PMCNCs played a crucial role in controlling the interfacial miscibility and tuning the phase morphol. of the nanocomposites. It is also essential to understand the role played by microphase sepn. in achieving nano-scaled morphol. control and in fine-tuning the resultant composite properties.
    37. 37
      Braun, B.; Dorgan, J. R. Single-Step Method for the Isolation and Surface Functionalization of Cellulosic Nanowhiskers. Biomacromolecules 2009, 10, 334– 341,  DOI: 10.1021/bm8011117
      37
      Single-Step Method for the Isolation and Surface Functionalization of Cellulosic Nanowhiskers
      Braun, Birgit; Dorgan, John R.
      Biomacromolecules (2009), 10 (2), 334-341CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)
      Surface modification of cellulosic nanowhiskers (CNW) is of great interest, esp. to facilitate their use as polymer reinforcements. Generally, alteration of the surface chem. is performed using multiple reaction steps. In contrast, this study demonstrates that the needed hydrolysis of amorphous cellulose chains can be performed simultaneously with the esterification of accessible hydroxyl groups to produce surface functionalized CNW in a single step. The reaction is carried out in an acid mixt. composed of hydrochloric and an org. acid (acetic and butyric are both demonstrated). Resulting CNW are of similar dimensions compared to those obtained by hydrochloric acid hydrolysis alone; sizes are verified by multiangle laser-light scattering and transmission electron microscopy. However, narrower diam. polydispersity indexes indicate that surface groups aid the individualization of the nanowhiskers (Px = 2.5 and 2.1 for acetic and butyric acid, Px = 3.0 for hydrochloric acid). More than half of the hydroxyl groups located on the CNW surface are substituted under the employed reaction conditions as detd. by quant. Fourier-transform IR-spectroscopy. The resulting surface modified CNW are dispersible in Et acetate and toluene indicating increased hydrophobicity and thus are presumably more compatible with hydrophobic polymers when used as a reinforcing phase.
    38. 38
      Spinella, S.; Lo Re, G.; Liu, B.; Dorgan, J.; Habibi, Y.; Leclère, P.; Raquez, J. M.; Dubois, P.; Gross, R. A. Polylactide/Cellulose Nanocrystal Nanocomposites: Efficient Routes for Nanofiber Modification and Effects of Nanofiber Chemistry on PLA Reinforcement. Polymer 2015, 65, 9– 17,  DOI: 10.1016/j.polymer.2015.02.048
      38
      Polylactide/cellulose nanocrystal nanocomposites: Efficient routes for nanofiber modification and effects of nanofiber chemistry on PLA reinforcement
      Spinella, Stephen; Lo Re, Giada; Liu, Bo; Dorgan, John; Habibi, Youssef; Leclere, Philippe; Raquez, Jean-Marie; Dubois, Philippe; Gross, Richard A.
      Polymer (2015), 65 (), 9-17CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      To improve the Heat Deflection Temp. of polylactide (PLA), nanocomposites were prepd. with modified cellulose nanocrystals (CNCs) by melt blending. The prepn. of acetate and lactate modified CNCs (AA- and LA-CNCs) was performed by a green one-pot dual acid (org. acid and HCl) method such that acid hydrolysis and Fischer Esterification occur in tandem. The degree of substitution for AA-CNCs and LA-CNCs, detd. by FTIR, are 0.12 and 0.13, resp. Relative to unmodified CNCs, esterification of CNC surfaces with lactate and acetate moieties resulted in a 40 °C increase in thermal stability. At 5 wt% loading of CNCs, LA-CNCs gave superior reinforcement below and above the glass temp. of PLA, corresponding to a 31% and 450% increase in PLA's storage modulus compared to neat PLA. An increase in PLA's heat deflection temp. by 10 °C and 20 °C was achieved by melt-blending PLA with 5 and 20% LA-CNCs, resp. The above studies provide indirect evidence that LA-CNCs were best dispersed (lowest tendency to aggregate) in the PLA matrix. This hypothesis was confirmed through direct visualization using AFM. Thus, a simple modification strategy for CNCs was devised that enables the formation of PLA nanocomposites with high extents of nanofiber dispersion within the matrix. Furthermore, the dispersion of CNCs in PLA matrixes is profoundly influenced by relatively small changes in the modification chem., in this case, appending lactate vs. acetate groups.
    39. 39
      Spinella, S.; Maiorana, A.; Qian, Q.; Dawson, N. J.; Hepworth, V.; McCallum, S. A.; Ganesh, M.; Singer, K. D.; Gross, R. A. Concurrent Cellulose Hydrolysis and Esterification to Prepare Surface-Modified Cellulose Nanocrystal Decorated with Carboxylic Acid Moieties. ACS Sustainable Chem. Eng. 2016, 4, 1538– 1550,  DOI: 10.1021/acssuschemeng.5b01489
      39
      Concurrent Cellulose Hydrolysis and Esterification to Prepare a Surface-Modified Cellulose Nanocrystal Decorated with Carboxylic Acid Moieties
      Spinella, Stephen; Maiorana, Anthony; Qian, Qian; Dawson, Nathan J.; Hepworth, Victoria; McCallum, Scott A.; Ganesh, Manoj; Singer, Kenneth D.; Gross, Richard A.
      ACS Sustainable Chemistry & Engineering (2016), 4 (3), 1538-1550CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
      Cellulose nanocrystals (CNCs) were modified with natural di- and tricarboxylic acids using two concurrent acid-catalyzed reactions including hydrolysis of amorphous cellulose segments and Fischer esterification, resulting in the introduction of free carboxylic acid functionality onto CNC surfaces. CNC esterification was characterized by Fourier transform IR spectroscopy, 13C solid state magic-angle spinning (MAS), and conductometric titrn. expts. Av. degree of substitution values for malonate, malate, and citrate CNCs are 0.16, 0.22, and 0.18, resp. Despite differences in org. acid pKa, optimal HCl cocatalyst concns. were similar for malonic, malic, and citric acids. After isolation of modified CNCs, residual cellulose coproducts were identified that are similar to microcryst. cellulose based on SEM and XRD anal. As proof of concept, recycling expts. were carried to increase the yield of citrate CNCs. The byproduct was then recycled by subsequent citric acid/HCl treatments that resulted in 55% total yield of citrate CNCs. The crystallinity, morphol., and substitution of citrate CNCs from recycled cellulose coproduct is similar to modified citrate CNCs formed in the first reaction cycle. Thermal stability of all modified CNCs under air and nitrogen resulted in T10% and T50% values above 256 and 323 °C, resp. Thus, they can be used for melt-processing operations performed at moderately high temps. without thermal decompn. Nanocomposites of poly(vinyl alc.) with modified CNCs (1 wt % malonate, malate, citrate, and unmodified CNCs) were prepd. An increase in the thermal decompn. temp. by almost 40 °C was obtained for PVOH-citrate-modified CNC nanocomposites.
    40. 40
      Lo Re, G.; Engström, J.; Wu, Q.; Malmström, E.; Gedde, U. W.; Olsson, R. T.; Berglund, L. Improved Cellulose Nanofibril Dispersion in Melt-Processed Polycaprolactone Nanocomposites by a Latex-Mediated Interphase and Wet Feeding as LDPE Alternative. ACS Appl. Nano Mater. 2018, 1, 2669– 2677,  DOI: 10.1021/acsanm.8b00376
      40
      Improved Cellulose Nanofibril Dispersion in Melt-Processed Polycaprolactone Nanocomposites by a Latex-Mediated Interphase and Wet Feeding as LDPE Alternative
      Lo Re, Giada; Engstroem, Joakim; Wu, Qiong; Malmstroem, Eva; Gedde, Ulf W.; Olsson, Richard T.; Berglund, Lars
      ACS Applied Nano Materials (2018), 1 (6), 2669-2677CODEN: AANMF6; ISSN:2574-0970. (American Chemical Society)
      This work reports the development of a sustainable and green one-step wet-feeding method to prep. tougher and stronger nanocomposites from biodegradable cellulose nanofibrils (CNF)/polycaprolactone (PCL) constituents, compatibilized with reversible addn. fragmentation chain transfer-mediated surfactant-free poly(Me methacrylate) (PMMA) latex nanoparticles. When a PMMA latex is used, a favorable electrostatic interaction between CNF and the latex is obtained, which facilitates mixing of the constituents and hinders CNF agglomeration. The improved dispersion is manifested in significant improvement of mech. properties compared with the ref. material. The tensile tests show much higher modulus (620 MPa) and strength (23 MPa) at 10 wt. % CNF content (compared to the neat PCL ref. modulus of 240 and 16 MPa strength), while maintaining high level of work to fracture the matrix (7 times higher than the ref. nanocomposite without the latex compatibilizer). Rheol. anal. showed a strongly increased viscosity as the PMMA latex was added, i.e., from a well-dispersed and strongly interacting CNF network in the PCL.
    41. 41
      Dufresne, A. Cellulose Nanomaterials as Green Nanoreinforcements for Polymer Nanocomposites. Philos. Trans. R. Soc., A 2018, 376, 20170040,  DOI: 10.1098/rsta.2017.0040
      41
      Cellulose nanomaterials as green nanoreinforcements for polymer nanocomposites
      Dufresne, Alain
      Philosophical Transactions of the Royal Society, A: Mathematical, Physical & Engineering Sciences (2018), 376 (2112), 20170040/1-20170040/23CODEN: PTRMAD; ISSN:1364-503X. (Royal Society)
      A review. Unexpected and attractive properties can be obsd. when decreasing the size of a material down to the nanoscale. Cellulose is no exception to the rule. In addn., the highly reactive surface of cellulose resulting from the high d. of hydroxyl groups is exacerbated at this scale. Different forms of cellulose nanomaterials, resulting from a topdown deconstruction strategy (cellulose nanocrystals, cellulose nanofibrils) or bottom-up strategy (bacterial cellulose), are potentially useful for a large no. of industrial applications. These include the paper and cardboard industry, use as reinforcing filler in polymer nanocomposites, the basis for low-d. foams, additives in adhesives and paints, as well as a wide variety of filtration, electronic, food, hygiene, cosmetic andmedical products. This paper focuses on the use of cellulose nanomaterials as a filler for the prepn. of polymer nanocomposites. Impressive mech. properties can be obtained for these materials. They obviously depend on the type of nanomaterial used, but the crucial point is the processing technique. The emphasis is on the melt processing of such nanocomposite materials, which has not yet been properly resolved and remains a challenge.
    42. 42
      Oksman, K.; Aitomäki, Y.; Mathew, A. P.; Siqueira, G.; Zhou, Q.; Butylina, S.; Tanpichai, S.; Zhou, X.; Hooshmand, S. Review of the Recent Developments in Cellulose Nanocomposite Processing. Composites, Part A 2016, 83, 2– 18,  DOI: 10.1016/j.compositesa.2015.10.041
      42
      Review of the recent developments in cellulose nanocomposite processing
      Oksman, Kristiina; Aitomaeki, Yvonne; Mathew, Aji P.; Siqueira, Gilberto; Zhou, Qi; Butylina, Svetlana; Tanpichai, Supachok; Zhou, Xiaojian; Hooshmand, Saleh
      Composites, Part A: Applied Science and Manufacturing (2016), 83 (), 2-18CODEN: CASMFJ; ISSN:1359-835X. (Elsevier Ltd.)
      A review. This review addresses the recent developments of the processing of cellulose nanocomposites, focusing on the most used techniques, including soln. casting, melt-processing of thermoplastic cellulose nanocomposites and resin impregnation of cellulose nanopapers using thermoset resins. Important techniques, such as partially dissolved cellulose nanocomposites, nanocomposite foams reinforced with nanocellulose, as well as long continuous fibers or filaments, are also addressed. It is shown how the research on cellulose nanocomposites has rapidly increased during the last 10 years, and manufg. techniques have been developed from simple casting to these more sophisticated methods. To produce cellulose nanocomposites for com. use, the processing of these materials must be developed from lab. to industrially viable methods.
    43. 43
      Park, S.; Baker, J. O.; Himmel, M. E.; Parilla, P. A.; Johnson, D. K. Cellulose Crystallinity Index: Measurement Techniques and Their Impact on Interpreting Cellulase Performance. Biotechnol. Biofuels 2010, 3, 10,  DOI: 10.1186/1754-6834-3-10
      43
      Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance
      Park Sunkyu; Baker John O; Himmel Michael E; Parilla Philip A; Johnson David K
      Biotechnology for biofuels (2010), 3 (), 10 ISSN:.
      Although measurements of crystallinity index (CI) have a long history, it has been found that CI varies significantly depending on the choice of measurement method. In this study, four different techniques incorporating X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) were compared using eight different cellulose preparations. We found that the simplest method, which is also the most widely used, and which involves measurement of just two heights in the X-ray diffractogram, produced significantly higher crystallinity values than did the other methods. Data in the literature for the cellulose preparation used (Avicel PH-101) support this observation. We believe that the alternative X-ray diffraction (XRD) and NMR methods presented here, which consider the contributions from amorphous and crystalline cellulose to the entire XRD and NMR spectra, provide a more accurate measure of the crystallinity of cellulose. Although celluloses having a high amorphous content are usually more easily digested by enzymes, it is unclear, based on studies published in the literature, whether CI actually provides a clear indication of the digestibility of a cellulose sample. Cellulose accessibility should be affected by crystallinity, but is also likely to be affected by several other parameters, such as lignin/hemicellulose contents and distribution, porosity, and particle size. Given the methodological dependency of cellulose CI values and the complex nature of cellulase interactions with amorphous and crystalline celluloses, we caution against trying to correlate relatively small changes in CI with changes in cellulose digestibility. In addition, the prediction of cellulase performance based on low levels of cellulose conversion may not include sufficient digestion of the crystalline component to be meaningful.
    44. 44
      Chen, L.; Wang, Q.; Hirth, K.; Baez, C.; Agarwal, U. P.; Zhu, J. Y. Tailoring the Yield and Characteristics of Wood Cellulose Nanocrystals (CNC) Using Concentrated Acid Hydrolysis. Cellulose 2015, 22, 1753– 1762,  DOI: 10.1007/s10570-015-0615-1
      44
      Tailoring the yield and characteristics of wood cellulose nanocrystals (CNC) using concentrated acid hydrolysis
      Chen, Liheng; Wang, Qianqian; Hirth, Kolby; Baez, Carlos; Agarwal, Umesh P.; Zhu, J. Y.
      Cellulose (Dordrecht, Netherlands) (2015), 22 (3), 1753-1762CODEN: CELLE8; ISSN:0969-0239. (Springer)
      Cellulose nanocrystals (CNC) have recently received much attention in the global scientific community for their unique mech. and optical properties. Here, we conducted the first detailed exploration of the basic properties of CNC, such as morphol., crystallinity, degree of sulfation and yield, as a function of prodn. condition variables. The rapid cellulose depolymn. and sulfation reactions under concd. acid concns. of around 60 wt% resulted in a very narrow operating window for CNC prodn. We found that CNC yields as high as 70 wt% from a bleached eucalyptus kraft pulp with glucan content of 78 wt% can be achieved under a tight range of reaction conditions and that a weighted av. length of over 200 nm and sulfur content (a measure of CNC surface charge) between 3 and 10 mg/g can be produced. This study provided crit. knowledge for the prodn. of CNC with characteristics tailored for different specific applications, significant to commercialization.
    45. 45
      Wickholm, K.; Larsson, P. T.; Iversen, T. Assignment of Non-Crystalline Forms in Cellulose I by CP/MAS 13C NMR Spectroscopy. Carbohydr. Res. 1998, 312, 123– 129,  DOI: 10.1016/S0008-6215(98)00236-5
      45
      Assignment of non-crystalline forms in cellulose I by CP/MAS carbon-13 NMR spectroscopy
      Wickholm, Kristina; Larsson, Per Tomas; Iversen, Tommy
      Carbohydrate Research (1998), 312 (3), 123-129CODEN: CRBRAT; ISSN:0008-6215. (Elsevier Science Ltd.)
      Non-cryst. forms of cellulose (I) in birch pulp, cotton linters, and Cladophora species were studied by CP/MAS 13C NMR spectroscopy. New assignments were made for the NMR-signals in the lower shift part of the C-4 region (80-86 ppm). These signals were assigned to I at accessible fibril surfaces, I at inaccessible fibril surfaces, and hemicellulose. Also, further evidence was found for para-cryst. I as an "in-fibril" form, inaccessible to the surrounding solvent.
    46. 46
      Gårdebjer, S.; Bergstrand, A.; Idström, A.; Börstell, C.; Naana, S.; Nordstierna, L.; Larsson, A. Solid-State NMR to Quantify Surface Coverage and Chain Length of Lactic Acid Modified Cellulose Nanocrystals, Used as Fillers in Biodegradable Composites. Compos. Sci. Technol. 2015, 107, 1– 9,  DOI: 10.1016/j.compscitech.2014.11.014
      There is no corresponding record for this reference.
    47. 47
      Park, S.; Johnson, D. K.; Ishizawa, C. I.; Parilla, P. A.; Davis, M. F. Measuring the Crystallinity Index of Cellulose by Solid State 13C Nuclear Magnetic Resonance. Cellulose 2009, 16, 641– 647,  DOI: 10.1007/s10570-009-9321-1
      47
      Measuring the crystallinity index of cellulose by solid state 13C nuclear magnetic resonance
      Park, Sunkyu; Johnson, David K.; Ishizawa, Claudia I.; Parilla, Philip A.; Davis, Mark F.
      Cellulose (Dordrecht, Netherlands) (2009), 16 (4), 641-647CODEN: CELLE8; ISSN:0969-0239. (Springer)
      The crystallinity index of cellulose is an important parameter to establish because of the effect this property has on the utilization of cellulose as a material and as a feedstock for biofuels prodn. However, it has been found that the crystallinity index varies significantly depending on the choice of instrument and data anal. technique applied to the measurement. We introduce in this study a simple and straightforward method to evaluate the crystallinity index of cellulose. This novel method was developed using solid state 13C NMR and subtraction of the spectrum of a std. amorphous cellulose. The crystallinity indexes of twelve different celluloses were measured and the values from this method were compared with the values obtained by other existing methods, including methods based on X-ray diffraction. An interesting observation was that the hydration of the celluloses increased their crystallinity indexes by about 5%, suggesting that addn. of water increased cellulose order for all the cellulose samples studied.
    48. 48
      Eichhorn, S. J.; Dufresne, A.; Aranguren, M.; Marcovich, N. E.; Capadona, J. R.; Rowan, S. J.; Weder, C.; Thielemans, W.; Roman, M.; Renneckar, S.; Gindl, W.; Veigel, S.; Keckes, J.; Yano, H.; Abe, K.; Nogi, M.; Nakagaito, A. N.; Mangalam, A.; Simonsen, J.; Benight, A. S.; Bismarck, A.; Berglund, L. A.; Peijs, T. Review: Current International Research into Cellulose Nanofibres and Nanocomposites. J. Mater. Sci. 2010, 45, 1– 33,  DOI: 10.1007/s10853-009-3874-0
      48
      Review: current international research into cellulose nanofibres and nanocomposites
      Eichhorn, S. J.; Dufresne, A.; Aranguren, M.; Marcovich, N. E.; Capadona, J. R.; Rowan, S. J.; Weder, C.; Thielemans, W.; Toman, M.; Renneckar, S.; Gindl, W.; Veigel, S.; Keckes, J.; Yano, H.; Abe, K.; Nogi, M.; Nakagaito, A. N.; Mangalam, A.; Simonsen, J.; Benight, A. S.; Bismarck, A.; Berglund, L. A.; Peijs, T.
      Journal of Materials Science (2010), 45 (1), 1-33CODEN: JMTSAS; ISSN:0022-2461. (Springer)
      A review. This paper provides an overview of recent progress made in the area of cellulose nanofiber-based nanocomposites. An introduction into the methods used to isolate cellulose nanofibers (nanowhiskers, nanofibrils) is given, with details of their structure. Following this, the article is split into sections dealing with processing and characterization of cellulose nanocomposites and new developments in the area, with particular emphasis on applications. The types of cellulose nanofibers covered are those extd. from plants by acid hydrolysis (nanowhiskers), mech. treatment and those that occur naturally (tunicate nanowhiskers) or under culturing conditions (bacterial cellulose nanofibrils). Research highlighted in the article are the use of cellulose nanowhiskers for shape memory nanocomposites, anal. of the interfacial properties of cellulose nanowhisker and nanofibril-based composites using Raman spectroscopy, switchable interfaces that mimic sea cucumbers, polymn. from the surface of cellulose nanowhiskers by atom transfer radical polymn. and ring opening polymn.
    49. 49
      Lo Re, G.; Spinella, S.; Boujemaoui, A.; Vilaseca, F.; Larsson, P. T.; Adås, F.; Berglund, L. A. Poly(ϵ-Caprolactone) Biocomposites Based on Acetylated Cellulose Fibers and Wet Compounding for Improved Mechanical Performance. ACS Sustainable Chem. Eng. 2018, 6, 6753– 6760,  DOI: 10.1021/acssuschemeng.8b00551
      49
      Poly(ε-caprolactone) Biocomposites Based on Acetylated Cellulose Fibers and Wet Compounding for Improved Mechanical Performance
      Lo Re, Giada; Spinella, Stephen; Boujemaoui, Assya; Vilaseca, Fabiola; Larsson, Per Tomas; Adaas, Fredrik; Berglund, Lars A.
      ACS Sustainable Chemistry & Engineering (2018), 6 (5), 6753-6760CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
      Poly(ε-caprolactone) (PCL) is a ductile thermoplastic, which is biodegradable in the marine environment. Limitations include low strength, petroleum-based origin, and comparably high cost. Cellulose fiber reinforcement is therefore of interest although uniform fiber dispersion is a challenge. In this study, a one-step wet compounding is proposed to validate a sustainable and feasible method to improve the dispersion of the cellulose fibers in hydrophobic polymer matrix as PCL, which showed to be insensitive to the presence of the water during the processing. A comparison between unmodified and acetylated cellulosic wood fibers is made to further assess the net effect of the wet feeding and chem. modification on the biocomposites properties, and the influence of acetylation on fiber structure is reported (ATR-FTIR, XRD). Effects of processing on nanofibrillation, shortening, and dispersion of the cellulose fibers are assessed as well as on PCL molar mass. Mech. testing, dynamic mech. thermal anal., FE-SEM, and X-ray tomog. is used to characterize composites. With the addn. of 20 wt % cellulosic fibers, the Young's modulus increased from 240 MPa (neat PCL) to 1850 MPa for the biocomposites produced by using the wet feeding strategy, compared to 690 MPa showed for the biocomposites produced using dry feeling. A wet feeding of acetylated cellulosic fibers allowed even a greater increase, with an addnl. 46% and 248% increase of the ultimate strength and Young's modulus, when compared to wet feeding of the unmodified pulp, resp.
    50. 50
      Svenningsson, L.; Sparrman, T.; Bialik, E.; Bernin, D.; Nordstierna, L. Molecular Orientation Distribution of Regenerated Cellulose Fibers Investigated with Rotor Synchronized Solid State NMR Spectroscopy. Cellulose 2019, 26, 4681– 4692,  DOI: 10.1007/s10570-019-02430-z
      50
      Molecular orientation distribution of regenerated cellulose fibers investigated with rotor synchronized solid state NMR spectroscopy
      Svenningsson, Leo; Sparrman, Tobias; Bialik, Erik; Bernin, Diana; Nordstierna, Lars
      Cellulose (Dordrecht, Netherlands) (2019), 26 (8), 4681-4692CODEN: CELLE8; ISSN:0969-0239. (Springer)
      A regenerated cellulose fiber is, in contrast to cotton, a man-made fiber. In the fiber prodn., the cellulose polymer is subject to various processing steps, affecting the underlying mol. orientation distribution, which is a detg. factor for mech. properties of the fiber. In this work, the mol. orientation distribution was detd. in a 13C natural abundance Lyocell regenerated cellulose fiber bundle using rotor synchronized magic angle spinning NMR spectroscopy (ROSMAS) to investigate the chem. shift anisotropy (CSA). The recorded signal intensities were compared with an anal. model of the expt. to find the order parameters reflecting the orientation of the fiber. The CSA tensor was calcd. using d. functional theory for the cryst. cellulose II structure, commonly found in regenerated cellulose, and is required as an input parameter. The expected order parameter values were only found when approximating the glycosidic bond and its CSA tensor as being parallel to the mol. frame with the order parameter P2 = 0.45±0.02 compared to P2 = 0.46±0.02 obtained with wide angle x-ray scattering on a fiber bundle. To make this method accessible to the community, we distribute the Matlab script for the simulation of spectra obtained by the ROSMAS expt. at github.com/LeoSvenningsson/ROSMAS.
    51. 51
      Moon, R. J.; Martini, A.; Nairn, J.; Simonsen, J.; Youngblood, J. Cellulose Nanomaterials Review: Structure, Properties and Nanocomposites. Chem. Soc. Rev. 2011, 40, 3941– 3994,  DOI: 10.1039/c0cs00108b
      51
      Cellulose nanomaterials review: structure, properties and nanocomposites
      Moon, Robert J.; Martini, Ashlie; Nairn, John; Simonsen, John; Youngblood, Jeff
      Chemical Society Reviews (2011), 40 (7), 3941-3994CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      This crit. review provides a processing-structure-property perspective on recent advances in cellulose nanoparticles and composites produced from them. It summarizes cellulose nanoparticles in terms of particle morphol., crystal structure, and properties. Also described are the self-assembly and rheol. properties of cellulose nanoparticle suspensions. The methodol. of composite processing and resulting properties are fully covered, with an emphasis on neat and high fraction cellulose composites. Addnl., advances in predictive modeling from mol. dynamic simulations of cryst. cellulose to the continuum modeling of composites made with such particles are reviewed (392 refs.).
    52. 52
      Girouard, N. M.; Xu, S.; Schueneman, G. T.; Shofner, M. L.; Meredith, J. C. Site-Selective Modification of Cellulose Nanocrystals with Isophorone Diisocyanate and Formation of Polyurethane-CNC Composites. ACS Appl. Mater. Interfaces 2016, 8, 1458– 1467,  DOI: 10.1021/acsami.5b10723
      52
      Site-Selective Modification of Cellulose Nanocrystals with Isophorone Diisocyanate and Formation of Polyurethane-CNC Composites
      Girouard, Natalie M.; Xu, Shanhong; Schueneman, Gregory T.; Shofner, Meisha L.; Meredith, J. Carson
      ACS Applied Materials & Interfaces (2016), 8 (2), 1458-1467CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      The unequal reactivity of the two isocyanate groups in an isophorone diisocyanate (IPDI) monomer was exploited to yield modified cellulose nanocrystals (CNCs) with both urethane and isocyanate functionality. The chem. functionality of the modified CNCs was verified with ATR-FTIR anal. and elemental anal. The selectivity for the secondary isocyanate group using di-Bu tin dilaurate (DBTDL) as the reaction catalyst was confirmed with 13C NMR. The modified CNCs showed improvements in the onset of thermal degrdn. by 35 °C compared to the unmodified CNCs. Polyurethane composites based on IPDI and a trifunctional polyether alc. were synthesized using unmodified (um-CNC) and modified CNCs (m-CNC). The degree of nanoparticle dispersion was qual. assessed with polarized optical microscopy. It was found that the modification step facilitated superior nanoparticle dispersion compared to the um-CNCs, which resulted in increases in the tensile strength and work of fracture of over 200% compared to the neat matrix without degrdn. of elongation at break.
    53. 53
      Abraham, E.; Kam, D.; Nevo, Y.; Slattegard, R.; Rivkin, A.; Lapidot, S.; Shoseyov, O. Highly Modified Cellulose Nanocrystals and Formation of Epoxy-Nanocrystalline Cellulose (CNC) Nanocomposites. ACS Appl. Mater. Interfaces 2016, 8, 28086– 28095,  DOI: 10.1021/acsami.6b09852
      53
      Highly Modified Cellulose Nanocrystals and Formation of Epoxy-Nanocrystalline Cellulose (CNC) Nanocomposites
      Abraham, Eldho; Kam, Doron; Nevo, Yuval; Slattegard, Rikard; Rivkin, Amit; Lapidot, Shaul; Shoseyov, Oded
      ACS Applied Materials & Interfaces (2016), 8 (41), 28086-28095CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      This work presents an environmentally friendly, iodine-catalyzed chem. modification method to generate highly hydrophobic, optically active nanocryst. cellulose (CNC). The high degree of ester substitution (DS = 2.18), hydrophobicity, cryst. behavior, and optical activity of the generated acetylated CNC (Ac-CNC) were quantified by TEM, FTIR, solid 13C NMR, contact angle, x-ray diffraction, and POM analyses. Ac-CNC possesses substantial enhancement in thermal stability (16.8%) and forms thin films with an interlayer distance of 50-150 nm, presenting cavities suitable for entrapping nano- and microparticles. Generated Ac-CNC proved to be an effective reinforcing agent in hydrophobic polymer matrixes for fabricating high performance nanocomposites. When integrated at a low wt. percentage (0.5%) in an epoxy matrix, Ac-CNC provided for a 73% increase in tensile strength and a 98% increase in modulus, demonstrating its remarkable reinforcing potential and effective stress transfer behavior. The method of modification and the unique properties of the modified CNC (hydrophobicity, crystallinity, reinforcing ability, and optical activity) render them a novel bionanomaterial for a range of multipurpose applications.
    54. 54
      Leszczynska, A.; Radzik, P.; Szefer, E.; Mičušík, M.; Omastová, M.; Pielichowski, K. Surface Modification of Cellulose Nanocrystals with Succinic Anhydride. Polymers 2019, 11, 866,  DOI: 10.3390/polym11050866
      54
      Surface modification of cellulose nanocrystals with succinic anhydride
      Leszczynska, Agnieszka; Radzik, Paulina; Szefer, Ewa; Micusik, Matej; Omastova, Maria; Pielichowski, Krzysztof
      Polymers (Basel, Switzerland) (2019), 11 (5), 866CODEN: POLYCK; ISSN:2073-4360. (MDPI AG)
      The surface modification of cellulose nanocrystals (CNC) is a key intermediate step in the development of new functionalities and the tailoring of nanomaterial properties for specific applications. In the area of polymeric nanocomposites, apart from good interfacial adhesion, the high thermal stability of cellulose nanomaterial is vitally required for the stable processing and improvement of material properties. In this respect, the heterogeneous esterification of CNC with succinic anhydride was investigated in this work in order to obtain CNC with optimized surface and thermal properties. The influence of reaction parameters, such as time, temp., and molar ratio of reagents, on the structure, morphol. and thermal properties, were systematically studied over a wide range of values by DLS, FTIR, XPS, WAXD, SEM and TGA methods. It was found that the degree of surface substitution of CNC increased with the molar ratio of succinic anhydride to cellulose hydroxyl groups (SA:OH), as well as the reaction time, while the temp. of reaction showed a moderate effect on the degree of esterification in the range of 70-110°C. The studies on the thermal stability of modified nanoparticles indicated that there is a crit. extent of surface esterification below which only a slight decrease of the initial temp. of degrdn. was obsd. in pyrolytic and oxidative atmospheres. A significant redn. of CNC thermal stability was obsd. only for the longest reaction time (240 min) and the highest molar ratio of SA:OH. This illustrates the possibility of manufg. thermally stable, succinylated, CNC by controlling the reaction conditions and the degree of esterification.
    55. 55
      Yu, H.; Sun, B.; Zhang, D.; Chen, G.; Yang, X.; Yao, J. Reinforcement of Biodegradable Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate) with Cellulose Nanocrystal/Silver Nanohybrids as Bifunctional Nanofillers. J. Mater. Chem. B 2014, 2, 8479– 8489,  DOI: 10.1039/C4TB01372G
      55
      Reinforcement of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with cellulose nanocrystal/silver nanohybrids as bifunctional nanofillers
      Yu, Houyong; Sun, Bin; Zhang, Dongzi; Chen, Guoyin; Yang, Xingyuan; Yao, Juming
      Journal of Materials Chemistry B: Materials for Biology and Medicine (2014), 2 (48), 8479-8489CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
      Green nanocomposites contg. biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and cellulose nanocrystals/silver (CNC-Ag) nanohybrids were synthesized and their properties were investigated. It was found that homogeneously dispersed CNC-Ag could act as bifunctional reinforcements to improve the thermal, mech. and antibacterial properties of PHBV. Compared to pristine PHBV, the tensile strength and the max. decompn. temp. (Tmax) of the nanocomposite with 10 wt% CNC-Ag were enhanced by 140% and 24.2 °C, resp. The nanocomposites displayed reduced water uptake and water vapor permeability along with lower migration level in both non-polar and polar simulants compared to the neat biopolymer, which can be related to the increased crystallinity and improved interfacial adhesion. Moreover, the nanocomposites showed strong antibacterial activity against both Gram-neg. E. coli and Gram-pos. S. aureus. The results of the study indicate that the high performance nanocomposites show great potential applications in the fields of food, beverage packaging and disposable overwrap films.
    56. 56
      Siqueira, G.; Fraschini, C.; Bras, J.; Dufresne, A.; Prud’Homme, R.; Laborie, M. P. Impact of the Nature and Shape of Cellulosic Nanoparticles on the Isothermal Crystallization Kinetics of Poly(-Caprolactone). Eur. Polym. J. 2011, 47, 2216– 2227,  DOI: 10.1016/j.eurpolymj.2011.09.014
      56
      Impact of the nature and shape of cellulosic nanoparticles on the isothermal crystallization kinetics of poly(ε-caprolactone)
      Siqueira, Gilberto; Fraschini, Carole; Bras, Julien; Dufresne, Alain; Prud'homme, Robert; Laborie, Marie-Pierre
      European Polymer Journal (2011), 47 (12), 2216-2227CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
      Polycaprolactone (PCL)/cellulose nanocomposites were prepd. by mixing PCL with surface modified sisal nanowhiskers (CNW) and microfibrillated cellulose (MFC) extd. from sisal fibers. The influence of cellulosic nanoparticles on the crystn. behavior of PCL was investigated by differential scanning calorimetry. Isothermal crystn. data were modeled with Avrami's kinetics, Lauritzen-Hoffman secondary nucleation theory and equil. m.ps. were detd. with the Hoffman-Weeks method. The cellulose nanoparticles, acting as nucleating agents, drastically accelerate the crystn. of PCL while depressing its equil. melting by 9-10°. The crystn. of MFC-nanocomposites is slightly faster than that of CNW-nanocomposites, in agreement with the slightly lower bulk activation energy for crystn. and nucleation parameter in the former. The results are discussed based on the differences of sp. surface area and surface chem. of nanoparticles, as well as the confinement phenomenon.
    57. 57
      Ten, E.; Jiang, L.; Wolcott, M. P. Crystallization Kinetics of Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate)/Cellulose Nanowhiskers Composites. Carbohydr. Polym. 2012, 90, 541– 550,  DOI: 10.1016/j.carbpol.2012.05.076
      57
      Crystallization kinetics of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhiskers composites
      Ten, Elena; Jiang, Long; Wolcott, Michael P.
      Carbohydrate Polymers (2012), 90 (1), 541-550CODEN: CAPOD8; ISSN:0144-8617. (Elsevier Ltd.)
      In this study, biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films with 1.2-4.6 wt% of cellulose nanowhiskers (CNWs) were manufd. by soln. casting using DMF as the solvent. Crystn. behaviors of PHBV/CNW composites were studied under isothermal conditions using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The changes in PHBV cryst. structure were studied using wide angle X-ray diffraction (WAXD). Avrami anal. was performed to study the effects of CNW concn. and temp. on the crystn. rate and crystallinity of PHBV. POM study confirmed the results from the Avrami anal. In particular, the results revealed the dual effects (i.e., nucleation and confinement) of CNWs on PHBV nucleation. Depending on the concn. of CNWs, the crystn. rate of PHBV could be either increased or decreased due to the combined effects. High crystn. temps. increased the diffusion rate of PHBV chains and the growth rate of PHBV spherulites. However, the nucleation effect of CNWs decreased at high crystn. temps.

  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.biomac.9b01760.

    • List of acronyms and compositions of prepared bionanocomposites, XRD spectrum, deconvolution of XRD spectrum and crystallinity index (χXRD) of modified and unmodified CNCs, CNCs average length (L) and diameter (D), and related aspect ratio (L/D), TGA and relative derivative DTG curves of modified and unmodified CNCs, evolution during time of functionalized CNCs suspension in chloroform, TGA and relative DTG curves of neat PHBV and composites with 2 and 5 wt % of CNCs_butyrate, thermal properties of neat PHBV and bionanocomposites at 2 and 5 wt % of different type of CNCs, TGA and relative derivative DTG curves of neat PHBV and bionanocomposites with 2 wt % of modified and unmodified CNCs, Flexural storage modulus and glass transition temperature, Tg, obtained from DMTA results (PDF)


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