Poly(lactic acid)-based biocomposites reinforced with modified cellulose nanocrystals

This work investigates reinforcing poly(lactic acid) (PLA) nanocomposites using triazine derivative-grafted cellulose nanocrystals (CNCs). A hydrophobic triazine derivative was synthesized and applied to modify CNCs to improve their thermal stability and diminish the hydrophilicity of the nanoparticles. CNCs before and after modification were used to reinforce PLA nanocomposites by a hot compression process. The results of thermogravimetric analysis indicated that the initial thermal decomposition temperature of modified nanocrystals was improved by approximately 100 °C compared to the original CNCs. That is, the thermal stability of modified cellulose nanocrystals was improved due to the shielding effect of CNCs by a hydrophobic aliphatic amine layer on the surface of the nanoparticles. The results of dynamic contact angle measurements revealed a decrease of hydrophilicity of the modified CNCs. The results from scanning electron microscopy and a UV–Vis spectrophotometer revealed that the compatibility between the modified nanocrystals and the PLA was improved. Finally, the results of tensile tests indicated a significant improvement in terms of breaking strength and elongation at the break point.     

Electrospun hyperbranched polylactic acid–modified cellulose nanocrystals/polylactic acid for shape memory membranes with high mechanical properties

The polylactic acid (PLA) nanofiber membranes reinforced with hyperbranched PLA‐modified cellulose nanocrystals (H‐PLA‐CNCs) were prepared by electrospinning. The H‐PLA‐CNCs and the nanofiber membranes were researched by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The outcomes embodied that the cellulose nanocrystals (CNCs) could be successfully improved by the hyperbranched PLA, which would offer powerful CNCs/matrix interfacial adhesion. Thus, the mechanical and shape memory properties of PLA can be improved by adding the H‐PLA‐CNCs. In particular, when the addition of H‐PLA‐CNCs was 7 wt%, the tensile strength and an ultimate strain of PLA composite nanofiber membranes was 15.56 MPa and 25%, which was 228% and 72.4% higher than that of neat PLA, respectively. In addition, the shape recovery rate of the PLA/5 wt% H‐PLA‐CNCs composite nanofiber membrane was 93%, which was 37% higher than that of neat PLA. We expected that this present study would provide unremitting efforts for the development of more effective approaches to prepare biology basic shape memory membranes with high mechanical properties.     

微生物合成的β-羟基丁酸酯与β-羟基已酸酯共聚物/聚乳酸共混材料(PHBHHx/PLA)的力学性能与生物降解性研究

通过熔融共混法制备了聚乳酸/微生物产β-羟基丁酸酯与β-羟基己酸共聚物的共混物(PLA/PHBHHx).采用拉伸力学试验研究了共混物的力学性能.通过土壤悬浊培养降解法和扫描电子显微镜(SEM)分析对共混材料的生物降解性能进行了研究.实验结果表明,随着PHBHHx含量的增加,共混物的拉伸强度和杨氏模量降低,而生物降解速率却显著提高.但是,在175h之前,重量组成比为20/80的共混物降解速率比纯PHBHHx还要快.综合分析表明,共混材料PLA/PHBHHx的重量比为20/80时,具有优良的力学性能和生物降解性.     

微生物合成的β-羟基丁酸酯与β-羟基己酸酯共聚物/聚乳酸共混材料(PHBHHx/PLA)的力学性能与生物降解性研究

通过熔融共混法制备了聚乳酸/微生物产β-羟基丁酸酯与β-羟基己酸共聚物的共混物(PLA/PHBHHx)。采用拉伸力学试验研究了共混物的力学性能。通过土壤悬浊培养降解法和扫描电子显微镜(SEM)分析对共混材料的生物降解性能进行了研究。实验结果表明,随着PHBHHx含量的增加,共混物的拉伸强度和杨氏模量降低,而生物降解速率却显著提高。但是,在175h之前,重量组成比为20/80的共混物降解速率比纯PHBHHx还要快。综合分析表明,共混材料PLA/PHBHHx的重量比为20/80时,具有优良的力学性能和生物降解性。     

Effect of ethylene-co-vinyl acetate-glycidylmethacrylate and cellulose microfibers on the thermal,rheological and biodegradation properties of poly(lactic acid) based systems

The properties and biodegradation behavior of blends of poly(lactic acid) (PLA) and ethylene-vinyl acetate-glycidylmethacrylate copolymer (EVA-GMA), and their composites with cellulose microfibers (CF) were investigated. The blends and composites were obtained by melt mixing and the morphology, phase behavior, thermal and rheological properties of PLA/EVA-GMA blends and PLA/EVA-GMA/CF composite films were investigated as a function of the composition. The disintegrability in composting conditions was examined by means of morphological, thermal and chemical analyses to gain insights into the post-use degradation processes. The results indicated a good compatibility of the two polymers in the blends with copolymer content up to 30 wt.%, while at higher EVA-GMA content a phase separation was observed. In the composites, the presence of EVA-GMA contributes to improve the interfacial adhesion between cellulose fibers and PLA, due to interactions of the epoxy groups of GMA with hydroxyls of CF. The addition of cellulose microfibers in PLA/EVA-GMA system modifies the rheological behavior, since complex viscosity increased in presence of fibers and decreased with an increase in frequency. Disintegration tests showed that the addition of EVA-GMA influence the PLA disintegration process, and after 21 days in composting conditions, blends and composites showed faster degradation rate in comparison with neat PLA due to the different morphologies induced by the presence of EVA-GMA and CF phases able to allow a faster water diffusion and an efficient PLA degradation process.     

The morphological,mechanical, rheological,and thermal properties of PLA/PBAT blown films with chain extender

Biodegradable poly(lactic acid) (PLA)/poly(butylene adipate‐co‐terephthalate) (PBAT) blends and films were prepared using melt blending and blowing films technique in the presence of chain extender‐Joncryl ADR 4370F. The ADR contains epoxy functional groups and used as a compatibilizer. The morphological, mechanical, rheological, thermal, and crystalline properties of the PLA/PBAT/ADR blown films were studied. Scanning electron microscopy micrographs of the films revealed more ductile deformation with increasing PBAT content. The addition of PBAT enhanced the toughness of the PLA film. Tensile tests indicated that the elongation at break increased from 20.5% to 334.6% in the machine direction and from 7.1% to 715.9% in the transverse direction. The Young modulus increased from 2690.5 to 395.6 MPa in the machine direction and from 2623.5 to 154.0 MPa in the transverse direction. The sealing strength of 40/60/0.15 PLA/PBAT/ADR film was the highest among all the samples up to 9.4 N 15 mm⁻¹. These findings gave important implications for designing and manufacturing polymer packaging materials.     

Effect of microcrystalline and nanocrystals cellulose fillers in materials based on PLA matrix

The aim of this work was to compare the effects of microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC) addition on the properties of PLA matrix. The CNC were obtained by acid hydrolysis of the MCC. Both MCC and CNC were separately incorporated in PLA at ratios of 3, 5 and 7 wt%. In some compositions, organophilic silica (R972) was added to improve the cellulose-matrix compatibility. The properties of the materials were evaluated by FTIR, XRD, NMR and mechanical tests. Functional groups and crystalline structure of MCC and CNC were determined by FTIR and XRD, respectively. NMR T₁H values showed that films containing CNC presented better interfacial interaction than those containing MCC, and indicated that R972 acts as compatibilizer. MCC and CNC acted as nucleating agents for PLA crystallization and there was an improvement in the mechanical performance of materials with the addition of CNC.     

Compatibilizing effects for improving mechanical properties of biodegradable poly (lactic acid) and polycarbonate blends

Mechanical, morphological and rheological properties of polycarbonate (PC) and poly (lactic acid) (PLA) blends with compatibilizers have been investigated. Three types of compatibilizers were used: poly(styrene-g-acrylonitrile)-maleic anhydride (SAN-g-MAH), poly(ethylene-co-octene) rubber-maleic anhydride (EOR-MAH) and poly(ethylene-co-glycidyl methacrylate) (EGMA). The maximum value of the mechanical properties such as impact and tensile strengths of the PC/PLA (70/30, wt%) blend before or after hydrolysis was observed when the SAN-g-MAH was used as a compatibilizer at the amount of 5 phr. From the interfacial tension between PC and PLA which was determined from the weighted relaxation spectra using Palierne emulsion model, minimum value of interfacial tension (0.08 mN/m) was observed when the SAN-g-MAH (5 phr) was used. From the morphological studies of the PC/PLA (70/30) blends, the PLA droplet size showed minimum (0.19 μm) at the 5.0 phr SAN-g-MAH. From the results of mechanical, morphological and rheological properties of the PC/PLA (70/30) blend, it is suggested that the SAN-g-MAH is the most effective compatibilizer to improve the mechanical strength of the PC/PLA (70/30) blends among the compatibilizers used in this study, especially at the amount of 5 phr.     

Preparation and properties of poly(lactic acid)/cellulolytic enzyme lignin/PGMA ternary blends

Poly(lactic acid)-based ternary blends consisting of poly(lactic acid)(PLA),cellulolytic enzyme lignin(CEL),and polyolefine grafting maleic anhydride(PGMA) were prepared by extrusion blending and the mechanical properties and the morphology of the ternary blends were investigated.It was found that the mechanical properties varied with various loading of the components in the blends.Compared to neat PLA,the tensile strength and the Young’s modulus of the ternary blends were decreased,but the elongation at break and the impact strength were effectively improved.Scanning electron microscope observations revealed that the CEL plays a bridging role between PLA and PGMA,enhancing the miscibility between them and resulting in the improvement of ductility and toughness of the ternary blends.Considering the cost and performance,we obtained the optimal blend PLA/CEL/ PGMA(80/20/20,w/w/w),of which the impact strength and the elongation at break were doubled as that of neat PLA,and the tensile strength remained moderate.     

脂肪族聚碳酸酯(PPC)与聚乳酸(PLA)共混型生物降解材料的热学性能、力学性能和生物降解性研究

通过溶液浇铸法制备了脂肪族聚碳酸酯与聚乳酸的共混物(PPC/PLA).采用示差热分析(DSC)和热重分析(TG)研究了材料的热性能.采用拉伸力学试验研究了共混物的力学性能.通过土壤悬浊拟环境培养降解实验法和扫描电子显微镜分析(SEM)对共混材料的生物降解性能进行了研究.实验结果表明,随着PPC含量的增加,共混物的拉伸强度和杨氏模量降低,而生物降解速率却显著提高.但是,在一定的降解时间内,某些比例共混物的降解速率比100%PPC还要快.综合分析表明,PPC/PLA是力学性能和降解性能可以互补的共混体系.     

Preparation and Properties of Poly（vinyl alcohol）/Chitosan Blend Bio-nanocomposites Reinforced by Cellulose Nanocrystals

The aim of this paper is to report the effect of the addition of cellulose nanocrystals（CNCs） on the mechanical, thermal and barrier properties of poly（vinyl alcohol）/chitosan（PVA/Cs） bio-nanocomposites films prepared through the solvent casting process. The characterizations of PVA/Cs/CNCs films were carried out in terms of X-ray diffraction（XRD）, transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, thermogravimetric analysis（TGA and DTG）, oxygen transmission rate（OTR）, and tensile tests. TEM and SEM results showed that at low loading levels, CNCs were dispersed homogenously in the PVA/Cs matrix. The tensile strength and modulus in films increased from 55.1 MPa to 98.4 MPa and from 395 MPa to 690 MPa respectively, when CNCs content went from 0 wt% to 1.0 wt%. The thermal stability and oxygen barrier properties of PVA/Cs matrix were best enhanced at 1.0 wt% of CNCs loading. The enhanced properties attained by incorporating CNCs can be beneficial in various applications.     

PLA,PPC和PHBV共混物的热性能、力学性能和生物降解性能研究

将聚乳酸(PLA)、聚碳酸酯(PPC)及β-羟基丁酸酯与β-羟基戊酸酯共聚物(PHBV)以溶液浇注法制备了各种不同比例的共混膜(60/20/20,40/20/40,40/40/20,20/60/20,20/40/40,20/20/60)。采用示差扫描量热分析(DSC)和热重分析(TG)研究了共混物的热性能,采用万能材料试验机研究了共混物的力学性能,通过土壤悬浊拟环境降解实验和扫描电子显微镜(SEM)研究了共混材料的环境生物降解性能。结果显示,该三元共混体系是部分相容的体系,PLA增加了材料的强度,PPC增加了材料的断裂伸长,PHBV则提高了材料的环境生物降解速率,三者优势互补,是一种有应用前景的生物降解共混体系。     

Physical blends of PLA with high vinyl acetate containing EVA and their rheological,thermo-mechanical and morphological responses

Rheological, morphological and thermo-mechanical responses of poly(lactic acid) (PLA)/ethylene-co-vinyl-acetate copolymer (EVA) blends at EVA volume fractions varying in the range of 0–0.35 were evaluated. The micro-structural analysis demonstrated dispersive mixing at low content and co-continuous morphology at 30 wt % of EVA in PLA. Dynamic rheology demonstrated enhanced storage modulus and complex viscosity (η*) with increase in frequency of the blends indicated strong phase interaction. Cole-Cole and Han plots indicated partial miscibility and incompatibility between the polymer matrix and the dispersed phase. Dynamic mechanical analysis (DMA) revealed slight increase in damping parameters which indicated interaction or reinforcement in the blends. Additionally, the thermogravimetric analysis (TGA) of the blends showed two step degradation and enhanced thermal stability.     

High-strength, healable, supramolecular polymer nanocomposites

A supramolecular polymer blend, formed via π-π interactions between a π-electron rich pyrenyl end-capped oligomer and a chain-folding oligomer containing pairs of π-electron poor naphthalene-diimide (NDI) units, has been reinforced with cellulose nanocrystals (CNCs) to afford a healable nanocomposite material. Nanocomposites with varying weight percentage of CNCs (from 1.25 to 20.0 wt %) within the healable supramolecular polymeric matrix have been prepared via solvent casting followed by compression molding, and their mechanical properties and healing behavior have been evaluated. It is found that homogeneously dispersed films can be formed with CNCs at less than 10 wt %. Above 10 wt % CNC heterogeneous nanocomposites were obtained. All the nanocomposites formed could be rehealed upon exposure to elevated temperatures although, for the homogeneous films, it was found that the healing rate was reduced with increasing CNC content. The best combination of healing efficiency and mechanical properties was obtained with the 7.5 wt % CNC nanocomposite which exhibited a tensile modulus enhanced by as much as a factor of 20 over the matrix material alone and could be fully rehealed at 85 °C within 30 min. Thus it is demonstrated that supramolecular nanocomposites can afford greatly enhanced mechanical properties relative to the unreinforced polymer, while still allowing efficient thermal healing.     

Effect of Carboxylic Acid Nucleating Agent on Crystallization and Mechanical Properties of PLA/PBS Blends

Poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) blends were prepared using a carboxylic acid salt as nucleating agent (NA). The effect of NA on the crystallization kinetics of PLA and PLA/PBS blend was investigated using a differential scanning calorimeter, a polarized optical microscope and a wideangle X-ray diffractometer. The crystallization rate of PLA component in PLA/PBS blends is increased effectively by NA through fast nucleation and growth rate of PLA α'-form crystal, which is confirmed by isothermal crystallization behavior of PLA/PBA/NA composites. The isothermal crystallization results also show that the incorporation of NA induces heterogeneous nucleation mechanism in PLA component. The increased number of crystal nuclei hinders the increase of average grain size of PLA component in composites but contributes to a higher crystallinity of both PLA and PBS components in PLA/PBS blends. Finally, the mechanical properties and dynamic mechanical properties of PLA/PBS/NA composites are improved because of the increased crystallinity, which are superior to that of PLA/PBS blend.     

XPS and wettability characterization of modified poly(lactic acid) and poly(lactic/glycolic acid) films

Poly(lactic acid) (PLA) and poly(lactic/glycolic acid) copolymers (PLGA) are biodegradable drug carriers of great importance, although successful pharmaceutical application requires adjustment of the surface properties of the polymeric drug delivery system to be compatible with the biological environment. For that reason, reduction of the original hydrophobicity of the PLA or PLGA surfaces was performed by applying a hydrophilic polymer poly(ethylene oxide) (PEO) with the aim to improve biocompatibility of the original polymer. PEO-containing surfaces were prepared by incorporation of block copolymeric surfactants, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic), into the hydrophobic surface. Films of polymer blends from PLA or PLGA (with lactic/glycolic acid ratios of 75/25 and 50/50) and from Pluronics (PE6800, PE6400, and PE6100) were obtained by the solvent casting method, applying the Pluronics at different concentrations between 1 and 9.1% w/w. Wettability was measured to monitor the change in surface hydrophobicity, while X-ray photoelectron spectroscopy (XPS) was applied to determine the composition and chemical structure of the polymer surface and its change with surface modification. Substantial reduction of surface hydrophobicity was achieved on both the PLA homopolymer and the PLGA copolymers by applying the Pluronics at various concentrations. In accordance with the wettability changes the accumulation of Pluronics in the surface layer was greatly affected by the initial hydrophobicity of the polymer, namely, by the lactide content of the copolymer. The extent of surface modification was also found to be dependent on the type of blended Pluronics. Surface activity of the modifying Pluronic component was interpreted by using the solubility parameters.     

Morphology and properties of biodegradable poly (lactic acid)/poly (butylene adipate-co-terephthalate) blends with different viscosity ratio

Phase morphology exerts a tremendous influence on the properties of polymer blends. The development of the blend morphology depends not only on the intrinsic structure of the component polymers but also on extrinsic factors such as viscosity ratio, shearing force and temperature in the melt processing. In this study, various poly (butylene adipate-co-terephthalate) (PBAT) materials with different melt viscosity were prepared, and then poly (lactic acid) (PLA)/PBAT blends with different viscosity ratio were prepared in a counter-rotating twin-screw extruder under constant processing conditions. The influence of viscosity ratio on the morphology, mechanical, thermal and rheological properties of PLA/PBAT (70/30 w/w) blends was investigated. The experimental results showed that the morphology and properties of PLA/PBAT blends strongly depended on the viscosity ratio. Finer size PBAT phase were observed for viscosity ratio less than 1 (λ < 1) compared to samples with λ > 1. It was found that the interfacial tensions of PLA and PBAT were significantly different when the viscosity ratio was changed, the lowest interfacial tensions (0.12 mN/m) was obtained when the viscosity was 0.77. Additionally, the maximal tensile strength in PLA/PBAT blends were obtained when the viscosity ratio was 0.44, while the maximal impact properties were obtained when the viscosity ratio was 1.95.     

Non-isothermal crystallization and oxygen permeability of PP/PLA/EVOH ternary blends

Journal of Thermal Analysis and Calorimetry - Casting films of polypropylene (PP), poly(lactic acid) (PLA) and ethylene vinyl alcohol copolymer (EVOH) ternary blends having different compositions...     

Crystallinity and dimensional stability of biaxial oriented poly(lactic acid) films

Transparent biaxial oriented poly(lactic acid) (BOPLA) films with improved dimensional stability were successfully prepared by controlling the crystallization of poly(lactic acid) (PLA). The crystalline morphology of PLA films can be manipulated by changing certain processing parameters, such as stretch ratio, heat setting temperatures, and heat setting time. Optical and mechanical properties as well as dimensional stability of the resulting polymer films are governed by their crystallinity and crystalline morphology. Crystallization behavior and kinetics of PLA, therefore, were investigated using wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC) techniques. Mechanical properties and the dimensional stability of the biaxial oriented PLA films were obtained and correlated with their processing conditions. Poly(lactic acid) films prepared by melt extrusion methods have great potential for food packaging, shrink labeling and protective film applications. However, shrinkage at elevated processing temperature should be minimized to avoid puckering of the polymer film. Shrinkage of less than 2% was achieved for a BOPLA film stretched 300% in both directions at 75 °C and then annealed at 160 °C for 30 s. Fabrication, properties, and potential applications of a series of biodegradable films will be described.     

Chemical modification of cellulose nanocrystals and their application in thermoplastic starch (TPS) and poly(3‐hydroxybutyrate) (P3HB) nanocomposites

The effect of sulfated (original), carboxylated (oxidized), and Jeffamines M2005‐grafted cellulose nanocrystals (CNCs) on the barrier and mechanical properties of thermoplastic starch (TPS) and poly(3‐hydroxybutyrate) (P(3HB)) matrices was investigated. CNCs were first oxidized via a catalytic reaction using NaClO as an oxidant and then grafted with an amine‐terminated ethylene oxide (EO)/propylene oxide (PO) copolymer (Jeffamine) by an amine‐acid coupling reaction. A degree of oxidation (DO) of 0.108 (mol/mol of anhydroglucose) was attempted for the carboxylated CNCs, whereas a degree of substitution (DS) of 0.04 (mol/mol of anhydroglucose) was determined for the M2005‐grafted CNCs. These values indicated satisfactory reactive process, with yields of 68% and 47.3% for the carboxylation and peptide coupling reactions, respectively. Fourier‐transform infrared spectroscopy (FTIR) analysis showed bands at 1643 cm^?1 and 1550 cm^?1 in the spectrum of M2005‐grafted CNCs, which qualitatively indicated the amide bond formation. In addition, the morphology and the zeta potential of modified CNCs ensured their homogeneity, stability, and surface degree of charge. In spite of a decrease in the solubility in water of the modified crystals, the procedure of chemical modification used avoided any variation in their crystalline structure and thermal stability. Then, the incorporation of sulfated, oxidized, or M2005‐grafted CNCs in matrices of TPS and P(3HB) allowed to produce reinforced nanocomposite films, with excellent barrier properties. Therefore, the chemical compatibility between CNCs and the polymer matrices is essential to produce attractive nanocomposites with improved mechanical properties for industrial applications.