Biodegradation and thermal decomposition of poly(lactic acid)-based materials reinforced by hydrophilic fillers

The effect of hydrophilic fillers (starch and wood-flour) on the degradation and decomposition of poly(lactic acid) (PLA) based materials was investigated. Biodegradation was evaluated by composting under controlled conditions in accordance with AS ISO 14855. Thermal decomposition was studied by thermogravimetry (TGA). Morphological variations during biodegradation were investigated by SEM examination. It was found that biodegradation rates of PLA/starch blends and PLA/wood-flour composites were lower than that of pure cellulose but higher than that of pure PLA. The biodegradation rate was increased from about 60% to 80% when the starch content was increased from 10% to 40% after 80 days. Both starch and wood-flour accelerated thermal decomposition of PLA, and starch exhibited a relatively stronger affect then wood-flour. The decomposition temperature of PLA was decreased about 40 °C when the filler content was increased to 40%. Small polar molecules released during thermal decomposition of starch and wood-flour were attributed to the thermal decomposition behaviours of the PLA based blends and composites and their role is further discussed in this paper.     

热致液晶聚酯共混物与复合材料研究

评述了热致液晶聚酯的共混物与复合材料的研究新进展,揭示了热行为与相容性、流变性与加工性以及形态结构与多种性能之间的内在联系,展望了应用于高强高模纤维与塑料、低热膨光纤涂层及低透气包装膜等高性能材料的前景.     

Properties of immiscible and ethylene-butyl acrylate-glycidyl methacrylate terpolymer compatibilized poly (lactic acid) and polypropylene blends

Poly(lactic acid) (PLA) and polypropylene (PP) blends of various proportions were prepared by melt-compounding. The miscibility, phase morphology, thermal behavior, and mechanical and rheological properties of the blends were investigated. The blends were immiscible systems with two typical morphologies, spherical droplet and co-continuous, and could be obtained at various compositions. Complex viscosity, storage modulus and loss modulus depend on the PP content. Thermal degradation of all blends led to two weight losses, for PLA and PP. The incorporation of PP improved the thermal stability of the blend. The effect of compatibilizer (ethylene-butyl acrylate-glycidyl methacrylate terpolymer, EBA-GMA) on the morphology and mechanical properties of 70/30 w/w PLA/PP blends was investigated. The tensile strength of these blends reached a maximum for 2.5 wt% EBA-GMA, and impact strength increased with increasing EBA-GMA content, suggesting that EBA-GMA is an effective compatibilizer for PLA/PP blends.     

Effects of polylactic acid and rPET minor components on phase evolution,tensile and thermal properties of polyethylene‐based composite fibers

High mechanical performance and partially biodegradable PE‐composite fibers modified with polylactic acid (PLA) and recycled polyethylene terephthalate (rPET) minor components were prepared using melt extrusion and hot drawing process. Rheological properties, morphology, tensile, and thermal properties were investigated. All blends exhibited shear thinning behavior except for starting PLA and rPET. PLA and rPET dispersed phases appeared as droplets in as‐extruded strand, and PLA droplets were mostly larger than those of rPET. The fibrillation of both PLA and rPET domains was achieved after further hot drawing as the fiber. The morphology and tensile properties of the fibers mainly depended on the types and contents of dispersed phases including draw ratios. The ultimate strength of the polymer fibers at draw ratio of 20 was more than 600 times higher than that of the as‐spun sample of the same composition. Remarkable improvement in secant modulus and ultimate strength was found for PE‐30PLA, but the drawing process of this composition encountered some difficulties and rough surface of the fiber was observed. The stiffness and tensile stress for PE‐10PLA‐10rPET fiber were clearly improved when compared with PE and PE‐10PLA. A decrease in thermal stability of PE/PLA composites was observed with increasing PLA content whereas additional presence of rPET significantly increased the stability of the composites both in nitrogen and in air. PE/PLA/rPET fiber possessing high stiffness with good thermal stability prepared in this work has high potential for being utilized as structural parts for load‐bearing applications.     

Effect of montmorillonite and chain extender on rheological,morphological and biodegradation behavior of PLA/PBAT blends

The effect of montmorillonite clay (MMT) and/or chain extender (CE) on rheological, morphological and biodegradation properties of PLA/PBAT blend was investigated. The biodegradation behavior was evaluated by CO₂ evolution in soil burial. CE incorporation resulted in an increase in the complex viscosity of PLA/PBAT blends, an increase in PLA crystallinity and a decrease in the dispersed phase diameter. MMT incorporation resulted in an increase in the complex viscosity, more pronounced shear-thinning behavior and a decrease in the dispersed phase diameter. CE incorporation resulted in a slight effect in the rheological properties of PLA/PBAT blend in the presence of MMT. Unfilled PLA/PBAT blend presented the highest amount of evolved CO₂, and the micrographs indicated that degradation tends to occur on the surface. MMT delayed biodegradation of PLA/PBAT blends even although their surfaces presented some cracks and holes in a few localized regions. PLA/PBAT + CE blend presented the lowest amount of evolved CO₂.     

Morphology control of poly(lactic) acid/polypropylene blend composite by using silanized cellulose fibers extracted from coir fibers

The objective of this work is the use of cellulose fibers extracted from coir fibers as Janus nanocylinders to suppress the phase retraction and coalescence in poly(lactic) acid/polypropylene bio-blend polymers via prompting the selective localization of cellulose fibers at the interface using chemical modification. The untreated and modified cellulose fibers extracted from coir fibers using a silane molecule (tetraethoxysilane) were used as reinforcement and as Janus nanocylinder at two weight contents (2.5 wt% and 5 wt%) to manipulate the morphology of the bio-blends. Their bio-composites with PLA-PP matrix were prepared via melt compounding (at PLA/PP: 50/50). The treatment effect on component interaction and the bio-composites properties have been studied via Scanning electron microscopy, infrared spectroscopy, and differential calorimetry analysis. The mechanical and rheological properties of nanocomposites were similarly assessed. Young's modulus and tensile strength of PLA-PP nanocomposites reinforced by silanized cellulose fibers show a great enhancement as compared to a neat matrix. In particular, there was a gain of 18.5% in Young's modulus and 11.21% in tensile strength for silanized cellulose fiber-based bio-blend composites at 5 wt%. From the rheological point of view, it was found that the silanized cellulose fibers in PLA-PP at both fibers loading enhances the adhesion between both polymers leading to tuning their morphology from sea-island to the continuous structures with the appearance of PLA microfibrillar inside of bio-composites. This change was reflected in the relaxation of the chain mobility of the bio-blend composites.

     

New PP/PLA/cellulose composites: effect of cellulose functionalization on accelerated weathering behavior (accelerated weathering behavior of new PP/PLA/cellulose composites)

Polylactic acid (PLA) was used as partial replacement for conventional thermoplastic matrix, new composites comprising cellulose, polypropylene (PP), and PLA being realized. In order to obtain a compatible interface between cellulosic pulp and polymeric matrix, two chemical modifications of cellulose with stearoyl chloride and toluene di‐isocyanate (TDI) were performed, structural changes being evidenced by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The composite materials were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, dynamic scanning calorimetry, impact, tensile and melt rheological tests, surface tension, and dynamic vapor sorption. Because promising results for impact strength and Young modulus were recorded when replacing 15% of PP with PLA in blends of PP with the same cellulosic pulp load, the aim of our study was to assess the behavior to accelerate weathering of composites comprising PP, cellulosic pulp, and PLA. Although the slight decrease in the mechanical properties was recorded after accelerated weathering, the use of functionalized cellulose successfully prevented the deterioration of surface materials, especially for composite comprising stearoyl chloride treated cellulose pulp. Copyright © 2015 John Wiley & Sons, Ltd.     

Structure‐property relationship,rheological behavior,and thermal degradability of poly(lactic acid)/fulvic acid amide composites

Fulvic acid amide (FAA) was synthesized with fulvic acid (FA) and urea. The structure of FAA was characterized by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Poly(lactic acid)/fulvic acid amide (PLA/FAA) composites were prepared by melt blending and compression molding. The nucleation effect of FAA on PLA was investigated by differential scanning calorimetry and polarized optical microscopy. Structure‐property relationship of PLA/FAA composites showed that FAA accelerated crystallization rate of PLA and improved toughness of PLA. Rotational rheological behavior of PLA/FAA composites showed that FAA increased the storage modulus of PLA. Capillary rheological analysis showed that the apparent viscosities of PLA composites were highly increased after the introduction of the FAA nucleating agent. Moreover, thermogravimetric analysis demonstrated that thermal degradability of PLA/FAA composites has been increased significantly compared with the neat PLA.     

聚乳酸/羧基化聚丙烯共混物的形态与热性能研究

以扫描电子显微镜、热重分析仪、差示扫描量热仪、热台偏光显微镜分别研究了聚乳酸/羧基化聚丙烯共混体系的相形态、热性能和结晶形态.结果显示,共混物熔体冷却时,聚乳酸和羧基化聚丙烯均形成球晶,但羧基化聚丙烯球晶较大而十字消光较暗,聚乳酸球晶尺寸较小而十字消光较亮,且聚乳酸球晶产生规则的、不连续的同心环线——裂纹,裂纹厚度约为1~2μm,且裂纹内部有微纤存在.当聚乳酸含量≤50%时,由于聚丙烯上羧基的存在而使共混体系具有较好的相容性.共混物的热分解过程分为三个阶段,热分解温度的变化是聚丙烯上的羧基、聚乳酸和聚丙烯骨架分解三种机制共同作用的结果,少量聚乳酸能够明显提高共混物中聚丙烯上羧基的热稳定性.共混物中的羧基化聚丙烯组分可以发挥稀释剂的作用,大幅度降低了聚乳酸的冷结晶温度.聚乳酸含量≥50%时,共混熔体降温时DSC谱图中聚乳酸和羧基化聚丙烯分别结晶,而聚乳酸含量<50%时,只观察到羧基化聚丙烯的结晶行为.     

Thermal characterization and electrical properties of Fe-modified cellulose long fibers and micro crystalline cellulose

Thermal properties of polylactic acid (PLA) filled with Fe-modified cellulose long fibers (CLF) and microcrystalline cellulose (MCC) were studied using thermo gravimetric analysis (TG), differential scanning calorimetry, and dynamic mechanical analysis (DMA). The Fe-modified CLFs and MCCs were compared with unmodified samples to study the effect of modification with Fe on electrical conductivity. Results from TG showed that the degradation temperature was higher for all composites when compared to the pure PLA and that the PLA composites filled with unmodified celluloses resulted in the best thermal stability. No comparable difference was found in glass transition temperature (T _g) and melting temperature (T _m) between pure PLA and Fe-modified and unmodified CLF- and MCC-based PLA biocomposites. DMA results showed that the storage modulus in glassy state was increased for the biocomposites when compared to pure PLA. The results obtained from a femtostat showed that electrical conductivity of Fe-modified CLF and MCC samples were higher than that of unmodified samples, thus indicating that the prepared biocomposites have potential uses where conductive biopolymers are needed. These modified fibers can also be tailored for fiber orientation in a matrix when subjected to a magnetic field.     

乙酰柠檬酸丁酯增韧竹粉/聚乳酸生物质复合材料的制备与性能

以竹粉(bamboo flour,BF)为生物质填料,乙酰柠檬酸丁酯(acetyl tributyl citrate,ATBC)为增韧剂,通过与聚乳酸(polylactic acid,PLA)熔融共混制备了BF/PLA增韧复合材料,并采用红外光谱、热重分析、转矩流变仪、扫描电镜及力学性能测试等考察了ATBC添加对BF/PLA复合材料结构与性能的影响。结果表明,ATBC可改善BF/PLA复合材料的加工流变性,降低复合材料玻璃化转变温度、冷结晶温度及熔融温度,但对复合材料的热稳定性没有影响。FTIR分析显示,ATBC的加入可使BF/PLA复合材料C—O红外吸收峰位增大,表明ATBC与PLA之间存在一定相互作用。当ATBC用量为15%时,BF/PLA复合材料断裂伸长率由增韧前的8.1%增加到35.6%,提高了339.5%。SEM图片显示,此时复合材料断面粗糙,表现出韧性断裂形貌。该研究结果可为进一步探索增韧竹纤维/聚乳酸复合材料制备及应用,提供试验数据和理论参考。     

Biodegradation of sequentially surface treated lignocellulose reinforced polylactic acid composites: Carbon dioxide evolution and morphology

Maple fibres were treated with a variety of sequential treatments, namely sodium hydroxide (NaOH), NaOH followed by acetylation, or NaOH followed by silanation. These fibres were incorporated into a polylactic acid (PLA) composite and the biodegradation effects were investigated. After 124 days, all composites had exceeded 90% biodegradation with most close to 100%. The PLA composite with the NaOH-treated fibres had the quickest onset of degradation (4.9 days) and highest peak rate of degradation (1.77% biodegradation/day) of all composites studied. Neat PLA had a similarly high peak rate of degradation at 1.85% biodegradation/day, but had a later onset of 11 days. Gel permeation chromatography (GPC) analysis showed the earlier onset of degradation of the composites was caused by increased hydrolysis during composite fabrication as well as composting. GPC showed the formation of up to three molecular weight bands in the PLA during composting which were hypothesised to be occurring by surface hydrolysis, bulk hydrolysis and hydrolysis at the fibre interface. Analysing the remaining composite revealed the NaOH treatment not only caused an increased rate of degradation in the PLA through increase fibre porosity, but also caused an increased rate of degradation in the fibre from the lack of surface waxes and hemicellulose. Similar, yet slower, behaviours were also seen in the NaOH followed by acetylation and NaOH followed by silane treated composites with all composites degrading more rapidly than the neat PLA and neat maple fibre samples.     

Cellulose nanofibril-reinforced biodegradable polymer composites obtained via a Pickering emulsion approach

Preparation of cellulose nanofibril (CNF)-reinforced, biodegradable polymer composites is challenging in that it’s hard to achieve good dispersion of the hydrophilic cellulose fibers in a hydrophobic polymer matrix. In this work, we developed a surfactant-free and efficient process to prepare CNF-reinforced poly (lactic acid) (PLA) composites from an aqueous dichloromethane Pickering emulsion self-emulsified by CNFs. CNF/PLA composites of homogeneous dispersion were obtained upon evaporation of CH₂Cl₂, filtration, drying and hot-pressing. Differential scanning calorimetry measurement revealed an enhanced crystallization capacity of the CNF/PLA composites. Thermogravimetric analysis indicated an increase of onset degradation temperature. The composites displayed an enhanced storage modulus compared with neat PLA throughout the testing temperature range, and especially in the high-temperature region (>70 °C). Enhancements of the flexural modulus and strength were also achieved.     

Thermal and degradation behavior of fique fiber reinforced thermoplastic matrix composites

The influence of untreated and treated fique fibers on the crystallization process and thermal degradation of different thermoplastic matrix composites has been evaluated. The fique fibers have been treated with different chemicals according with the type of thermoplastic matrix employed. Additionally, a copolymer of poly(propylene) with maleic anhydride (MAPP) has been used as compatibilizer. The treatments introduce an increment on the thermal stability of fique fibers respect to untreated fibers. Crystallization is affected by the presence of fique fibers showing important differences for each type of composites. Fiber presence has an important influence on the matrix morphological characteristics, as observed by dynamical mechanical analysis. This revised version was published online in August 2006 with corrections to the Cover Date.     

聚(ε-己内酯-L-丙交酯)无规共聚物与聚乳酸共混材料的制备与性能

通过开环聚合,合成不同比例的ε-己内酯(ε-CL)与L-丙交酯(L-LA)的无规共聚物P(CL/LLA)。 将上述共聚物P(CL/LLA)与聚乳酸(PLLA)共混,制备了PLA/P(CL/LLA)共混材料。 并对其相容性、热性能、力学性能进行了研究。 结果表明,共聚物P(CL/LLA)与PLA相容性与共聚物中LA单元含量和链段的平均长度有密切关系,P(CL/LLA)中LA链段平均长度达到3.4以上时,可以与PLA很好的相互作用。 同时共聚物P(CL/LLA)中-CL-链段有很好的柔性,可以很好的改善PLLA的韧性,使PLLA材料的断裂伸长率达到500%以上。     

Exploration on the characteristics of cellulose microfibers from Palmyra palm fruits

To obtain cellulose microfibers from Palmyra palm fruit fibers, a new succession of specific chemical treatments including acidified chlorination, alkalization, and acid hydrolysis have been developed. Cellulose microfibers obtained were characterized by different techniques. The chemical analysis indicated an increase in α-cellulose content and decrease in lignin and hemicellulose for the cellulose microfibers over raw fibers. Fourier transform infrared and ¹³C NMR spectra confirmed the removal of non-cellulosic (lignin and hemicellulose) components after chemical treatments. The X-ray diffraction results revealed that the cellulose I was partly transformed into cellulose II by chemical treatments and the crystallinity index of cellulose microfibers was significantly increased as compared to raw fibers owing to removal of non-cellulosic components. Thermogravimetric analysis results demonstrated that the thermal stability was enhanced noticeably for cellulose microfibers than for the raw fibers. The scanning electron micrographs illustrated cleaner and rough surfaces for the cellulose microfibers when compared to those of raw fibers.     

Mechanical,thermal and rheological properties and morphology of poly (lactic acid)/poly (propylene carbonate) blends prepared by vane extruder

In this study, the poly (lactic acid) (PLA) and poly (propylene carbonate) (PPC) blends with different compositions were prepared by a novel vane extruder based on elongation rheology. The mechanical properties, morphologies, crystallization behavior, thermal stability, and rheological properties of the blends were investigated. Mechanical test showed that PLA could be toughened by PPC to some extent, and the impact strength of the PLA was maximized when PPC content was about 30%. Differential scanning calorimetry analysis revealed that PPC had little effect on the melting process, the crystallization behavior of PLA component in the blend was improved, and the cold crystallizability of PLA decreased with the increase of PPC content when the PPC content was less than 50%. Thermogravimetry analysis showed that the thermal stability of the blends was improved by compounding with PLA. Scanning electron microscope showed that the dispersion of PLA droplets in PPC matrix was better than that of PPC droplets in PLA matrix. Rheological test showed that the melt viscosity of the pure PLA and the blend with 10% PPC was insensitive to shear rate, and the blends melt appeared shear thinning phenomenon with the increase of PPC content. It also showed that the blends microstructure changed with the addition of PPC and the blends with PPC content in a certain range had similar stress relaxation mechanism. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrospun fibers of poly(ethylene terephthalate) blended with poly(lactic acid)

Fibrous blends of polyethylene terephthalate (PET) and polylactic acid (PLA) were fabricated by electrospinning (ES) from a common solvent, at concentrations of PET/PLA = 100/0, 70/30, 50/50, 30/70, and 0/100. Oriented fiber mats were studied either as-spun, or after a cold-crystallization treatment. Scanning electron microscopy of as-spun amorphous fibers showed that addition of PLA into the ES solution prevents occurrence of beads. In some compositions, two glass transitions were observed by temperature-modulated differential scanning calorimetry indicating that the two components in the ES fibers were phase separated. Thermogravimetric analysis was used to study thermal degradation at high temperatures. PLA degrades at a temperature about 100 °C lower than that of PET, and holding or cycling the blends to high temperature can result in the degradation of PLA. Degree of crystallinity was determined using DSC for as-spun and cold-crystallized ES blend fibers. The degree of crystallinity of each blend component is reduced by the presence of the other blend component, and the overall crystallinity of the blend fibers is less than that of the homopolymer fibers. Wide-angle X-ray scattering results show that oriented crystals were formed in the blended electrospun fibers collected on a rotating collector. The cold-crystallization process leads to both PET and PLA crystallizations. Oriented crystallites form even when the fiber is crystallized with its ends free to shrink.     

Synthesis,Characterization, and Hydrolytic Degradation of Polylactide/Poly(ethylene glycol)/Nano-silica Composite Films

Poly(lactic acid) (PLA)/PEG/nano-silica composite degradable films have been prepared by solvent casting method. IR measurements showed that vibration of C–O–C group was confined by silica network. SEM results showed that nano-silica particles were dispersed uniformly in the PLA/PEG matrix. TGA results indicated that the thermal decomposition temperature rose with the increase of nano-silica content. The tensile strength of composite film increased by the addition of nano-silica particles into PLA/PEG matrix. The degradation rate of PLA/PEG/nano-silica composites increased with the acidic medium of degradation. On the other hand, the slower degradation was obtained in the neutral buffer solution. PLA/PEG/nano-silica composites were found to exhibit almost similar degradation behavior as that of PLA/PEG films.     

Novel elastomeric polyurethane fibers modified with polypropylene microfibers

Extrusion of immiscible polymer biphasic blends to form in situ microfibers of the minor component in the matrix of the major component is an elegant way to create composites with new properties. The process was used to obtain thermoplastic polyurethane elastomers modified with polypropylene microfibers. The effect of phase interaction on blend morphology and properties was studied by running a series of blends with and without a maleated polypropylene compatibilizer. Six different blends were prepared: three with compatibilizer and three without the compatibilizer. All blends contained polypropylene as a minor component (80/20; 90/10 and 95/5). Extrusion spinning of polyurethane/polypropylene blends with and without compatibilizer resulted in polyurethane fibers modified with highly-oriented polypropylene microfibrils at all component ratios. Increasing polypropylene concentration in the thermoplastic polyurethane matrix increased hardness and modulus, but did not affect tensile strength and lowered elastic recovery.