Basalt fiber reinforced and elastomer toughened polylactide composites: Mechanical properties,rheology, crystallization,and morphology

A series of the reinforced and toughened polylactide (PLA) composites with different content of basalt fibers (BF) were prepared by twin screw extruder. The toughness of BF/PLA composite s was improved further by the addition of polyoxyethylene grafted with maleic anhydride (POE-g-MAH), ethylene–propylene–diene rubber grafted with maleic anhydride (EPDM-g-MAH), and ethylene-acrylate-glycidyl methacrylate copolymer (EAGMA), relatively. The mechanical properties, rheology, crystallization, and morphology of BF/PLA composites were studied. The results showed that basalt fiber had significant reinforcing and toughening effect in comparsion with glass fiber. EAGMA was more effective in toughening BF/PLA composites than POE-g-MAH and EPDM-g-MAH. When the content of EAGMA achieved to 20 wt %, the impact strength of BF/PLA/EAGMA composite increased to 33.7 KJ/m², meanwhile the value was improved by 71.1% compared with pure PLA. According to dynamic rheometer testing, the use of the three kinds of elastomers increased the melt dynamic viscosity. Differential scanning calorimetry analysis showed that POE-g-MAH and EPDM-g-MAH can decrease the cold crystallization temperature (T_cc) to approximately 20°C and dramatically improve crystallinity (χ_c) of BF/PLA composites. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of alkali and alkali/silane treatments of corn fibers on mechanical and thermal properties of its composites with polylactic acid

Different chemically modified (including treatments with alkali alone and a combination of alkali and silane coupling agent) corn fibers (CFs) have been used as reinforcements in polylactic acid (PLA) matrix to improve the mechanical and thermal properties of the CF/PLA composites. A comparative study has been made to find out how the two treatments affect the mechanical and thermal properties such as tensile, flexural, and impact strengths and glass transition temperature (T_g), crystallinity, and heat deflection temperature (HDT) of the CF/PLA composites. Scanning electron microscopy analyses have been conducted to evaluate the fiber–matrix adhesion. It has been observed that the treatment with a combination of alkali and silane is more efficient in strengthening fiber–matrix bonding, and thus more significantly improving the tensile and flexural strengths, crystallinity, T_g, and HDT of the CF/PLA composites than the treatment with alkali alone. However, alkali treatment produces the optimal impact strength. Mechanisms have been proposed to interpret the observed changes in mechanical and thermal properties as a result of fiber treatments. It is inferred that the surface treatment of CFs with a combination of alkali and silane may also be applied in other CF–polymer composite systems. POLYM. COMPOS., 37:3499–3507, 2016. © 2015 Society of Plastics Engineers     

Thermal and mechanical properties of plasticized poly(L‐lactide) nanocomposites with organo‐modified montmorillonites

Nanocomposites of poly(lactide) (PLA) and the PLA plasticized with diglycerine tetraacetate (PL‐710) and ethylene glycol oligomer containing organo‐modified montmorillonites (ODA‐M and PGS‐M) by the protonated ammonium cations of octadecylamine and poly(ethylene glycol) stearylamine were prepared by melt intercalation method. In the X‐ray diffraction analysis, the PLA/ODA‐M and plasticized PLA/ODA‐M composites showed a clear enlargement of the difference of interlayer spacing between the composite and clay itself, indicating the formation of intercalated nanocomposite. However, a little enlargement of the interlayer spacing was observed for the PLA/PGS‐M and plasticized PLA/PGS‐M composites. From morphological studies using transmission electron microscopy, a finer dispersion of clay was observed for PLA/ODA‐M composite than PLA/PGS‐M composite and all the composites using the plasticized PLA. The PLA and PLA/PL‐710 composites containing ODA‐M showed a higher tensile strength and modulus than the corresponding composites with PGS‐M. The PLA/PL‐710 (10 wt %) composite containing ODA‐M showed considerably higher elongation at break than the pristine plasticized PLA, and had a comparable tensile modulus to pure PLA. The glass transition temperature (T_g) of the composites decreased with increasing plasticizer. The addition of the clays did not cause a significant increase of T_g. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Morphological,mechanical, and thermal characterization of biopolymer composites based on polylactide and nanographite platelets

This work focuses on development and optimization of polylactide (PLA) and nanographite platelets (NGP) based composites to display possible superior mechanical and improved thermal stability. Melt blending and dry mixing methods of fabrication were employed at temperature of 180°C. Different Loading fractions of NGP were incorporated into polymer matrix. Morphological evaluation techniques such as XRD and TEM were applied to determine the degree of dispersion of NGPs into PLA matrix. Mechanical properties were evaluated and correlated to structural morphologies of PLA/NGP composites. Thermal properties of composites were studied to examine possible changes in T_g, T_c, T_m, and percentage crystallinity of these composites. The effect of mixing was also explored through double extrusion of some samples. It was concluded that composites containing 3 wt% NGP showed optimum mechanical performance without any significant changes in the thermal characteristics. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effects of different silane coupling agents on structure and properties of starch–chitosan–kaolin composites

Effects of different silane coupling agents on clay surface modification were studied. Herein, functionalized superfine kaolin was compounded with starch–chitosan (SCS) to prepare starch–chitosan-functionalized superfine kaolin composite. The characterization results showed that kaolin (K) was successfully modified; the composite formed a dense intercalated structure. The glass-transition temperature (T _g) was measured by differential scanning calorimetry and dynamic mechanical analysis. It decreased by 60 °C which attested the crystallinity of SCS. The results of thermogravimetric analysis showed that the fastest weight-loss temperature (T_max) was elevated by over 50 °C for composites. Mechanical properties of the composites were explored by electronic universal testing machine. Tensile strength and elongation of composites were improved by 4.7 and 10.9 times. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48050.     

Thermal and mechanical properties of compression‐molded pMDI‐reinforced PCL/gluten composites

Many biopolymers and synthetic polymers composites were developed by different researchers for environmental protection and for cost reduction. One of these composites is polycaprolactone (PCL) and vital wheat gluten or wheat flour composites were prepared and compatibilized with polymeric diphenylmethane diisocyanate (pMDI) by blending and compression‐molding. PCL/pMDI blend exhibited glass transition (T_g) at ?67°C (0.20 J/g/°C) and vital gluten at 63°C (0.45 J/g/°C), whereas no T_g was recorded for wheat flour. Although T_g was unmistakable for either PCL or gluten, all composite exhibited one T_g, which is strong indication of interaction between PCL and the fillers. Several samples amongst the blended or compression‐molded composites exhibited no T_g signifying another confirmation of interaction. The ΔH of the endothermic (melting) and the exothermic (crystallization) for PCL was decreased as the percentage of gluten or flour increased, whereas the overall ΔH was higher for all composites compared to the theoretical value. The presence of pMDI appeared to strengthen the mechanical properties of the composites by mostly interacting with the filler (gluten or flour) and not as much with PCL. The FTIR analysis ruled out covalent interaction between PCL, pMDI, or the fillers but suggested the occurrence of physical interactions. Based on the data presented here and the data published earlier, the presence of pMDI did not change the nature of interaction between PCL and gluten, but it improved the mechanical properties of the composite. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of alkali treatment on flax fiber for use as reinforcements in polylactide stereocomplex composites

The flax and equivalent proportion of poly(l ‐lactic acid)/poly(d ‐lactic acid) (PLLA/PDLA) were melt compounded and injection molded to prepare flax‐reinforced polylactide stereocomplex (sc‐PLA) bio‐composite, and the effect of alkali treatment on the structure and properties of flax as well as the flax/sc‐PLA composite was investigated. SEM and FTIR results showed hemicellulose in flax was almost completely removed after alkali treatment and the treated flax (ALK‐flax) bundles were more separated with a cleaner surface than untreated flax (UN‐flax). DSC results showed homo‐crystallites (hc, T_m = 160–170°C) and stereocomplex crystallites (sc, T_m ～210°C) coexisted in sc‐PLA and flax/sc‐PLA composites. Compared with sc‐PLA, the total crystallinity and sc‐crystallinity of flax/sc‐PLA composite increased regardless of whether the flax were treated with alkali, whereas ALK‐flax/sc‐PLA composite showed a little higher crystallinity than UN‐flax/sc‐PLA composite. TGA results confirmed ALK‐flax/sc‐PLA composite had a higher thermal degradation temperature than UN‐flax/sc‐PLA composite. The mechanical tests indicated although the mechanical properties of sc‐PLA increased significantly by reinforcing with flax, the ALK‐flax/sc‐PLA composite showed little lower mechanical properties than UN‐flax/sc‐PLA composite. The alkali treatment of flax had no obvious influence on the Vicat softening temperature (VST) of flax/sc‐PLA composites, a higher heat resistance with VST at ～155°C could be obtained for flax/sc‐PLA composite. POLYM. ENG. SCI., 55:2553–2558, 2015. © 2015 Society of Plastics Engineers     

Thermal and biodegradation properties of poly(lactic acid)/fertilizer/oil palm fibers blends biocomposites

Poly(lactic acid) (PLA) and NPK fertilizer with empty fruit bunch (EFB) fibers were blends to produced bioplastic fertlizer (BpF) composites for slow release fertilizer. Thermal properties of BpF composites were investigated by thermogavimteric analysis (TGA), differential scanning calorimetry (DSC), and morphological and degradation properties were anlayzed by scanning electron microscopy (SEM), soil burial test, respectively. TGA themogram display that neat PLA, PLA/NPK, and BpF composites degradate at different temperatures. DSC curves of PLA and other composites exhibited same glass transition temperature (T_g) value indicating that both major blend components are miscible. The T_g, crystallization temperature (T_c), melting temperature (T_m) values also decreased with increased amount of fertilizer and fibers. The T_m of BpF composites did not change with an increase in fertilizer content because thermal stability of PLA and PLA/NPK composites was not affected. Soil burial and fungal degradation test of PLA, PLA/NPK, and BpF composites were also carried out. Soil burial studies indicated that BpF composites display better biodegradation as compared with neat NPK. Fungal degradation study indicated that fungi exposure times of BpF composites show higher value of degradation as compared with PLA/NPK. We attribute that developed BpF composites will help oil palm plantation industry to use it as slow release fertilizer. POLYM. COMPOS. 36:576–583, 2015. © 2014 Society of Plastics Engineers     

纳米SiO2包覆微晶纤维素对PBS/PLA复合材料性能的影响

以纳米二氧化硅(nano-SiO2)表面包覆的微晶纤维素(MCC)为填料,采用熔融共混的方法制备了聚乳酸/聚丁二酸丁二醇酯（PLA/PBS）复合材料。运用扫描电子显微镜、热重分析仪、差示扫描量热仪、动态热力学分析仪等方法研究了nano-SiO2对PLA/PBS/MCC复合材料的力学性能、热稳定性以及结晶行为的影响。结果表明,nano-SiO2包覆在MCC表面后与PLA/PBS熔融共混提高了nano-SiO2在聚合物材料中的分散性,改善了MCC与树脂基体的相容性;添加5 %（质量分数,下同）MCC的PLA/PBS/MCC复合材料,与同样添加量的PLA/PBS/nano-SiO2-MCC复合材料相比,其储能模量、冲击强度以及结晶度分别提高了13.04 %、11.70 %、71.92 %。     

Biocomposites of poly(lactic acid) and lactic acid oligomer-grafted bacterial cellulose: It's preparation and characterization

This work demonstrates the synthesis of lactic acid oligomer-grafted-untreated bacterial cellulose (OLLA-g-BC) by in situ condensation polymerization which increased compatibilization between hydrophobic poly(lactic acid) (PLA) and hydrophilic BC, thus enhancing various properties of PLA-based bionanocomposites, indispensable for stringent food-packaging applications. During the synthesis of OLLA-g-BC, hydrophilic BC is converted into hydrophobic due to structural grafting of OLLA chains with BC molecules. Subsequently, bionanocomposites films are fabricated using solution casting technique and characterized for structural, thermal, mechanical, optical, and gas-barrier properties. Morphological images showed uniform dispersion of BC nanospheres in the PLA matrix, which shows strong filler–matrix interaction. The degradation temperatures for bionanocomposites films were above PLA processing temperature indicating that bionanocomposite processing can be industrially viable. Bionanocomposites films displayed decrease in glass transition (T_g) and ~20% improvement in elongation with 10 wt % fillers indicating towards plasticization of PLA. PLA/OLLA-g-BC films showed a slight reduction in optical transparency but had excellent UV-blocking characteristics. Moreover, dispersed BC act as blocking agents within PLA matrix, reducing the diffusion through the bionanocomposite films which showed ~40% improvement in water-vapor barrier by 5 wt % filler addition, which is significant. The reduced T_g, improved elongation combined with improved hydrophobicity and water-vapor barrier make them suitable candidate for flexible food-packaging applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47903.     

Thermal properties and crystallization behaviors of polylactide/redwood flour or bamboo fiber composites

A series of polylactide/redwood flour (PLA/RWF) and polylactide/bamboo fiber (PLA/BF) composites were successfully prepared using a solution mixing procedure. Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (XRD) were employed to characterize these composites. Thermal properties and crystallization behaviors of PLA composites were determined by their respective techniques of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). With the increasing content of fibers, the glass transition temperature (T _g ), crystallization temperature (T _c ), and melting temperature (T _m ) of PLA/RWF composites decreased first and then increased, but T _g and T _m of PLA/BF composites increased first and decreased afterwards. It is suggested that fibers could improve the segmental mobility of PLA; meanwhile, the different morphologies, sizes, and densities of RWF and BF have different effects on thermal properties of composites. Under the increasing content of RWF, the crystallization rate of the composite increased first and decreased afterwards. When the content of RWF was 5%, the crystallization rate was at its maximum. It could be possible that the addition of fibers was able to nucleate PLA and increase the degree of crystallinity, but the excess content of fibers easily led to heterogeneous composites and subsequent poor crystallization behaviors. In a word, thermal properties and crystallization behaviors of PLA composites were regularly changing by increasing content of fibers.     

Physico-chemical,thermal, and mechanical properties of PLA-nHA nanocomposites: Effect of glass fiber reinforcement

In this study, tri-layered composites were prepared by reinforcing poly-lactic acid (PLA) nano-hydroxyapatite (n-HA) (1 and 5 wt%) and 20 mol% continuous phosphate glass fibers (PGF). Initially, the effect of addition of 1 and 5% n-HA on the structural, thermal, mechanical, and thermo-mechanical properties of 100% PLA was investigated. With 5 wt% n-HA addition the tensile modulus (TM), flexural modulus (FM), tensile strength (TS), and flexural strength (FS) of 100% PLA was improve by 14.9, 47.4, 6, and 32.9%, respectively. Whereas, the un-notched impact strength of the nanocomposites suffer 2% deterioration. However, T _g decreased by 0.3°C and T _c increased by 10°C as 5 wt% n-HA was added to 100% PLA. Afterwards, the 5% n-HA/PLA composite were reinforced with 20 mol% continuous PGF and the TM, FM, TS, and FS of the tri-layered composites were 162.6, 412.5, 28.4, and 157.4% higher as compared to 100%PLA. Furthermore, the storage modulus of the 1% n-HA-filled composites was 500 MPa lower than 100%PLA, while 5 wt% n-HA-filled composites showed similar storage modulus as 100% PLA. 5 wt% n-HA-filled composite showed the highest peak of loss modulus which may be attribute to the chain segment of PLA matrix after the incorporation of HA. Thus, n-HA and PGF reinforcement resulted in improved mechanical properties of the composites and have great potential as biodegradable bone fixation device with enhanced load-bearing ability.     

Preparation,characterization, and improvement of hollow epoxy particle‐toughened vinyl ester composites for high‐end applications

Spherical hollow epoxy particles (HEPs) that can serve as advanced reinforcing fillers for vinyl ester thermosets were prepared using the water‐based emulsion method. The HEP fillers were incorporated into the vinyl ester matrices at different loading amounts, ranging from 0 to 9 wt %, to reinforce and toughen the vinyl ester composite. The optimum mechanical properties of the HEP‐toughened epoxy composite can be achieved by the addition of 5 wt % HEP filler into the vinyl ester matrices. The toughening and strengthening of the epoxy composites involved the interlocking of vinyl ester resins into the pore regions on the HEP fillers. The toughening and interlocking mechanisms of HEP‐toughened vinyl ester composites were also proposed and discussed. The addition of HEP fillers into vinyl ester matrices increased the glass transition temperature (T_g) and thermal stability of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and physical properties of polylactide/cellulose nanowhisker/nanoclay composites

Polylactide (PLA) has been getting lots of interests in step with global concerns on sustainable green technology because it is biodegradable with reasonable mechanical strength and can be processed quite easily. But, to compete with commodity polymers in the market PLA‐based green composites need to have higher mechanical and thermal properties. Therefore, in this study, cellulose nanowhiskers (CNWs) as well as nanoclay were used as nanofillers to improve physical properties of PLA. CNWs were prepared from microcrystalline cellulose (MCC) powder by acid hydrolysis, and confirmed by TEM. To improve interfacial bonding between PLA and CNWs maleic anhydride‐grafted PLA (MAPLA) was prepared and used as a compatibilizer. PLA‐based composites were prepared by melt mixing followed by compression molding. Mechanical properties of the composites were measured by UTM and DMA. The melt mixing conditions were optimized first, and then composition was optimized step by step to obtain a PLA‐based green composite with excellent physical properties. CNWs were much better than MCC powder as reinforcing natural fillers. MAPLA and nanoclay could improve considerably physical properties of the PLA‐based composites. Compared to the PLA/MCC composite the tensile strength of the PLA/CNW/MAPLA/nanoclay composite was almost doubled and the glass transition temperature of the composite was 23°C higher, making the composite possible for commercial applications. POLYM. COMPOS., 2013 © 2013 Society of Plastics Engineers     

Morphology,mechanical properties,and durability of poly(lactic acid) plasticized with Di(isononyl) cyclohexane‐1,2‐dicarboxylate

Di(isononyl) cyclohexane‐1,2‐dicarboxylate (DINCH) was used as a new plasticizer for poly(lactic acid) (PLA), and the effects of DINCH and tributyl citrate ester (TBC) on the morphology, mechanical and thermal properties, and durability of PLA were compared. DINCH has limited compatibility with PLA, leading to PLA/DINCH blends with phase separation in which DINCH forms spherical dispersed phase. TBC is compatible with PLA and evenly distributed in PLA. Plasticized PLA with 10 and 20 phr DINCH have a constant glass transition temperature (T_g) of 50°C and are stiff materials with high elongation at break and impact strength. TBC could significantly decrease the T_g and increase the crystallinity of PLA, and PLA/TBC (100/20) blend is a soft material with a T_g of 24°C. The durability of plasticized PLA was characterized by weight loss measurement under water immersion, mechanical properties, and thermal analysis. The results reveal that PLA/DINCH blends have better water resistance and aging resistance properties than PLA/TBC blends, which is attributed to the relatively high hydrophobicity of DINCH and high T_g of PLA/DINCH blends. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Characterization of biodegradable polymers by inverse gas chromatography. III. Blends of amylopectin and poly(L‐lactide)

The morphology changes and surface thermodynamics of blends of amylopectin (AP)–poly(L ‐lactide) (PLA) were investigated over a wide range of temperatures and compositions using the inverse gas chromatography method. Twenty‐five solutes were selected such as alkanes, acetates, oxy, halogenated, and six‐member ring families. They provided a variety of specific interactions with the blends' surface. The morphology showed two regions, some others showed a de‐polymerization above 130°C. These zones enabled the estimation of T_g and T_m of AP, PLA, and the blends. Blending AP with PLA caused a decrease in AP's T_g value due to the reduction of the degree of crystallinity of the blend. Exothermic values of χ₂₃ were obtained indicating the compatibility of AP and PLA at all temperatures and weight fractions of AP–PLA. The miscibility was favored at 75%AP, only 25%AP–75%PLA composition influenced the degree of crystallinity. The dispersive component of the surface energy of the blends ranged from 16.09 mJ/m² for the pure AP as high as 58.36 mJ/m² at 110°C when AP was mixed with PLA in a 50–50% ratio. The surface energy was at its highest value when the composition was 75% of AP, in good agreement with χ₂₃ values. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Production and investigation of structure and properties of polyethylene–polylactide composites

Under conditions of shear deformations, low-density polyethylene (LDPE) and polylactide (PLA) composites are obtained in rotor disperser. The production of these composites allows one to use polymers derived from natural raw and to reduce the cost of the materials on their base. The addition of rigid PLA leads to increase in elastic modulus from 200 for LDPE to 1190 for LDPE–PLA (50:50 wt %) composites and in tensile strength from 13.3 for LDPE to 17.8 for LDPE–PLA. By differential scanning calorimetry method, it is shown that LDPE and PLA are incompatible. Using X-ray diffraction analysis, it is found that degree of crystallinity of composites decreases from 46.1 at 50:50 wt % to 36.9 at 80:20 wt % component ratios with the rise in LDPE content. Tests on fungus resistance show that the composites containing 50 wt % PLA are more resistant than the composites containing 30 wt % PLA. First by gel-permeation chromatography method, it is shown that composite degradation after exposure in soil is accompanied by the PLA chain scission and depolymerization with formation of monomers and dimers (M _w of PLA decreases from 118,860 to 80,100). The obtained composites can be applied as packaging materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47598.     

Enhanced mechanical properties of poly(lactic acid) composites with ultrathin nanosheets of MXene modified by stearic acid

MXene modified by stearic acid (Ti₃C₂T_x-g-SA) is incorporated into poly(lactic acid) (PLA) matrix to prepare Ti₃C₂T_x-g-SA/PLA composites. The effects of Ti₃C₂T_x-g-SA to pure PLA are investigated, including crystallization, mechanical, and thermal properties. Fourier transform infrared spectroscopy and X-ray diffraction analyses confirm that Ti₃C₂T_x interlayer is successfully intercalated by SA, and the interlayer spacing of Ti₃C₂T_x is increased. Differential scanning calorimetry illustrates that the cold crystallization enthalpy (ΔH_cc), melting enthalpy (ΔH_m), and crystallinity (X_c) of Ti₃C₂T_x-g-SA/PLA composites are improved by the plasticization and heterogeneous nucleation effect of Ti₃C₂T_x-g-SA. Specially, the Ti₃C₂T_x-g-SA/PLA composites exhibit excellent mechanical properties at an appropriate content of the Ti₃C₂T_x-g-SA. Compared with pure PLA, the elongation at break of the Ti₃C₂T_x-g-SA/PLA composite is increased 5.9-fold (up to 131.6%) when only containing 0.5 wt % Ti₃C₂T_x-g-SA. Besides, the Ti₃C₂T_x-g-SA/PLA composites exhibit good thermal stability in the low loading (lower than 1 wt %) of Ti₃C₂T_x-g-SA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48621.     

Effect of silk fiber to the mechanical and thermal properties of its biodegradable composites

In recent years, natural fiber‐reinforced biodegradable thermoplastics are being recognized as an emerging new environmentally friendly material for industrial, commercial, and biomedical applications. Among different types of natural fibers, silk fiber is a common type of animal‐based fiber, has been used for biomedical engineering and surgical operation applications for many years because of its biocompatible and bioresorbable properties. On the basis of our previous study, a novel biodegradable biocomposite for biomedical applications was developed by mixing chopped silk fiber and polylactic acid (PLA) through the injection molding process. This article is aimed at studying the dynamic mechanical and thermal properties of the composite in relation to its biodegradation effect. At the beginning, it was found that the initial storage modulus of a silk fiber/PLA composite increased while its glass transition temperature decreased as compared with a pristine PLA sample. Besides, the coefficient of linear thermal expansions (CLTE) of the composite was reduced by 28%. This phenomenon was attributed to the fiber–matrix interaction that restricted the mobility of polymer chains adhered to the fiber surface, and consequently reduced the T_g and CLTE. It was found that the degraded composite exhibited lower initial storage modulus, loss modulus and tan delta (tan δ) but the T_g was higher than the silk fiber/PLA composite. This result was mainly due to the increase of crystallinity of the composite during its degradation process. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhancing gas barrier performance of polylactic acid/lignin composite films through cooperative effect of compatibilization and nucleation

In this work, lignin was used as a heterogeneous nucleating agent to increase polylactic acid (PLA) crystallinity. To enhance the gas barrier performance of PLA/LG composite films, two graft copolymers, polylactide-graft-glycidyl methacrylate (PLA-g-GMA) and polylactide-graft-poly (ethylene glycol) methyl ether methacrylate (PLA-g-PEGMA) were successfully synthesized and separately used as compatibilizers to modify PLA/LG composite properties such as interfacial adhesion, crystallinity, and mechanical properties. Since crystallites can act as obstacles to gas diffusion, the higher the crystallinity of the polymer matrix, the better gas barrier performance of the composite film will be. The crystallinity and crystalline structure of the PLA matrix was demonstrated by wide-angle X-ray diffraction and differential scanning calorimetry results. Since LG particles can act as efficient heterogeneous crystal nucleating agents, a roughly 50% reduction in oxygen permeability (P_O2) was obtained by adding 1 phr LG to the PLA matrix (PLA/1LG). Following addition of 10 phr PLA-g-GMA to the PLA/LG composite, PLA/PLA-g-GMA/LG composite films showed lower gas barrier properties than PLA/LG composites without added compatibilizer. Moreover, the interfacial adhesion of PLA/LG composites was significantly improved after addition of PLA-g-GMA. Therefore, PLA/PLA-g-GMA/3LG showed the highest tensile strength, 33% higher than that of neat PLA. Following addition of 10 phr PLA-g-PEGMA to the PLA/LG composite, the long liner side chains of PLA-g-PEGMA were able to act as nucleating agents for PLA to promote the crystallization of PLA. Accordingly, PLA/PLA-g-PEGMA/3LG with 3 phr LG showed a roughly 86% reduction in P_O2 when compared with neat PLA film.