Nanocomposites of PLA/PP blends based on sepiolite

In the present study, the effectiveness of four polymers grafted with maleic anhydride used as compatibilizers in blends with poly(lactic acid) and its composites with sepiolite as matrices was evaluated in terms of transmission and scanning electron microscopy, oscillatory shear flow and tensile properties. Two polypropylenes were used as dispersed phases in the blends prepared in a corotating twin-screw extruder. Results showed that the compatibilized blends prepared without clay have higher susceptibility to isothermal degradation and higher tensile toughness than those prepared with sepiolite. The blend with the grafted metallocene polyethylene as compatibilizer exhibited the highest tensile toughness. The composites based on polyblends with polypropylene displayed lower tensile strength and Young’s modulus values, increased values of elongation at break, tensile toughness, complex viscosity, and storage modulus compared to those of the nanocomposite of PLA. These results are related to the clay dispersion, to the type of morphology of the different blends, to the grafting degree of the compatibilizers, and to the migration of the sepiolite toward the PP interface.     

Poly(lactic acid)–thermoplastic poly(ether)urethane composites synergistically reinforced and toughened with short carbon fibers for three‐dimensional printing

In this study, we prepared short‐carbon‐fiber (CF)‐reinforced poly(lactic acid) (PLA)–thermoplastic polyurethane (TPU) blends by melt blending. The effects of the initial fiber length and content on the morphologies and thermal, rheological, and mechanical properties of the composites were systematically investigated. We found that the mechanical properties of the composites were almost unaffected by the fiber initial length. However, with increasing fiber content, the stiffness and toughness values of the blends were both enhanced because of the formation of a TPU‐mediated CF network. With the incorporation of 20 wt % CFs into the PLA–TPU blends, the tensile strength was increased by 70.7%, the flexural modulus was increased by 184%, and the impact strength was increased by 50.4%. Compared with that of the neat PLA, the impact strength of the CF‐reinforced composites increased up to 1.92 times. For the performance in three‐dimensional printing, excellent mechanical properties and a good‐quality appearance were simultaneously obtained when we printed the composites with a thin layer thickness. Our results provide insight into the relationship among the CFs, phase structure, and performance, as we achieved a good stiffness–toughness balance in the PLA–TPU–CF ternary composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46483.     

EVA熔体流动速率对PLA/EVA共混物性能的影响

通过熔融共混法制备了聚乳酸（PLA）/乙烯-乙酸乙烯酯共聚物（EVA）共混物,采用SEM、DSC、旋转流变仪等研究了VA质量分数为28%,熔体流动速率（MFR）不同的EVA对PLA/EVA共混物性能的影响。结果表明,EVA熔体流动速率越小,其在PLA基体中分散越均匀,EVA颗粒粒径也越小。共混物的结晶度随EVA熔体流动速率的增大而增大,但PLA的玻璃化转变温度（Tg）基本不受EVA的影响。PLA/EVA共混物的复数黏度和储能模量均随EVA的熔体流动速率的增高而减小。力学性能测试结果表明,当EVA的质量分数为15%时,PLA的断裂伸长率明显升高,冲击强度约是纯PLA的2倍。     

Effect of clay type and polymer matrix on microstructure and tensile properties of PLA/LLDPE/clay nanocomposites

Polylactide (PLA)/linear low‐density polyethylene (LLDPE), (PLA/LLDPE), blends and nanocomposites were prepared by melt mixing process with a view to fine tune the properties. Two different commercial‐grade nanoclays, Cloisite® 30B (30B) and Cloisite® 15A (15A) were used. A terpolymer of ethylene, butylacrylate (BA) and glycidylmethacrylate (GMA) was used as a reactive compatibilizer. The influence of type of clay on the morphology and mechanical properties of two PLA‐rich and LLDPE‐rich blend systems was studied. Morphological analysis using X‐ray diffraction, transmission electron microscopy, and scanning electron microscopy revealed that the organoclay layers were dispersed largely at the interface of PLA/LLDPE. Decreasing the PLA content changed the morphology from droplet‐in matrix to coarse co‐continuous. In comparison with 30B, due to less affinity of 15A towards compatibilizer and PLA phase, the reduction of the size of dispersed phase was less than that of the equivalent 30B composites. The mechanical results demonstrated that the composites containing both types of organoclay exhibited higher modulus but lower elongation and tensile strength as compared to the neat blends. The injection molded nanocomposites were shown to have the sequential fracture behavior during tensile test. The tensile testing results on the neat blends and nanocomposites showed significant increase in elongation at break and decrease in the modulus as compared with the neat PLA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 749‐758, 2013     

Toughening polylactide with epoxidized styrene–butadiene impact resin: Mechanical,morphological, and rheological characterization

Styrene–butadiene impact resin (SBC) was chosen as the toughening agent to improve the tensile toughness of polylactide (PLA). Epoxidized SBC (ESBC) with different epoxidation degree were prepared by epoxidation using in situ peroxoformic acid method and a series of PLA/SBC(ESBC) blends were prepared by melt blending. The elongation at break of the PLA/ESBC blends was greatly improved, which was reflected in the slight decrease in the tensile strength and tensile modulus. Moreover, the tensile strength and tensile modulus were not significantly affected by the epoxidation degree of ESBC. For example, the incorporation of ESBC28.8% (30 wt %) to PLA caused an obvious increment of elongation at break from 3.5% of pure PLA to 305.0%, while the tensile modulus and tensile strength decreased to 80 and 78% of pure PLA, respectively. Scanning electron microscopy observations of cryo‐fractured surface morphology and particle size analysis demonstrated that the compatibility of the PLA/ESBC blends was improved significantly compared to PLA/SBC blend. PLA/ESBC(70/30) blends exhibited shear‐thinning behavior over the range of the studied shear rate. With an increase in shear rate, the non‐Newtonian index of the blends decreased gradually. Furthermore, the flow behavior of PLA/ESBC(70/30) blends was more sensitive to the shear rate than pure PLA. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46058.     

Effects of mixing protocols on impact modified poly(lactic acid) layered silicate nanocomposites

Poly(lactic acid)/2 wt % organomodified montmorillonite (PLA/OMMT) was toughened by an ethylene‐methyl acrylate‐glycidyl methacrylate (E‐MA‐GMA) rubber. The ternary nanocomposites were prepared by melt compounding in a twin screw extruder using four different addition protocols of the components of the nanocomposite and varying the rubber content in the range of 5–20 wt %. It was found that both clay dispersion and morphology were influenced by the blending method as detected by X‐ray diffraction (XRD) and observed by TEM and scanning electron microscopy (SEM). The XRD results, which were also confirmed by TEM observations, demonstrated that the OMMT dispersed better in PLA than in E‐MA‐GMA. All formulations exhibited intercalated/partially exfoliated structure with the best clay dispersion achieved when the clay was first mixed with PLA before the rubber was added. According to SEM, the blends were immiscible and exhibited fine dispersion of the rubber in the PLA with differences in the mean particle sizes that depended on the addition order. Balanced stiffness‐toughness was observed at 10 wt % rubber content in the compounds without significant sacrifice of the strength. High impact toughness was attained when PLA was first mixed with the clay before the rubber was added, and the highest tensile toughness was obtained when PLA was first compounded with the rubber, and then clay was incorporated into the mixture. Thermal characterization by DSC confirmed the immiscibility of the blends, but in general, the thermal parameters and the degree of crystallinity of the PLA were not affected by the preparation procedure. Both the clay and the rubber decreased the crystallization temperature of the PLA by acting as nucleating agents. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41518.     

聚甲基乙撑碳酸酯/乙烯-乙烯醇共聚物/黏土复合材料的流变性能与阻透性能

采用熔融共混的方法制备了聚甲基乙撑碳酸酯(PPC)/黏土和PPC/乙烯-乙烯醇共聚物(EVOH)/黏土纳米复合材料,测试了复合材料的流变性能和阻氧性能,并对其微观形态进行了分析。结果表明,当基材PPC相对分子质量较高时,PPC/黏土复合材料的复数黏度、储能模量和耗能模量也较高;随着黏土和相容剂马来酸酐接枝聚乙烯（PE-g-MAH）的添加, PPC/EVOH复合材料的复数黏度和模量明显增加,PE-g-MAH的加入使PPC、EVOH和黏土之间的界面作用力增强,改善了PPC与EVOH的相容性,同时提高了PPC/EVOH复合材料的阻氧性能。     

Mechanical,rheological, and crystallinity properties of polylactic acid/polyethylene glycol-polydimethylsiloxane copolymer blends by melt blending

Polylactic acid (PLA) is high in strength and modulus, but its applications are limited partly due to its inherent brittleness. It is difficult to keep the toughness and transparency of modified PLA without damaging its tensile strength and crystallinity. To improve the properties of PLA, polyethylene glycol-polydimethylsiloxane copolymer (PEG-PDMS) was incorporated to PLA via melt blending. By incorporating only 5 wt% of PEG-PDMS into PLA matrix, the elongation at break of the blends increased from 6% to 58% and the tensile strength was found to be 48.8 MPa. Differential scanning calorimetry demonstrated that the crystallinity of PLA/5%PEG-PDMS blends reached 33.5%. At the same time, the energy storage modulus (G) and complex viscosity (η*) of the blends had been improved. UV–vis test showed the light transmittance of the PLA/5%PEG-PDMS blends was slightly decreased. The toughened materials are sufficient to cope with the challenges brought by complex environments, achieving an efficient toughening effect.     

Effect of blending conditions on mechanical,thermal, and rheological properties of plasticized poly(lactic acid)/maleated thermoplastic starch blends

This research work has concerned a study on relationship between structure and properties of maleated thermoplastic starch (MTPS)/plasticized poly(lactic acid) (PLA) blend. The aim of this work is to investigate the effects of blending time, temperature, and blend ratio on mechanical, rheological, and thermal properties of the blend. The MTPS was prepared by mixing the cassava starch with glycerol and maleic anhydride (MA). Chemical structure of the modified starch was characterized by using a FTIR technique, whereas the degree of substitution was determined by using a titration technique. After that, the MTPS prepared by 2.5 pph of MA was further used for blending with triacetin‐plasticized PLA under various conditions. Mechanical, thermal, and rheological properties of the blends were evaluated by using a tensile test, dynamic mechanical thermal analysis, and melt flow index (MFI) test, respectively. It was found that tensile strength and modulus of the MTPS/PLA blend increased with the starch content, blending temperature, and time, at the expense of their toughness and elongation values. The MFI values also increased with the above factors, suggesting some chain scission of the polymers during blending. SEM images of the various blends, however, revealed that the blend became more homogeneous if the temperature was increased. The above effect was discussed in the light of trans‐esterification. Last, it was found that mechanical properties of the PLA/MTPS blend were more superior to those of the normal PLA/TPS blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Processing and properties of polymeric nano‐composites

Polymeric nano‐composites are prepared by melt intercalation in this study. Nano‐clay is mixed with either a polymer or a polymer blend by twin‐screw extrusion. The clay‐spacing in the composites is measured by X‐ray diffraction (XRD). The morphology of the composites and its development during the extrusion process are observed by scanning electron microscopy (SEM). Melt viscosity and mechanical properties of the composites and the blends are also measured. It is found that the clay spacing in the composites is influenced greatly by the type of polymer used. The addition of the nano‐clay can greatly increase the viscosity of the polymer when there is a strong interaction between the polymer and the nano‐clay. It can also change the morphology and morphology development of nylon 6/PP blends. The mechanical test shows that the presence of 5–10 wt.% nano‐clay largely increases the elastic modulus of the composites and blends, while significantly decreases the impact strength. The water absorption of nylon 6 is decreased with the presence of nano‐clay. The effect of nano‐clay on polymers and polymer blends is also compared with Kaolin clay under the same experimental conditions.     

Biopolymer blends based on polylactic acid and polyhydroxy butyrate‐co‐valerate: Effect of clay on mechanical and thermal properties

Biodegradable polymer blends consisting of polylactic acid (PLA) and polyhydroxy butyrate‐co‐valerate (PHBV) have been prepared by melt mixing in a twin screw extruder and followed by injection molding technique. Cereplast PLA containing starch as an additive was used to make the blends. The effects of three different types of clay (montmorillonite, bentonite, and chemically modified bentonite) on the mechanical and thermal properties of the blends were studied. The ratio of PLA and PHBV (w/w) was maintained at 70:30 while the weight of clay was fixed at 1%. The addition of clay was found to result in a slight increase in tensile strength and modulus. Viscoelastic studies revealed that the damping property of the blends decreased with the addition of clay. This was attributed to the decreased segmental motion in the molecular chains. The morphology of the blends has been investigated by environmental scanning electron microscopy and a homogenous surface was observed for the blend containing montmorillonite. POLYM. COMPOS., 36:2042–2050, 2015. © 2014 Society of Plastics Engineer     

PLA/chain‐extended PEG blends with improved ductility

Melt blending of polylactic acid (PLA) and a chain‐extended polyethylene glycol (CE‐PEG) have been performed in an effort to toughen the PLA without significant loss of modulus and ultimate tensile strength. The chain‐extended PEG was prepared with melt condensation of a low molecular weight PEG and 4,4′‐methylenebis(phenylisocyanate) (MDI) for enhancement of the molecular weight of PEG. The thermal and mechanical properties, miscibility and phase morphologies of blends were investigated. By using thermal and fracture surface analysis, the blends were found to be a partially miscible system with shifted glass transition temperatures. The addition of CE‐PEG leads to slight decrease in tensile strength and modulus, while the elongation at break is characterized by an important increase (540%), compared with neat PLA and PLA/PEG (low molecular weight PEG, M_n = 35,000). The relative ductility of PLA/CE‐PEG is 40 times higher than that of neat PLA. The brittle fracture of neat PLA was transformed into a ductile fracture by the addition of CE‐PEG. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Morphology and properties of the biosourced poly(lactic acid)/poly(ethylene oxide‐b‐amide‐12) blends

Biosourced poly(lactic acid) (PLA) blends with different content of poly(ethylene oxide‐b‐amide‐12) (PEBA) were prepared by melt compounding. The miscibility, phase structure, crystallization behavior, mechanical properties, and toughening mechanism were investigated. The blend was an immiscible system with the PEBA domains evenly dispersed in the PLA matrix. The PEBA component suppressed the nonisothermal melt crystallization of PLA. With the addition of PEBA, marked improvement in toughness of PLA was achieved. The maximum for elongation at break and impact strength of the blend reached the level of 346% and 60.5 kJ/m², respectively. The phase morphology evolution in the PLA/PEBA blends after tensile and impact tests was investigated, and the corresponding toughening mechanism was discussed. It was found that the PLA matrix demonstrates obvious shear yielding in the blend during the tensile and impact tests, which induced energy dissipation and therefore lead to improvement in toughness of the PLA/PEBA blends. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Morphology,mechanical, and rheological properties of poly(lactic acid)/ethylene acrylic acid copolymer blends processing via vane extruder

This work aimed to study, for the first time, the melt blending of poly(lactic acid) (PLA) and ethylene acrylic acid (EAA) copolymer by a novel vane extruder to toughen PLA. The phase morphologies, mechanical, and rheological properties of the PLA/EAA blends of three weight ratios (90/10, 80/20, and 70/30) were investigated. The results showed that the addition of EAA improves the toughness of PLA at the expense of the tensile strength to a certain degree and leads the transition from brittle fracture of PLA into ductile fracture. The 80/20 (w/w) PLA/EAA blend presents the maximum elongation at break (13.93%) and impact strength (3.18 kJ/m²), which is 2.2 and 1.2 times as large as those of PLA, respectively. The 90/10 and 80/20 PLA/EAA blends exhibit droplet‐matrix morphologies with number average radii of 0.30–0.73 μm, whereas the 70/30 PLA/EAA blend presents an elongated co‐continuous structure with large radius (2.61 μm) of EAA phase and there exists PLA droplets in EAA phase. These three blends with different phase morphologies display different characteristic linear viscoelastic properties in the low frequency region, which were investigated in terms of their complex viscosity, storage modulus, loss tangent, and Cole‐Cole plots. Specially, the 80/20 PLA/EAA blend presents two circular arcs on its Cole‐Cole plot. So, the longest relaxation time of the 80/20 blend was obtained from its complex viscosity imaginary part plot, and the interfacial tension between PLA and EAA, which is 4.4 mN/m, was calculated using the Palierne model. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40146.     

Compression molding and melt‐spinning of the blends of poly(lactic acid) and poly(butylene succinate‐co‐adipate)

Poly(lactic acid) (PLA) is a biobased polymer made from biomass having high mechanical properties for engineering materials applications. However, PLA has certain limited properties such as its brittleness and low heat distortion temperature. Thus, the aim of this study is to improve toughness of PLA by blending with poly(butylene succinate‐co‐adipate) (PBSA), the biodegradable polymer having high toughness. Polymer blends of PLA and PBSA were prepared using a twin screw extruder. The melt rheology and the thermal property of the blends were examined. Further the blends were fabricated into compression molded parts and melt‐spun fiber and were subjected to tensile and impact tests. When the PBSA content was low, PBSA phase was finely dispersed in the PLA matrix. On the other hand, when the PBSA content was high, this minor phase dispersed as a large droplet. Mechanical properties of the compression molded parts were affected by the dispersion state of PBSA minor component in PLA matrix. Impact strength of the compression molded parts was also improved by the addition of soft PBSA. The improvement was pronounced when the PBSA phase was finely dispersed in PLA matrix. However, the mechanical property of the blend fibers was affected by the postdrawing condition as well as the PBSA content. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41856.     

Synthesis and characterization of linear low‐density polyethylene/sepiolite nanocomposites

Linear low‐density polyethylene (LLDPE)/sepiolite nanocomposites were prepared by melt blending using unmodified and silane‐modified sepiolite. Two methods were used to modify sepiolite: modification before heat mixing (ex situ) and modification during heat mixing (in situ). The X‐ray diffraction results showed that the position of the main peak of sepiolite remained unchanged during modification step. Infrared spectra showed new peaks confirming the development of new bonds in modified sepiolite and nanocomposites. SEM micrographs revealed the presence of sepiolite fibers embedded in polymer matrix. Thermogravimetric analysis showed that nanocomposites exhibited higher onset degradation temperature than LLDPE. In addition, in situ modified sepiolite nanocomposites exhibited higher thermal stability than ex situ modified sepiolite nanocomposites. The ultimate tensile strength and modulus of the nanocomposites were improved; whereas elongation at break was reduced. The higher crystallization temperature of some nanocomposite formulations revealed a heterogeneous nucleation effect of sepiolite. This can be exploited for the shortening of cycle time during processing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical performance of re‐extruded and aged graphene/polypropylene nanocomposites

In the present research polypropylene/expanded graphite (PP/ExpG) and polypropylene/graphene nanoplatelet (PP/GNP) composites were prepared by melt blending and their morphology and tensile properties were investigated. Although both reinforcements improved the elastic modulus of PP, PP/GNP composite presented better dispersion of the nanofiller in the polymer matrix and it was selected for further re‐extrusion and ageing experiments. The re‐extrusion affected the content of crystal phases of PP in pure PP and in its nanocomposite with GNP and increased their elastic modulus. The ageing of one and five times re‐extruded PP caused an increase of the β‐crystal phase and the formation of voids in the cross‐section. GNPs seem to protect the PP matrix from ageing as in Fourier transform IR spectra of PP/GNP nanocomposite, both one and five times extruded, the peak corresponding to carbonyl degradation products of PP was barely visible. The tensile properties of aged nanocomposites, one and five times re‐extruded, were similar to those of the corresponding non‐aged composites, whereas in aged PP the tensile strength and strain decreased significantly compared to non‐aged PP. The anti‐ageing effect of graphene can prolong the life of the PP matrix. © 2017 Society of Chemical Industry     

丙烯酸酯接枝改性天然橡胶增韧聚乳酸

通过在天然橡胶(NR)分子链上接枝甲基丙烯酸甲酯(MMA)和丙烯酸丁酯(BA),制备了三种丙烯酸酯接枝改性NR:NR-g-PMMA,NR-g-PBA和NR-g-(PMMA,PBA)。采用核磁共振氢谱对三种接枝物进行了化学结构鉴定。将接枝改性后的NR和未改性的NR与PLA采用哈克密炼机熔融共混,分别制备了PLA/NR,PLA/NR-gPMMA,PLA/NR-g-PBA和PLA/NR-g-(PMMA,PBA)共混物,研究了接枝改性NR和未改性NR含量对共混物力学性能和热性能的影响。各共混物的拉伸弹性模量和拉伸强度均随接枝改性NR和未改性NR含量的增加而降低,断裂伸长率和缺口冲击强度随接枝改性NR和未改性NR含量的增加而提高。其中,PLA/NR-g-PBA共混物的断裂伸长率和缺口冲击强度比其它共混物提高的幅度大,当NR-g-PBA的质量分数为5%时,PLA/NR-g-PBA共混物的断裂伸长率达到78%,缺口冲击强度为5.2 k J/m2,而纯PLA的断裂伸长率仅为7.7%,缺口冲击强度为2.5 k J/m2,说明NR接枝分子柔顺性较高的BA更有利于促进其与PLA共混物的韧性提高。热分析结果表明,PLA/NR-gPBA共混物的热稳定性相比于纯PLA也有所提高。     

Development and characterization of solid and porous polylactide‐multiwall carbon nanotube composites

This article describes the fabrication of solid and porous polylactide (PLA)‐multiwall carbon nanotube (MWNT) composites prepared using melt blending and subsequent batch processing of porous structures. The morphology and thermal, rheological and electrical properties of the PLA‐MWNT composites prepared with MWNT concentrations of 0, 0.5, 1, 2, and 5 wt% were characterized. The composite structure consisted of identifiable regions of MWNT aggregation and MWNT dispersion. Increasing MWNT content was found to increase the thermal stability and crystallization kinetics of PLA. The addition of MWNT to PLA significantly increased the melt viscosity and electrical conductivity of the composites. Based on rheological and electrical measurements, a continuous MWNT network structure in PLA was found to form when the concentration of MWNT is increased from 0.5 wt% (0.33 vol%) to 1 wt% (0.66 vol%). As many current day applications of polymers and polymer composites require lightweight and low‐density materials, porous PLA‐MWNT composites were fabricated from a batch porous structure processing technique. Porous PLA‐MWNT composites containing 2 and 5 wt% MWNT had lower relative densities, which is attributed to the higher viscosity of the composites suppressing collapse of the porous structure during processing. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Ethylene vinyl acetate copolymer nanocomposites based on (un)modified sepiolite: Flame retardancy,thermal, and mechanical properties

Flame retardant ethylene‐vinyl acetate (EVA) nanocomposites were prepared by melt blending using unmodified and modified sepiolite. Modification process of sepiolite was carried out by using 3‐aminopropyltrimethoxysilane in water/ethanol medium. Thermal, mechanical, and flame retardancy properties of the prepared nanocomposites were evaluated and compared with each other. X‐ray diffraction and scanning electron microscopy indicated that sepiolite fibers are well‐dispersed in EVA matrix. By the addition of (un)modified sepiolite, both flame retardancy and thermal stability characteristics first improved, and then deteriorated, indicating a direct relationship between these properties. It was also found that sepiolite protects carbonyl groups of EVA from further degradation. Most interestingly, a simultaneous increase in both ductility and toughness was observed in the prepared composites. Whatever the evaluated properties were, whether the mechanical, thermal, or flame retardancy, the improved properties were more remarkable when modified sepiolite was utilized. POLYM. COMPOS., 38:1302–1310, 2017. © 2015 Society of Plastics Engineers