The role of nanofillers on the degradation behavior of polylactic acid

This study examines the effect of type and content of various nanofillers on the aging behavior of polylactic acid (PLA)/nanocomposites compared with that of pristine PLA, under specific environmental conditions, namely 80% relative humidity, 40°C temperature, and exposure time up to 6 months. Two different types of nanosized fillers (silica and montmorillonite, MMT) at three different weight fractions as well their mixtures were used for this purpose. The role of the various nanofillers on the aging of pristine PLA and its nanocomposites was investigated in terms of several experimental techniques including Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and tensile testing. All studied samples, except those of PLA/MMT/Si nanocomposites, exhibited the same trend in properties during aging. In particular, no significant changes are noted after 1 month of aging. The materials after 3 months of aging experienced a dramatic lowering of the stress–strain curve, whereas at 6 months a reverse effect was observed. Comparing the effect of nanofiller types on the degradation, one could conclude that PLA/MMT nanocomposites exhibit a more homogeneous degradation effect, having a higher impact on yield stress in comparison with silica. In contrast, silica has a greater effect in Young's modulus and strain at break, compared with MMT. The peculiar behavior of the PLA/MMT/Si nanocomposites during aging is explained by the hindering action of the mixture of the two nanofillers on the molecular reordering of the PLA chains in the amorphous region. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Thermo-mechanical properties of high density polyethylene – fumed silica nanocomposites: effect of filler surface area and treatment

High density polyethylene was melt compounded with various untreated (hydrophilic) or surface treated (hydrophobic) fumed silica nanoparticles, having different surface areas. The thermo-mechanical properties of the resulting nanocomposites have been thoroughly investigated. Field emission scanning electron microscopy revealed that nanofiller aggregation was more pronounced as the silica surface area increased, while nanofiller dispersion improved with a proper filler functionalization. The homogeneous distribution of fumed silica aggregates at low filler content allowed us to reach remarkable improvements of thermal stability, evidenced by an increase of the degradation temperature and a decrease of the mass loss rate with respect to neat matrix, especially when surface treated nanoparticles were utilized. Interestingly, the stabilizing effect produced by fumed silica nanoparticles was accompanied by noticeable enhancements of the ultimate tensile mechanical properties, both under quasi-static and impact conditions. Concurrently, a progressive enhancement of both elastic modulus and tensile stress at yield with the filler amount, was observed.     

Effect of the compatibilizing agent on the structure,mechanical and thermal properties of polylactide filled with modified and unmodified montmorillonite

Polylactide (PLA) nanocomposites were prepared by an extrusion technique using a twin‐screw extruder. Nanofil2 (N) and montmorillonite (MMT) K10 (S) were used as nanoclays. To improve the nanoclay dispersion in the PLA matrix, a compatibilizer was introduced [poly(ε‐caprolactone) (K)]. The structure and morphology of obtained materials were determined using X‐ray diffraction technique and transmission electron microscopy. Thermal properties of nanocomposites were reviewed based on differential scanning calorimetry and differential thermogravimetry. Mechanical properties such as tensile stress and tensile strength were also studied. The introduction of layered silicates without a compatibilizer into PLA matrix did not improve the mechanical properties of the obtained nanocomposites. This research indicated that the compatibilizing agent can be used to improve the dispersion of Nanofil2 nanofiller, which resulted in the improvement of mechanical properties and at the same time did not affect the dispersion of the unmodified MMT. POLYM. COMPOS., 35:1330–1337, 2014. © 2013 Society of Plastics Engineers     

The role of nanofillers on (natural rubber)/(ethylene vinyl acetate)/clay nanocomposite in blending and foaming

Nanocomposite foams were fabricated from 60/40 wt% ethylene vinyl acetate (EVA)/natural rubber (NR) blends by using azodicarbonamide as a blowing agent. Two different nanofillers (sodium montmorillonite and organoclay) were employed to study their effects on foam properties. The results were also compared with conventional (china clay)‐filled foams. Transmission electron microscopy, X‐ray diffraction, scanning electron microscopy, and three‐dimensional Microfocus X‐ray computed tomography scanning analysis were performed to characterize the EVA/NR blend morphology and foam structures. The results revealed that the nanofiller acted as a blend compatibilizer. Sodium montmorillonite was more effective in compatibilization, generating better phase‐separated EVA/NR blend morphology and improving foam structure. Higher filler loading increased the specific tensile strength of rubber foams. The rubber nanocomposite foam showed superior specific tensile strength to the conventional rubber composite foam. The elastic recovery and compressive strength of the nanocomposite foams decreased with increasing filler content, whereas the opposite trend was observed for the conventional composite foams with china clay. The thermal conductivity measurement indicated that the nanofiller had better beneficial effect on thermal insulation over china clay filler. From the present study, the nanofillers played an important role in obtaining better blend morphology as compatibilizer, rather than the nucleating agent and the nanofiller content of 5 phr (parts by weight per hundred parts of rubber) was recommended for the production of EVA/NR nanocomposite foams. J. VINYL ADDIT. TECHNOL., 21:134–146, 2015. © 2014 Society of Plastics Engineers     

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     

Morphology,mechanical properties,and thermal stability of rigid PVC/clay nanocomposites

PVC/Poly(ε‐caprolactone) (PCL)/organophilic‐montmorillonite (OMMT) and PVC/Polylactide (PLA)/OMMT nanocomposites were prepared by a two‐step process. PCL/OMMT and PLA/OMMT master batches were prepared by melt blending using a two‐roller mill first, and then they were blended with PVC via extrusion. PVC/OMMT nanocomposites were also prepared using a two‐roller mill. Morphology, mechanical properties, and thermal stability were investigated. The formation of exfoliated or intercalated nanocomposites was confirmed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Only the PVC/PCL/OMMT nanocomposite showed both higher tensile strength and stiffness than unfilled PVC. Atomic force microscopy (AFM) indicated dependency of this behavior not only on the clay dispersion, but also on the adhesion between the OMMT and the polymer matrix. Furthermore, scanning electron microscopy (SEM) showed that the large plastic deformation of the PVC/PCL matrix also contributed to the strength increase of the PVC nanocomposites. The effect of PCL/OMMT on the improvement of the thermal stability of PVC was remarkable while the effect of PLA/OMMT was moderate. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Effects of different interphases on the mechanical properties of cured silanized silica‐filled styrene–butadiene/polybutadiene rubber blends for use in passenger car tire treads

Polybutadiene (BR) and styrene–butadiene (SBR) rubbers containing the same loading of precipitated silica nanofiller were prepared. The silica surfaces were pretreated with bis(3‐triethoxysilylpropyl) tetrasulfide to chemically bond the silica to the rubber. The rubber compounds were mixed together for different times and at different temperatures to produce SBR/BR blends. The mass fraction and composition values of the interphases in the blends were subsequently determined with modulated‐temperature differential scanning calorimetry. These properties changed substantially as a function of mixing temperature and mixing time. The hardness, tensile strength, elongation at break, stored energy density at break, tear strength, modulus, abrasion resistance, heat buildup, and loss tangent of the cured blends were measured over a wide range of test conditions. Elongation at break, stored energy density at break, tearing energy, and abrasion resistance benefited from increases in the mass fraction of the interphase. The remaining properties were influenced mainly by the filler loading and mixing time of the two rubber compounds. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Melt processing of poly(L‐lactic acid) in the presence of organomodified anionic or cationic clays

Poly(L ‐lactic acid) (PLA) films are in use for various types of food packaging; however, a wider range of applications would be possible if the barrier properties of these films could be improved. To make such improvements, combinations of PLA with two nanofillers, laurate‐intercalated Mg‐Al layered double hydroxide (LDH‐C₁₂) and a cationic organomodified montmorillonite (MMT) clay (Cloisite® 30B), were investigated. The dispersion of these fillers in PLA by melt processing was explored using two methods, either by mixing the nanofillers with PLA granulate immediately before extrusion or by preparation and subsequent dilution of PLA‐nanofiller masterbatches. After melt processing of these materials, PLA molecular weight, thermal stability, film transparency, morphology, and permeability characteristics were determined. Direct addition of LDH‐C₁₂ drastically reduced the PLA molecular weight. Although this reduction in molecular weight was still very significant, it was less when a PLA/LDH‐C₁₂ masterbatch was processed. In contrast, there was no significant reduction in PLA molecular weight when processing with Cloisite® 30B. However, film transparency was compromised when either LDH or MMT nanofillers were used. Evidence from DSC analyses showed a significant increase in heat of fusion when LDH‐C₁₂ was dispersed in PLA compared with Cloisite® 30B, likely indicating a difference in nucleating properties. Complementary optical purity analyses suggested that racemization as a result of processing could influence the PLA crystallinity as determined by DSC in certain cases. A reduction in thermal stability when incorporating LDH‐C₁₂ could be a direct result of PLA molecular weight reduction. XRD and TEM analyses showed that both Cloisite® 30B‐ and LDH‐C₁₂‐based PLA composites yielded exfoliated and intercalated morphologies, but nanofiller agglomeration was also seen when LDH‐C₁₂ was used. PLA/Cloisite® 30B nanocomposite films exhibited significant enhancement in oxygen and water vapor barrier properties, but no such improvement was found in PLA/LDH‐C₁₂ nanocomposite films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Multiscale modeling of interface debonding effect on mechanical properties of nanocomposites

Mechanical behavior of SiO₂ nanoparticle‐epoxy matrix composites was investigated via finite element analysis with an emphasis on the nanofiller‐interphase debonding effect using a three‐dimensional nanoscale representative volume element (RVE). The new model, in which a cohesive zone material (CZM) layer is considered as an inclusion‐interphase bonding, can be applied to polymer nanocomposites reinforced by inclusions of different forms, including spherical, cylindrical, and platelet shapes. Upon validation by experimental data, the model was used to study the effects of interphase properties, nanoparticle size, and inclusion volume fraction on the mechanical properties of nanocomposites. According to the results, taking into account the inclusion‐interphase debonding provides more precise results compared with perfect bonding, especially in nanocomposites with nanoparticles of smaller size. Moreover, the outcomes disclosed that the amount of changes in the elastic modulus by particle size variation is higher when the relative thickness (the interphase thickness to the particle diameter ratio) increases. For relative thicknesses lower than a critical value, the particle size and the interphase properties have negligible effect on the elastic modulus of the nanocomposite, and the elastic modulus of nanocomposite mostly depends on nanofiller content. POLYM. COMPOS., 38:789–796, 2017. © 2015 Society of Plastics Engineers     

Mechanical,thermal, and morphological properties of injection molded poly(lactic acid)/SEBS‐g‐MAH/organo‐montmorillonite nanocomposites

Poly(lactic acid)/organo‐montmorillonite (PLA/OMMT) nanocomposites toughened with maleated styrene‐ethylene/butylene‐styrene (SEBS‐g‐MAH) were prepared by melt‐compounding using co‐rotating twin‐screw extruder followed by injection molding. The dispersibility and intercalation/exfoliation of OMMT in PLA was characterized using X‐ray diffraction and transmission electron microscopy (TEM). The mechanical properties of the PLA nanocomposites was investigated by tensile and Izod impact tests. Thermogravimetric analyzer and differential scanning calorimeter were used to study the thermal behaviors of the nanocomposite. The homogenous dispersion of the OMMT silicate layers and SEBS‐g‐MAH encapsulated OMMT layered silicate can be observed from TEM. Impact strength and elongation at break of the PLA nanocomposites was enhanced significantly by the addition of SEBS‐g‐MAH. Thermal stability of the PLA/OMMT nanocomposites was improved in the presence of SEBS‐g‐MAH. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Poly(lactic acid)/low‐density polyethylene blends and its nanocomposites based on sepiolite

Poly(lactic acid) (PLA) nanocomposite ternary blends based on unmodified sepiolite were prepared by melt blending using a corotating twin‐screw extruder. Two grafted polymers were used as compatibilizer agents, in an effort to increase the PLA tensile toughness. The influence of incorporating a low‐cost commodity low‐density polyethylene, as dispersed phase to the composites on thermal degradation, and rheological and tensile properties was studied. The morphology of the blends and composites was determined through transmission and scanning electron microscopy techniques. Results showed that the compatibilized blends prepared without clay have higher thermal degradation susceptibility and tensile toughness than those prepared with sepiolite and significant changes in complex viscosity and melt elasticity values were observed between them. The nanocomposite blends exhibited similar thermal degradation, lower tensile strength, and Young's modulus values and increased elongation at break and tensile toughness, complex viscosity, and storage modulus compared with 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 localization of the sepiolite in the different phases, the thermomechanical degradation of the PLA matrix phase during melt blending and the grafting degree of the compatibilizers used. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Wood flour/polylactide biocomposites toughened with polyhydroxyalkanoates

Polylactide (PLA)‐based wood–plastic composites (WPCs) were successfully manufactured by extrusion blending followed by injection molding. The effects of polyhydroxyanoates (PHAs) on the mechanical and thermal properties and the morphologies of the PLA‐based WPCs were investigated with mechanical testing, thermal analysis, and scanning electronic microscopy (SEM). The inclusion of PHAs in the PLA‐based WPCs produced an increase in the impact resistance and a decrease in the tensile strength. The brittle–ductile transition of the impact strength for the PLA‐based WPCs toughened with PHAs was confirmed when the wood flour content was between 15 and 35 wt %. SEM images showed that the fracture surfaces of the PLA‐based WPCs toughened with PHAs were rougher than that of their nontoughened counterparts. The ternary PLA‐based WPCs exhibited ductile fracture during mechanical testing. Differential scanning calorimetry (DSC) showed that addition of PHAs into the composites caused deviations of the cold crystallization temperature and melting temperature of PLA. Thermogravimetric analysis indicated that the PHAs reduced the thermal stability of the PLA‐based WPCs. PHAs can be a green toughening agent for PLA‐based WPCs. The specific properties evidenced by the biocomposites may hint at their potential application, for example, in the automotive industry and civil engineering. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

叶片挤出机制备PLA/MMT复合材料性能的研究

利用以拉伸形变为主导的叶片挤出机制备了不同质量比的聚乳酸/蒙脱土(PLA/MMT)纳米复合材料,通过透射电子显微镜(TEM)和X射线衍射仪(XRD)表征了该复合材料的微观结构及形貌,并探讨了不同含量的MMT对PLA/MMT复合材料的力学性能以及动态力学性能的影响。结果表明:PLA分子链插入MMT片层之间,形成了具有插层结构的PLA/MMT纳米复合材料;该复合材料的拉伸强度、拉伸模量及冲击强度均随着MMT含量的增加呈先增后减的趋势;当MMT含量为2.5%时,复合材料的综合力学性能达到最佳,其中拉伸模量比纯PLA提高了170%,冲击强度则提高了130%,说明少量MMT的加入对PLA能起到增强增韧的作用。另外,动态力学性能测试结果表明,随着MMT含量的增加,复合材料的玻璃化转变温度有下降的趋势。     

Thermal,morphological, and mechanical properties of biobased and biodegradable blends of poly(lactic acid) and chemically modified thermoplastic starch

In this study, poly(lactic acid) (PLA) was blended with chemically modified thermoplastic starch (CMPS) in a twin‐screw extruder. The characteristic properties of PLA/CMPS blends were investigated by observing the morphology, thermal, and mechanical properties, and biodegradability. Differential scanning calorimetry showed that the PLA/CMPS were thermodynamically immiscible. However, scanning electron microscopy and Fourier transform infrared studies revealed that the interfacial adhesion was improved by the PLA‐g‐starch copolymers that were formed at the interface through a transesterification reaction between PLA and CMPS. The crystallinity of the PLA component in the blend was increased by the addition of the CMPS and was highly affected by the morphology of the blend. The tensile strength and elongation were found to decrease in a linear trend with increasing CMPS content. The biodegradability of the blends increased with increasing CMPS content, while initial time lag decreased. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Investigation of miscibility and phase structure of a novel blend of poly(lactic acid) (PLA)/acrylic rubber (ACM) and its nanocomposite with nanosilica

In this work, a novel polymer blend containing poly(lactic acid) (PLA) as a biocompatible and biodegradable thermoplastic and acrylic rubber (ACM) is prepared and the miscibility and phase structure of the blend and its nanocomposite (PLA/ACM/nanosilica) are investigated through theoretical and experimental methods. To predict the phase diagram of the blend, a compressible regular solution model was employed, in which an upper critical solution temperature was observed. The model predicted that PLA/ACM blends are immiscible over the whole composition range at temperatures below 260 °C. Performing scanning force microscopy on the blend showed phase separated structures for the blends containing different amounts of the PLA and ACM. This was in accordance with the results of dynamic mechanical analysis, which revealed two distinct glass transition temperatures for the studied blends. The effect of nanometer sized silica particle on morphology and rheological properties of these blends was also investigated. Scanning force microscopy results showed much reduction of droplet size in the blends containing 2 wt % nanosilica. This was attributed to the suppression effect of nanosilica on the droplets coalescences. Rheological measurements confirmed the interaction of both components with the silica nanofiller. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45499.     

Effects of annealing time and temperature on the crystallinity and heat resistance behavior of injection‐molded poly(lactic acid)

The effects of annealing time and temperature on the crystallinity of injection‐molded poly(lactic acid) (PLA) were investigated using differential scanning calorimetry and wide‐angle x‐ray diffraction. Differential scanning calorimetry, tensile test, and dynamic mechanical analysis showed that an increase in crystallinity in the PLA parts from the annealing treatment offers several benefits such as a higher glass transition temperature, better heat resistance, and greater storage modulus and tensile strength. Based on the experimental data, the degree of crystallinity, annealing time, and annealing temperature were found to closely follow the time–temperature superposition relationship. Namely, a master curve could be constructed based on either the Williams–Landel–Ferry equation or the Arrhenius relationship by shifting the crystallinity isotherms in the logarithmic scale horizontally along the log‐time axis. This relationship provides a quantitative guideline for annealing postinjection‐molded PLA parts to improve the heat resistance and mechanical properties. An increase of over 17% and 26% in tensile strength was achieved at an annealing temperature of 80°C for 30 min and 65°C for 31 h, respectively. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Preparation and some properties of stereocomplex‐type poly(lactic acid)/layered silicate nanocomposites

Stereocomplex‐type poly(lactic acid)‐ [PLA]‐ based blends were prepared by solution casting of equimolar PLLA/PDLA with different amounts of organo‐modified montmorillonite. The homocrystallization and stereocomplexation of PLAs were enhanced by annealing of the blends. The stereocomplexation of PLAs, intercalation of the polymer chains between the silicates layers, and morphological structure of the filled PLAs were analyzed by wide‐angle X‐ray diffraction and transmission electron microscope. Thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), and tensile test were performed to study the thermal and mechanical properties of the blends. The homo‐ and stereocomplex crystallization of neat PLLA/PDLA were enhanced by annealing. The effect of annealing on the crystallization was emphasized by the addition of clay. With this structural change, thermal stabilities properties were also improved by the addition of clay. The silicate layers of the clay were slightly stacked but intercalated and distributed in the PLA‐matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Characterization and electrical conductivity of poly(ethylene glycol)/polyacrylonitrile/multiwalled carbon nanotube composites

Poly(Lactic acid) (PLA)‐layered silicate nanocomposite films were prepared by solvent casting method. The films were irradiated with Co⁶⁰ radiation facility at dose of 30 kGy. The effect of γ irradiation on mechanical properties of the neat PLA and nanocomposites was evaluated by data obtained from tensile testing measurements. The tensile strength of the irradiated PLA films increased with addition of 1 wt % triallyl cyanurate indicating crosslink formation. Significant ductile behavior was observed in the PLA nanocomposites containing 4 pph of nanoclay. Incorporation of nanoclay particles in the PLA matrix stimulated crystal growth as it was studied by differential scanning calorimetry. The morphology of the nanocomposites characterized by transmission electron microscopy and X‐ray diffraction revealed an exfoliated morphology in the PLA nanocomposite films containing 4 pph of nanoclay. Only very small changes were observed in the chemical structure of the irradiated samples as it was investigated by Fourier transform infrared spectroscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Epoxy‐silica nanocomposites: Preparation,experimental characterization,and modeling

Silica nanoparticles having different sizes were obtained by the sol‐gel process and characterized. The prepared nanoparticles were subsequently used as reinforcing fillers to prepare epoxy‐based composites with a silica content ranging from 1 to 5 wt %. SEM analysis and tensile tests carried out on the silica‐epoxy nanocomposites indicated the absence of particle aggregation and a reinforcing effect in terms of increased elastic modulus. Mechanical properties were also modeled by using a finite element code able to construct a numerical model from a microstructural image of the material. A more reliable model was prepared by considering the presence of an interphase layer surrounding the particles with intermediate elastic properties between the epoxy and the inclusions and a characteristic size proportional to the particle radius. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2382–2386, 2005     

Processing and properties of PLA/thermoplastic starch/montmorillonite nanocomposites

Thermoplastic starch (TPS) and polylactic acid (PLA) were compounded with natural montmorillonite (MMT) using a twin‐screw extrusion process to investigate the structure and properties of these nanocomposites and to examine the use of water to enhance clay exfoliation. Tensile and essential work of fracture measurements were performed on standard dumbbell shape samples and on double notched samples to determine the effect of MMT and PLA/TPS interfacial modification on the mechanical and fracture properties of the materials. The nanocomposite structure was investigated using X‐Ray diffraction, transmission electron microscopy, and atomic force microscopy. Differential scanning calorimetric analysis was performed on the materials to determine the effect of TPS and MMT on PLA crystallization and physical aging. It was found that the TPS can intercalate the clay structure and that the clay was preferentially located in the TPS phase or at the blend interface. This led to an improvement in tensile modulus and strength and to a reduction in fracture toughness. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers