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Gao C.,Center for Polymer from Renewable Resources | Gao C.,CSIRO | Gao C.,Monash University | Ma H.,Center for Polymer from Renewable Resources | And 7 more authors.
Polymer Engineering and Science

The microstructure and thermal and mechanical properties of poly(lactic acid) (PLA) fibers after thermal treatment under both taut and free conditions at different temperatures were studied by differential scanning calorimetry, wide-angle X-ray diffraction, microscopy with polarized light, an acoustic method and tensile testing. In particular, the effects of thermal treatment conditions on crystallinity, molecular orientation, and mechanical properties, as well as their interrelationships, were investigated. Both the crystal orientation and crystallinity of the PLA fibers were higher after thermal treatment under taut conditions, even though the molecular orientation was not higher. Thermal treatment relaxed orientated segments, which resulted in increasing crystallinity; however, it did not indicate that the overall molecular alignment of the chains (molecular orientation) would necessarily be high. Tensile strength and elongation were increased with increasing treatment temperature up to 150°C, which corresponded to crystallinity and chain relaxation. The crystallinity detected by XRD, enthalpy measured by DSC, birefringence, and molecular orientation were compared to distinguish the effects of crystallinity, orientation of polymer chains, and crystals. Copyright © 2012 Society of Plastics Engineers. Source

Gao C.,Center for Polymer from Renewable Resources | Gao C.,Monash University | Gao C.,CSIRO | Meng L.,Center for Polymer from Renewable Resources | And 6 more authors.
Composites Science and Technology

Uniaxial poly(lactic acid)-based self-reinforced composites have been developed by bonding poly ( l-lactic acid) (PLLA) fibers by depositing poly(D, l-lactic acid) (PDLLA) which was dissolved in ethyl acetate. The microstructure and the thermal and mechanical properties of this self-reinforced composite have been characterized using scanning electron microscopy, dynamic mechanical analysis, and tensile testing. The results revealed that after ethyl acetate treatment, the PLLA fibers maintained their geometry and orientation well, had an increased crystallinity, and showed a slightly damaged surface. Electron microscopy and thermal analysis showed that the interface between the PLA fiber and the PLA matrix had good compatibility, which was expected since they possess the same chemical structure. The modulus, tensile strength, and elongation, as well as the thermal stability of uniaxial poly(lactic acid) self-reinforced composites, were all significantly greater than those of the PDLLA film. The results showed that we have developed a method to prepare PLA composites with enhanced mechanical properties, without the problem of narrow processing temperature window normally required when using traditional thermal processing techniques. © 2015 Elsevier Ltd. Source

Zhang L.,Center for Polymer from Renewable Resources | Zhang L.,CSIRO | Zhang L.,Monash University | Wang Y.,Center for Polymer from Renewable Resources | And 6 more authors.
Colloid and Polymer Science

This work focuses on the study of rheological and gel properties of hydroxypropyl methylcellulose (HPMC)/hydroxypropyl starch (HPS) blends. It was found that both rheological properties in solution and gel behaviors in hydrogel of the blends depended on polymer/solvent concentration, HPMC/HPS ratio, and temperature. At higher temperature, all the blending samples showed hydrogel behavior, while at lower temperature, the suspensions with higher HPS ratio displayed hydrogel-like behavior but the gels were able to be destroyed at higher frequencies. With an increase of the HPS ratio, the fluid behavior index deceases, meaning the solution shows more obvious pseudoplastic behavior. However, the fluid consistency index increases, meaning that viscosity increases with increase of HPS content. The strength of HPMC gel was weakened by additional of HPS at higher temperature, while the HPS gel was weakened by addition of HPMC at lower temperatures. Viscosities of both HPMC and HPS were balanced by the blending at different temperatures since one is thermal and other is cool gel, which improves the processability for many applications. © 2014, Springer-Verlag Berlin Heidelberg. Source

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