Isothermal crystallization kinetics of thermoplastic starch/poly(lactic acid) composites

The thermoplastic starch/poly(lactic acid) (TPS/PLA) composites were prepared using PLA melt blending with glycerol plasticized-starch. A systematic study of the isothermal crystallization kinetics of TPS/PLA composites was performed by differential scanning calorimetry (DSC) at different crystallization temperatures (T-c). The analysis based on the Avrami theory, which was applied to describe the process of isothermal crystallization, indicated that the spherulite growth rate, overall crystallization rate, and activation energy (Delta E-a) of TPS/PLA composites were remarkably affected by the incorporation of TPS. TPS acts as a nucleating agent, improving the crystallinity of PLA in the composites. Furthermore, according to Lauritzen-Hoffman kinetic theory, the fold surface free energy (sigma(e)) of PLA blends is found to be higher than that of neat PLA. leading to a higher work of chain folding (q) and is ascribed to a general constraint of the PLA chain mobility in the composite melt due to the presence of TPS. (C) 2011 Elsevier Ltd. All rights reserved.