Polylactide/Nano- and Micro-Scale Silica Composite Films. II. Melting Behavior and Cold Crystallization

Nonisothermal crystallization of polylactide (PLA)/silica composites prepared by (i) directly blending the PLA with nanoscale colloidal silica sol and by (ii) a sol-gel process are studied by differential scanning calorimeter (DSC) at various heating rates. Samples quenched from the molten state exhibited two melting endotherms (T-ml and T-mh) due to melt-recrystallization during the DSC scans. Lower heating rate and the presence of silica particles generate a lower peak intensity ratio of T-ml/T-mh. The nonisothermal crystallization kinetics is analyzed by modified Avrami model, Ozawa model, and Liu-Mo models. The modified Avrami and Liu-Mo models successfully described the nonisothermal cold crystallization processes, but Ozawa is inapplicable. The nucleation constant (Kg) is calculated by modified Lauritzen-Hoffman equation and the activation energy by Augis-Bennett, Kissinger, and Takhor models. These calculated parameters indicate consistently that the nanoscale silica particles seem to form more heterogeneous nucleation to increase crystallization, but microscale one form hindrance to retard crystallization. (c) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 3149-3156, 2009