Polylactide/nano- and micro-scale silica composite films. II. Melting behavior and cold crystallization
摘要：
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 (Tml and Tmh) due to melt-recrystallization during the DSC scans. Lower heating rate and the presence of silica particles generate a lower peak intensity ratio of Tml /Tmh. 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 ucleation to increase crystallization, but microscale one form hindrance to retard crystallization.
