Nonisothermal crystallization of polylactide (PLA)/silica composites prepared by (i) directly blending the PLA with nanoscale colloidal silica sol and by (ii) a solgel 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 (K g ) 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.
Polylactide (PLA)/silica composite films were prepared by two methods: blending nanoscale colloidal silica sol and sol-gel. The nano and microscale silica particles, respectively, were well dispersed in PLA when observed using scanning electron microscopy and transmission electron microscope. The mechanical and thermal stability of composite films were measured before and after hydrolysis by Instron and thermogravimetric analysis. The fillers increase tensile strength, Young's modulus, thermal stability, and hydrolysis resistance with increasing silica content. The nanoscale particles exhibit better effects than the microscale ones. The activation energy, E a , of thermal decomposition is also simulated by the Kissinger and Ozawa equation. The results also show that the thermal stability is increased by the incorporation of silica particles and is lowered by hydrolysis.
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