Melting and non-isothermal crystallization behaviors of polypropylene and polypropylene/montmorillonite nanocomposites under pressurized carbon dioxide

Abstract

Both the melting and non-isothermal crystallization behaviors of polypropylene (PP) and PP/montmorillonite (MMT) nanocomposites under atmospheric N2 and pressurized CO2 were carefully studied by using high-pressure differential scanning calorimeter (DSC). Jeziorny modified Avrami and Mo's methods were applied to analyze the non-isothermal crystallization kinetics, respectively. The Avrami exponent decreased with CO2 pressure while increased with the addition of nano-MMT. The Mo's methods demonstrated a success for the systems investigated. The cooling rate needed to reach a certain crystallinity (FT) showed that the crystallization rates fluctuated with increasing CO2. This trend was flattened after introducing nano-MMT because of its heterogeneous effects. The activation energy, Ea, decreased with increasing CO2 pressure while increased in the presence of nano-MMT. The overall crystallization rate characterized by the crystallization half-time, t1/2, showed an decrease in PP/MMT nanocomposites, indicating that MMT had significant heterogeneous nucleation effect on enhancing the crystallization rate despite hindering the polymer chain movement.