Non-isothermal crystallization behavior of clay-reinforced polypropylene nanocomposites

Abstract

In this study, the non-isothermal crystallization kinetics of polypropylene (PP) in the presence of nanoclay particles were investigated using differential scanning calorimetry (DSC) with various cooling rates varying from 0.5°C/min to 80°C/min. Such kinetics were compared with those obtained for the pure PP matrix. The modified Avrami analysis was used to describe the non-isothermal crystallization process. The results obtained indicate that the presence of nanoclay significantly affected the crystallization rate of the PP resin, since an increase of the crystallization temperature as the nanoclay content increased was observed. This was attributed to the nucleating ability of these particles. Moreover, it was seen that the increase of both the cooling rate and the nanoclay content decreased the Avrami exponent n, suggesting a change in the obtained crystalline shape. For the nanocomposite materials, as well as for neat PP, the mechanism of crystallization was found to undergo two transitions, at about 5°C/min and 40°C/min. This suggests that the surface-induced nucleation at the clay particles follows the same mechanisms as those of the complete spherulitic structure. However, a lower value of activation energy for crystallization was obtained as the clay content increased, confirming the nucleating effect of clay particles.

Keywords

• activation energy
• montmorillonite
• nanocomposite
• non-isothermal crystallization
• polypropylene