NONISOTHERMAL CRYSTALLIZATION KINETICS OF CALCIUM-CARBONATE FILLED BETA-CRYSTALLINE PHASE POLYPROPYLENE COMPOSITES

The non-isothermal crystallization behaviour of high purity beta-phase and alpha-phase polypropylene (PP) and their calcium carbonate-tilled composites was investigated by means of differential scanning calorim etry. High purity beta-PP polymer was prepared by adding an effective beta-nucleator consisting of equal amounts of pimelic acid and calcium stearate. The crystallization temperature and crystallization rate co efficient of pure beta-PP polymer were considerably higher than those of the alpha-PP polymer. This was due to the beta-PP polymer containin g nucleating agents, which act as nuclei for beta-spherulites. The cal cium carbonate content had little or no effect on the crystallization rate coefficient and Ozawa exponent of the beta-phase PP in the compos ites. On the other hand, the crystallization temperature, crystallizat ion rate coefficient and Ozawa exponent of the alpha-phase PP composit es depended on the calcium carbonate loading. The effect of calcium ca rbonate additions on the crystallization of alpha-PP and beta-PP is di scussed.