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.