Crystallization kinetics of polypropylene fractions

The overall crystallization rate of polypropylene fractions was studied dilatometrically, and the crystallization behavior was considered in relation to the stereoregularity of the samples. The study includes a photomicroscopic analysis of the nucleation, formation, and growth of spherulites, as well as an evaluation by means of rapid x-ray scanning techniques of the increase of crystallinity within the spherulites. A theory was applied to the discussion of crystallization behavior in which two stages of growth were introduced: (a) growth at the spherulite interface, and (b) secondary crystallization within the spherulite. These were described in terms of Avrami-type equations with differing parameters.