ON THE KINETICS OF SHEAR-INDUCED CRYSTALLIZATION IN POLYPROPYLENE

With short term shearing at low degrees of supercooling a method has b een developed by which nucleation during shearing can effectively be s eparated from the subsequent crystal growth, which, in these experimen ts, mainly occurs after the cessation of the flow. In this way the kin etics of nucleation by shear could be unravelled for isotactic polypro pylene. The required measurement consists of the monitoring of the opt ical retardation which increases with the monitoring time and levels o ff by saturation. From these measurements conclusions could be drawn w ith respect to the modes of formation of the nuclei and of their type. Model predictions could be confirmed with the aid of electron microgr aphs.