Shear-induced crystallization in injection moldings of Ziegler-Natta and metallocene based isotactic polypropylenes

摘要

A comparative analysis of the shear-induced crystallization of metallocene and Ziegler-Natta based isotactic polypropylenes (i-PP's) was carried out. Numerous injection molding runs were performed and the effect of the shear-induced crystallization on the moldings was elucidated. The simulation of the injection molding process was performed using our unified crystallization model proposed earlier. The gapwise distributions of birefringence, crystallinity, spherulite size and thickness of the shear-induced crystallization layer in moldings were measured along with the mechanical properties of the moldings. The effects of processing conditions on these properties were determined. The measured values of crystallinity, spherulite size and thickness of the shearinduced crystallization layer were compared witht he results obtained from the simulation of the injection molding process.