INJECTION-MOLDING OF SEMICRYSTALLINE POLYMERS .1. MATERIAL CHARACTERIZATION

Various material data for an isotactic polypropylene were acquired for the simulation of the injection molding of this material. Viscosity as a function of shear rate and temperature was measured using a capillary rheometer at high shear rates and a cone-and-plate rheometer at low shear rates. Heat-flow properties, characterizing kinetics and induction time of quiescent crystallization, were obtained from DSC measurements. Material data characterizing shear-induced crystallization were obtained from extrusion experiments through a slit die with subsequent quenching of the material in the die after various rest times. The thickness of the shear-induced crystallization layer was measured along with the birefringence in this layer. A model of shear-induced crystallization developed by Janeschitz-Kriegl and co-workers was used to fit the kinetic data. Thus, kinetic parameters such as the limiting shear rate below which no shear-induced crystallization can occur and the characteristic time for the relaxation of birefringence were obtained. (C) 1995 John Wiley & Sons, Inc.