INFLUENCE OF INJECTION RATE AND MELT TEMPERATURE ON POLYPROPYLENE DURING INJECTION-MOLDING WITHOUT PACKING

The molecular degradation of isotactic polypropylene, which occurs during injection moulding without packing, has been studied. Particular attention was given to the effects of injection rate and melt temperature on the molecular weight distribution of the polypropylene. Selected layers of the plates produced were analyzed to determine changes in the molecular weight averages by gel permeation chromatography. Molecular weight distributions were obtained for surface layer and core. Serious degradation (-30% in weight average) is caused mainly by high melt temperatures. The effect of high shear rates and high shear stresses was found to be less. The result of thermal and mechanical measurements are correlated with the polymer degradation especially as measured by changes in the weight average molecular weight. © 1990.