Effects of reprocessing conditions on the properties of unfilled and talc-filled polypropylene

The effects of repetitive injection molding cycles at different temperatures and shear rates on the structure and mechanical properties of unfilled and talc-filled polypropylene were studied. The main effect of reprocessing in both materials is a decrease in molecular weight of the polymeric matrix, which is more marked and concomitant with breaking of particles at high shear levels. The chemical structure, however, remains unchanged. The observed degradation processes only slightly affect the crystalline behaviour and the small strain properties of the materials studied. However, the break properties are affected, their decrease depends on the filler content and they appear more sensitive to high shear level than to high processing temperatures. (C) 1996 Elsevier Science Limited