Degradation effects on the rheological and mechanical properties of multi-extruded blends of impact-modified polypropylene and poly(ethylene-co-vinyl acetate)

摘要

Polypropylene-(ethylene-propylene) heterophasic copolymer (PP-EP)/poly(ethylene-co-vinyl acetate) (EVA) blends of different composition were multiply-extruded (nine cycles) in order to evaluate the degradation effects on the molecular weight as well as on the rheological and mechanical properties. A decrease in molecular weight was observed in the first three reprocessing cycles, then this parameter remained almost constant in further recycling. Such initial decrease was attributed to chain scissions occurring mainly in the PP-EP copolymer. As expected, the melt flow index increased with the number of processing cycles. Unlike the tensile strength, which showed no clear tendency, the impact strength and elongation were improved with recycling. In particular, the elongation showed a remarkable increase at EVA contents of 40 and 60 wt.%, that was apparently due to changes in morphology. (C) 2004 Elsevier Ltd. All rights reserved.