FRACTURE-TOUGHNESS OF POLYPROPYLENE COPOLYMERS - INFLUENCE OF INTERPARTICLE DISTANCE AND TEMPERATURE

A heterophasic reactor grade polypropylene-ethylene copolymer (RAHECO( R)) was diluted with a propylene-ethylene random copolymer to get mate rials with constant EPR/PE-particle diameter but various interparticle distances. According to the results of instrumented impact tests, bri ttle-to-tough transitions were found at similar to 20 degrees C, -10 d egrees C, 0 degrees C, +10 degrees C and room temperature. The critica l interparticle distance shifts linearly over the range of temperature s from about 0.4 mu m at -20 degrees C to 1.3 mu m at room temperature . The results were compared with measurements of conventional notched Charpy impact strength at room temperature. The transition from brittl e to tough impact behaviour was correlated to a transition of micromec hanical deformation mechanisms from cavitation bands to croids. Cavita tion of the rubber particles was always the first step of deformation. The in situ HVEM investigations additionally show that the particle d istribution should be as homogeneous as possible. (C) 1997 Elsevier Sc ience Ltd.