MICRODEFORMATION MECHANISMS IN PROPYLENE ETHYLENE BLOCK COPOLYMER

Blends of propylene ethylene block copolymer (PEB) and propylene homopolymer (PP) were prepared to give various rubber contents (4-20 wt %). By diluting the PEB with PP with molecular weight equal to that of the PEB matrix, molecular characteristics of all the blends were kept constant. The rubber particle size and size distribution of all the blends were almost constant, so that the interparticle distance decreased with increased rubber content. According to the observation of the fracture behavior at -20-degrees-C, a brittle to ductile transition was found at the rubber content of 16 wt %. Microdeformation behavior of the blends was investigated in the region of brittle to ductile transition by using transmission electron microscopy. In the case of the brittle sample with low rubber content, crazing and voiding were observed. Whereas even in the ductile sample with high rubber content, crazing certainly took place before shear yielding. The origin of ductile fracture could possibly be attributed to the relaxation of strain constraint by the microvoids contained in the craze.