Effect of dynamic crosslinking on impact strength and other mechanical properties of polypropylene/ethylene-propylene-diene rubber blends

The deformation and fracture behavior of several dynamic vulcanizate blends of isotactic polypropylene with ethylene-propylene-diene rubber (EPDM) was examined and compared with those of uncrosslinked blends of PP/EPDM. These blends were prepared by melt mixing in an internal mixer at 190 degreesC i n a composition range of 10-40 wt % EPDM rubber. The variation in yield str ess, the strength of fibrils of the craze, and the number density of the EP DM rubber domains (morphology fixation) that are dominant factors for enhan cing interfacial adhesion and toughness in dynamic vulcanizate blends were evaluated. The ductility and toughness of these materials were explained in light of the composition between crack formation and the degree of plastic deformation through crazing and shear yielding. The physicomechanical prop erties including the hardness, yield stress, Young's modulus, percentage el ongation, impact strength, flexural strength, and flexural modulus of dynam ic vulcanized blends were found to be consistent and displayed higher value s compared with uncrosslinked blends. The nucleation effect of the crosslin ked particles and the decrease of crystallinity of the EPDM rubber were als o considered to contribute to the improvement in the impact strength. (C) 2 000 John Wiley & Sons, Inc.