Fracture toughness of multiphase polypropylene composites containing rubbery and particulate inclusions

The fracture toughness of binary and ternary phase polypropylene (PP) composites containing ethylene-propylene rubber (EPR) and glass beads, has been studied using the J-integral method at 23 and -20 degrees C. For determining J(c), analysis of the stress-whitening zone was found to be more meaningful than the commonly used blunting line approach. Functionalized EPR was found to be more effective toughening additive for PP than EPR, in both binary and ternary phase compositions. Crack growth mechanisms were examined by scanning electron microscopy, in rubber-modified blends, cavitation and shear yielding were found to be the primary toughening mechanisms, while in ternary phase composites particle-matrix debonding played a major role.