RELATIONSHIP BETWEEN MORPHOLOGY AND MICROMECHANICAL TOUGHENING MECHANISMS IN MODIFIED POLYPROPYLENES

Deformation and fracture processes of two types of modified polypropyl enes (PPs) were investigated in situ by high voltage electron microsco py (HVEM, 1 MV) and scanning electron microscopy (SEM). One type of PP modified with ethylene-propylene block copolymer rubber (EPR) showed a variation in particle size and interparticle distance with content o f ethylene. In the other series of modified PP, Al2O3 filler particles with concentrations of 10 and 60 wt % were used. The micromechanical toughening mechanism was comparable in both types. Deformation structu res in both systems are closely connected with cavitation and void for mation: the systems modified with EPR show void formation inside the m odifier particles; in the systems modified with Al2O3, debonding occur s at the interface between the particles and the matrix. Additionally, the effect of the morphology of the modifier particles on micromechan ical deformation processes was studied. The experiments showed that be sides particle size and center-to-center distance between particles, t he ratio of center-to-center distance to particle diameter plays an im portant role. Models (three-stage mechanism) for the micromechanical d eformation process are proposed. (C) 1996 John Wiley & Sons, Inc.