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SYNOPSISDeformation and fracture processes of two types of modified polypropylenes (PPs) were investigated in situ by high voltage electron microscopy (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 of ethylene. In the other series of modified PP, A1203 filler particles with concentrations of 10 and 60 w t % were used. The micromechanical toughening mechanism was comparable in both types. Deformation structures in both systems are closely connected with cavitation and void formation: the systems modified with EPR show void formation inside the modifier particles; in the systems modified with Alto3, debonding occurs at the interface between the particles and the matrix. Additionally, the effect of the morphology of the modifier particles on micromechanical deformation processes was studied. The experiments showed that besides particle size and center-to-center distance between particles, the ratio of center-to-center distance to particle diameter plays an important role. Models (three-stage mechanism) for the micromechanical deformation process are proposed.

The micromechanical deformation processes of impact‐ modified polypropylene (PP) with core– shell particles derived from PP/EPR (ethylene– propylene– rubber) block copolymers and PP/PA/SEBS‐g‐MA (polypropy‐­lene / polyamide / polystyrene ‐ block ‐ poly(ethene ‐ co ‐ but ‐1‐ene)‐block‐polystyrene‐graft‐maleic anhydride) graft copolymers have been investigated by in‐situ tensile tests in high‐voltage electron microscopy. Morphology studies in transmission electron microscopy show that the morphology of modifier particles is drastically affected by their concentration. It was found that the driving mechanism for the initiation of plastic deformation is a controlled microvoid formation, which is caused by cavitation in the stretched rubber shell under mechanical loading. According to the inherent properties and phase structures of modifier particles, a single or multiple cavitation appears with or without fibril formation at the interface between the modifier particles and the matrix. The Predominant mechanism for the improvement of toughness is the shear yielding of the ligaments of matrix material induced by local stress concentration by the microvoids. © 1998 John Wiley & Sons, Ltd.