STABILITY OF PLASTIC-DEFORMATION AND TOUG HNESS OF POLYPROPYLENE BLENDS WITH ETHYLENE-PROPYLENE RUBBER

Stability of plastic deformation and toughening mechanism of the polyp ropylene blended with ethylene-propylene rubber as modifier have been studied by three point bending of a U-notched bar under plane strain. The variation of the mode of plastic deformation that accompanied the addition of modifiers was explained in terms of the theory of instabil ity of plastic deformation in the region of pre-formed voids under dil atational stress. The toughening mechanism was understood through the relaxation of stress concentration into a stress level lower than the strength of fibrils by the release of constraint of strain due to the formation of voids. The stability of the plastic deformation of polypr opylene (PP) blended with ethylene-propylene rubber (EPR) as a modifie r was lower than that of unblended PP.