Fracture behavior of styrene-ethylene-propylene rubber-toughened polypropylene

The morphology and fracture behavior of isotactic polypropylene toughened b y styrene-ethylene-propylene (PP/SEP) were investigated. The SEP rubber, ha ving an average particle size of 0.2 mu m, is found to be well dispersed in the PP matrix. The fracture toughness of SEP-modified PP is greatly improv ed. The toughening mechanism investigation shows that a widespread crazing zone is generated in the crack tip damage zone. An intense narrow damage ba nd in the center of crazed zone is formed. Crazing and shear yielding are f ound to be the dominant toughening mechanisms in PP/SEP. The crazes are ini tiated only by large SEP particles in the blend. The small SEP particles (< 0.3 mu m) can neither cavitate nor trigger crazing. As a result, large sca le shear deformation is suppressed in this blend. These findings are consis tent with the notion that the crack tip plane strain constraint has to be r elieved in magnitude in order for the deviatoric stress to reach a critical value for widespread shear banding.