Energy absorption of high-impact polystyrene under tensile loading

Fracture energy for two kinds of high impact polystyrene (HIPS) which contained relatively small rubber particles was evaluated by static tensile tests. The two HIPSs had similar rubber contents but differed in size, morphology of rubber particles, and molecular weight of matrix (polystyrene). One had core-shell type particles averaging 0.4 mu m in diameter (weight average molecular weight: 221500) (0.4CSL), and the other 1.0 mu m diameter particles of salami type (weight average molecular weight: 292400) (1.0SH). The 1.0SH absorbed seven times more energy than the 0.4CSL. The deformation behavior was studied using optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). TEM micrographs revealed different deformation mechanisms. In the 0.4CSL, there were microcracks in the matrix with rubber particle cavitation. In the 1.0SH, there were rubber particle cavitation and large elongation of the rubber particles. The matrix deformation in this system is considered to be dominated by shear yielding. In both systems, crazes were observed only in small regions near the fracture surface. Crazing was the dominant deformation mechanism only at the crack tip of 0.4CSL.