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 te nsile 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 molec ular weight: 292400) (1.0SH). The 1.0SH absorbed seven times more ener gy than the 0.4CSL. The deformation behavior was studied using optical microscopy, scanning electron microscopy (SEM), and transmission elec tron microscopy (TEM). TEM micrographs revealed different deformation mechanisms. In the 0.4CSL, there were microcracks in the matrix with r ubber particle cavitation. In the 1.0SH, there were rubber particle ca vitation and large elongation of the rubber particles. The matrix defo rmation 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.