TOUGHENING OF POLYSTYRENE BY NATURAL RUBBER-BASED COMPOSITE-PARTICLES.3. FRACTURE MECHANISMS

Impact testing has allowed the toughness of PS blends to be correlated with the morphology of the dispersed rubber phase, which was a natura l rubber (NR) in particle form, coated with a shell of polystyrene (PS ) or polymethylmethacrylate (PMMA). PS subinclusions were also introdu ced into the NR core. The impact resistance of the prepared PS blends began to rise steeply at a particle content of about 18 wt %. Transmis sion electron microscopy (TEM) in combination with osmium tetroxide st aining techniques, allowed direct analysis of the crazing and cavitati on processes in the composite natural rubber particle-toughened PS ble nds. Bulk samples were studied at high and slow deformation speeds. Di fferent deformation mechanisms were effective, depending on the locati on of the observed stress-whitened zone relative to the notch tip. The apparent fracture mechanisms in rubber-toughened PS blends were also studied by scanning electron microscopy. PS blends containing polydisp erse natural rubber-based particles or monodisperse poly(n-butylacryla te)-based particles, and commercial high-impact polystyrene, were comp ared.