TOUGHENING OF POLYSTYRENE BY NATURAL RUBBER-BASED COMPOSITE-PARTICLES.2. INFLUENCE OF THE INTERNAL STRUCTURE OF PMMA AND PS-GRAFTED CORE-SHELL PARTICLES

This work was focused on the influence of the internal structure of na tural rubber (NR)-based core-shell particles on the toughness of polys tyrene (PS). Several emulsion polymerization processes were used to co ntrol the degree of grafting of the NR phase and the site of polymeriz ation, which determines the final morphology of the prepared composite NR-based particles. PS subinclusions were introduced into the NR core in order to determine their influence on the deformation behaviour of PS. A continuous extrusion process was adapted for the direct feeding of the wet NR-based latexes into the molten PS matrix. Impact testing indicated that core-shell particles based on NR containing a large nu mber of small crosslinked PS subinclusions toughened PS most effective ly. A very effective toughening agent is obtained if a hard shell of 2 5 wt % crosslinked PMMA surrounds the composite rubber particle. Graft ing of NR chains during the subinclusion synthesis has to be avoided s ince a high rubber particle modulus is detrimental for craze nucleatio n in PS. From the fracture surface morphology the craze nucleating and stabilizing efficiency of composite NR particles having different mor phologies or grafting degrees could be deduced.