Improvement of Impact Strength of Polystyrene by Compounding with Styrene-Grafted Ethylene Propylene Elastomeric Copolymers

Abstract

Abstract Ethylene propylene copolymers having good elastomeric properties lend themselves very well to improving impact strength of fragile polymeric materials, such as polystyrene. In order to obtain good results, the percentage of copolymer to be added should be chosen in such a way that the strength of the resulting mixture is as high as possible, but compatible, however, with the practically useful values of the hardness and of the modulus of elasticity, which decrease regularly with an increase in the percentage of elastomer. The best results, for an equal percentage of elastomer, are obtained when the polystyrene is mixed with polystyrene grafted on the ethylene propylene copolymer, rather than with the ethylene propylene copolymer alone. This we attribute to the improved dispersion of the elastomer in the polystyrene matrix that is found in case of the use of the graft polymer. Thus, formation of vitreous and elastomeric microphases, rather than of macrophases, occurs, and there is a better adhesion between these. The use of a graft polymer prevents, in practice, the phenomena of migration and sorting of the phases, and guarantees the maintenance over a period of time of a microphasic structure. The use of a saturated elastomer, such as that used by us, permits, additionally, an improvement in the resistance to aging, in comparison with the traditional materials consisting of mixtures of polystyrene and unsaturated elastomers.