Compatibilizing effect of poly(styrene)-block-poly(isoprene) copolymers in heterogeneous poly(styrene)/natural rubber blends

Abstract

Compatibility of poly(styrene) (PS)/natural rubber (NR) blend is improved by the addition of diblock copolymer of poly(styrene) and cis-poly(isoprene) (PS-b-PI). The compatibilizing effect has been investigated as a function of block copolymer molecular weight, composition and concentration. The effect of homopolymer molecular weight, processing conditions and mode of addition on the morphology of the dispersed phase have also been investigated by means of optical microscopy and scanning electron microscopy. A sharp decrease in phase dimensions is observed with the addition of a few percent of block copolymers. The effect levels off at higher concentrations. The leveling off could be an indication of interfacial saturation. For concentrations below the critical value, the particle size reduction is linear with copolymer volume fraction and agrees well with the prediction of Noolandi and Hong. The addition of the block copolymer improves the mechanical properties of the blend. An attempt is made to correlate the mechanical properties with the morphology of the blends.