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The paper demonstrates the efficacy of natural rubber-g-poly (styrene-co-acrylonitrile) (NR-g-SAN) copolymers as impact modifier for SAN. The impact behaviour of SAN /NR-g-SAN blends were studied as a function of cross-link density of NR, percent grafting, rubber content in the blend and the AN content in the grafted chain. The cross-link density of NR had no significant effect on impact strength of the blends whereas increase in percent grafting (PG) of the rubber significantly improved the impact strength. Thus the impact strength increased four times when the PG of the rubber was increased from 34.2 to 65%. Further increase in PG decreased the impact strength. Similar trend was observed on increase in the rubber content, the maximum impact strength was observed at 20% rubber. The impact strength also depended on the acrylonitrile content of the grafted chain. Tensile and flexural strength and modulus of these blends were not influenced by PG and AN content in the grafted chain whereas these properties decreased with the increase in the rubber content. Scanning electron microscopic studies of the impact fractured surfaces showed cavitation of rubber particles and craze induced matrix deformation. Dynamic mechanical studies confirmed the two-phase structure of these blends. [ABSTRACT FROM AUTHOR]

This article describes the graft copolymerization of methyl methacrylate (MMA) on to natural rubber (NR) by emulsion polymerization using cumene hydroperoxide and tetraethylene pentamine as redox initiators in NR latex. The effect of surfactants, crass-link density of NR, NR/MMA ratio, and mode of addition of monomer on particle morphology is investigated by a transmission electron microscope (TEM). The percent grafting increases with the increasing MMA content while the graining efficiency decreases. Secondary nucleation of poly(methyl methacrylate) (PMMA) is observed when oleic acid is used as a surfactant, while sodium dioctyl sulphosuccinate (SDSS) and nonionic nonyl phenol poly(ethylene oxide), give core-shell morphology. In all the samples, the smaller rubber particles are heavily coated with PMMA while the larger particles are coated only at higher MMA content. At a given feed rate of the monomer, higher cross-link density of NR results in a more uniform shell. Ultramicrotomed sections of the latex particles show an interpenetrating network-like structure. [ABSTRACT FROM AUTHOR]