MODIFICATION OF DEPROTEINIZED NATURAL RUBBER BY GRAFTING WITH MALEIC ANHYDRIDE VIA DIFFERENTIAL MICROEMULSION POLYMERIZATION TECHNIQUE

Abstract

This work involves a novel technical route for synthesizing graft copolymers of maleic anhydride (MA) onto natural rubber (NR). To improve the grafting efficiency (G.E) and reduce gel content in the grafts, deproteinizing the rubber latex (DPNR) was conducted before the grafting reaction. Styrene as a comonomer was used to increase the G.E, and a differential microemulsion polymerization (DMP) technique was applied for the grafting reaction. The effects of initiator and monomer amount, reaction temperature, reaction time, monomer addition rate, and ST/MA ratio on the G.E and gel content were investigated. Grafting kinetics under the influences of styrene comonomer were investigated. The MA grafting onto DPNR provided higher G.E and a lower gel content than grafting onto NR. The graft copolymers obtained by the DMP method provided much better results with respect to G.E compared to those provided by the conventional method. Adding copolymerizing styrene to the grafting process improves the efficiency of MA grafting and also enhances the graft copolymerization rate. The graft copolymer so obtained was used as a compatibilizer for vulcanized NR/acrylonitrile-butadiene-styrene (ABS) blends. The effects of blend proportions, phenolic curative content, and graft copolymer on mechanical, dynamic, thermal and morphological properties of the blends were investigated. Tensile strength and hardness of the blends increased with increasing ABS content while elongation at break decreased. These blends showed a greater elastic response than that of neat ABS. Thermal stability of the blends increased with increasing ABS content. SEM micrographs of the blends showed a two-phase morphology system. Adding the graft copolymer as a blend compatibilizer produced non-uniform vulcanized NR and ABS phase morphology that affected the mechanical properties.