Graft copolymerization of methyl methacrylate onto natural rubber latex by microwave induction

Abstract

Natural rubber (NR) is an unsaturated elastomer with excellent mechanical properties. However, NR has poor resistance to oxidation, oil and organic solvents mainly due to its unsaturated chain structure and nonpolarity. These drawbacks have limited its industrial applications. The graft copolymerization via latex phase is one of chemical modification methods to improve NR‟s properties. To enhance the polarity of NR, methyl methacrylate (MMA) was grafted onto the NR in the presence of cumene hydroperoxide (CHPO) and tetraethylene pentamine (TEPA) as redox initiators. However, conventional graft copolymerization generally needs long reaction time (ca. 6-8 h). Due to less energy consumption with faster heating rate, the microwave irradiation was used to induce graft copolmerization of MMA onto NR latex. By comparing with the conventional grafting method at 60%grafting efficiency, the graft copolymerization of MMA onto NR induced by microwave at 100 W required short reaction time (ca. 15 min); whilst, upto 7 h was needed when the conventional method was carried out. The influence of initiator concentration, monomer concentration, microwave power and exposure time on the grafting properties were statistically evaluated by a two level factorial design and univariate experiments. The graft natural rubber (GNR) was characterized by FT-IR and 1H-NMR spectroscopy. Furthermore, the particle morphology of GNR was also characterized by using transmission electron microscope (TEM).