Natural rubber / nitrile rubber blends compatibilized by graft copolymer of styrene and acrylonitrile onto natural rubber

Natural rubber (NR) has excellent mechanical properties, but has the relatively poor oil resistance which is opposite to nitrile rubber (NBR). Thus, the direct blending of these two rubbers is expected as the solution to enhance the mechanical properties and oil resistance of the blends. However, the mechanical performance of this blends are poor due to the incompatibility caused by difference polarity between these rubbers. Therefore, the modification of NR structure via graft copolymerization of acrylonitrile (ACN) and styrene (ST) onto NR for using as the compatibilizer in NR/NBR blends was the aim of this work. The graft copolymerization was carried out by both of solution method using benzoyl peroxide (BPO) or 2,2́ azoisobutyronitrile (AIBN) as initiators and emulsion method initiated by potassium persulfate (K2S2O8) or cumene hydroperoxide /tetraethylene pentamine; CHPO/TEPA). The influence of reaction parameters: the initiator concentration, reaction temperature and nitrogen pressure was investigated. The structure of grafted copolymer on NR structure was analyzed by spectroscopic techniques. It was found that the optimum condition for preparing the graft NR was carried out by the solution graft copolymerization using wt ratio of ACN/ST 3/1 initiated by 5 parts by weight of BPO at 70°C under 2 bar of nitrogen pressure for 6 h to achieve the maximum percentage of graft copolymer as 85.0%. The graft NR product (GNR) was used as a compatibillizer for NR/NBR blends. The results indicated that the increase in the GNR content in the blends improved the mechanical properties and oil resistance of NR/NBR vulcanizates. The tensile fracture surfaces of NR/NBR blends examined by scanning electron microscope (SEM) showed the better interfacial adhesion between two rubber phases after addition of GNR in the blends.