Graft copolymerization of natural rubber with fluorine containing monomer

Abstract

The blending of two elastomers with different polarities and vulcanization systems such as natural rubber (NR) and fluoroelastomers (FKM) leads to the incompatibility and phase separation resulting in poor mechanical properties of finishing rubber products. The chemical modification via graft copolymerization is the technique to promote the compatibility of the blends with dissimilar properties. In this study, the fluorine containing monomer used for grafting onto NR backbone was 2,2,2-trifluoroethyl methacrylate (TFEM) via free radical graft copolymerization carried out by both of melt-mixing and solution-grafting processes initiated by benzoyl peroxide (BPO). The grafting properties were investigated as functions of grafting process, initiator and monomer concentration, reaction temperature and time. Under the optimum conditions, it was found that the obtained graft natural rubber (GNR) contained the maximum level of grafting efficiency as 1.34 % with grafted poly (2,2,2-trifluoroethyl methacrylate) (PTFEM) content as 0.26 phr. The structure of GNR was analyzed by using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and nuclear magnetic resonance spectroscopy (NMR). The glass transition temperature of samples was characterized by differential scanning calorimetry (DSC). The GNR was then applied as the compatibilizer for NR/FKM vulcanizates. The amount of GNR at 15 phr yielded the maximum tensile strength of the vulcanizate as 9.93 MPa, which was 5.31 times higher than that of incompatibilized one (1.87 MPa) due to the higher homogeneity of constituent phases.