Thioacetate-and mercapto-modified hydrogenated natural rubber as compatibilizers for rubber blends

Abstract

Natural rubber (NR) is deteriorated by thermal and oxidative degradation due to its high level of unsaturated carbon double bond. Hydrogenation is the technique that can reduce the unsaturation of NR and thus improve thermal and oxidative resistance. Therefore, the hydrogenated natural rubber (HNR) is expected to improve the thermal and oxidative resistance of rubber blends containing diene-based elastomers. However, the mechanical performance and the compatibility of the blends are poor due to the difference of the unsaturation level between these rubbers. Thus, the modification of the HNR structure with thioacetate and mercapto groups to be used as the competibilizer for of HNR/NR blends was the aim of this work. The effect of thioacetic acid and initiator concentration including reaction time on the extent of reaction was investigated for the functionalized thioacetate in HNR structure. The methanolysis of thioacetate-modified HNR (HNRTA) in NaOH methanolic solution using varied concentration and reaction time provided mercapto-modified HNR (HNRSH). The structure and the content of additional functional groups on the resulting product were analyzed by FT-IR spectroscopy and 1H-NMR spectroscopy. The addition of HNRTA or HNRSH as the compatibilizers in HNR/NR blends could accelerate the vulcanization and increased the tensile strength of the blends. A scanning electron micrographs demonstrated that these functionalized HNRs led a co-continuous morphology in the tensile fracture surface of the blends. The reactive compatibilization was also confirmed by the enhancement of crosslink density and the reduction of damping values characterized by dynamic mechanical analysis. Moreover, the functionalized HNRs improved the thermal and ozone resistance of the blends.