Silica and silane coupling agent for irt situ reinforcement of acrylonitrile-butadiene rubber

In situ silica reinforcement for the acrylonitrile-butadiene rubber (NBR) v ulcanizates, which were premixed with a conventional silica (VN-3) and gamm a-mercaptopropyltrimethoxysilane (gamma-MPS), was achieved by the sol-gel r eaction of tetraethoxysilane (TEOS) using ethylenediamine. It was observed that the reinforcement efficiency tended to increase with the increase of m echanically premixed conventional silica. From the observations of transmis sion electron microscopy and scanning electron microscopy, the simultaneous use of VN-3 and gamma-MPS was found to promote the formation of large sili ca particles and clusters with a relatively good dispersion by the sol-gel reaction of TEOS in the NBR vulcanizate. The results of hysteresis measurem ents supported this promotion. It was considered to be due to the surface m odification of VN-3 by the sol-gel reaction of TEOS and the presence of gam ma-MPS which worked as a dispersion agent for silica particles. The relatio nship between the mechanical properties and the morphology of the in situ s ilica filled vulcanizates is discussed.