Comparative behavior of in situ silica generation in saturated rubbers: EPDM and hydrogenated natural rubber

Role of carbon-carbon double (C=C) bonds content and their position in ethylene-propylene diene ter-polymer (EPDM), hydrogenated natural rubber (HNR) and natural rubber (NR) on in situ silica formation using tetraethoxysilane (TEOS) as a silica precursor is comparatively investigated. Glass transition temperature (T-g) reflecting rubber chain flexibility is found as an important factor for in situ silica generation via swelling method. Despite of similar solubility parameters, NR has higher TEOS-swelling degree resulting in the higher in situ silica content (30.8 phr) than EPDM (3.50 phr) and HNR (10.4-17.6 phr) due to the higher Tg of EPDM and HNR providing the less chain flexibility to be swollen in TEOS solution. The morphological analysis implies that C=C bonds in saturated rubbers may be agglomeration sites for in situ silica particles. For practical applications, saturated rubbers containing in situ silica/NR vulcanizates showed the improvement of mechanical properties and resistance of thermal and ozone degradation. (C) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44748.