Silica reinforcement of epoxidized natural rubber by the sol-gel method

The sol-gel technique was employed to prepare silica-reinforced vulcanizates using tetraethylorthosilicate (TEOS) and epoxidized natural rubber (ENR). The rubber was first precured with 3-aminopropyltriethoxysilane (APS) by heat pressing at 180 degrees C for a range of cure time. The resultant rubber sheets or vulcanizates were swelled in TEOS, and subsequently subjected to a sol-gel reaction in butylamine aqueous solution. Hydrolysis and condensation of the TEOS resulted in the formation of silica particles in the rubber network yielding silica-contained vulcanizates. Silica content as high as 28% and TEOS-to-silica conversion of over 60% were observed. When prepared under certain reaction conditions, the sol-gel vulcanizates obtained were more rigid and stronger than a typical sulfur-cured ENR vulcanizate that contained comparable amount of silica. Comparative stress-strain and dynamic mechanical property analysis suggest that chemicals bond are formed between the silica particles and the rubber network in the ENR-APS-sol-gel vulcanizate. Thus, the ''in situ'' silica reinforcement of ENR was successfully established.