SILICA REINFORCEMENT OF EPOXIDIZED NATURAL-RUBBER BY THE SOL-GEL METHOD

The sol-gel technique was employed to prepare silica-reinforced vulcan izates using tetraethylorthosilicate (TEOS) and epoxidized natural rub ber (ENR). The rubber was first precured with 3-aminopropyltriethoxysi lane (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 so lution. Hydrolysis and condensation of the TEOS resulted in the format ion of silica particles in the rubber network yielding silica-containe d vulcanizates. Silica content as high as 28% and TEOS-to-silica conve rsion of over 60% were observed. When prepared under certain reaction conditions, the sol-gel vulcanizates obtained were more rigid and stro nger than a typical sulfur-cured ENR vulcanizate that contained compar able amount of silica. Comparative stress-strain and dynamic mechanica l property analysis suggest that chemicals bond are formed between the silica particles and the rubber network in the ENR-APS-sol-gel vulcan izate. Thus, the ''in situ'' silica reinforcement of ENR was successfu lly established.