Moisture cure and in‐situ silica reinforcement of epoxidized natural rubber

Epoxidized natural rubber (ENR) was first precured with 3‐aminopropyltriethoxysilane (APS) by the normal compression molding technique. The resultant sheet was further subjected to moisture cure, via hydrolysis and condensation reactions, by soaking it in water. The moisture‐cured sample, when prepared under appropriate reaction conditions, demonstrated partial strain‐induced crystallization behavior and moderate tensile strength, as opposed to typical peroxide‐cured and sulfur‐cured vulcanizates. The suitability of the ENR–APS precured sample for in‐situ silica reinforcement by the sol–gel process, using tetraethyl orthosilicate (TEOS) as the silica precursor, was also demonstrated. Silica content as high as 36% by weight could be incorporated into the rubber, and TEOS‐to‐silica conversion of over 60% was observed. Comparative analysis with a typical peroxide‐cured sample that was subjected to the same sol–gel process indicates that the silica in the final ENR–APS sol–gel vulcanizate is chemically bound to the rubber network.