The Influence of Fumed Silica Properties on the Processing, Curing, and Reinforcement Properties of Silicone Rubber

Abstract

Abstract The present study uses a commercial heat cured silicone rubber formula (including a process aid) and mixing techniques to investigate the effect of varying fumed silica properties—including load, surface area, silica structure level, and surface pretreatment levels—on the rubber processing, curing, and cured physical properties. Based on the results, a simple silica network reinforcement model was developed to explain the changes in processing, curing, and vulcanizate properties of the silicone elastomers. The network is held together by silica-silica interactions and silica-polymer-silica bridge bonds between the silica aggregates. Increasing the silica loading, surface area, and structure level increases the number of interactions and hence the network strength. The pretreatment of the silica surface with organosilane molecules reduces the strength of silica-silica and silica-polymer interactions, therefore, weakening the silica network. Furthermore, the good interrelations between the initial plasticity, crepe hardening, curing, modulus yield, and durometer values strongly supports the concept of the presence of a silica network within the compounds under the low strain conditions of the tests.