Preparation of Silica-Based Rubber Compounds without the Use of a Silane Coupling Agent through the Use of Epoxidized Natural Rubber

Abstract

The present study represents a new concept: the possibility of preparing a rubber compound filled with silica without the use of a silane coupling agent. For this purpose two different types of silica have been compounded with two different grades of epoxidized natural rubber (ENR) without the use of a silane coupling agent. The mechanical and other properties of the resulting compounds have been compared with two reference compounds prepared from natural rubber (NR) and silica with and without the addition of a silane coupling agent bis-(triethoxysilylpropyl)tetrasulfane (TESPT). It is shown that by using ENR as rubber component together with silica, it is possible without the use of coupling agents to achieve significantly improved mechanical properties with respect to similar NR compounds without coupling agents. The reason for these improvements lies in the polar nature of ENR which interacts strongly with the silica surface by hydrogen bonding mechanism. This does not happen when NR or another non-polar rubber component is used. Thus, in this latter case the use of silane coupling agents to make the silica surface more non-polar and hydrophobic is needed to have a good reinforcing effect and overall performances from the composite studied.