Use of epoxidized natural rubber as a compatibilizer in silica-filled natural rubber compounds

Silica-filled natural rubber (NR) tire tread compounds with epoxidized natural rubber (ENR) as a compatibilizer were investigated. The ENRs were prepared by an in-situ performic epoxidation reaction and characterized by proton nuclear magnetic resonance spectroscopy. The epoxide levels of 10, 38 and 51 mole% with ENR contents of 2.5-15.0 phr were used as compatibilizers in the silica-filled NR compounds. Cure characteristics, flocculation rate constant, bound rubber contents, and mechanical properties of the silica-filled NR were studied. Increasing the mole% of epoxide and ENR contents increased cure and scorch times of the silica-filled compounds, while silica flocculation decreased, when compared with a silica-filled compound without ENR. Total bound rubber and chemically bound rubber contents of the compounds which indicate interaction/reaction between the epoxide groups of ENR and silanol groups on the silica surface also increased with increasing epoxide levels. The addition of ENR as a compatibilizer decreased the Mooney viscosity of the compounds, which can be related to an improvement of silica dispersion in the compounds. Tensile strength and reinforcing index of the vulcanizates increased with increasing mole% of epoxide and ENR contents up to 7.5-10.0 phr.