Effect of silane coupling agents on the mooney scorch time of silica-filled natural rubber compound

Abstract

Mooney scorch time and cure index of silica-filled natural rubber ( Hevea Brasiliensis type) compound with and without the presence of silane coupling agents were studied in the temperature range 110–160°C using a Mooney Shearing Disk Viscometer. Two types of silane coupling agents, viz γ-mercaptopropyltrimethoxysilane (A-189) and bis(triethoxysilylpropyl)tetrasulphide (Si-69) of various loadings were used to study the effect of silane coupling agents on the scorch property of natural rubber. Results indicate that the Mooney scorch time and cure index decreases with increasing A-189, but increases with increasing Si-69. This observation is attributed to the catalytic effect of the thiol group in A-189 which enhances the rate of vulcanization, whereas in the case of Si-69, cure retardation is associated with the steric hindrance effect of its bulky end groups. The apparent activation energy for various loadings of silane coupling agents was determined and discussed.