EFFECT OF SILANE COUPLING AGENTS ON THE MOONEY SCORCH TIME OF SILICA-FILLED NATURAL-RUBBER COMPOUND

Mooney scorch time and cure index of silica-filled natural rubber (Hev ea Brasiliensis type) compound with and without the presence of silane coupling agents were studied in the temperature range 110-160 degrees C using a Mooney Shearing Disk Viscometer. Two types of silane coupli ng agents, viz gamma-mercaptopropyltrimethoxysilane (A-189) and bis(tr iethoxysilylpropyl)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 cu re index decreases with increasing A-189, but increases with increasin g Si-69. This observation is attributed to the catalytic effect of the thiol group in A-189 which enhances the rate of vulcanization, wherea s in the case of Si-69, cure retardation is associated with the steric hindrance effect of its bulky end groups. The apparent activation ene rgy for various loadings of silane coupling agents was determined and discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.