Marching modulus phenomena are often observed in silica-reinforced solution styrene-butadiene rubber/butadiene rubber (S-SBR/BR) tire tread compounds. When such a situation happens, it is difficult to determine the optimum curing time, and as a consequence the physical properties of the rubber vulcanizates may vary. Previous studies have demonstrated that the curing behavior of silica compounds is related to the degree of silanization. For the present work, the effect of silanization temperature and time on the marching modulus of silica-filled rubber was evaluated. The correlations between these mixing parameters and their effect on the factors that have a strong relation with marching modulus intensity (MMI) were investigated: the amount of bound rubber, the filler flocculation rate (FFR), and the filler-polymer coupling rate (CR). The MMI was monitored by measuring the vulcanization rheograms using a rubber process analyzer (RPA) at small (approximately 7%) and large (approximately 42%) strain in order to discriminate the effects of filler-filler and filler-polymer interactions on the marching modulus of silica-filled rubber compounds. The results were interpreted via the correlation between these factors and their effect on the MMI. A higher temperature and a longer silanization time led to a better degree of silanization, in order of decreasing influence.
Keywords: marching modulus; mixing; silanization; silica compound; tire tread.