Evaluation of silane effect as a coupling agent for metakaolin

This study aimed at evaluating the coupling effect of silane Si69 bis(triethoxysilylpropyl)tetrasulfide in metakaolin (MK) in automobile tire tread compounds based on a styrene-butadiene rubber/butadiene rubber blend. A reference compound of a typical tread recipe, filled with silica and carbon black, was used as a reference due to the acknowledged effect of TESPT in silica incorporation in elastomers. A silica sample without silane was also prepared. Silica was then completely substituted by MK, producing two samples, with and without silane. The samples were tested for crosslink density, rheometry, and morphology, and the vulcanization reaction parameters were determined and evaluated. Silane improved the interaction between MK and the polymer matrix, evidenced by the increase in crosslink density and vulcanization reaction rate, the same effect silane causes on silica-filled composites. Morphology also revealed that silane increased MK dispersion and adhesion to rubber. On the other hand, MK seems not to be as reinforcing as silica, considering that maximum torque is related to the stiffness of the material, with MK exhibiting lower values for this parameter.