Contribution of filler–filler interaction and filler aspect ratio in rubber reinforcement by silica and mica

Abstract

The reinforcement degree offered by silica as a spherical filler with low aspect ratio and high filler–filler interaction was compared with mica as a platelet filler with higher aspect ratio and lower filler–filler interaction. By replacing half of the carbon black with silica or mica in a typical formulation, rubber composites were prepared and their properties were evaluated under two conditions: In the first one, the impact of increasing the amount of a chemical surface modifier, namely silane TESPT (bis triethoxysilylpropyl tetrasulfide), was investigated and in the second one, the increasing amount of a physical modifier namely DPG (diphenyl guanidine) on the performance of the two fillers was explored. The resulting composites were subjected to physico-mechanical experiments including the bound rubber, tensile test, and the dynamic mechanical thermal analysis (DMTA). Results indicated that the greater amount of filler–filler interaction resulting from the higher SiO₂ and hydroxyl content in silica has a dominating role over the aspect ratio of mica which is then led to a remarkable difference in their bound rubber. However, the mica-containing composites were capable of competing with silica when the DPG was used. Nevertheless, the compound only containing carbon black with 19.7 MPa of tensile strength and 24.4 kgf/cm of tear strength showed the best mechanical properties among other fillers, and by replacing 30 phr carbon black, these properties decreased approximately 15 ± 3%. Based on DMTA findings, promising data were obtained for the mica-reinforced rubbers with regard to the tire application.