Shifting Properties of Silica Reinforced Natural Rubber Based Truck Tire Tread Compounds by Small Amounts of Hybrid Fillers towards Better Overall Performance

Modern high-performance tire treads are presently commonly reinforced with silica as rubber fillers because they raise key tire performance criteria such as lower rolling resistance and higher wet grip compared to carbon black-filled rubber. The present work aims at a synergistic effect of silica with different additional fillers in order to shift tire performance with respect to wet grip and rolling resistance for safety and fuel savings, respectively towards a better abrasion resistance, all characterized by the dynamic mechanical properties of the vulcanized compounds. The use of small amounts of secondary fillers or hybrid fillers in silica-reinforced tire tread compounds has the potential to improve tire performance further. In the present work, two secondary fillers: organoclay nanofiller and N134 carbon black were added to silica-based natural rubber compounds at a proportion of silica/secondary filler of 45/10 phr. The compounds were prepared with variable mixing temperatures based on the procedure commonly used for silica-filled NR systems. The results of Mooney viscosity, Payne effect, cure behavior and mechanical properties imply that the silica hydrophobation and coupling reaction of the silane coupling agent between the silica and elastomer are significantly enhanced by organoclay due to an effect of its modifier: an organic ammonium derivative. This modifier has an effect on scorch safety and cure rate. The compounds where carbon black was added as a secondary filler do not show this improvement. They give inferior filler dispersion compared to the pure silica-filled compound, attributed to an inappropriate high mixing temperature and the large specific surface area of the carbon black used. The dynamic mechanical properties indicate that organoclay as a secondary filler has the potential to improve the wet traction and rolling resistance of a tire tread, while the use of carbon black in silica-filled NR does not change these properties.