The interaction of functionalized SBRs with silica and ZnO and its effect on dynamic mechanical properties

Since its introduction in 1992, silica has become a widely used filler in passenger tire treads. Compared to carbon black filled compounds, it brings about the benefit of lower rolling resistance and consequently lower vehicle fuel consumption: a global concern nowadays. But replacement of carbon black by silica is rather difficult, since the latter is a polar filler and has a low compatibility with non-polar rubbers. In order to solve the problem of low filler-polymer compatibility and interactions as well as to improve filler dispersion, coupling agents were introduced for silica-filled compounds. These coupling agents, predominantly bi-functional silanes, interact with the hydrophilic silica surface on one side and the hydrophobic rubber chains on the other side, thereby creating chemical coupling. Styrene butadiene rubber (SBR), which is functionalized with polar and/or reactive groups, enables the polymer to directly physically or chemically interact or bond with silica and has the potential to further improve the dispersion of the filler and reduce the hysteresis of the resulting material. In the present work, two functionalized SBRs, one backbone modified with carboxylate moieties and the other one modified with dithiol groups, are used. The effect on dynamic mechanical properties of a silica filled passenger car tire tread compound is studied. In addition, the effect of zinc oxide on the compound properties is discussed, since it can interfere with the silanization reaction and may also react with the functionalized polymers. The results show the significant potential of these modified SBRs to reduce rolling resistance while maintaining wet grip.