Influence of molecular properties of SSBR and BR types on composite performance

Abstract

Modern passenger car tire tread compounds usually consist of a polymer blend of Solution Styrene-Butadiene Rubber (SSBR) and Butadiene Rubber (BR) in combination with a silica/silane system. To further enhance the compatibility between the nonpolar polymer and the polar silica, different functional groups can be introduced at the end or along the polymer chains. The influence of such a polymer functionalization of SSBR and BR on the processing behavior as well as on mechanical and dynamic properties was investigated for silica-filled tire tread model compounds. Silica-filled functionalized SPRINTAN™ SLR 4602 was blended with non-functionalized SPRINTAN™ 363H and functionalized SPRINTAN™ 884 L in three ratios: 90/10, 80/20 and 70/30. The two BRs differ in five analytical properties: molecular weight, vinyl content, cis-content, glass transition temperature (Tg) and functionalization. All five properties influence the composite properties in a different way. The functionalization is the dominating influencing parameter in this study. The presence of the functionalization improves the rubber-filler-interaction. This leads to better dynamic and mechanical properties of the model tread compound: The reinforcement index is increased and the tan δ at 60 °C, as lab predictor for the tire rolling resistance, is reduced while the tan δ at 0 °C, as lab predictor for wet grip, is similar to the non-functionalized BR. Furthermore, the Tg of the whole blend compound dominates the dynamic-mechanical behavior, as expected. In the case of BR, the functionalization has the dominating influence on the tan δ, the effect of Tg plays a minor role. These new insights support the development of new functionalized polymers to improve the overall tire performance.

Keywords

• SSBR
• BR
• Silica
• Silane
• Rubber blends
• Rheology