Sensitivity of Marching Modulus of silica-filled SBR/BR compounds to filler type and polymer ratio

Silica-silane filler systems are very successful in passenger car tire treads as they considerably improve tire performance, mainly rolling resistance. However, this technology has its drawbacks in terms of processing: longer mixing cycles, two or three mixing stages, as well as influences on the curing behavior of the compound. One specific problem related to the latter is a marching modulus, which makes determination of the correct curing time difficult. As a consequence, the properties of silica compounds might vary. In this study, the influence of polymer ratio as well as dispersibility of silica on the curing kinetics is investigated.
The polymers used in general with a silica-silane filler system in tread compounds are sSBR and BR, and the ratio of these two polymers significantly influences curing behavior as well as marching modulus. This is a consequence of differences in compatibility of the filler with the two polymers, and in reactivity of the two polymers to form sulfur bonds.
The dispersibility of the silica is also expected to influence the curing kinetics due to differences in relative surface area and in interaction with the curatives. However, when comparing different silica grades, no significant influence on marching modulus was found.