Influence of silica filler distribution on properties of tire rubber treads, as related to silica characteristics
Louis-Philippe A.E.M. Reuvekamp and Jacques W.M. Noordermeer*,
Twente University, Dept. of Rubber Technology
P.O. Box 217, 7500 AE Enschede, the Netherlands
Objective: Silica has grown substantially over the last decade as reinforcing filler for rubber tire treads, for reason of lower rolling resistance compared to carbon black reinforcement. So-called highly dispersible silicas are being used. The objective was to identify the primary silica characteristics, influencing the performance in tire treads. Experimental approach: The effect of rubber mixing conditions on macro- as well as on microdispersion of silica was studied, using conventional till highly dispersible silicas with different BET-surfaces and Structure. Macro-dispersion was studied by optical means, micro-dispersion with Atomic Force Microscopy (AFM). Summary of results: The macro- and microdispersion vary with difference in silica samples, particularly with various DBP-structures. Low structured silicas show poor macrodispersion, vs. medium structured/semi dispersible and very good microdispersion for highly structured/highly dispersible silicas. Microdispersion measurements show an increased level of primary silica particles for higher structured silicas, where these are primarily dispersed to the microdispersion level, with only 15-20% remaining in the macrodispersion regime. The dynamic mechanical properties of a tire tread primarily depend on the microdispersion level. Too large filler-filler interactions, causing poor dynamic mechanical properties, are mainly due to aggregates with a size over 600 nm. Also the tensile properties are primarily influenced by the presence of aggregates with diameters larger than 600 nm.