Carbon black/silica hybrid filler networking and its synergistic effects on the performance of styrene-butadiene rubber composites

This study shows how carbon black/silica hybrid filler networking leads to synergistic properties in styrene-butadiene rubber (SBR) composites. The effects of low concentrations of silica, the secondary filler, on flocculation and network formation/breakdown (Payne effect) of carbon black, the primary filler in the SBR composites, were evaluated. There was a critical silica concentration at which this synergy was observed, but it disappeared at higher concentrations due to network formation by silica itself. A mismatch between the carbon black and silica surface energies was shown to be the determining parameter. Critical loading of silica was also observed for vulcanization of rubber composites, at which the enthalpy of vulcanization increased considerably. Enhancements in the final properties, such as mechanical strength and wear resistance, were explained by improvements in the dispersion of carbon black and vulcanization of rubber at the critical loading of silica. Synergistic effects of adding silica, as a secondary filler, to styrene-butadiene rubber composites highly filled with carbon black was investigated. It was shown that there is a critical concentration of silica at which improvements in the Payne effect, mechanical properties, abrasion resistance, and heat build-up were at extrema. This behavior was attributed to the filler networking in the hybrid filler systems, at which work of adhesion in a three-component system was considered as the driving force for flocculation of the primary filler and final morphology of fillers in hybrid composites.