Exploring Epoxy-Functionalized Polysulfide as a VOC-Free and Highly Effective Interfacial Modifier for Silica-Filled Rubber Composites

Silica-filled rubber composite is the main component of the "green tire" featured with a high fuel economy. Nowadays, incorporating sulfur-containing silane coupling agents (SSCAs) to improve the compatibility between silica and rubber is essential to optimizing the comprehensive properties of the resultant composites. However, SSCA synthesis requires multistep procedures and organic solvents and many intractable issues, such as low modification efficiency and volatile organic compound (VOC) emissions, cannot be resolved with regard to the use of SSCAs. Herein, we presented the facile synthesis of an epoxy-engineered polysulfide (SPVE) via inverse vulcanization of styrene, 1,2-epoxy-4-vinylcyclohexane, and sulfur and utilized it as a new-brand modifier for silica-filled rubber composite. The coupling mechanism of SPVE is revealed. Specifically, the polysulfides of SPVE can graft onto rubber chains; meanwhile, the epoxy groups of SPVE readily react with silanol groups on the silica surface, creating molecular linkages between rubber and silica. Consequently, incorporating SPVE remarkably improves silica dispersion and enhances the interfacial adhesion of the composites, thereby leading to superior mechanical properties and significantly decreased hysteresis loss. Compared with the commonly used SSCA, bis-[3-(triethoxysilyl)-propyl] tetrasulfide, SPVE exhibits a higher coupling efficiency without VOC emissions, providing an environmentally friendly solution for the manufacture of energy-saving tires.