Constructing a robust triple-interaction network for high-performance bio-based epoxidized natural rubber/silica nanocomposites via synergistic two-step silica modification

The dispersion of fillers is crucial for the mechanical performance of rubber products. Typically, Silane Coupling Agents (SCAs) are added to the rubber matrix together with silica, relying on high temperature and mechanical shearing for simultaneous surface modification and dispersion. However, this in-situ method often yields uncontrollable modification degrees and poor dispersion efficiency. To address this issue, a two-step silica surface-modification strategy using SCAs was developed, and the modification mechanism was systematically investigated. First, Bis-(γ-triethoxysilylpropyl)-disulfide (TESPD) was grafted on the silica surface via a condensation reaction between hydrolyzed TESPD and surface hydroxyl groups to prepare TESPD-silica. Subsequently, the TESPD-silica was further modified with γ-Mercaptopropyltrimethoxysilane (KH580) to obtain TESPD-silica-KH580. The successful grafting of the coupling agents was confirmed by FTIR, TGA, and surface hydroxyl group analysis. Compared with TESPD-silica, TESPD-silica-KH580 exhibited the lowest surface hydroxyl content and the most improved dispersion behavior. On this basis, Epoxidized Natural Rubber (ENR) nanocomposites were prepared with different types and loadings of modified silica, demonstrating improved filler dispersion and static/dynamic mechanical properties. Among them, TESPD-silica-KH580 showed the best comprehensive performance. This is attributed to its ability to act as a coupling bridge between double bonds and epoxy groups via its surface thiol and silanol groups, forming a triple-interaction rubber-filler network. This structure promotes the formation of a robust triple-interaction rubber-filler network, thereby significantly enhancing the overall performance of the nanocomposites.