Catalytic effect of ZnO anchored silica nanoparticles on rubber vulcanization and cross-link formation

ZnO nanoparticles (NPs) anchored on SiO2 (ZnO/SiO2) demonstrated to be an activator of higher efficiency in the sulfur crosslinking of isoprene rubber (IR) in comparison with conventional microcrystalline ZnO. The better performance of this innovative catalytic filler has been associated with: (i) the faster Zn reaction with stearic acid and curatives, to form the sulfurating complexes at the beginning of the curing process; (ii) the faster formation of large amounts of mono- and di- sulfide cross-linking short chains through a breaking-down mechanism of longer poly-sulfide chains, which account for the higher cross-linking density of the final cured material. In the first step of the curing reaction activated by ZnO/SiO2, the formation of a stearate bridged dimeric zinc complex has been suggested as potential highly reactive intermediate responsible for accelerating the cross-linking reaction