Effect of the silica-rubber interface on the mechanical, viscoelastic, and tribological behaviors of filled styrene-butadiene rubber vulcanizates

In this research, the effects of the surface modification of silica by low-molecular-weight hydroxyl-terminated polybutadiene (HTPB) are compared with those of bis(3-triethoxysilylpropyl)tetrasulfide (TESPT) on the mechanical, viscoelastic, and tribological properties of styrene-butadiene rubber (SBR) vulcanizates. Both modifiers have the ability to make covalent bonds with the rubber matrix, but with different interfacial characteristics controlling the final properties. The results displayed improvements in the tribological behavior of both modified silica-filled vulcanizates over pristine silica- and carbon black-filled vulcanizates. However, the HTPB modification method, despite providing a finer dispersion of the silica in the rubber, did not result in better tribological properties for the vulcanizates compared with those of the TESPT modification method. It was discussed that the HTPB modifier did not enhance tribological properties, especially abrasion resistance, as much as the TESPT modifier did because of the soft and flexible interface that was created in the presence of the HTPB modifier, in contrast to the rigid interface in the presence of TESPT. Molecular structure of silica surface modifiers greatly controls the performance of silica-filled styrene-butadiene rubber (SBR) through interfacial characteristics of the composites. Soft nature of low molecular-weight hydroxyl terminated polybutadiene (HTPB) and small number of its covalent bounds to the rubber matrix was compared with large number of rigid covalent bounds made between bis(3-triethoxysilylpropyl)tetrasulfide (TESPT) and rubber. Despite the better dispersion of silica modified with the former, the latter ensures higher transfer of stress to particles at large strains, inducing improved strength and abrasion resistance to composites.