Interfacial coupling efficiency of functionalised rubbers on silica surfaces

Understanding filler-polymer interactions at the interfaces is an important aspect for rubber reinforcement development. Recent technology in the field of silica-rubber reinforcement has led to an increasing interest in functionalised rubbers, since they can directly react and enhance interactions with silica filler, and hence improved rubber reinforcement. The present work aims to better understand the role of different reaction variables, i.e. time, temperature, rubber concentration, solvent, surfactants, sonication, specific surface area of silica, rubber type, and catalyst, on rubber deposition on silica surface in a model reaction in solution of silica and functionalised rubbers. Results from the Design of Experiments (DoEs) study, i.e. One-Factor-At-a-Time (OFAT), Plackett-Burman (P-B) and Full-Factorial (FF) designs showed that all studied factors have a negligible effect on interfacial coupling efficiency of rubber to silica surface. Accessibility of the functional groups at the rubber molecules and the steric hindrance due to large polymeric molecular chains seem to be the most limiting factors, resulting in low coupling efficiency. Effects of the investigated reaction parameters and plausible mechanisms involved in rubber-silica coupling reactions are elucidated.