Plasma polymerization of acetylene onto silica: an approach to control the distribution of silica in single elastomers and immiscible blends

Surface modification of silica by acetylene plasma polymerization is applied in order to improve the dispersion in and compatibility with single rubbers and their blends. Silica, used as a reinforcing filler for elastomers, is coated with a polyacetylene (PA) film under vacuum conditions. Water penetration measurements show a change in surface energy due to the PA-film deposition. The weight loss measured by thermo-gravimetric analysis (TGA) is higher for the PA-coated silica compared to the untreated filler, confirming the deposition of the PA film on the silica surface. Time of flight-secondary ion mass spectrometry (ToF-SIMS) shows the well-defined PA cluster peaks in the high mass region. Scanning electron microscopy (SEM) measurements show silica aggregates, coalesced by the coating with smooth and uniform surfaces, but without significant change in specific surface area. Elemental analysis by energy dispersive X-ray spectroscopy (EDX) measurements also confirms the deposition of the polymeric film on the silica surface, as the carbon content is increased. The performance of single polymers and their incompatible blends based on S-SBR and EPDM, filled with untreated, PA- and silane-treated silica, is investigated by measurements of the bound rubber content, weight loss related to bound rubber, cure kinetics, reinforcement parameter, Payne effect, and mechanical properties. The PA- and silane-modified silica-filled pure S-SBR and EPDM samples show a lower filler–filler networking compared to the unmodified silica-filled elastomers. Decrease in the reinforcement parameter (F) for the plasma-polymerized silica-filled samples also proves a better dispersion compared to silane-modified and untreated silica-filled samples. On the other hand, the PA-silica-filled samples show a higher bound rubber content due to stronger filler–polymer interactions. Finally, the PA-silica-filled pure EPDM and S-SBR/EPDM blends show high tensile strength and elongation at break values, considered to be the result of best dispersion and compatibilization with EPDM.