Bleed-out suppression of silicone rubber by electron beam crosslinking

Abstract

A silicone rubber with a highly crosslinked surface layer was synthesized by a two-step crosslinking reaction with thermal processing and subsequent electron beam (EB) irradiation. The effect of the EB irradiation on the silicone rubber was evaluated by measuring the volume swelling ratio, shore hardness, tensile breaking strength, and water contact angle of the EB-crosslinked silicone rubber. The silicone rubber was effectively crosslinked as the EB irradiation increased. The optimal EB irradiation dose to form the EB-crosslinked structure in the silicone rubber was 500 kGy. Insufficient EB irradiation does not form a sufficient EB-crosslinked structure, while excessive EB irradiation dose would decompose the silicone rubber. The finer crosslinked structures of the surface layer of the silicone rubber formed by EB irradiation could function as a leak-proof filter to prevent the bleed-out of low-molecular-weight siloxanes inside the silicone rubber. The effect of the type of EB-crosslinking agent on the bleed-out suppression effect was investigated. The bleed-out suppression effect was improved in the following order: no EB-crosslinking agent < ethylene glycol dimethacrylate < silicone diacrylate < trimethylolpropane trimethacrylate (TMPTMA). The thermally and EB-crosslinked silicone rubber with TMPTMA successfully reduced the bleed-out ratio by approximately 60%, compared to the thermally crosslinked silicone rubber without EB irradiation and EB crosslinking agent.