Low molecular weight silicone fluid content and diffusion in RTV silicone rubber coating

Room temperature vulcanizing (RTV) silicone rubber has been widely used to coat porcelain insulators to render water repellency to prevent formation of water filming on the surface and thus to suppress the leakage current and consequent flashover. The hydrophobicity is maintained even after a layer of contamination has built-up on the surface. This has been attributed to the diffusion of the low molecular weight (LMW) silicone fluid from the bulk to the surface of the RTV and then on to the surface of the pollution deposits. It has been reported that there was a reduction in the quantity of LMW polymer chains on the surface of an aged RTV specimen when compared to a virgin specimen. This paper explores some of the factors governing the lifetime of the RTV coating. Alumina trihydrate (ATH) filler and various formulations were used. The content of LMW silicone fluid and the diffusion of LMW from the bulk to the surface were determined in RTV coatings having thicknesses from 0.17 to 0.99 mm, ATH particles from 1.0 to 75 μm and different carrier solvents, by using extraction techniques in analytical hexane. The roles of the LMW content and the diffusion process in the lifetime of the coating were evaluated for different formulations of RTV