Wettability of naturally aged silicon and EPDM composite insulators

The wettability of aged surfaces and of the bulk of naturally aged silicone and EPDM (ethylene-propylene diener monomer) insulator housings and silicone elastomer insulator coatings was studied. The samples were taken either directly from the insulators or treated by exposing them to corona discharges and/or to saline pollution. The results show that the contact angles of the silicone rubber insulator surfaces are larger than the contact angles of the RTV (room-temperature vulcanizing) silicone rubber coating and of the EPDM rubber insulator surfaces, especially when the surfaces are aged. When the insulators were exposed to corona discharges, the contact angles of the silicone rubber insulators are reduced but after exposure recover with time. The contact angles of the EPDM rubber insulators, however, continue to reduce after the exposure. When exposed to artificial saline pollution, the silicone rubber insulators show a limited recovery of their contact angles with time, while when exposed to corona discharge after saline pollution, they show a recovery of the contact angle after the exposure. The recovery time is dependent on the exposure time to the corona discharges. The EPDM samples do not show any recovery of their contact angles, either when left to rest after the salt deposition or, when after the salt deposition, they undergo a subsequent exposure to corona discharges. Furthermore, such an exposure may be deleterious for the EPDM polymer and the insulator surface may become completely hydrophylic