Evaluation of several polymer films for use as electrical insulators

A facility was developed in which polymer samples were aged to 32,700 h with an applied load of 6.9 MPa and at temperatures of 70, 110, 135, and 160°C. The aging environment was 0.4 MPa (4 atm) SF6 containing either 4 or 40 Pa (40 or 400 µatm) H2O. The polymers evaluated to 32,700 h were polyethylene terephthalate, polycarbonate, polyparabanic acid, polyethersulfone, and polyimide. Polysulfone and polyetherimide were aged to 11,200 h. Only polyethylene terephthalate showed any interaction with the environment, and this was in the form of higher moisture causing greater reductions in fracture strain. Electrical breakdown measurements were made on most of the aged samples, and there were no reductions in breakdown voltage as a result of aging. The sticking temperatures between polymers was determined to be 160°C for polyethylene terephthalate; 110°C for polycarbonate; 160°C for polysulfone; and >160°C for polyetherimide, polyethersulfone, polyparabanic acid, and polyimide.