Effects of gamma-ray irradiation on dielectric surface breakdown of polybutylene polymers

Polymer materials are required to be used in radiation environments of space and nuclear power stations as insulation materials. For the use of polymer materials in such regions, it must be confirmed whether the electrical performance under radiation environments is different from that without radiation. This paper describes the effects of gamma-ray irradiation on dielectric breakdown of polybutylene naphthalate and terephthalate by applying a DC pulse voltage. Both the polybutylene naphthalate and polybutylene terephthalate were irradiated in air up to 100 kGy and then up to 1000 kGy with dose rate of 10 kGy/h by using a ⁶⁰Co gamma-source. The total dose of gamma-ray irradiation effects on the time to dielectric breakdown and the discharge quantity of discharge current were discussed. Obtained results show that with increasing the total dose of gamma-ray irradiation, the time to dielectric breakdown increased with polybutylene naphthalate, but decreased with polybutylene terephalate. With increasing the total dose of gamma-ray irradiation, the discharge quantity decreased with polybutylene naphthalate, but increased with polybutylene terephalate. The experimental results suggest that the chemical structure plays a main role in the result of the radiation reaction, which is related to cross-linking and degradation reactions. Dielectric properties are improved by the irradiation for polybutylene polymers which contain more combined phenyls in the main chain.