Electrical conduction of ethylene-vinyl acetate copolymer and their blend

Though high energy radiation is irradiated to polyethylene insulation of wires as a method to improve the heat-resistive property, it may cause the problem of dielectric breakdown due to the induction of extremely intense space charge field because the carrier is captured to the trap centers during irradiation. Most of the carriers remaining in polyethylene over a long period after the irradiation of high energy radiation exist in or on the surface of crystals. Accordingly, it is expected that the remaining carrier condition can be changed if the extent of crystallization and crystalline form of polyethylene are varied. This paper discusses the effect of crystallization on electrical conduction by varying the extent of crystallization and the size of fine crystals of polyethylene using copolymerizing technique. In unirradiated samples, the electrical conductivity of either ethylenevinyl acetate copolymer or its blend increases with the increase of vinyl-acetate content. Thermally stimulated current after γ-irradiation relates strongly to crystal melting and especially that of the blend is controlled greatly by the existing low density polyethylene. It was found that reduction of the extent of crystallization and of the size of fine crystals is one of the effective means as a countermeasure to space charge due to high energy irradiation. To achieve it, copolymerization is better as compared with undesirable blending. (Wakatsuki, Y