Radiation modification of functional properties in PVC/mica electrical insulations

Summary The effects of γ-irradiation on poly(vinyl chloride) blended with fillers (plasticizer, lead stabilizer and mica) are presented. Mechanical and electrical investigations were carried out on samples that received doses of maximum 160 kGy. The results on tensile strength, volume resistivity and loss factor prove that poly(vinyl chloride) may be used as electrical insulator after short γ-exposure. Because mica plays a role of absorbent for hydrochloric acid formed by PVC degradation, favorable properties are obtained for dose up to 120 kGy. The volume resistivity decreases constantly while tan δ remains unchanged for a large frequency range (10²–10⁵ cps). Mica content of 14% induces a decrease in unirradiated PVC of one order of magnitude. After irradiation at 160 kGy volume resistivity increases of about five times relative to 40 kGy irradiated samples. At 150 kGy tensile strength decreases only with 10%, and elongation at break presents a light modification in the selected dose range. The largest differences between the maximum current values obtained for applied doses are presented by PVC with the highest concentration of mica (14%). At 40 kGy, when the degradation becomes relevant, the dipoles are not efficiently trapped by mica and the current does not attend a steady state for a long period (more than half an hour). For higher doses the steady-state current is reached after only 1–3 minutes, due to crosslinking. Some considerations concerning the consequences of high energy exposure of poly(vinyl chloride) on electrical behaviour are presented.