Conduction mechanisms in epoxy resin systems: influence of gamma-irradiation

Studies of γ-irradiation to dose levels of 2 MGg of two epoxy resin systems have been undertaken. Using both thermally stimulated current measurements and d.c. current measurements, changes in the polymer structure and conduction processes were identified. The conduction process in both cases was found to be ionic as shown by the linear current-voltage characteristics. This behaviour occurred over a temperature range of approximately 120oC. From this data activation energies of 0.9 and 2.16 eV were obtained for the two resin systems. In addition ion jump distances were found to be of the order of 10-8 m, as derived from deviation from Ohmic behaviour under high field conditions. In the case of one resin this deviation occurred at appreciably lower applied fields and was attributed to homo-charge injection from the electrodes. The other resin showed some space charge effects in the thermally stimulated discharge spectrum. γ-Irradition effects caused in one system a lowering of Tg with an increase in d.c. conductivity which were both affected by post irradiation annealing. The causes were attributed to ion production and chain scission during irradiation. The other resin system exhibited an increase in Tg and a decrease in conductivity, these effects being attributed to radiation-induced crosslinking. (author)