Evaluation of thermal and electrical aging of an insulating composite material by dielectric and microstructural investigations

Thermal and electrical aging of an insulating composite material, obtained from a modified solventless bisphenolic epoxy resin, with a modified anhydride as curing-agent, filled with 60 wt% of calcined alumina, has been investigated by dielectric methods and scanning electron microscopy. The results point out that chemical changes in polymer matrix and microstructural changes in the overall material can be monitored by the proposed methods. Thermal and electrical aging cause both chemical and microstructural effects, which seem to exert counter-balancing effects on material dielectric strength and endurance. Combined-stress aging is especially deleterious, producing large microvoids and early failures in the material. A brief outline of these effects is given.