Effects of thermal aging on the characteristic breakdown behavior of Nano-SiO2-BOPP and BOPP films

The effects of thermal stress on the breakdown behavior of biaxially oriented polypropylene (BOPP)-silica nanocomposite thin film and commercial BOPP film was evaluated with a step stress experiment in the temperature range of 50...110 °C. Weak spots were measured in thermally aged unfilled BOPP films but not in the PP-silica, which in turn displayed increasing scatter of the breakdown voltages and the scattering seemingly settled to a certain level. No weak spots were measured in un-filled BOPP films removed after highest temperatures. The behavior of un-filled films is speculated to result from either actual polymer aging in addition to the statistical nature of breakdown phenomena or from thermally-activated processes possibly involving antioxidants. The different behavior in the nanocomposite was speculated to result from polymer-nanoparticle interactions possibly countering the effects of antioxidants and hindering weak spot formation. The results demonstrate the different behavior of polymer-nanocomposites and traditional BOPP films under thermal stress and highlight the importance of evaluating the aging behavior of new materials.