Dielectric integrity of silica-PAI nanocomposites at elevated temperature

It has been shown that in many cases, the addition of nanoscale metal oxide fillers to polymers leads to an improvement in dielectric breakdown strength at room temperature. However, in some cases electrical insulation is exposed to elevated temperatures. A thermally stable polymer material, such as polyamideimide (PAI), is desired for these applications. For this reason, breakdown strength measured at elevated temperatures is required, since this property is expected to degrade with an increase in temperature. The addition of nanoparticles has been shown to increase PAI decomposition temperature and is also expected to mitigate the effect of increased temperature on dielectric properties. In this paper, AC and DC breakdown strength of PAI and nanosilica filled PAI are reported at room temperature and elevated temperatures. (200-340°C) Test temperatures were well below the decomposition range of polyamideimide as measured by thermogravimetric analysis (TGA). Silica composites at all loadings (whether treated or untreated) were shown to have a higher AC and DC breakdown strength at elevated temperatures than unfilled material. Dielectric spectroscopy results are also presented.