Influence of moisture adsorption in high temperature dielectrics

The complex permittivity and loss factor were measured and studied in aramid paper (NOMEX 410) and in fluoropolymer (TEFZEL) film. Parallel plate capacitor method was employed in these measurements. In both cases specimens of 125 micrometer were selected and the dielectric properties were investigated as a function of frequency, temperature and various degrees of moisture adsorption. Capacitance and dielectric loss measurements were taken from frequency range 120 Hz to 1 MHz and temperature range from 20 to 200 degree centigrade. At 120 Hz aramid paper has a relative permittivity of 2.55 and dissipation factor of 0.0086, which increases both with temperature and frequency. It was also confirmed from the investigation that when moisture content increases beyond 5.96% wt, there is an increase in dissipation factor. In TEFZEL film at 120 Hz, relative permittivity of 2.14 and dissipation factor of 0.00089 for completely dried material was measured. Due to adsorption of water, relative permittivity increases by 3.3%, while 26.7% increase in loss peak was calculated. The moisture adsorption rate in TEFZEL film is comparatively lower than aromatic polyamide (aramid) paper. These loss peaks were easily removed by drying the sample so it is concluded that water dipoles cause the relaxation process in fluoropolymer films with adsorbed moisture.