Dielectric Properties of Boron Nitride Filled Epoxy Composites

In this paper, we report some preliminary measurements on the dielectric response and properties of boron nitride filled epoxy resin composites consisting of a typical anhydride cured bisphenol-A epoxy resin system. Both conventional stirring and ultrasonic processing had been used to obtain fine dispersion of the microfillers in the matrix. Dielectric spectroscopy of the samples has been undertaken in the frequency domain from 10^-2 Hz to 10⁶ Hz and in the temperature range from -50 to 120 degC. The results showed that the dielectric constant of the composites increase slightly with increasing concentration of fillers. A broad loss peak is present in the low frequency region in all samples from pure epoxy resin to composites with 20 wt% of boron nitride. This peak moves to higher frequencies with increasing temperature, and no obvious difference in position and shape of this peak is found across all levels of filling at each temperature. The dc conduction current has also been measured in the temperature range from -50 to 120 degC. The results showed that there is no significant difference in the dc conduction current across this temperature range and there is only a weak dependence on the concentration of the fillers above 60 degC.