Dielectric properties of epoxy/BN micro- and meso-composites: Dielectric response at low and high electrical field strengths

By incorporating boron nitride (BN) in epoxy resin, we aimed to affect the morphology of the underlying composites. Two different filler sizes, one micrometric with an average grain size of 9 μm and a sub-micrometric one with 0.5 μm, have been used to form composites. The amount of each type of BN in the matrix has been varied from 1 to 5 wt%. Dielectric response measurements at ambient temperature revealed slightly lower real permittivity values of BN composites over neat epoxy and also an increase in imaginary permittivity. In addition, the BN composites had improved thermal stability of properties as compared to neat epoxy, due to lower values in real permittivity as well as in dielectric loss, for temperatures above glass transition temperature. Further dielectric spectroscopy showed significantly decreased values in both real and imaginary permittivity of BN composites, when subjected to high field strengths and very high temperatures compared to measurements at low field strengths. Differential Scanning Calorimetry (DSC) measurements have shown that reticulation was likely to be hindered due to numerous agglomerations in the matrix for the case involving the sub-micrometric BN composite with 5 wt% filler content.