Enhanced Boron Nitride/Polyolefin Blends for High Voltage Applications

The effect of improved exfoliation on the electrical properties of hexagonal boron nitride (h-BN) composites based on polyethylene and polypropylene was studied. Chemical and thermal treatments were used to obtain exfoliated h-BN which was initially added to the host polymer at 2 wt. %. Scanning electron microscopy was used to study the particle dispersion, whilst measurements of AC breakdown strength and electrical conductivity were used to assess dielectric performance. It was found that an acid/hydrogen peroxide method was effective at exfoliating h-BN as evinced by an absence of large micron-scale aggregates in electron micrographs. A 20% increase in AC breakdown strength and a factor of 5 decrease in the electrical conductivity was attained relative to the unfilled host polymer. Composites employing exfoliated h-BN were then compared to analogous systems employing untreated h-BN over a wide compositional range. Whilst there was some advantage in incorporating untreated h-BN over the properties of the unfilled host polymer, the use of treated h-BN allowed maximum AC breakdown strength to be obtained at much lower filler loadings (∼2%) than hitherto reported. This allows a much smaller h-BN loading to be used for enhanced dielectric properties, reducing manufacturing costs. In addition, at high filler loadings, the thermal conductivity could be usefully improved. Such enhanced materials could be deployed in high voltage cables and capacitors.