Effect of filler type and particle size distribution on thermal properties of bimodal and hybrid – BN/Boehmite-filled EP-Novolac composites

Abstract

In this study, the combination of hexagonal Boron Nitride (BN) and Boehmite are investigated towards their potential to enhance both the thermal and flame retardant properties in Epoxy Novolac matrices for electrical applications. The focus of this scientific work is to correlate the fillers’ particle size (distribution), morph ology, content, dispersion and orientation, which are investigated with microscopic methods (SEM, TEM), with the resulting thermal properties. Both filler types are studied systematically in monomodal and bimodal filler distribution and finally in a hybrid combination, both with variation in the relative compositions. The thermal properties of the resulting composites are determined via TGA (thermal decomposition), DMA (Tg), and heat flow meter for thermal conductivity. The effect on flame retardancy is examined with Cone Calorimetry. The results show that the thermal conductivity is strongly dependent on filler type, content and particle size (distribution) strongly affecting the resulting microstructure. With increasing filler content and the higher the filler’s aspect ratio, the more pronounced is the enhancement of the thermal conductivity and flame retardancy. Furthermore, the variation in the relative composition of the bimodal filler distributions and hybrid combination demonstrates the potential to design and trigger the formation of the micro- structured network in a smart way improving the through-plane (z-direction) heat dissipation.