Epoxy-assisted ball milling of boron nitride towards thermally conductive impregnable composites

It remains a major challenge to develop insulating polymeric composites with high thermal conductivity and low viscosity for impregnation applications. Hexagonal boron nitride (hBN) has proven a competitive thermal conductivity enhancer for polymers. However, when introduced into a polymer matrix, raw BN usually undergoes severe sedimentation and thus uneven distribution throughout the matrix, which undermines the uniformity in thermal conductivity and other physical properties. In this work, BN was ball milled with part of the host epoxy resin in slurry state and then directly mixed with the rest in the same pot to obtain a composite resin. Without the tedious processes of filler separation, purification and re-dispersion, the epoxy-assisted slurry-state ball milling greatly improved the suspension stability of BN platelets in epoxy resin, leading to a uniform filler distribution after curing. Consequently, the thermal conductivity of epoxy resin was boosted from 0.19 W·m⁻¹·K⁻¹ by 132% to 0.44 W·m⁻¹·K⁻¹ with the addition of 9.1 wt% loading of BN. Moreover, the composite resin demonstrated high impregnation performance on litz wire. The material preparation method developed in this work is facile, time-effective and scalable, especially suitable for fabricating thermally conductive yet low-viscosity composite resins for impregnation applications. The method may also be extended to develop other polymeric composites incorporated with layer-structured filler materials.