Nano-micro structure of functionalized boron nitride and aluminum oxide for epoxy composites with enhanced thermal conductivity and breakdown strength

Polymer-based composites with high thermal conductivity and breakdown strength have become increasingly desirable in both the electronic and electric industries. Herein, we have designed a nano-micro structure of 2-D micro-scale hexagonal boron nitride (h-BN) and 0-D nano-scale alpha-alumina (alpha-Al2O3) hybrid fillers for epoxy composites with high thermal conductivity and breakdown strength. So as to improve interface interaction, both fillers are functionalized with hyperbranched aromatic polyamide (HBP). It is found that both structure design and surface modification play important roles. Surface modification can enhance many physical properties of composites, such as thermal conductivity, thermal stability and breakdown strength. Importantly, the nano-micro structure presents noticeable synergistic effects on both thermal conductivity and ac breakdown strength. The obtained composite with 26.5 vol% fillers presents a high thermal conductivity of 0.808 W m(-1) K-1 (4.3 times that of epoxy). In addition, the breakdown strength of the composite at 4.4 vol% content is up to 40.55 kV mm(-1), 21.5% higher than that of neat epoxy (33.38 kV mm(-1)).