Thermal and electrical conductivity of a graphene-based hybrid filler epoxy composite

The development of polymer-based composites with thermal transport capability has now become essential in response to the efficient thermal management required in electronic and energy conversion devices. In this work, a novel hybrid filler consisting of graphene nanoplatelet (GNP) and boron nitride microparticles (micro-BN) is used to improve the thermal conductivity of epoxy composite. The GNPs with an average lateral size of 8 µm and an average thickness of 5 nm are in the same volume range with the 1 µm size micro-BN particles. According to the results, the thermal conductivity of the composites changes abruptly with increasing micro-BN loading at fixed GNP loading, which is attributed to the formation of a percolative network through the composite. By using 20% vol. hybrid filler, the thermal conductivity of epoxy increases from 0.22 to 5.64 W/m K, which is 147% higher than the thermal conductivity of GNP composite due to the synergistic effect. Finally, as a secondary filler in the GNP epoxy composite, nano-BN is compared with the micro-BN. It is observed that for thermal conductivity enhancement, the addition of nano-BN is not as effective as micro-BN. On the other sides, unlike nano-BN, by adding of micro-BN, the electrical conductivity of GNP epoxy composite does not change significantly. It is found that for the size of the GNPs used here, 1 µm size of micro-BN is an optimized value that leads to the formation of a strong percolated network of fillers through the composite.