Exfoliated boron nitride nanosheet/MWCNT hybrid composite for thermal conductive material via epoxy wetting

Herein, we describe the fabrication of thermally conductive composites based on an epoxy matrix with a hybrid filler of hexagonal boron nitride (h-BN) and multi-walled carbon nanotubes (MWCNTs) via the wetting method. The h-BN particles were exfoliated to boron nitride nanosheets (BNNSs) by heating in a tubular furnace with steam and sonication. The h-BN particles in the composite were densely packed and oriented almost perpendicular to the bottom. On the other hand, the BNNSs were more loosely packed and randomly oriented, and exhibited higher through-plane thermal conductivity despite the low filler content. After the incorporation of MWCNTs, the filler thermal conductivities of both the composites significantly increased. In particular, 9 wt% of MWCNTs was sufficient to increase the thermal conductivity of the BNNS composite from 3.12 to 4.25 W m−1 K−1 because of the intercalation of the nanotubes between the BNNSs, which provided a three-dimensional heat flow path. Moreover, the MWCNTs interrupted the dense particle packing and the filler concentration was reduced from 56.7 to 43.8 wt%. In the case of h-BN composite, this effect was relatively weak because the nanotubes were agglomerated between the micron-sized BN particles.