Surface modification and magnetic alignment of hexagonal boron nitride nanosheets for highly thermally conductive composites

With the current development of microelectronic technology, thermally conductive and electrically insulating encapsulation materials are in urgent demand. Hexagonal boron nitride nanosheets (BNNSs) possess a highly anisotropic thermal property. Therefore, the thermal conductivity of the BNNSs-based composites can be dramatically increased through the orientation of fillers. However, it is still difficult to well align BNNSs at high loadings due to the intensive aggregation. Herein, highly ordered thermoplastic polyurethane elastomer (TPU)/BNNSs composites are successfully fabricated by the combination of filler modification and magnetic alignment. The effective covalent modification with 2,4-tolylene diisocyanate (TDI) greatly increases the dispersibility of fillers, thus making it easy to well orient BNNSs at high loadings. The highly aligned fillers result in much higher in-plane thermal conductivity than the composites filled with disordered or less-ordered unmodified BNNSs. The thermal conductivity is as high as 5.15 W m^-1 K^-1 at 30 wt% loading. Moreover, the composite simultaneously exhibits low dielectric constant, low dielectric dissipation factor and excellent thermomechanical properties. These results reveal the promising application of such highly-ordered composites in advanced electronic packing.