Enhanced Thermal Conductivity in Polymer Nanocomposites via Covalent Functionalization of Boron Nitride Nanotubes with Short Polyethylene Chains for Heat-Transfer Applications

Boron nitride, which possesses high thermal conductivity, is often incorporated into polymer matrixes for thermal management. The enhancement in the thermal conductivity depends on the filler shape, size, effective dispersion in the matrix, and interfacial thermal resistance between the filler and matrix, and the last two are the most challenging issues. To address these challenges, in this study two different covalent functionalization approaches on boron nitride nanotubes (BNNTs) with short polyethylene (PE) chains are employed: one based on the Williamson reaction and the other on nitrene [1 + 2] chemistry. The covalent connection between the nanotubes and the polymer is confirmed by Fourier transform infrared, X-ray photoelectron microscopy, tandem thermogravimetric–infrared spectroscopy analysis and energy-filtered transmission electron microscopy. The modification of BNNTs with short polymer chains has resulted in an excellent strategy to modulate the interface in polymer composites. Tuning the interface has a strong influence on thermal transport, and up to an ∼250% increase in the thermal conductivity of BNNT-HDPE nanocomposites has been observed when the loading increases from 20 to 40 wt % of PE-modified BNNTs due to the improved dispersion and reduced interfacial thermal resistance. The materials described here show the potential for heat-transfer applications.