Boron nitride nanotubes (BNNTs) are analogous nanostructures to carbon nanotubes (CNTs), possessing similar properties such as Young's modulus and thermal conductivity, but superior resistance to oxidation and thermal stability. In addition, BNNTs are insulating materials, whereas CNTs are electrically conductive. They could be used as reinforcements in polymeric matrices as heat dissipators or as protective coatings in harsh environments. However, when incorporating them into polymers, one main drawback is their tendency to agglomerate. To improve their dispersion, covalent surface modification can be applied, with solvent-free approaches being preferred. Herein, we used syngas photo-initiated chemical vapour deposition (PICVD) to incorporate oxygen functionalities on the surface of BNNT. X-ray photoelectron spectroscopy analysis showed a highly oxidized BNNT surface after treatment. In addition, a decrease in water contact angle and an increase in surface energy were observed for the treated material. These results open new possibilities to incorporate hydrophilic BNNTs surfaces into polar polymers or other matrices of interest.

The use of boron nitride nanotubes (BNNTs) for fabrication of thermally conductive composites has been explored in the last years. Their elevated thermal conductivity and high mechanical properties make them ideal candidates for reinforcement in polymeric matrices. However, due to their high tendency to agglomerate, a physical or chemical treatment is typically required for their successful incorporation into polymer matrices. Our previous study about the dispersibility of BNNTs allowed determination of good solvents for dispersion. Here, we performed a similar characterization on styrene-butadiene rubber (SBR) to determine its solubility parameters. Although these two materials possess different solubility parameters, it was possible to bridge this gap by employing a binary mixture. The solvent casting approach followed by hot pressing was chosen as a suitable method to obtain thermally conductive SBR/BNNT composites. The resulting nanocomposites showed up to 35% of improvement in thermal conductivity and a 235% increase in storage modulus in the frequency sweep, when a BNNT loading of 10 wt% was used. However, the viscoelastic properties in the amplitude sweep showed a negative effect with the increase in BNNT loading. A good balance in thermal conductivity and viscoelastic properties was obtained for the composite at a BNNT loading of 5 wt%.

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