Hydroxylated boron nitride nanotube-reinforced polyvinyl alcohol nanocomposite films with simultaneous improvement of mechanical and thermal properties

Stable dispersion of boron nitride nanotube (BNNT) in a solvent is a critical challenge that has restricted the development of potential applications. In this study, stable BNNT aqueous dispersions are obtained by direct tip sonication in water without any surfactant and organic solvent. BNNTs are functionalized with hydroxyl groups (OH) as a result of the tip sonication-assisted hydrolysis. The energy from tip sonication results in the disentanglement of the as-received BNNT clusters and partial B-N bond cleavage to unzip nanotubes. Using the BNNT aqueous dispersion, a transparent, strong, and ductile OH-BNNT-reinforced polyvinyl alcohol (PVA) multifunctional nanocomposite film is prepared. Tensile fracture strength, Young's modulus, and elongation at failure of 1.0 wt% OH-BNNT/PVA nanocomposite film increased by 46%, 55%, and 45%, respectively, in comparison with pure PVA film. The addition of a mere 1.0 wt% BNNT contributed to a significant (25%) improvement in thermal conductivity. Simultaneous improvement in mechanical and thermal properties is attributed to the superior intrinsic properties of homogenously dispersed BNNTs and strong interfacial interactions between OH-BNNT and PVA chains.