Flexible, Thermally Conductive, and Anisotropic Boron Nitride Nanotube-Based Heat Spreading Fabrics

This study reports on the development of flexible boron nitride nanotube (BNNT) fabrics and significant improvements to their anisotropic thermal conductivity and mechanical toughness. Through BNNT purification and isotopic enrichment with ¹¹B, the in-plane thermal conductivity was improved nearly 5-fold (from 1.80 to 8.26 W m^–1 K^–1), while maintaining a low through-plane thermal conductivity (0.13 W m^–1 K^–1). This resulted in an extremely high anisotropic ratio of 62, the highest reported anisotropy and magnitude in thermal conductivity for bulk BNNT materials. Mechanical testing revealed that BNNT purification doubled fabric strength and tripled toughness, owing to BNNT bundling and alignment. These results highlight the importance of BNNT purity in enhancing thermal and mechanical properties of bulk BNNT fabrics. As a highly porous nanomaterial, BNNT fabrics hold great potential as composite preforms or, given their flexibility and toughness, as standalone high temperature, electrically insulating thermal management materials.