BNNT thermal management materials for high-power systems

Thermal interface materials may be enhanced through the dispersion of refined boron nitride nanotubes (BNNTs) into a polymer matrix material and one or more microfillers. A refined BNNT material may be formed by reducing free boron particle content from an as-synthesized BNNT material, and in some embodiments reducing h-BN content. Reducing these species improves the thermal conductivity of the BNNTs. Refined BNNTs may be deagglomerated to reduce the size and mass of BNNTs in agglomerations when the deagglomerated BNNT material is dispersed into a target polymer matrix material. The deagglomerated BNNT material may be lyophilized prior to dispersion in the matrix material, to retain the deagglomeration benefit following return to solid state. The surface of the deagglomerated BNNT material may be modified, with one or more functional groups that improve dispersibility and heat transfer in the target polymer matrix material.