Boron nitride/boron nitride nanotube composite fibers and methods of making and use thereof

A method of making a boron nitride/boron nitride nanotube composite fiber, the method comprising:

• forming a mixture comprising a plurality of boron nitride nanotubes, a polymeric boron nitride precursor, a polymer, and a solvent, wherein the mixture is formed by:
• forming a first dispersion by dispersing the plurality of boron nitride nanotubes in a first solvent;
• forming a second dispersion by dispersing the polymeric boron nitride precursor in a second solvent;
• contacting the second dispersion with the polymer to form a third dispersion;
• and
• contacting the first dispersion with the third dispersion;
• spinning the mixture to form precursor fibers comprising the plurality of boron nitride nanotubes, the polymeric boron nitride precursor, and the polymer, wherein the precursor fibers have a first average outer diameter;
• wherein spinning the mixture comprises electrospinning, wet jet fiber pulling, wet spinning, dry spinning, dry-jet wet spinning, or combinations thereof;
• drawing the precursor fibers to form drawn fibers, wherein the drawn fibers have a second average outer diameter, the second average outer diameter being less than the first average outer diameter;
• and
• heating the drawn fibers while the drawn fibers are under tension to substantially remove the polymer and to substantially convert the polymeric boron nitride precursor to boron nitride, thereby forming the composite fiber.