High crystallinity BN fiber derived from organic–inorganic hybrid BNNS/polyborazine precursor

Employing inorganic nanofillers as reinforcements to modify the mechanical and electromagnetic properties of organic materials has been documented to be an extremely efficient method. Herein, an inorganic BN nanosheet (BNNS) was employed to promote the mechanical performance and optimize the crystal structure of ceramic BN materials. First, spinnable hybrid BNNS/polyborazine precursors with different mixing ratios were synthesized by high-temperature polymerization. The exfoliation and amine-functionalization of BNNSs were achieved by ball milling before they were doped into pure borazine monomer (PMAB) through a deamination reaction. The results demonstrate that the dopant of modified BNNS (aBNNS) promotes the ceramic yield of hybrid precursors (up to 66.3%) without destroying fiber spinnability. HP-0.05% shows optimal spinnability with low flow activation energy (1.04 kJ/mol). The finest diameter of green fibers spun by them could reach 5.61 µm, with a smooth and integral surface. Then the influence of aBNNS on the fiber micro-structure and mechanical performance was also measured. It is found that aBNNS benefits the improvement of fiber density (from 1.6 to 2.0 g/cm 3 ), and significantly enhances the crystallinity from 66.65% to 94.28%. Thus, the strength is increased by nearly 60% (up to 1.2 GPa) and the Young's modulus is increased by about 72% (up to 125.0 GPa). The incorporation of trace BNNS offers new insight and potential for the preparation of high-performance BN fibers.