Beyond Percolation Threshold Loading of Polyacrylonitrile Electrospun Nanofibers with Boron Nitride Nanotubes for Use in High-Temperature Composites

Boron nitride nanotubes (BNNTs) have unique thermomechanical properties that make them excellent candidates for use in structural heat resistant composites, but their usage has been limited in the past due to difficulties associated with dispersing the material into a usable configuration. Techniques to facilitate dispersion into solution, such as functionalization and surface activation of the BNNTs, alter and degrade desirable properties of the material, and high surface energies of BNNT make it difficult to obtain sufficient concentrations to take advantage of those properties by using conventional mixing techniques. This research demonstrates homogeneously dispersed electrospinning sol–gel solutions of up to 20 wt % unfunctionalized boron nitride nanoparticles (BNPs) and BNNTs in polyacrylonitrile (PAN) by using a novel high g-load mixing technique. It confirms that the BNPs and BNNTs influenced bulk PAN properties such as glass transition temperature (Tg) and tensile strength. It also indicates that the BNNTs were loaded beyond the percolation threshold, and the load-bearing structure of the electrospun composite transitioned to a stable core of interconnected nanofiller due to increasing levels of boron nitride present. This was evident by the increase in tensile strength of the composite and in the creation of a stable mat of interconnected BNNTs after PAN pyrolysis. The research highlights the advantages of utilizing unfunctionalized material and points to the success of high g-loading as a viable mixing technique for high weight percentage of unfunctionalized BNNTs.