Paper Title
Strengthening of Electrospun Polymer Microfibers With Boron Nitride Nanotubes

Abstract
Boron nitride nanotubes (BNNTs) possess many extraordinary structural and physical properties and are promising fillers for light and strong polymer nanocomposite materials. The bulk mechanical property enhancement of nanotube-polymer nanocomposites critically depends on effective interfacial load transfer, which, however, is difficult to quantify in experiments. This is in part because the added nanotubes tend to aggregate and bundle because of strong inter-nanotube van der Waals interactions. These hard-to-avoid processing defects disrupt the intimate nanotube-polymer interfacial contact as well as nanotube alignment inside the composite, leading to lower reinforcement efficiencies. In this work, the mechanical properties of BNNT-reinforced polymethyl methacrylate (PMMA) nanocomposite microfibers are investigated with a focus on understanding how effective interfacial load transfer translates to bulk property enhancement. The BNNT-PMMA nanocomposite microfiber is manufactured with superior nanotube alignment using electrospinning techniques. The local interfacial load transfer characteristics are characterized based on in situ Raman micromechanical measurements. The effective interfacial shear strengths of 0.1%, 0.5%, and 0.65% BNNT-PMMA microfibers are found to be about 78.4 MPa, 60.9 MPa, and 50.7MPa, respectively, which commensurate with substantial improvements in Young’s modulus and tensile strength. The study reveals the constitutive contribution of the nanotube-polymer interfacial strength to the composite’s mechanical properties. The findings contribute to a better understanding of the process-structure-property relationship and the reinforcing mechanism of nanotube-based nanocomposites.. Keywords - Boron Nitride Nanotubes, Interfacial Load Transfer, Mechanical Enhancement, Polymer Nanocomposites