Mechanical Characterization of Electrospun Boron Nitride Nanotube-Reinforced Polymer Nanocomposite Microfibers

Boron nitride nanotubes (BNNTs) possess many extraordinary structural and physical properties and are promising fillers for reinforcing polymers towards lightweight and high-strength nanocomposite materials. The interfacial load transfer in the bulk nanotube-reinforced polymer composite plays a critical role in property enhancement but is difficult to characterize quantitatively. This is in part because the added nanotubes are prone to aggregate and bundle due to inter-nanotube van der Waals interactions. These hard-to-avoid phenomena disrupt the seamless nanotube-polymer interfacial contact as well as nanotube alignment inside the composite, which decreases the bulk property enhancement. Here, we investigate the mechanical properties of electrospun BNNT-reinforced polymethyl methacrylate (PMMA) nanocomposite microfibers. The viscous force in the electrospinning process facilities the nanotube alignment, which is quantitatively characterized by using polarized Raman spectroscopy techniques. The local load transfer on the BNNT-PMMA interface inside the nanocomposite microfiber is characterized based on <i>in situ</i> 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 correspond to substantial improvements in Young’s modulus and tensile strength. The study reveals the constitutive role of the nanotube-polymer interfacial strength in the composite’s mechanical property enhancement. The findings contribute to a better understanding of the process-structure-property relationship and the reinforcing mechanism of nanotube-based nanocomposites.