Effect of Nanofiber Orientation and Annealing on the Structure and Properties of Polyimide Nanowebs

Polyimide (PI) nanowebs were prepared by imidization of their precursors, polyamic acid (PAA) nanowebs, fabricated by electrospinning with various process variables, and then subjected to an additional hot drawing process. Their random and uniaxial morphologies of PAA and PI nanowebs could be formed by controlling the collecting roller speed of electrospinning apparatus. The SEM image of the PI nanoweb showed that high collecting-roller speed and hot drawing effectively aligned the nanofibers in the PI nanowebs. Wide-angle X-ray diffraction (WAXD) analysis was performed to investigate the crystalline orientation of PI in the nanowebs and confirmed that annealing highly-aligned PI nanowebs imparted enhanced crystallinity of PI nanowebs. We were able to increase the tensile strength of the PI nanoweb from 28.6 MPa to 58.4 MPa by raising the collecting roller speed from 250 rpm to 1500 rpm and increased to a maximum of 83.2 MPa through an additional hot drawing at 400 °C for 30 min.