Formation of interfiber bonding in electrospun poly(etherimide) nanofiber web

Electrospinning is a very useful technique to produce polymer nanofiber webs [1–10]. A pendant droplet of the polymer solution at the capillary tip is deformed into a conical shape under the electrostatic field. When the electrostatic forces overcome the surface tension, a charged jet is ejected. The jet moves towards a ground plate acting as an counter electrode. A thin polymer fiber is deposited on the counter electrode. Electrospun polymer nanofiber webs have different morphologies depending on the specific polymer properties. Most electrospun nanofiber webs do not have interfiber bonding. If electrospun nanofiber webs have interfiber bonding, the web will have stronger physical properties. In the previous work [5], we prepared and characterized electrospun poly(etherimide) (PEI) nanofibers. The electrospun PEI nanofiber web does not have interfiber bonding. In this study, we treated thermally the electrospun PEI nanofiber web to improve the physical property by introduction of interfiber bonding. Changes of morphology and tensile property of the electrospun PEI web with the interfiber bonding were investigated. ULTEM 1000 of General Electric Co. was used as poly(etherimide) (PEI). Its glass transition point is 225 ◦C. 1,1,2-Trichloroethane (TCE, bp = 110– 115 ◦C) of Aldrich Co. was used as the solvent. PEI of 14 wt% was dissolved in TCE. Pasteur pipette with 1 mm of diameter was used as the solution reservoir. A drum shaped counter electrode with a diameter of 220 mm was located below the reservoir. The winding drum was rotated at speed of 30 rpm during the electrospinning. The fibers were collected on aluminum foil covering the tubular layer. The distance between the tip of the capillary and the counter electrode (tip-tocollector distance, TCD) was 150 mm and the applied voltage was 15 kV. The electrospun nanofiber web was thermally treated at 80–240 ◦C for 1 h in a convection oven. The morphol-