Hot-pressed electrospun PAN nano fibers: An idea for flexible carbon mat

Fibers on the nano scale are characterized by its high surface area per unit mass which is associated with high surface free energy. It seems to be an interesting idea to take advantage of this high free surface energy in electrospun in-plane randomly oriented (quasi-isotropic) multi-layered PAN fibrous mat by stabilizing the as electrospun structure at 220 degrees C under suitable pressure in oxygen environment; such treatment not only activates its high surface energy but also allows the contribution of larger number of molecules on the nano fiber surfaces as well as enhances the bonding between fibers. Mechanical examination of the hot pressed electrospun PAN Nano fibers mat showed higher flexibility than commercial carbon fiber as well as 2-D structure that can be advantageous in applications where the forces are equal in all directions and no specific orientation are required. Stress-strain curves of the hot pressed electro-spun PAN mats showed ductile behavior. The absolute values for tensile strength ranged from 55 to 63 MPa similar to some ductile pure metals such as aluminum, with much larger strain (6.5-8.25%). The modulus value for the fabric was found to be a measure for the enhanced surface free energy (nano size bond) and not the measure for single nano fiber properties, which was proved by preliminary examination for the fracture pattern of the fabric mat. This revealed de-lamination between the mat's layers breaking the bond in between within a value approximately equal or slightly larger than the modulus for bulk PAN polymer (2.80-3.04 GPa) with measured Poisson's ratio of 0.33. Raman analysis for the hot pressed samples showed a formation of disordered carbon structure at 1360 cm(-1) and ordered carbon structure at 1580 cm(-1). (C) 2008 Elsevier B.V. All rights reserved.