Effect of the polyacrylonitrile mass fraction on the structure of coaxial polyacrylonitrile/mesophase pitch composite fibers

Abstract

AbstractTo minimize structural heterogeneity during graphitization of polyacrylonitrile (PAN)‐based carbon fibers, the present authors prepare coaxial composite fibers with PAN as the skin and a PAN/MP mixture as the core by wet spinning with coaxial spinning needles. With increasing PAN mass fraction in the skin‐layer solution, the crystallinity of the coaxial composite fibers increases from 24.3% to 31.4%, and the crystal plane spacing of the coaxial composite fibers decreases from 0.529 to 0.523 nm. The tensile strength of the coaxial composite fibers increases by 122%, attributable to the crystallinity increase from 24.3% at 10 wt% PAN to 31.4% at 15 wt% PAN. Scanning electron microscope images of the coaxial fibers demonstrate that the cortical region changes from a porous, loose structure to a less porous, denser structure. Gray value testing of the coaxial composite fibers shows that transition layers formed at the interface between the cortex and core layers, which was formed for the outward diffusion of the core‐layer MP and PAN mixed solution. With increasing PAN mass fraction, because of the high viscosity of the cortical PAN solution, diffusion of the core‐layer mixed solution to the cortical layer decreases, resulting in a 75.2% increase in the core area ratio of the coaxial composite fibers.