Effect of mesophase pitch/polyacrylonitrile mixture as the core‐layer on the interphase region structure of coaxial polyacrylonitrile/mesophase pitch composite fibers

Abstract

AbstractCoaxial composite fibers with a cortex of polyacrylonitrile (PAN) and a core layer of mesophase pitch (MP) and PAN have been prepared by the wet spinning method, formed in a mixed solution of N,N‐dimethylformamide and deionized water to optimize the composition of the core‐layer mixture. The XRD curves of the PAN/MP coaxial composite fibers only showed the crystalline and amorphous diffraction peaks of PAN. With increasing MP mass fraction in the mixed PAN/MP solution, the crystallinity of the coaxial composite fiber gradually decreased from 27.95% to 26.21%, because MP intermixed between the PAN macromolecules, weakening the interaction between the PAN molecular chains. In the core layer of the coaxial composite fibers, spherical MP particles were dispersed in the network structure of PAN. Different proportions of PAN/MP mixed solution will result in different core structure. The coaxial composite fiber consisted of a core layer with a low gray value, a transition layer with increasing gray value, and a cortex with a high gray value. From the core layer to the cortex, taking Group C as an example, the C content gradually decreased from 68.64% to 61.23% and the N content gradually increased from 13.68% to 22.19%, which was consistent with the gradual decrease of the MP content and the gradual increase of the PAN content. Gray‐value analysis, micro‐region EDS, and SEM showed that a transition layer structure formed at the junction of the cortex and core layer. The size and amplitude of the transition layer were related to the viscosity of the mixed PAN/MP solution, and high MP content in the mixed PAN/MP solution was conducive to formation of a stable and good interface structure.