Structure evolution in all-aromatic, poly(p-phenylene-vinylene)-derived carbon fibers

Carbon fiber (CF) structure is strongly influenced in terms of CF's crystallinity, crystallite dimensions, orientation, and interlayer spacing by the structure of the CF precursor, including its sp2/sp3 carbon content, and the process parameters for spinning, oxidative stabilization, and carbonization/graphitization. In order to retrieve information about structure formation in all-aromatic CF precursors, poly(p-phenylene-vinylene) (PPV) fibers have been prepared through dry spinning of a sulfinyl-based precursor polymer followed by thermal conversion into PPV. By applying different stretch ratios, different degrees of orientation were realized. Subsequent thermal conversion of these PPV fibers into CFs with and without additional tension during carbonization allowed for following structure formation in the final CFs. Wide-angle X-ray scattering and Raman data were recorded at different stages of carbonization and compared to those of a poly(acrylonitrile)-derived CF as well as to lignin- and cellulose-derived CFs. Structure formation during carbonization was correlated with the sp2/sp3 carbon content of the CF precursors. The all-sp2 carbon precursor PPV was found to favor crystallite growth in the direction of the CF axis, parallel to the individual graphite planes, and formation of ordered graphitic structures at an earlier stage and to a higher extent than in high-/all-sp3 carbon precursors.