Effect of nitrogen pretreatment on the skin-core structure of thermal oxidative stabilization polyacrylonitrile fibers

摘要

Polyacrylonitrile precursor was pretreated under nitrogen to study the effect of the extent of cyclization of pretreated fibers on the chemical structure, crystal structure and skin-core structure of thermal oxidative stabilization (TOS) fibers. Based on the FTIR spectra, the cyclization degree of pretreated fibers was quantitatively calculated by a combination of peak-fitting and second-derivative operations. Combining the results of wide-angle X-ray diffraction, Raman spectroscopy and scanning electron microscope analysis, pretreatment was beneficial to increase the cyclized structure of TOS fibers, but inhibited the oxidation reactions in the TOS process. As the increase of cyclization degree of pretreated fibers, the oxygen content and crystal size of TOS fibers decreased and the crystal interplanar spacing increased; in the skin layer of TOS fibers, the I-D/I-G ratio increased and brittle fracture area decreased. When the cyclization degree of pretreated fibers was in the range of 10%-35%, the skin-core structure of TOS fibers was weakened, which demonstrated that proper pretreatment before TOS process can improve the skin-core structure.