The polyacrylonitrile (PAN) fibers undergo three different thermal stabilization processes: complete cyclization in nitrogen, one-step direct oxidation and complete cyclization in nitrogen first and then oxidation in air. The oxygen content is used as the evaluation standard for the degree of pre-oxidation and the fibers with the similar oxygen content obtained by the one-step method and the two-step method are compared. The fibers completely cyclized in nitrogen are used as the reference. TGA, FTIR, XPS, and SEM are used to analyze the thermal stability, structure, and morphology of the three stable fibers. Some differences in the structure of the two-step method and the one-step method are found, but they have no major impact on the final carbon fibers properties, and the two-step method can effectively shorten the time required for the pre-oxidation process. In short, pretreatment in nitrogen can improve the stabilization efficiency of PAN fibers, which is conducive to the production of low-cost carbon fibers and the promotion of the application of carbon fibers.
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