During oxidative stabilization, the chemical structure, crystalline structure and morphological structure of dry-jet wet-spinning polyacrylonitrile fibers have great changes. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to systemically investigate the evolution of chemical structure, crystalline structure and fibril structure. The research suggests that the cyclization reactions of C=N proceed in the beginning when stabilization temperature is lower than 245 °C, and ON transforms into C=N and C=C conjugate structures. The crystalline structure changes obviously, and it can be concluded that the stabilization reactions take place in amorphous region at first and then extend to crystalline region as the stabilization progresses. The fibrils in polyacrylonitrile fibers and stabilized fibers of early stabilization stage were separated by the method of ultrasonic etching. But when temperature was higher than 240 °C, fibrils compactly combined with each other and no separated fibrils appeared.
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