Aggregate states of PAN in the process of fiber formation

Changes to the crystalline state and orientation texture of PAN fibers during coagulation, wet-drawing, hot-drawing and the drying densification stage were studied by XRD, SEM and acoustic velocity measurements, from which the evolution of PAN aggregate state in the fiber formation process was derived. Results showed that the crystalline state of PAN, which could be described as two-phase with distinct pseudocrystalline (ordered) and amorphous (disordered) phases, was largely produced during the coagulation stage, and the orientation texture was mainly controlled by wet-drawing and hot-drawing. The former plays an important role in the crystalline perfection, while the effect of the latter is to improve the degree of orientation. The drying densification process favors the growth of pseudocrystalline regions while consolidating the orientation texture.