Study on the coagulation mechanism of wet-spinning PAN fibers

The mechanism of coagulation process of polyarylonitrile (PAN) wet-spinning was studied based on the numerical analysis of the coagulation of viscous polymer solution by diffusional interchange with a bath. Experiments were performed in order to determine the diffusion coefficient of solvent and non-solvent. The numerical solutions of Fick's second law equations for diffusion were obtained by using the MOL method. The microstructure of nascent fibers is investigated by Transmission Electron Microscope (TEM) and Electron Probe Microanalyser (EPMA). It is found that the speed of outflow solvent is more rapid than that of influent non-solvent. The speed of concentration change of solvent and non-solvent is rapid in outside layers of filament (0.2R) and slow in inner layers. The solvent concentration is keeping a high value at the center of filament. TEM and EPMA show that the microstructure is a typical layered structure. The thickness of dense skin is about 0.2R. The core region of fiber is very loose.