The Formation Of Orientation Structure Of Pan Nascent Fiber During Dry Jet Wet-Spinning Process

The formation of orientation structure of PAN nascent fiber during dry jet wet-spinning process was investigated in this thesis. By dividing the dry jet wet-spinning process into four stages, such as solution, shearing by flowing, stretching in the air layer and the coagulation. The evolution of the morphology of PAN molecular chains was clarified in detail. Based on the experimental analysis of wide angle X-ray diffraction (WAXD), differential scanning calorimeter, acoustics velocity method and rheometer methods, the results indicated that,(1)In PAN/DMSO solution, the macromolecular chains were randomly distributed in the solvent as coil state. The wrapping of the chains was influenced by temperature and concentration as well as the shear rate.(2)While the PAN/DMSO solution flowing across, the nuzzle the unwrapping of molecular chains was occurred with the shearing force and forming a kind of pre-ordered structure.(3)During the stretching process in the air layer, the molecular chains were extended and the physical crosslink was weaken by the axial stretching although the entropy elastic recovery was there. The orientation structure was improved.(4)With the increasing of drawing ratio, the orientation factor of the dry jet wet-spinning nascent fiber gradually improved. At the same drawing ratio, compared with the nascent fiber made by wet-spinning, the orientation factor of the nascent fiber produced by wet-spinning is higher. During the dry jet wet-spinning process, the coagulation bath concentration can affect the Hermann orientation factor. In addition, tensile force is conducive to improve the amorphous orientation factor.Based on the experiment results, from the viewpoint of molecular motion, the model for describing the evolution of the aggregation structure of PAN molecular chains was proposed both in wet-spinning and dry jet wet-spinning processes.