Study On The Dry-Wet Spinning Of High Concentration Pan/Dmso Solution

Carbon fiber is a kind of high-technology fiber material with a series of excellent performances, such as high modulus, high intensity, corrosion resistance, heat resistance and so on. Polyacrylonitrile (PAN)-based carbon is the most widely used carbon fiber and its integrated performance is the best. The performance of PAN-based carbon fiber is determined by the quality of PAN precursor fiber to a large extent. At present, PAN-based carbon fibers fabricated domestically are generally at low quality level compared with those produced by some developed countries. However, the low-quality PAN precursor fibers are the major bottleneck to restrict the improvement of PAN-based carbon fiber. The primary task is to improve the quality of PAN precursor fiber. In this dissertation, intermeshing co-rotating twin screw extrusion was used to prepare high concentration PAN/DMSO spinning solution. In order to prepare high quality PAN precursor, high solid content PAN precursor was prepared by dry-wet spinning and its structure and performance were studied.In the steady shear rheology test, the changes of viscosity of PAN/DMSO spinning solution with shear rate at different concentration and different temperature were studied. By fitting shear rate-viscosity curves, the zero shear rate viscosity of spinning solution at different concentration could be calculated which indicated that the temperature had a limited effect on the viscosity of PAN/DMSO spinning solution. When the temperature was beyond a certain value, the change of viscosity with temperature was little. The flow activation energy of PAN/DMSO spinning solution at different concentration were calculated through Arrhenius equation. Results indicated spinning solution had high flow activation energy and strong sensitivity to temperature at high concentration and low shear rate. In the dynamic shear rheology test, the viscoelasticity transformation of higher concentration PAN/DMSO spinning solution appeared at lower shear rate. However, the elastic property of spinning solution made a distinct extrusion swell which was adverse to the stability of spinning. The shear rate should be decreased properly to reduce the elastic property of spinning solution at high concentration.Intermeshing co-rotating twin screw extrusion could solve a series of problems in preparing high concentration PAN/DMSO spinning solution for its excellent processability of polymer, such as dissolution and deaeration. The intensive shear of the kneading block could dissolve PAN sufficiently. Moreover, the viscosity of high concentration PAN/DMSO spinning solution could reach the standard of dry-wet spinning by sufficient shear. The optical microscope images of the spinning solution deaerated and not deaerated indicated that intermeshing co-rotating twin screw extrusion was effective to the deaeration of PAN/DMSO spinning solution.SEM, mechanical tests, WAXD, optical microscope were conducted to characterize the structure and properties of different solid content PAN precursor. Results showed that the compactness of high content PAN precursor was better and the grooves in the surface was fewer. However, due to its large diameter more stretch ratio would be required to reduce its fineness. Through the boiling water stretch analysis of different solid content PAN precursor, high solid content PAN precursor had greater stretch ratio whose breaking strength, crystallinity, orientation, grain size were larger and the property of the precursor was better.