The Extrusion Molding Process And Rheological Properties Of PAN/DMSO Solution

Carbon fiber is a kind of new-style material with a series of excellent performances, such as high tenacity, high modulus, heat-resistance, corrosion resistance and so on. As a kind of reinforcing fiber of advanced material, it is widely used in all fields. Polyacrylonitrile(PAN) fiber is one of the industrial synthetic fibers. Among the precurors available for producing carbon fibers, PAN fiber is the most commonly used and promising precursors. Now, it is popularly accepted that the quality of high-performance carbon fibers depends mainly on the structure and quality of the precursor fibers.In this thesis, high molecular weight was added into PAN/DMSO solution, and the PAN precurors were obtained by means of dry-jet wet-spinning technology. The static and dynamic rheological behaviors of PAN/DMSO solutions and the mechanical properties and crystallinity of PAN precurors have been investigated respectively by using a cone-plate rheometer. The thesis mainly deals with the properties of precurors, the rheological behavior and Spinnability of spinning solutions with the addition of high molecular weight PAN.By polymerizing solution, the preparation of polymers of high molecular weight polyacrylonitrile process has been explored at low conversion by means of investigating the three parameters, the first monomer (AN) concentration, the second monomer (IA)concentration, polymerization temperature. It is the basis of high molecular weigh reinforcing ordinary molecular weigh of polyacrylonitrile spinning solution. To obtain the highest conversion rate, AN concentration was 45%; the IA concentrations was 0; the polymerization reaction temperature was 70℃. Maximum viscosity average molecular weight can be obtained when AN concentration was 40%, the IA concentrations was 0; the polymerization reaction temperature was 50℃.The Static and Dynamic Rheological Behaviors of PAN/DMSO solutions have been investigated respectively by using a cone-plate rheometer. The results showed that, the spinning solutions exhibited a shear thinning non-Newtonian fluid. The spinning solutions showed shear thinning at high shear rates. The viscosities of the solutions decreased with the rising of the temperature at low shear rate. The viscosities of the solutions increased by adding high molecular weight PAN; and it appropriately reducedα/ηeffectively, thus improving the spinnability and enhanced the spinning stability. The slight increase of storage modulus G' would not affect the spinnability, but should be controlled in a suitable scope.The PAN precurors were obtained by means of dry-jet wet-spinning technology. The fiber morphology, structure and properties were studied in detail. The results showed that, with the increase of the ratio of length to diameter (L/D) of spinneret hole and the draw down ratio, export swell effect became weaker. The cross section of spun fibers obtained through dry and wet spinning process is kidney-shaped. The greater height of air gap contributed to the orientation of PAN molecule polymer under the action of drawing, and the proper height is 3mm. With the increase of the ratio of length to diameter (L/D) of spinneret hole, the fiber breaking strength increased significantly.10 times more than the total draw ratio, the draw ratio increased and fiber strength decreased. When 5-8 times, the strength greatly improved. There exists a most appropriate tension between 8 to 10 times. While L/D increases, precursor crystallinity increases slightly. With the increase of second boiling water draw ratio, the fiber crystallinity and grain size in the fiber axial direction have been greatly improved.