| Cellulose dissolves in N-methyl-rnorpholine-N-oxide (NMMO)/water directly without forming cellulosic derivatives. Then the solution is spun into fibers via special dry-jet wet spinning. This process is called Lyocell process. Lyocell fibers, made via Lyocell process, are of excellent properties, such as high dry strength, high wet strength, degradable, and the process is environmentally friendly and the solvent can be recycled. Owing to these advantages, Lyocell fiber is a promising substitute for the viscose fiber (Rayon), whose process pollutes the environment heavily.Nowadays, most of Lyocell fibers are spun from the cellulose pulp of the polymerization degree between 500 and 600, and their usage is limited in raiment industry. However, several properties of Lyocell fibers accord with the standards for the precursor of excellent carbon fiber, such as round cross section, homogenous structure, and high strength. So Lyocell fiber is the potential precursor of carbon fiber. Currently, only Thuringian Institute for Textil-und Kunststoff-Forschung(TITK) has done some research on this process and due to the military secret, little report is revealed. In China, only researchers from our group have done some research on this area.In the dissertation, research was proceeded concerning Lyocell fiber for the precursor of carbon fiber. The studies on the rheological properties of different cellulose/NMMO H2O solutions and with the presence of NH4Cl showed that these solutions were shear thinning solutions under our experimental conditions. The zero shear viscosity is proportional to the polymerization degree of the pulp. And with the increase of the polymerization degree, the elasticity of the solution and the structural viscosity increased accordingly, the viscosity was more sensitive to the change of the temperature, and the spinnability declined. With the increase of NHUCI, the zero shear viscosity and apparent viscosity of cellulose/NMMO H2O solutions increased. The dynamic rheology method is used to predict the molecular weight and molecular weight distribution of different cellulose pulps, and the results were validated by GPC and curammonium method.The research showed that using cellulose pulps of high molecular weight was an effective way to improve the strength of Lyocell fiber for the precursor of carbon fiber. Sothe degreased-cotton with DP=13 60 was selected and an orthogonal experiment was designed to optimize the processing conditions. Lyocell fibers of high mechanical properties were produced, the strength 8.95cN/dtex and the modulus 163.40 cN/dtex.In addition to cellulose pulps of high molecular weight, cellulose pulps of medium molecular weight modified by NEfyCl could also be spun into Lyocell fibers with good mechanical properties. However, the modification effect was influenced by the properties of cellulose pulps, cellulose concentration in solutions and the amount of NHUCl.Wide-angle X-ray diffraction and Polarizing Microscope were used to investigate the structure of different Lyocell fibers. The results illustrated that under our experimental conditions, with the increase of drawing-down ratio, the overall degree of orientation and crystalliniry increased. Besides, the addition of NH4Cl caused the crystallinity and orientation of modified Lyocell fibers to rise, and thus the fibers' mechanical performance improved as well. The surface of Lyocell fiber was smoother than that of Rayon, and the cross section was round, so the morphology and the structure of Lyocell fibers were closer to the standards for the precursor of carbon fiber.Zhang Songjie Major: Material Science Supervised by Prof. Shao Huili...
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