The Preparation And Charateristics Of Ultrahigh Molecular Weight Polyacrylonitrile And Solution For Carbon Fiber

Polyacrylonitrile-based carbon fiber is one of the most widely used and promising carbon fibers. As the precursor of PAN-based carbon fiber, the quality of PAN precursor determines the performance of final carbon fiber to a large extent. PAN molecular weight is an important factor affecting the quality of the PAN precursor, the preparation of ultra-high molecular weight polyacrylonitrile is imminent.In this thesis, the weight average molecular weight over1.5million acrylonitrile-itaconic acid copolymers were prepared by the water phase suspension polymerizations. Shear and extensional theological measurements of spinning solution adding the copolymers were executed and the extensional performance of gel films, prepared by the spinning solution, was researched.First, the effect of polymerization technologies on weight-average molecular weight and conversion rate were researched in the polyacrylonitrile-itaconic acid water phase suspension polymerizations which were initiated by azobisisobutyronitrile. The composition, thermal properties and crystallinity of copolymers were characterized. The results indicated that the molecular weight of copolymer increased with the increase of AIBN content, monomer concentration and duration of reaction, and decreased when the content of IA in the monomer and temperature of polymerization increased. The conversion rate of copolymerization monomer increased with increasing concentration of AIBN, monomer content and duration of reaction, and decreased when content of IA in the monomer was increased. In addition, copolymer molecular weight and the conversion rate increased with the PVA content increases first and then decreasing. Introduction of IA can effectively moderate the exothermic of PAN polymers, but the crystallinity of copolymer decreased in the presence of IA. Ultrahigh molecular weight polyacrylonitrile copolymers and medium molecular weight polyacrylonitrile were uniformly dissolved in dimethyl sulfoxide to obtain the spinning solution and the shear rheological behavior of the solution was executed. It was found that the solution exhibited shear-thinning. Both elastic modulus and viscous modulus increased with frequency and decreased with temperature. Complex viscosity of the solution decreased with the increase of frequency and temperature. The existence of a small amount of UHMWPAN represented little influence on the homogeneity and polydispersity of PAN solutions.Finally, the effects of UHMWPAN on the extensional rheological behavior of PAN solutions were investigated, and the factors affecting the tensile properties of the gel films were also analyzed. The results testified that PAN solution containing a small amount of UHMWPAN had stronger strain hardening, which helps to increase the jet stretch ratio in spinning. Gel films prepared from the solution with a lower concentration of UHMWPAN copolymers could bear a higher multiple of second-stage tensile draw than those prepared with higher UHMWPAN concentration, in a certain temperature, after extruded to an extrusion draw radio of16, and tensile modulus and strength of the gel film were better.