Study On Formation Mechansim Of PAN Precursor Spun From PAN/DMSO Solution By Dry-jet Wet-spinning Technology

There are large gaps in the properties and production of polyacrylonitrile (PAN) carbon fiber between our country and foreign countries. The precursor is regarded as the primary element responsible for these gaps. There are few reports about the science research for the national security. So it is urgent to clarify the formation of precursor in the behalf of better carbon fiber. The study of thermodynamics of PAN solution and of the relationship between the component concentration of fiber and the radial structure in fiber science should have been put more attention into. And the formation mechanism of PAN solution hasn't been made clear.This thesis would put some efforts on the study of thermodynamics of PAN/DMSO solution system. The Flory-Huggins interaction parameters were obtained with the experimental methods and theoretical ones. Thus the bimodal lines were calculated by Flory-Huggins polymer solution theory. Based on the simple growth rings model and the Fick diffusion law, the component concentration functions were evolved. And another method was tried through the solution of the second Fick diffusion law. The formation mechanism of PAN fiber was studied with the helps of SEM and AFM.Some useful results were gotten on the basis of thermodynamics of PAN solution system: the interaction parameters had an important effect on the position of bimodal line in the phase diagram; the more stronger interaction is, the nearer to the PAN-DMSO axis the bimodal line was; thebimodal lines were almost parallel to the PAN-DMSO axis; after associated by Boom function, it was founded that the obtained line would have a turn at some PAN volume fraction and the slope and intercept were different in different systems, which were all related with the interaction parameters; three methods about changing the initial component of spinning solution were obtained by the qualitative analysis so that the coagulation behavior would been adjusted.The mass transfer dynamics of diffusion is very important and some studies were tried to set up the component concentration functions. The polymer solution stream was divided as several growth rings and the concentration distribution along the fiber radius was evolved from the first Fick diffusion law. Another method was tried to solve the second Fick diffusion law. The diffusion coefficients were calculated by different theoretical functions. The diffusion coefficients were different from the calculated data, because PAN could hinder solvent and non-solvent in diffusion and the data were apparent. The analysis of the experimental results from Koji Terada showed that the apparent diffusion coefficients were influenced by the temperature, spinneret radius and coagulant concentration. The radius variation of fiber could have two effects, which were the variations of the diffusion surface and the diffusion gradient. The component concentration along the radius of fiber spun from PAN/DMSO solution was obtained with the use of calculated diffusion coefficients. And the results calculated from the two different mass transfer functions were similar with each other. The solvent concentration was of radial gradient and the solvent on the surface of fiber reached the equilibrium state instantaneously. The gel dynamics experiments showed that the gel formation law was similar with the other polymer systems, which wasrelated with dense surface under the soft coagulating condition and the thickening gel; the square of gel thickness was linear with coagulation time. The qualitative analysis of the surface puckers of fibers spun from wet spinning and dry-jet wet spinning was made. The positions where the die swell appeared were not the same and the die swell appeared at the air gap where the fiber would markedly been elongated and vary little in the coagulant, thus the surface of fiber spun from dry-jet wet spinning was more smooth. The radial component concentration gradient was responsible for the radial structure of PAN fiber spun from dry-jet wet spinning. The thicker surface with microvoid structure of...