Study Of Phase Separation Of Pan-dmso-h₂o Systems And The Forming Mechanism Of Pan Precursor

Due to their excellent performances, such as high strength, high modulus, good heat- and erosion- resistance, carbon fibers are widely used as reinforced fibers for various advanced materials in all kinds of fields. Especially, high performance carbon fibers are also widely used for construction, oil industry, ocean exploitation, auto industry, transportation and sports entertainment etc.There are large gaps in the properties of PAN-based carbon fibers between the homemade and foreign products. PAN precursors have been the key factor for producing high performance carbon fiber. The fiber-forming in the coagulation bath have obviously effects on the structure and properties of PAN precursors. However, the mechanism of the fiber-forming in the coagulation bath is not clear up to date, so it is very important to deeply investigate the fiber-forming mechanism in order to prepare high quality precursor. The fiber-forming is occurred in the coagulation bath both in wet spinning and dry-jet wet spinning, where the phase separation takes place, leading to the precipitation of the polymer and the formation of the fiber. If the coagulation conditions are different, the track followed by the phase separation is also changed and thus a variation in the structure and performance of the obtained precursors. Therefore, it is important to investigate phase separation behavior of PAN-DMSO-H₂O systems in the coagulation bath.In the paper, the phase separation behaviors of PAN-DMSO-H₂O systems are investigated with cloud point method and the phase diagrams of PAN-DMSO-H₂O ternary system at different temperatures are obtained, which can be used to guide the preparation of PAN spinning solution and the choice of the fiber-forming conditions for spinning PAN precursors with desired structures. There are few such research reports up to date.The results obtained were as follows:In determining of the compositions of cloud points, the method by titration had many advantages, such with high precision, low CV% and simple operation. Experimental cloud points in the accessible low polymer content range presented an ideal linearized correlation (R² >0.9936). According to the linearized correlation, higher polymer concentrations were extrapolated to produce a full ternary phase diagram at different temperature.The temperature and concentration of the coagulation bath solution and the composition of PAN spinning solution had obviously effects on the track of the phase separation and the structure and properties of the fiber. We can control the track of the phase separation by adjusting the composition of PAN spinning solution and the temperature and DMSO concentration of the coagulation bath solution in wet spinning and dry-jet-wet spinning.Wet spinning and dry-jet-wet spinning were concentrated and coagulated process. During these two coagulation processes, the route of phase separation would take into the two-phase region above the critical point where the PAN concentration is higher than that of the spinning dope; The closer the composition of the spinning solution is to the bimodal curve, the more rapid phase separation occurred, thereby producing the better structure and mechanical properties of the obtained as-spun fiber.