The Mechanism Of Dry-Jet Wet Spinning Of Pan Based Carbon Fiber And Its Computer Modeling

Carbon fibers of high strength and high modulus have been developed as new advanced materials since 1960s, which can be compounded with resin, metal, ceramics and glass. Carbon fibers have some particular properties such as anti-fatigue, anti-erode and light weight etc., which have been widely used in the fields of aviation, spaceflight, navigation, chemical and electronic industry. Carbon fibers have been the high technology fibers in the fiber industry. Carbon fiber can be made by carbonization in the high temperature from fibers of rayon, PAN and pitch. With the rapid technology development, PAN-based carbon fibers become the main role in the carbon fiber industry. Researchers in home and abroad show no difference that the precursors of carbon fiber must be of high purity, high strength, high compactness and uniformity of structure if we want to obtain the outstanding properties of carbon fibers.In this paper, based on the PAN/DMSO/H₂O system, mathematic models are established to analysis the influence of different processingparameters. When modeling the dope flowing in the spinneret channel, the distribution of dope velocity in radius can be obtained. From the results, we find that the velocity attains the maximum at 0.6R and the shear stress attains the maximum at 0.76R. The shear force of exterior layer is much larger than that of the interior layer. In the modeling the rheology of PAN dope, firstly the Klevin model is used to simulation the viscoelastic dope. Using math software MatCAD to solve the partial difference equations, we can figure out that how the velocity, force and diameter of the dope changes at the different swell ratios and different apparent elongation ratios.In addition, thermodynamic theory is firstly applied to calculate the bimodal line and spinodal line of the PAN/DMSO/H2O system and the ternary phase diagram is obtained. According the phase diagram, the fiber formation route can be tracked. Firstly we estimate the total gelation time in the coagulation bath. Then with the help of computer, the numerical solution of the Fick diffusion equation can be solved by finite element method.Finally we discuss the mechanism of formation for skin layer and hole. After the polymer solution stream immerges into the coagulation bath, the interface between coagulation solution and polymer solution is influenced by the mass transfer. The composition is changed, then due to phase separation , the dense phase and thin phase appear. Because the thinphase is compatible with the coagulation bath, the dense phase is left in the interface only. If the concentration of nonsolvent in dense phase is not over the critical concentration of gelation, the dense phase will be extended. Thus the uniformity skin will form. The thin phase in the interface layer is the beginning of hole, some of them will be disappear in the post heat treatment.