Study On Formation Mechanism Of PAN-Based Carbon Fiber Precursor In Wet-spinning Process Computer Modeling

PAN-based carbon fibers have some excellent properties,such as high strength, high modulus,heat-resistance and anti-erosion ect.,which have been widely used in the fields of spaceflight chemical and engineering industry.There are large gaps in the properties and production of PAN-based carbon fiber between our country and advanced foreign countries.The precursor is regarded as the primary element responsible for these gaps.There is few reports about the science research for the patents.So it is urgent to clarify the formation mechanism of precursor which is significant to our carbon fiber industry.In this paper,the spinning solution's shear and tensile flowing are studied and the radial distribution of dope velocity,shear stress and shear force are obtained.The constitutive equations of Newtonian fluids and Non-Newtonian fluids are used to describe the distribution of velocity during the precursor's tensile and the modeling results show that the acceleration is decreased with the increasement of the velocity.The phase separation happened in coagulation bath is very important for PAN-based carbon fiber precursor.On account of importance of interaction parameters between components for the phase separation,it is necessary to study on interaction parameters.Based on PAN/DMSO/water system,thermodynamic theory is applied to calculate the system's phase diagram.The key process of the diffusion interchange in coagulation bath determines the structure formation and the properties of PAN fiber and this process is affected by the existence of 'skin-core' structure.With the help of computer,the numerical solution of the Fick diffusion equation is solved by finite element method and the distribution of water on the precursor cross-section is obtained.Base on the equation of gel layer increasing,we disclose the linear relationship between the gel layer's increasement and the concentration of water on the precursor cross-section.During tensile process. the rheological behavior is determined mostly by the 'skin'.Based on the experimental data,a 'skin-core' model is established to describe the affect of 'skin-core' structure's during the tensile process.Through this model,we can draw conclusions as follows:the low concentration of coagulant near the spinneret will help increase the spinning velocity because of the fast formation of 'skin' and can increase the stretching rate as well since the dope's tensile viscosity falls.