Research On The Key Technology Of Polyarcylonitrile Shaped Fiber Preparation Based On Dynamic Simulation

China’s polyacrylonitrile carbon fiber production capacity is in the global leading position,but the overall carbon fiber products are still in the middle and lower reaches of the level,and the high-end carbon fiber is still monopolized by Japan and the United States.Polyacrylonitrile shaped fiber can be prepared with excellent properties such as light weight,thin thickness,high strength and good wave absorption.Dry-jet wet spinning is one of the main methods for the preparation of polyacrylonitrile fiber,however,due to the many and complex factors affecting the spinning and forming process of shaped fiber,the shaped spout hole size structure parameters and spinning process parameters interact,the circular fiber spinning kinetic model is difficult to apply to the shaped fiber forming process,which restricts the development of polyacrylonitrile shaped fibers.Dry-jet wet spinning is one of the main methods to prepare polyacrylonitrile fibers,however,due to the number and complexity of factors affecting the spinning and forming process of heterogeneous fiber,shaped spout hole size structure parameters and spinning process parameters interact,circular fiber spinning kinetic model is difficult to apply to the shaped fiber forming process,which restricts the development of polyacrylonitrile shaped fiber.This paper investigates the key technologie for the preparation of polyacrylonitrile shaped fiber based on kinetic simulations,mainly including the following:First,the density and specific heat capacity of the polyacrylonitrile polymer solution are measured by volume expansion method and differential scanning calorimetry,respectively,and the steady-state and dynamic rheological properties are tested for the polyacrylonitrile spinning stock solution at temperatures from 30°C to 70°C using the rheological method.It was found that:the density of the solution decreased from 1.12g/cm³ to 1.07 g/cm³ when the spinning solution is warmed up from 30°C to 70°C,and the specific heat capacity of the solution increased from 1.84 J/g·°C to 1.99 J/g·°C.The relaxation time of the solution decreased from 0.53 s to 0.09 s when Spinning solution temperature is increased,and the viscoelastic transition point of the solution system shifts from 158 rad/s to 400 rad/s.The viscoelastic transition can occur at a smaller shear rate,and the viscous flow activation energy E_ηis 29.12 k J/mol calculated according to the Arrhenius equation.Then,based on the polyacrylonitrile fiber solution dry-jet wet spinning kinetic model,the effect of the entry angle,micro-hole depth,micro-hole cross-sectional size,inlet flow rate and spinning temperature of the trilobal spinneret on the flow and extrusion of polyacrylonitrile spinning solution was explored through simulation calculations,and the trilobal spinneret size structure parameters were optimized to provide parameters for the spinneret cap processing.The results show that:the pressure of the solution that extrude normally from the trilobal spinneret is around 6.0 MPa;the vortex phenomenon can be eliminated when the inlet angle of the spinneret is set at 30 45;the spinning temperature is 40°C and the flow rate is 2.72×10^-9m³/s,the spinning solution is extruded normally,no diffuse flow phenomenon and silk strip adhesion phenomenon,good spinnability;The optimized structural parameters of the trilobal micropore are 0.45 mm in depth,0.6 mm in leaf length and 0.1 mm in leaf width.Finally,the changes of the trilobal fiber surface temperature and fiber cross-section in the air section were measured online,and the equation of the heat transfer coefficient of the trilobal fiber in the air section in dry and wet spinning was corrected by inverse fitting.Numerical simulations were used to optimize the spinning process parameters,and the results showed that when the length of the air section was about 30 mm and the draft ratio was within 3 times,the filament could complete the deformation before entering the coagulation bath.The anisotropy of the virgin fiber under different coagulation bath conditions was investigated by experimentally varying the coagulation bath temperature and concentration,and it was found that the smallest fiber anisotropy was prepared at 10°C coagulation bath temperature and 70%coagulation bath concentration,and the largest fiber anisotropy was prepared at 30°C coagulation bath temperature and 10%coagulation bath concentration.