| Ionic liquids (ILs), as novel solvent for polyacrylonitrile (PAN), some progress has been madein research field in the past decade. Because of the cost and recycling of ILs, it is limited incommercial process. However, with the unique properties which are different from the normalsolvents, it is suggested that the spinning technologies of PAN solutions with ILs as solvent couldnot be considered as the traditional solutions. All the distinctive characters of PAN/IL solutionsimply that more work should be done on the spinning dynamics which would be helpful to thedesign of spinning technology.Firstly, the density and heat capacity of PAN/1-butyl-3-methyl imidazole chloride ([BMIM]Cl)solutions with different PAN concentration were measured by using dilatometry and differentialscanning calorimetry (DSC). The quantitative relationship between the density, heat capacity andtemperature was established by linear regression. The profiles development of diameter andsurface temperature in the air gap of PAN process were measured online. The heat transfercoefficient equation was established according to the relationship between the temperature andvelocity, cross sectional area of the filament.The dynamic model for dry-jet wet spinning of PAN/[BMIM]Cl solution had been establishedthrough the combination of experiment and calculation. Continuity equation was establishedassuming that the solution was incompressible fluid. Based on rheology properties of the solution,Phan-Thien-Tanner (PTT) model was selected to obtain the constitutive equation of shear andextensional flow. The dependence of viscoelasticity on the temperature was studied and thequantitative relationship between rheological parameters and temperature was formulated.Momentum equation was established by neglecting surface tension and energy equation wasestablished by ignoring the phase transition. The rationality and reliability of the model wasverified by comparing the computational results with the experimental data. Results showed thatgeneralized Newton model could not reflect the strong elastic behavior of polymer solutionaccurately. And it could not predict the die swell phenomenon when the initial boundary conditionwas set at the exit of the spinneret because the shear and extensional flow behavior of the solutionhas not been considered. While the PTT model with the initial condition set at the entrance of thespinneret could predict the die swell phenomenon better, and the calculated data of diameter andtemperature corresponded well with the experimental data.Finally, the influence of the parameters of spinneret (aspect ratio, entrance angle) and spinning process (draw velocity, length of air gap) on the spinning dynamic were discussed on the basis ofmodel optimization. Results showed that spinneret parameters mainly affected the flow conditionand die swell behavior of the solution within the spinneret orifice, while spinning technology hada profound influence on the die swell behavior and the movement of the filament in the air gap.With increasing aspect ratio, the overall pressure drop through the spinneret increased and the dieswell ratio dropped. By reducing the entrance angle of spinneret orifice, the vortex could beeliminated and die swell ratio also decreased effectively while the overall pressure drop rose. Thevelocity, temperature and stress between surface and core showed little difference along the spinline. With other spinning conditions kept constant, an increase in drawing velocity wasaccompanied by a broadening velocity gradient profile as well as a remarkable raise in itsmaximum value, which moved away from the direction of the spinneret orifice. Moreover, thestress became larger at high drawing velocity. The effect of the length of air gap on temperaturewas not significant. An increase of the length in air gap led to an increase in die swell but thedecrease in the diameter and stress of the filament indicated that a larger deformation could bepresented in the air gap by increasing this length. |
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