Segmented poly (urethane-urea) (SPUU) fibers such as spandex fibers are usually produced by dry spinning process. The processing conditions for dry spinning of SPUU can be optimized by computer simulation.
In this work, a simulation model is proposed for the dry spinning process where the SPUU dope in the liquid state is first extruded from the nozzle in the shape of spinline, then the solvent in the spinline is removed by the blowing of hot gas while elongated, and finally a few spinlines come to a fiber in the solid state after they are twisted. The deformation behavior, solvent concentration, temperature of spinline and so on can be predicted with this model.
Governing equations composed of the equations of continuity, motion, energy, rheology and deflection were derived under the assumption of Newtonian fluid. Simulations for dry spinning process were carried out with various diffusion coefficients previously reported for two kinds of solvents (dimethyl formamid (DMF), dimethyl acetamide (DMAc)) and three measurement methods of diffusion coefficients (Moiré pattern, Film and Dope methods), where Moiré pattern method gives the mutual diffusion coefficient for the liquid-liquid system, Film method gives the diffusion coefficient of solvent into the film which changes from the solid state to the semisolid state during measurement, and Dope method gives the diffusion coefficient of solvent from the dope which changes from the liquid state to the (semi-) solid state during measurement.
The temperature distribution in the spinning chamber was linearly approximated in the distribution close to a practical plant. The simulation model can predict the residual solvent concentration, temperature, cross sectional area, spinning stress and deflection of spinline.
The simulation results denoted that the change of solvent concentration is mainly determined in the hot gas zone even if the diffusion coefficients are different. Therefore, the deformation behavior of spinline is chiefly governed in the hot gas zone. And there is little change found in the interim zone and blowing zone.