Acid for Catalytic Polyesterification Simulation for Dry Spinning Process with New Logistic Method of Diffusion Coefficient Dependent on Solvent Concentration and Temperature

摘要

The optimum dry spinning conditions for segmented poly(urethane-urea) (SPUU)-solvent (dimethylacetamide (DMAc)) system, are very important for improvement of the productivity. But it is very difficult to find the optimum conditions by experiments. Therefore, it is desired to be predicted dry spinning process by computer simulation.In the previous works, the diffusion coefficient obtained by the Moiré pattern method has been used for simulation of dry spinning process. The diffusion coefficient gives mutual diffusion for the liquid-liquid system. So, the method cannot cover whole dry spinning process from the spinneret (liquid state) to the take up position (solid state). The state of spinline continuously changes with both solvent concentration and spinline temperature from liquid to solid in a practical process. The state transition points from liquid to semisolid and from semisolid to solid depend on both solvent concentration and temperature. In order to express spinline state continuously changing in practical plant, the authors have tried to simulate the spinline behavior with Hybrid, Logistic and New hybrid methods. Residual solvent concentration simulated by Hybrid method is higher than practical one. The difference between the simulated result and practical one is assumed to be caused by the state transition points of fixed only residual solvent concentration not temperature. Logistic method can predict the closer residual solvent concentration to a practical one than Hybrid method, but the residual solvent concentration simulated by Logistic method is slightly lower than that obtained by practical plant. This small difference is very important for the design of dry spinning chamber and the grasp of optimum dry spinning conditions. New hybrid method expresses the dependence of diffusion coefficient on both solvent concentration and temperature in the spinline, where the whole dry spinning process is divided into five sections with spinline state. New hybrid method can accurately express the state transition points changing with solvent concentration and temperature .The simulated residual solvent concentration is very closer practical plant concentration. But the method have fault as used several diffusion equation with each spinline state. In order to accurately predict residual solvent concentration and easily express diffusion coefficient in continually changing spinline state, New logistic method will be proposed in this paper. The method can express the whole dry spinning process from the spinneret (Dope state) to the Take-up position (Solid state) with one diffusion equation. The simulated residual solvent concentration in spinline is very closer the practical plant solvent concentration than that by the others method.The differences of simulated residual concentration among New logistic method and other ones will be discussed in this study.