Precipitation Kinetics of Cellulose in the Lyocell Spinning Process

The average concentration of N-methylmorpholine-N-oxide (NMMO) in the running Lyocell filament was measured in the coagulation process by which the precipitation kinetics of cellulose in the Lyocell process was studied. It was found that there are two diffusion regimes in the coagulation process of cellulose in the Lyocell process. The fast regime is completed within 1 s, causing formation of hydrogen bonds between the molecules of NMMO and water. The apparent diffusion coefficients of NMMO in both the fast and slow regimes of the coagulation process of the Lyocell process were estimated by Fickʹs second law. It was found that apparent diffusion coefficients in both the fast and slow regimes decrease with increasing filament diameter and NMMO concentration in the coagulation bath. The apparent diffusion coefficient of NMMO in the fast regime is about one-tenth of that in the slow regime, which is in the range of 4-8 × 10^-7 cm^2/s.