New insights into the air gap conditioning effects during the dry-jet wet spinning of an ionic liquid-cellulose solution

In this paper, we report new results related to the development of a novel regenerated cellulose fiber process of the Lyocell type, denoted Ioncell™, and characterized by the use of a powerful direct cellulose solvent, 1,5-diaza- bicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]) a superbase-based ionic liquid (IL). The focus of this work is on the effects of air gap conditioning (AGC) during the dry-jet wet spinning operation. The installation of an AGC system on the spinning line led to significant improvements of the fiber properties. The fiber titer variation decreased significantly, and the fiber toughness increased by approximately 50% when controlling the temperature and the relative humidity in the airgap using a convective air flow. The presence of water vapor in the air stream was a determinant factor for the improvement of the fiber elongation. The interaction of water vapor with the spinning dope was investigated using dynamic vapor sorption. The diffusion coefficient of water vapor inside the dope could be identified from those experiments and used in a numerical simulation model of the heat and water vapor transfer in the air gap between the spinning dope and the surrounding air. The experimental and simulation results suggest that dope convective cooling and surface hydration lead to a higher fiber toughness.