A novel, small-volume vertically arranged spin bath was successfully developed for an air gap lyocell-type spinning process. A maximum regeneration bath length with a minimum free volume characterizes the concept of the new spin bath. Using the ionic liquid (IL) 1,5-diazabicyclo[4.3.0]non-5-enium acetate [DBNH][OAc], the spin bath showed very good spinning performances of IL-cellulose dopes at high draw ratios and spinning duration for single filament spinning experiments. Using this new device, it was possible to get a step further in the optimization of the Ioncell ® process and simulate a process closed loop operation by performing single filament spinning in IL/H 2 O mixtures. Good dope spinnability and preserved fibers mechanical properties were achieved in a coagulation bath containing up to 30 wt% IL. It is only at 45 wt% of IL in the bath that the spinnability and fibers mechanical properties started to deteriorate. The fibers fibrillar structure was less pronounced in ILcontaining spinning bath in comparison to a pure water bath. However, their crystallinity after washing was preserved regardless of the spinning bath composition. The results presented in this work have a high relevance to the upscaling of emerging IL-based cellulose dissolution and spinning processes.

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.