Investigations for the use and recyclability of the ionic liquid [MTBDH][AcO] as a solvent in air‐gap‐wet spinning process

Abstract The direct dissolution of cellulose offers a pathway to production of regenerated textile fibers. However, fiber production in the Lyocell process requires a high recyclability of the solvent. Some compounds from the class of ionic liquids (IL) may have higher dissolving capacities together with a higher thermal stability than the conventional N‐methylmorpholin‐N‐oxide (NMMO), which makes them more valuable in an industrial process. A promising representative of such an advanced solvent for Lyocell process, 7‐Methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene acetate ([MTBDH][AcO]) was investigated in this study. A series of 21 consecutive cellulose dissolving and spinning trials via dry‐jet wet spinning was conducted with the same batch of solvent. In the spinning trials, the cellulose was regenerated into water consisting spinning bath. The solvent was recycled by removing the water from the spin bath via distillation in reduced pressure. Due these drastic changes in the water content of the IL during the whole process, the hydrolytic stability is an important aspect to assess the recyclability of the IL and viability of the whole process. The chemical composition of the IL was monitored by means of NMR spectroscopy. Although there was an increase of hydrolysis level of the solvent, cellulose could be dissolved constantly and spun to obtain staple fibers. The spinning behavior deteriorated slowly along the additional cycles, along with a measured increase in zero‐shear viscosity of the spinning dope. Nevertheless, the physical properties of the obtained fibers were barely influenced by the changes of the ionic liquid.