Ioncell® is a Lyocell-based technology for production of man-made cellulose fibres. This technology exploits the intrinsic dissolution power of superbase-based ionic liquids (ILs) towards cellulose. The regenerated fibres are produced via a dry-jet wet spinning process, in which the cellulose filaments are stretched in an air gap before regenerating in an aqueous coagulation medium. In order to commercialize this process, it is essential to prove the techno-economic feasibility of this technology. That said, many important criteria are to be met, among them selecting a solvent with high cellulose dissolution power, proving a stable spinning process and yielding fibres of good mechanical properties. Most of all, it is critical to demonstrate the recovery of the solvent from the coagulation bath without impairing its solvation power. This study reports on the spinnability and recyclability of the IL 7-methyl-1,5,7-triazabicyclo[4.4.0] dec-5-enium acetate ([mTBDH][OAc]) over five cycles in comparison to 1,5-diaza-bicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]). The ILs were recovered from the coagulation bath by consecutive thermal treatments under reduced pressure. Accordingly, the recovered ILs were utilized to dissolve 13 wt.% cellulose in each cycle, without the addition of make-up IL, to form a homogeneous solution suitable for the dry-jet wet spinning. Using [mTBDH] [OAc], cellulose could be fully dissolved in all five cycles. In contrast, cellulose dissolution was only possible with fresh [DBNH][OAc] as the ability to dissolve cellulose was lost after the first recovery. This study focuses on the composition of the recovered ILs and the extent of side-products generation. Additionally, we present the rheological properties of the solutions as well as the macromolecular and mechanical properties of th e regenerated fibres. Also, the toxicity of both solvents was investigated using Vibrio fischeri bacteria. Finally, the spun fibres from al l [mTBDH][OAc] spinning trials were combined to produce a demonstration dress (Paju), designed and sewn by Marimekko Design House in Finland.

Lyocell fibers have received increased attention during the recent years. This is due to their high potential to satisfy the rising market demand for cellulose-based textiles in a sustainable way. Typically, this technology adopts a dry-jet wet spinning process, which offers regenerated cellulose fibers of excellent mechanical properties. Compared to the widely exploited viscose process, the lyocell technology fosters an eco-friendly process employing green direct solvents that can be fully recovered with low environmental impact. N-methylmorpholine N-oxide (NMMO) is a widely known direct solvent that has proven its success in commercializing the lyocell process. Its regenerated cellulose fibers exhibit higher tenacities and chain orientation compared to viscose fibers. Recently, protic superbase-based ionic liquids (ILs) have also been found to be suitable solvents for lyocell-type fiber spinning. Similar to NMMO, fibers of high mechanical properties can be spun from the cellulose-IL solutions at lower spinning temperatures. In this article, we study the different aspects of producing regenerated cellulose fibers using NMMO and relevant superbase-based ILs. The selected ILs are 1,5-diazabicyclo[4.3.0]non-5-ene-1-ium acetate ([DBNH]OAc), 7-methyl-1,5,7-triazabicyclo[4.4.0] dec-5-enium acetate ([mTBDH]OAc) and 1,8-diazabicyclo[5.4.0]undec-7-enium acetate ([DBUH]OAc). All ILs were used to dissolve a 13 wt% (PHK) cellulose pulp. The study covers the fiber spinning process, including the rheological characterization of the various cellulose solutions. Moreover, we discuss the properties of the produced fibers such as mechanical performance, macromolecular properties and morphology. Graphic abstract

for the coffee breaks and the after-work chats. To my family, Simone you were my additional motive. Your help and support in my last year have been priceless. Thank you, Magdy, my dear father and brother, for your love and support. Finally, to my mother, you are the first person I think of whenever I want to share something. I still talk to you, and you still listen. Mother, although you have departed from this world, in my heart you always live.

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.

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