Superbase-based protic ionic liquids for cellulose filament spinning

Abstract

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

Stretch-Induced Crystallization of Cellulose Spun from Ionic Liquid Solution

“…With an increase in the SR from 0 to 51, the tensile strength and elastic modulus of cellulose fibers increase significantly from 120.0 ± 9.2 MPa and 4.6 ± 0.6 GPa to 632.2 ± 32.0 MPa and 26.2 ± 1.8 GPa, respectively, possibly due to the increased crystallinity and enhanced oriented structure of the fiber. These results confirmed that solution stretching induced total molecular orientation and crystallization during the transition from solution to gel via coagulation, so dry fibers with a high SR could achieve high thermal stability and mechanical properties Figure c shows the strong correlation of the total molecular orientation factor, crystallinity, and mechanical properties.…”

Limitations of Cellulose Dissolution and Fiber Spinning in the Lyocell Process Using [mTBDH][OAc] and [DBNH][OAc] Solvents

“…Only minor agglomerates were formed during spinning that are typical for a small-scale batch spinning process. The scanning electron microscopy images of the fibers, at DR 2 and 12, show a correlation of increased stretching on uniforming the fibers and eliminating surface irregularities (Elsayed et al 2021). The structural properties of the regenerated fibers were accessed by birefringence and WAXS measurements to estimate the crystalline and amorphous regions, summarized in Table 9.…”

Hydrophobization of the Man-Made Cellulosic Fibers by Incorporating Plant-Derived Hydrophobic Compounds

“…Ioncell fibers are lyocell type fibers produced via dry-jet wet spinning using a nontoxic and environmentally benign solvent, 1,5-diazabicyclo [4.3.0] non-5-ene acetate ([DBNH]­OAc), a nonimidazolium-based ionic liquid . Ioncell fibers exhibit outstanding fiber properties that are superior to cotton, viscose, and NMMO type lyocell fibers. − …”