Development of a novel process for the production of man-made cellulosic fibers from ionic liquid solution

Abstract

This study presents the development of a novel process for producing man-made cellulosic fibers from an ionic liquid solution, the so called Ioncell-F process. It examines the full production chain from efficient dissolution of cellulose in ionic liquid to the suitability of the spun fibers for textile applications. A dry-jet wet spinning process consisting of the extrusion of a polymer solution at mild temperature through a multi-filament spinneret into an aqueous coagulation bath via an air gap was employed for the regeneration of cellulose into filaments. For preparation of the spinning dopes, 1-ethyl-3-methylimidazolium acetate and 1,5-diazabicyclo[4.3.0]non-5-enium acetate were used as solvents for different commercial dissolving pulps. Both ionic liquids showed an excellent capability in dissolving cellulose at mild conditions. Minor cellulose depolymerization was obtained at a temperature below 85 ºC with a low shearing rate. The intrinsic properties of the dissolved raw material, such as the degree of polymerization and molar mass distribution, exhibited a significant influence on the viscoelastic properties of the resulting polymer solution, and were monitored by oscillatory shear rheology and extensional rheology. The viscoelastic properties of the cellulose/ionic solution played a key role in determining the so called "spinning window" required to achieve optimal spinnability. The tested 1-ethyl-3-methylimidazolium acetate/cellulose solution showed poor processing ability, while the 1,5-diazabicyclo[4.3.0]non-5-enium acetate/cellulose solution revealed effective spinning capability, resulting in the production of high-tenacity cellulosic staple fibers. The fundamental spinning concepts were investigated and contributed to the determination of the spinning window. Cellulosic fibers, covering a wide spectrum of structural and mechanical properties, were manufactured by varying the applied stretch of the extruded filaments. Ioncell fibers belong to the category of Lyocell fibers, provided that they are produced commercially, and display appropriate structural and mechanical behavior to be converted into yarn, and subsequently converted to knitted and woven fabrics. The excellent performance of the Ioncell spun yarn during the knitting and weaving process confirmed the competitive quality of the yarn and its suitability for the production of apparel. The future of this technology as an alternative to the viscose and NMMO-based Lyocell processes is promising, based on the development of a viable solvent-recovery step.