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

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

Deformation mechanisms in ionic liquid spun cellulose fibers

This is the final version of the article. Available from the publisher via the DOI in this record.The molecular deformation and crystal orientation of a range of next generation regenerated cellulose fibers, produced from an ionic liquid solvent spinning system, are correlated with macroscopic fiber properties. Fibers are drawn at the spinning stage to increase both molecular and crystal orientation in order to achieve a high tensile strength and Young’s modulus for potential use in engineering applications. Raman spectroscopy was utilized to quantify both molecular strain and orientation of fibers deformed in tension. X-ray diffraction was used to characterize crystal orientation of single fibers. These techniques are shown to provide complimentary information on the microstructure of the fibers. A shift in the position of a characteristic Raman band, initially located at ∼1095 cm−1, emanating from the backbone structure of the cellulose polymer chains was followed under tensile deformation. It is shown that the shift rate of this band with respect to strain increases with the draw ratio of the fibers, indicative of an increase in the axial molecular alignment and subsequent deformation of the cellulose chains. A linear relationship between the Raman band shift rate and the modulus was established, indicating that the fibers possess a series aggregate structure of aligned crystalline and amorphous domains. Wide-angle X-ray diffraction data show that crystal orientation increases with an increase in the draw ratio, and a crystalline chain slip model was used to fit the change in orientation with fiber draw ratio. In addition to this a new model is proposed for a series aggregate structure that takes into better account the molecular deformation of the fibers. Using this model a prediction for the crystal modulus of a cellulose-II structure is made (83 GPa) which is shown to be in good agreement with other experimental approaches for its determination.The Engineering and Physical Sciences Research Council (EPSRC) is acknowledged for funding provided under Grant No. EP/L017679/1

The fiber-matrix interface in Ioncell cellulose fiber composites and its implications for the mechanical performance

Fiber-reinforced composites based on natural fibers are promising alternatives for materials made of metal or synthetic polymers. However, the inherent inhomogeneity of natural fibers limits the quality of the respective composites. Man-made cellulose fibers (MMCFs) prepared from cellulose solutions via wet or dry-jet wet spinning processes can overcome these limitations. Herein, MMCFs are used to prepare single fiber epoxy composites and UD composites with 20, 30, 40, and 60 wt% fiber loads. The mechanical properties increase gradually with fiber loading. Young's modulus is improved three times while tensile strength doubles at a loading of 60 wt%. Raman spectroscopy is employed to follow conformational changes of the cellulose chains within the fibers upon mechanical deformation of the composites. The shift of the characteristic Raman band under strain indicates the deformation mechanisms in the fiber. Provided stress transfer occurs through the interface, it is a direct measure of the fiber-matrix interaction, which is investigated herein. The shift rate of the 1095 cm−1 band decreases in single fiber composites compared to the neat fibers and continues to decrease as the fiber loading increased.Peer reviewe

Ioncell-F: A High-strength regenerated cellulose fibre

In this paper, we report the development of a novel regenerated cellulose fibre process of the Lyocell type, denoted Ioncell-F. The process is 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. Compared with the commercial NMMO-based Lyocell fibre process, airgap spinning can be conducted at higher cellulose concentration in the dope, while temperature during dissolution and spinning can be maintained at a lower level. Owing to the generally milder process conditions, the cellulose is less degraded which contributes to both higher fibre yield and better strength properties. In this study we demonstrated the effect of different cellulose concentrations and draw ratios on the fibre properties. The highest tenacities, consistently above 50 cN/tex, were achieved by spinning from 15 and 17 wt% cellulose solutions. A very high initial modulus of up to 34 GPa makes the Ioncell-F fibres very interesting for technical applications such as a reinforcing fiber in composites. The chain orientation in the fibre direction, particularly in the amorphous regions, revealed the best correlation with the elastic modulus and the tensile strength of the Ioncell-F fibres, in agreement with other high-tenacity regenerated cellulose fibres as reported in the literature.</p