Dry-Jet Wet Spinning of Technical and Textile Filament Fibers from a Solution of Wood Pulp and Waste Cotton in an Ionic Liquid

Abstract

This dissertation presents the further development of IONCELL technology for the productionof modified and composite man-made cellulosic fibers using waste and virgin lignocellulosicmaterials. IONCELL technology consists of a dry-jet wet spinning process using an ionic liquid asa polymer solvent. Different structural features of the IONCELL fibers spun from cellulose- [DBNH]OAc solutionwere studied against their mechanical properties with wide- and small-angle scattering techniques.It was observed that the change in crystallite size or orientation does not correlate with anymechanical properties. However, by increasing the draw ratio, the sample crystallinity, amorphousand void orientation, specific surface, and sorption/desorption properties of the fibers changesignificantly. The effect of the addition of lignin and/or xylan to the spinning dope on the fibers' mechanicalproperties and surface chemistry was also studied. The results showed the surface properties canbe fine-tuned by changing the composition of the fibers. In addition, the fibers produced fromcellulose with xylan and/or lignin as an additive showed declined tensile strength. The fibersdeformability increased since these additives contributed to the amorphous parts of the fibers.Moreover, the swelling test indicated the three-component fibers had the least change in theircross-sectional area. Chemical modification in the solution of cellulose and its spinning to acetylated cellulose filamentswas investigated. This study proved the degree of substitution can be adjusted precisely to achievethe desired properties. For instance, cellulose with the degree of substitution values of 0.05–0.75was successfully spun, and fibers reached particularly high tensile strength values (525–750 MPaconditioned and 315–615 MPa wet) and elastic moduli values between 10 and 26 GPa. The IONCELL process was utilized for the chemical upcycling of cotton wastes. Implementing thisprocess, complete and residue-free dissolution of waste cotton and the conversion of this material into virgin cellulose fibers with high tensile strength (850 MPa) were achieved. We addressed the problem that waste cotton is an inhomogeneous feedstock with a broad variation in molecularproperties. In order to reduce and adapt the required degree of polymerization of the cotton waste,either an aqueous acid or an enzymatic treatment was conducted. Alternatively, the cotton wastewas mixed with pre-hydrolysis kraft pulp with a low degree of polymerization to obtain themacromolecular properties necessary for spinning. In addition, we described the physicochemicalproperties of the respective solutions as a key to ensure successful spinning of high-performancefibers. The resulted IONCELL fibers showed significantly better mechanical properties than the commercially available Viscose, Lyocell or virgin cotton fibers, mainly due to the higher total orientation of the cellulose chains.