Comparison of Regenerated Cellulose Fibers Spun from Ionic Liquid Solutions with Lyocell Fiber

Abstract

Regenerated cellulose fibers were prepared by dry-jet wet spinning of cellulose solutions using three different solvents: the ionic liquids 1-butyl-3-methylimidazolium chloride (BMIMCl) and 1-ethyl-3- methylimidazolium diethyl phosphate (EMIMDEP), and the solvent used in the lyocell process, N-methylmorpholine N-oxide monohydrate (NMMO·H₂O). The mechanical properties and fibrillation tendencies of fibers prepared under the same spinning conditions were compared. The results showed that fibers generated using BMIMCl exhibited the highest tensile and knot strengths, and the highest fibrillation resistance, followed by fibers spun using EMIMDEP and NMMO·H₂O. Structural analyses by wide angle X-ray diffraction and polarizing microscopy revealed that the high total molecular orientation of fibers spun from BMIMCl solution contributed to their high tensile strength and Youngʼs modulus. We observed the coagulation behavior in water of each cellulose solution and found that the coagulated cellulose gels were transparent using BMIMCl, translucent using EMIMDEP, and opaque using NMMO·H₂O. These differences in appearance are due to different void structures formed in the regenerated cellulose depending on the solvent. For BMIMCl, the transparency of the cellulose gel indicated a dense inner structure, resulting in high knot strength and good fibrillation resistance of the fibers. In contrast, the opaque appearance of cellulose gel regenerated from NMMO·H₂O solution is due to the presence of coarse voids, in turn closely related to the lower knot strength and fibrillation resistance of the fibers. The results indicate that BMIMCl is the best of the three tested solvents for preparing high performance regenerated cellulose fiber.