Dry Jet-Wet Spinning of Cellulose/N-Methylmorpholine N-oxide Hydrate Solutions and Physical Properties of Lyocell Fibers

In dry jet-wet spinning of a cellulose/N-methylmorpholine N-oxide hydrate solution, the effects of the hydration number n in NMMO hydrates and the concentration and molecular weight of cellulose are investigated in terms of the physical properties of the fibers. Dry jet-wet spinning of lyocell fibers is also investigated using three different set-ups; a piston type, an N² gas pressure type, and spinning equipment with an extruder. The effects of spinning conditions such as the spin draw ratio, air gap distance, and composition of the coagulation bath are investigated. The physical properties of the fibers such as birefringence, initial modulus, and tensile strength increase with a decrease in n and an increase in the air gap distance and spin draw ratio. The relationship between the physical properties and the fiber denier is newly suggested in this spinning system. The tensile fracture morphology reveals that fibers from the NMMO hydrate containing less water have more fibrils due to their higher molecular orientation. Further, the orientation structure of the cellulose becomes more noticeable with the decreased hydration levels of the solvent because it produces thicker and longer fibrils when the cellulose fibers are treated with an ultrasonic generator. The crystallite size of the cellulose depends on the composition of NMMO in the coagulation bath. The crystallite size also decreases with the increased air gap distance.