Content area
Full Text
ABSTRACT
In dry jet-wet spinning of a cellulose/N-methylmorpholine TV-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 N^sup 2^ 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.
Recent technical breakthroughs have solved problems associated with toxicity by directly dissolving cellulose in much less toxic organic solvents such as W-methylmorpholine N-oxide (NMMO), dimethyl acetamide containing LiCl, and phosphoric acid. McCorsley et al. first found that cellulose could be dissolved in NMMO hydrates [26]. Cellulose fibers obtained by direct spinning methods without regeneration of cellulose by solvent were given the generic name of lyocell [12].
Courtaulds tried to set up an environmentally benign spinning process by dissolving cellulose in NMMO by eliminating water from the mixture of cellulose and aqueous NMMO [8, U]. They achieved commercial success in 1992 under the trademark of Tencel. More recently at the Korea Institute of Science and Technology, we developed a novel process for manufacturing lyocell fibers [20, 21].
McCorsley [27] investigated in detail the spinning of a cellulose solution in an NMMO solvent system. Through an extrusion apparatus, the resulting solution was...