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ABSTRACT
This article describes the physical properties of lyocell fibers spun from an isotropic cellulose spinning dope in N-methyl morpholine N-oxide (NMMO) monohydrate (IPS lyocell fibers). Wide angle x-ray diffraction (WAXD) experiments on the crimped fibers exhibit little difference in the crystal structure of ips and Tencel lyocell fibers: both fibers reveal a cellulose II structure. However, the ips lyocell fibers have a lower tensile modulus than Tencel by about 12.5%, although they have a similar tensile strength. Wetting and subsequent drying shift the loss tangent values higher, which is more remarkable for the IPS lyocell fibers dried under tension. Further, the IPS lyocell fibers dried under tension have a sharper alpha-transition peak than the fibers dried without tension. The ips lyocell fibers exhibit excellent wet tensile strength: 90% of tensile strength is retained after wetting twice in distilled water. In addition, the Irs lyocell fibers show good chemical stability to acids and alkalis, except for an extremely strong alkali-pH 14. Mercerization of the IPS lyocell fibers in the buffer solution of pH 14 notably decreases the tensile modulus but increases elongation.
Cellulose is one of the most abundant natural resources on earth, and there has been extensive research on the films, plastics, and fibers from this material. The history of cellulose fibers dates back to the 1860s, when the first rayon fibers were commercialized by Courtaulds. But the so-called rayon process includes toxic chemical treatments to block hydroxyl groups of cellulose to prepare a spinnable solution, sometimes causing ecological problems. Many attempts have been made to invent new solvents to directly dissolve cellulose, and some successful results have been reported [4]. Among these, N-- methyl morpholine N-oxide (NMMO) hydrate turned out to be the best solvent, leading to the commercial success of cellulose fibers under the trade name of Tencel by Courtaulds in 1994. Other lyocell processes include Lenzing Lyocell and TITK Alceru [2]. These processes are advantageous because they are environmentally benign, using nontoxic NMMO hydrates instead of toxic carbon disulfide, which can be almost totally recycled.
The cellulose fibers produced by direct dissolution have the generic name of lyocell. The lyocell fiber has a highly crystalline structure in which crystalline domains are continuously dispersed along the fiber axis. This offers...