Lyocell™ fibers

Textured semiconductor surfaces, 14 847 Textured yarn, 11 178 Texture mapping technique, 10 339-341 of lyocell fibers, 11 271 Texturing... 

As an example using NMMO solution, the spinning of fibers consisting of blends of cellulose with cationic starch was investigated for the purpose of improving moisture absorbability, dyeability, and enzymatic degradability compared with standard Lyocell fibers [69]. 

N-McLhylmorpholine-N-oxidc monohydrate, a tertiary, aliphatic amine N-oxide, is able to dissolve cellulose directly, i.e. without chemical derivatization, which is used on an industrial scale as the basis of the Lyocell process [ 1, 2], This technology only requires a comparatively low number of process steps compared for instance to traditional viscose production. Cellulose material - mainly fibers - are directly obtained from the cellulose solution in NMMO no chemical derivatization, such as alkalization and xanthation for rayon fibers, is required [3]. The main advantage of the Lyocell process lies in its environmental compatibility very few process chemicals are applied, and in the idealized case NMMO and water are completely recycled, which is also an important economic factor. Even in industrial production systems NMMO recovery is greater than 99%. Thus, compared with cotton and viscose the Lyocell process pertains a significantly lower specific environmental challenge [4]. Today, Lyocell fibers are produced on an industrial scale, and other cellulosic products, such as films, beads, membranes and filaments, are also currently being developed or are already produced commercially. 

The process of cellulose regeneration in the form of lyocell fibers is significantly simpler than that of the viscose rayon process. It is illustrated in O Fig. 16. A solution containing 14% cellulose, 10% water, and 76% NMMO plus stabilizers is extruded at a temperature slightly above 100 °C into an aqueous NMMO-bath from which cellulose is precipitated [74,75]. The extrusion has been described as a melt-spinning process that has recently made it possible to manufacture cellulosic self-bonded meltblown nonwovens as well [76]. 

CHA 05] Chang Lang Y., Chung Hee P., Yun-kyung K., et al, BiodegradabiUty of viscose Rayon and Lyocell fibers , Journal of the Korean Society of Clothing and Textiles,... 

As Rosenau et al. [49] indicated that paper grade pulp, unbleached chemical pulp, cotton and rayon fiber wastes, or even paper wastes can be used as raw materials for Lyocell fiber production, even though problems with spinnability may be encountered in some cases. In preparation for spinning dope, a 50-60% aqueous NMMO is used with the addition of 0.01 0.10% antioxidant to prevent cellulose degradation. A typical antioxidant is PG [50]. In a typical Lyocell industrial process, the slurry is produced from cellulose pulp and an aqueous NMMO solution. Typical compositions are 50-60% NMMO, 20 30% water, and 10-15% pulp [48]. Subsequently excess water is efficiently evaporated at temperatures lower than 150°C and... 

The final properties of Lyocell fibers depend on a number of variables that are grouped in Figure 10.35. As shown in the figure, the final fiber strength will depend on the properties of... 

Although, heat setting generally affects the degree of crystallinity of synthetic fibers such as PET, Nylon 6, or Nylon 66, drying of these fibers has little effect. Fink et al. [37] recently discovered that extensive drying for Lyocell fibers under small tension leads to an increase in... 

Lyocell fibers have outstanding properties. The main advantages of these fibers in comparison to viscose fibers are the following ... 

Typical properties of Lyocell fibers are summarized in Table 10.5. Tensile properties can be improved further by introducing ammonium chloride and other additives [72]. One of the disadvantages of Lyocell fibers is the tendency for fibrillation (see Figure 10.38). Interestingly, the fibers exhibit very unique hand. 

Freshly coagulated Lyocell fibers show low crystalline orientation for the (110) plane however, as NMMO is extracted, the orientation of the dry fibers is improved. Extensive drying often causes fibrils to cluster into larger structural units (bundles). Fink et al. [37] estimated that the diameter of the bundles is around 25 nm. Definitely, Lyocell fibers have fibrillar morphology that is affected by posttreatment thermal processes. 

FIGURE 10.37 Fiber cross section of (a) Lyocell fiber and (b) Viscose fiber. (From Fink, H.P., Weigel, P., Purz, H.J., and Ganster, J., Prog. Polym. ScL, 26,1473,2001. Reprinted with permission of Elsevier B. V.)... 

Carbacell fibers have a smooth surface at the fracture thus indicating a lack of the fibrillar morphology that is usually associated with Lyocell fibers. The property profile of Carbacell fibers largely matches that of viscose fibers [90]. 

Lyocell tibers have been explored in blends. Chang et al. [141] prepared Lyocell based blends. Poly(vinyl alcohol) (PVA), poly(vinyl alcohol-co-ethylene) (EVOH), and poly(acrylic acid-co-maleic acid) (PAM) were used as fillers in blends with lyocell produced through solution blending. The results showed that blends with PVA exhibit the best tensile properties. Thus, Lyocell fibers have recently been used as reinforcement for thermoplastic fiber composites. 

At present there is one exception to the above situation. Cellulose is readily soluble in N-methyl morjiioline N-oxide (NMMO) and so-called lyocell fibers are being spun from solutions of cellulose in this solvent However, NMMO, being an ether readily forms explosive peroxides and must be properly stabilized before use. 

Ibbett et al. (2007) used complementary isotherm and NMR relaxation (the transverse relaxation time of the water protons in the saturated fiber samples) techniques to characterize a series of solvent-spun cellulosic (lyocell) fibers treated with amethylol urea type resin. Cross-finking reduced overall fiber swelling, caused a loss of both large and small pores, a reduction of the pore volume accessible (0.1-0.45 cmVg at water retention up to 1.2 cm /g) to large dye (Direct Blue 71,... 

The polynosic rayons enjoyed a revival of fortimes in the 1990s when the new lyocell fiber produced by Courtaulds (Tencel )—a solvent spim fiber with polynosic properties— became popular in ladies apparel and denim. By 2001 however the Toyobo Tufcel plant in Japan had been closed and at the time of writing, it is likely to be transferred to China where lower labor costs would allow it to compete more effectively with lyocell (see below). 

Regenerated fibers produced via the direct dissolution of cellulose in organic solvents are generically known as lyocell fibers. 

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