Fibrillation, Lyocell fibers

Figure 2.31 Fibrillated lyocell fibers (Courtaulds Lyocell, 1994)...

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 10.41 Fibrillation resistance of Lyocell fibers that were coagulated in water and various alcohols. (From Fink, H.P., Weigel, P., Purz, H.J., and Ganster, J., Prog. Polym. Sci., 26, 1473, 2001. Reprinted with permission of Elsevier B. V.)... 

The untreated cellulose substrates were examined by scanning electron microscopy prior to the autoclave experiments. The dissolving pulp (Figure la) and the cotton fibers have textured surfaces with clearly visible fibrils. The lyocell fibers on the other hand are nearly devoid of surface features (Figure lb). The cellophane film has a completely flat surface with a few spherical shaped inhomogeneities, while the cellulose membranes display distinct porous structures. The 1.0 pm cellulose membranes were clearly inhomogeneous, with large flat areas interspersed with porous structures. 

Lyocell fibers offer advantages with their properties and environment friendly production processes. Fibrillation, which is among the most important properties of lyocell fiber, can be used to produce an appealing fabric touch called peach-skin effect . ... 

Lyocell fibers consist entirely of cellulose. One fiber is composed of uniformly thick fibrils distributed over the whole cross section. This structure is another difference from the traditional fibers from regenerated cellulose, which is usually characterized by a core-sheath structure. The evolution of this fibrillar structure can be explained by the rapid segregation processes occurring during the regeneration of the cellulose from the spinning solution. This structure (Fig. 2.30) imparts the particular properties of the lyocell fiber. 

Especially important is the potential of lyocell fibers to fibrillate. If the wet fibers are mechanically strained perpendicular to their fiber axis, the finest hairs parallel to the fiber axis split and lie away from the fiber like fleece (Fig. 2.3f). 

Based on the potential of variation during their manufacture, lyocell fibers can be processed into fabrics as staple fibers or as filament yarns in traditional processes. Lyocell fabrics such as wovens, nonwovens, technical textiles, or even papers may differ in their handle and look. The degree of fibrillation influences properties such as air permeability, filtration capability, and so forth (Burger et al, 1995). 

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