Fibrillation lyocell

Fibrillated lyocell used in special paper applications. 

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

The precise effects obtained are dependent on the fabric quality, the type of cellulase enzyme and the application conditions, but no mechanical forces are involved in removal of the fibrils. The process has attracted considerable attention and is now one of the main methods of defibrillating lyocell fabrics [94,101-114]. Simultaneous treatment with cellulase and protease enzymes has been applied to the biofinishing of wool/cotton blends [115]. 

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.)... 

Cheng, Q. Wang, S. Zhou, D. Zhang, Y. Rials, T. (2007b). Lyocell-derived cellulose fibril and its biodegradable nanocomposite. Journal of Nanjing Forestry University, Vol. 31, No. 4, pp. 21-26, ISSN 1000-2006... 

Current lyocell, like the almost identical polsmosic viscose rayons developed half a century ago (33), has so far proved to have similarly hmited and variable potential in the fashion textile markets for which it, and the process for making it, was designed. Whether a cheaper, high-fibrillation version would improve lyocell s prospects in nonwovens is still open to debate. 

Lyocell has all the benefits of being a cellulosic fibre, in that it is fully biodegradable and absorbent. It has high strength in both the wet and dry state. It blends well with fibres such as cotton, linen and wool. In common with other highly oriented cellulosic fibres, lyocell fibrillates when the fibre... 

Other treatments to give specific fibre properties can also be performed -in particular various chemical treatments are used to control fibre fibrillation (e.g. as for the Tencel AlOO and Lenzing lyocell LF grades). 

Conventional liquor jet machines will always be problematical because the fabric rope does not move sufficiently in running on the machine and uncontrolled localised fibrillation can develop. We have seen the introduction of air jet technology to help in rope re-orientation and hence with fibrillation control, together with the introduction of new processing routes to reduce the high cost of lyocell piece finishing. Fabric behaviour understanding has... 

Studies of lyocell fabrics processed with conventional open width techniques demonstrate the virtues of lyocell with low-cost production techniques and have shown the excellent easy care performance that lyocell can deliver in combination with resin finishing. The softness, fluidity and drape characteristics shine through even without fibrillation. 

The fibrillation on the fabric surface changes the light reflectance behaviour. This gives rise to the bloom or frosted look on a peach-touch lyocell fabric. The degree of fibrihahon will influence the apparent colour. 

The acceptance of lyocell by the garment processing industry was relatively straightforward as they were already used to enzyme systems for indigo denim. (It is also interesting to note that cellulase enzymes were only introduced for textiles in the mid-1980s so prior to that lyocell would have been impossible to process to a controlled fibrillated finish.)... 

Lyocell can be processed in conventional open width systems. Because the mechanical action on the fabric is virtually eliminated the result is a flat classical fabric. Aesthetical differentiation is reduced against cotton, but the lyocell (or blend) will still be softer and more fluid than a cotton comparison. No fibrillation occurs on lyocell fabrics that have been open width processed, but they still retain a soft handle with an imderlying bounce and resilience. 

As with any fabric, chemical finishing is an important aspect of the process and this is especially true when considering the finishing of open-width processed lyocell fabrics. In such processing, resination is the method of controlling fibrillation. If too little resin is fixed then fabrics will fibrillate on subsequent washing, too much and physical performance deteriorates. It is also important to include appropriate softeners and auxiliary products into the chemical finish so that performance and handle are appropriate to the customer s requirements. 

The application of 2-3% omf (on mass of fibre) fixed resin appears to be optimal for easy-care properties, dependant on the fabric constmction and weight. Application levels of 2% omf are needed to stop fibrillation on domestic washing. In addition to the resin, the choice of softener can have a large effect on the easy-care performance of fabrics, and it is important to consider the whole formulation and build it up to give the required performance. Silicone micro-emulsions penetrate yams more than the macro-emulsions. Polyethylene dispersions aid sewing and build the handle of the fabric, whilst some soft acrylic-based chemicals can increase the abrasion resistance. It is also worth remembering that caustic soda or liquid ammonia treatment in preparation will help to increase the easy-care rating of lyocell fabrics. 

The normal glyoxal-based easy-care resins significantly impair the dyeability of cellulosic fibres so they cannot be used as a treatment prior to dyeing. To prevent a lyocell fabric from fibrillating during jet dyeing for example, other types of cross-link chemicals had to be considered to modify the fibre s behaviour. 

Nanofibrillated fibres may also be used to make nonwovens using the wetlaid process. Fibrillation is the process of splitting fibres into fibrils or thin filaments, and is commonly conducted using wet mechanical beating to partially separate fibres into their component fibrils [16]. Nanofibrous cellulose has been produced from lyocell, cotton, and wood pulp, although the fibre diameter variation is high [17]. Fibril diameters between 0.05 and 0.5 pm have been observed, with an average of 0.3 pm, but a small number of microscale fibres (2—5 pm) are inevitable. 

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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