THE TREATMENT OF LYOCELL FABRICS
Lyocell is a material obtained by a new process of regeneration of cellulosic fibers. If compared to the traditional way of obtaining viscose, this process offers significant advantages under the ecological point of view. Moreover, the mechanical characteristics of Lyocell are better than those of the cotton.
Unluckily, during the water-washing processes the Lyocell fabric exhibits a strong tendency to produce the so-called "pilling" on the surface. The pilling leads to anti-esthetical globular agglomerations. A consequence of this phenomena is the loss of brightness of the fabric, which should be preserved at any cost, since it represent a factor that strongly characterize the Lyocell. Another matter of concern is the formation of irregular stripes, which tend to be particularly evident in this kind of fabric. For this reason, in the desizing bath (where the formation of the strikes usually take place) is added an addictive constituted by a highly viscous anionic polymeric solution.
The removal of the pilling on the surface requires the employment of strong and prolonged enzymatic treatment with cellulases.
A 
B
A - Pilling in the surface of a Tencell fabric seen at the microscope
B - Biopolishing with cellulase enzymes
Anyway, the choice of the cellulase cannot be casual. In fact, the Lyocell fabric opposes a strong resistance to the action of the cellulases, which therefore must be very active. In the other hand, the lightness of many clothes made by Lyocell requires a particular care choosing enzymes that are too aggressive. Further consideration must be done when the fabric is constituted by blends "cotton-Lyocell" or "linen-Lyocell". In those cases, in fact, the different resistance of each material toward the cellulase must be evaluated. Of course, the most problematic case is represented by the blends "linen-Lyocell". The weakness toward cellulase that characterizes linen is in contrast with the strong resistance exhibited by Lyocell. Here below there is a short and simplified guide that may help in the choice of cellulases for the various kind of blends.
Whole cellulase (conventional)
Due to the high aggressiveness given by the synergic action of the components "endo" and "exo", the so-called "whole cellulase" can be used with significant advantages on fabrics constituted by 100% Lyocell.
Modified cellulase (Endo-enriched)
Cellulases enriched with their component "endo" (the one that are able to break cellulosic chains in any point of their lenght) exhibit characteristics that are similar to those shown by "conventional" cellulases. In the other hand, endo-enriched cellulases generally cause a fabric strength loss that is about 20% less than the "conventional" counterpart. For that reason, endo-enriched cellulases are suitable for the treatment of garnments 100% Tencell that are very light, as well as treatment of cotton-Lyocell blends. More in general, one may state that endo-enriched cellulases are recommended when it is required a "controlled" biopolishing.
Modified cellulase (greatly enriched with Endo-Cellulase)
Cellulases that are very rich in their component "endo" lose great part of their aggressiveness. The loss of aggressiveness is mainly due to the missing synergic action of the "exo" component, which attacks the chain ends. This kind of products do not perform well on fabrics 100% Lyocell, while result only acceptable on cotton-Lyocell blends. However, they find on linen-Lyocell blends the perfect substrate to work on. In fact, for the above mentioned reasons, linen-Lyocell blends requires a biopolishing in highly controlled conditions, which only this kind of cellulases can provide.
Finishing
One of the best characteristic of Lyocell garments is the outstanding "soft and smooth hand" that make that fabric similar to silk. In way to enhance this characteristic, one may add in the last bath a microemulsion of reactive aminosiloxanes. These products can improve the brightness of the fabric and greatly enhance the sensation of softness and smoothness. Moreover, they can also improve the resistance to abrasion, preventing the formation of pilling after repeated washing processes.
Another treatment that is able to add value to Lyocell garments involves the employment of particular emulsions of reactive resins that are able to produce the so-called "Wash & Wear" effect. "Wash & Wear" clothes do not require ironing, and they are ready to wear after washing, even after 20 cycles. Last but not least, those reactive resins can dramatically diminish the tendency of Lyocell to exhibit the return of the pilling on its surface.
Dr. Gianni Maiani - ©
Copyright 1999
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