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Wet processing of garments made from fabrics in Lyocell

Lyocell is a new fibre originally manufactured as an alternative to viscose, which is environmentally harmful. These are solvent spun cellulosic fibres produced by dissolving wood pulp in amine oxide. A cellulose solution is produced, which is spun out into fibres. Tencel is one of the brand names of Lyocell. This paper deals with the successful processing routes of this new fibre.

The basic processing route

A peach skin effect is the characteristic of Lyocell fibres. This requires three processing stages - prefibrillation, defibrillation and refibrillation. Prefibrillation (primary fibrillation) is the process of splitting of surface hairs on the fabric to obtain a tangled mess. The whole fabric is seen as areas of pilling. This is followed by defibrillation using mechanical action as well as enzymatic treatment with cellulases. The surface of the fabric is now clean and is followed by refibrillation (secondary fibrillation). This time, micro-hairs are generated on the surface of the fabric and are responsible for the peach skin effect. Lyocell is used in a number of areas. Denim is one of them.

Denim processing routes

The prefibrillation is carried out during desizing. Adding a lubricant into the water before the water touches the garment is very essential during the process as Lyocell swells quickly in water and sets in any creases that may have formed. The process can be speeded up by using a high temperature amylase. Defibrillation is carried out using cellulase. Neutral pH products are preferred as they give a softer hand and slightly less back staining. Refibrillation is carried out during the softening process.

Garment washing routes

These are similar to denim processing routes but the secondary fibrillation has to be carried out carefully as it affects the apparent shade of the fabric. This is cue to a light scattering effect and dark shades take on a washed out look. This problem can be partially overcome by the use of fluorocarbons or silicone finishes that alter the light reflecting characteristics of the fabric.

The best way to obtain the desired effect during dyeing is to defibrillate during the scouring process. A mildly alkaline scour is required and some amount of desizing as pre-treatment should be done first. After defibrillation by cellulase enzyme, the enzyme need not be denatured if dyeing is carried out immediately. Dyeing followed by softening gives the final effect. As the dye affinity of Lyocell is greater than cotton or viscose, the dye strike rate should be controlled by reducing the salt and alkali concentration. The rate of temperature rise and speed of the machine have to be controlled to ensure slow diffusion of the dyes into fabric. All kinds of dyes like direct, vat, reactive, sulphur and pigment are in use.

Lyocell in blends

During the processing of blends, conditions are decided upon with the less robust fibre in mind and the more robust one is allowed to take its own course. One has to be particularly careful in case of a delicate fibre like Lyocell in combination with a more delicate one like linen as defibrillation conditions should be effective but should not damage the linen. As different fibres have different affinity for the same dye, selection of dye has to be done carefully to produce a level fabric appearance.

Many new techniques of producing the same effect are being investigated. These include using a tumbler dryer to remove primary fibrillation and generate the secondary fibrillation. Trials in this area are being carried out by Tencel R&T and results are expected soon.

Source: www.resil.com