Lyocell fibre treatments

Sewage treatment. Lyocell fibres degrade completely within 8 days in a typical sewage farm anaerobic digester, where the residence cycle is about 20 days. Synthetic fibres showed slight reductions in strength after 12 weeks. 

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). 

Pre-treatment of the fabric in caustic soda can be very effective in improving both fabric performance and aesthetic. It is very widely used in commercial lyocell fabrics. In caustic soda, lyocell swells very significantly in its diameter but very little in length. The maximum effect is at 10% to 12% concentration, but mercerisation conditions can also be used. The swelling of the fibres will increase the diameter of the yams in the fabric and this will cause the fabric to shrink. This step needs to be carried out with the fabric in open width form and if the fabric is allowed to shrink during caustic treatment its bulk will be significantly enhanced. 

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. 

TAHT (Triacroyl hexahydrotriazine (5.4)) will cross-link lyocell under alkaline conditions. Pre-treatment of the fibre using this chemical during the manufacturing process has proved successful. In the AlOO process developed... 

---