Dyeing lyocell

Most of the dyes used on Lyocell are more stable at acidic than alkaline pH, so this application has primarily been carried out using acidic cellulase from Trichoderma. The cellulase used can be the entire crude cellulase or modified cellulases with gentler action, depending on the size of the pills and the robustness of the fabric. 

Ibbett et al. (2007) used complementary isotherm and NMR relaxation (the transverse relaxation time of the water protons in the saturated fiber samples) techniques to characterize a series of solvent-spun cellulosic (lyocell) fibers treated with amethylol urea type resin. Cross-finking reduced overall fiber swelling, caused a loss of both large and small pores, a reduction of the pore volume accessible (0.1-0.45 cmVg at water retention up to 1.2 cm /g) to large dye (Direct Blue 71,... 

Lyocell fabrics are readily made on most commercially available knitting machines. The best quality fabrics are made with high quality yams and slightly shorter stitch lengths to minimise the risk of work up and pilling during dyeing and subsequent use. 

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. 

There is much to be still learnt about the dyeing of PLA but it would seem that processes are available to achieve commercial viability. In real terms, it is not that long ago that fibers such as lyocell and indeed PET were introduced to the textile world, with many technical difficulties in their processing. These are now well accepted fibers and it will be interesting to watch as PLA follows a similar course. 

Rencheng T, Jianping Z, Shiying M. Lyocell textile dyeing and finishing technology. Beijing China Textile Press 2001. p. 28—29. 

---