Professional guide

Rayon

Dissolving wood is the main process which creates viscose materials. Rayon, or viscose is a cellulose fibre.

This is done by using solvents, which can be harmful to the environment since this currently involves the use and subsequent disposal of great volumes of various chemical auxiliaries, especially Carbon Disulphide. Major volumes of waste water are also produced for process reasons and need to be disposed of very carefully. Good news is that scientists now have found a more eco-friendly way of dissolving wood by using ionic liquids, with much less heat and pressure, and with very low toxicity and remaining biodegradable. Once this is adopted by the industry, the eco-profile of lower grade viscose – including the production of bamboo-based materials – will become a lot greener.

Two other processes, that result in modal and lyocell, are much more eco-friendly. As mentioned in the section on raw-materials, they have EU-flower classification. In the production of lyocell, one uses a solvent which is fully recovered and recycled back in to the production process. Modal is a second-generation cellulose fibre that is characterized by superior textile care properties. Lyocell represents the latest generation of cellulose fibres, it is the most flexible in terms of application, being suitable for knits, wovens and non-wovens. Its unique textile properties including highly effective moisture management for superb comfort, natural bacterial suppression and next-to-skin benefits. Tencel® is the brand name for lyocell fibres produced by Lenzing. In Austria, where Lenzing’s pulp mill is integrated with its fibre plant, beech wood from nearby forests is used as raw material for viscose and modal. Eucalyptus from South Africa is the feedstock for lyocell production.

The whole process is complete in three hours

Viscose, modal and lyocell fibres consume a significant amount of water during their industrial processing: between 100 cubic m3/ton for lyocell and up to 500 m3/ton for viscose and modal. These figures are low compared to the amount of water used to artificially irrigate cotton: 7000 m3/ton in Israel, 29000 m3/ton in Sudan. The lyocell manufacturing process differs from that of other regenerated cellulosics, such as viscose, in that it proceeds without the formation of intermediate compounds and there is no curing or ripening stage. Therefore, the whole process is complete in three hours, rather than 24 hours typically required. Shortened processing time implies savings in energy and water per unit production. The minimal use of chemicals means that pure cellulose pulp changes only physically rather than chemically. As a result lyocell fibre is 100 % biodegradable. However, lyocell can not be defined as organic, since the change is at a molecule level, which is not accepted in an organic process.

Bamboo textiles tend to be made from bamboo pulp in old viscose plants, which may explain the presence of heavy metals in many of the fibre samples tested. In the US and Canada is no longer legal to call viscose made from bamboo for anything but viscose or rayon, because of the chemical treatment.