The chemistry of viscose production explained simply

Short answer: Cellulose from the plant is turned into a solution with the help of chemicals, pressed through fine nozzles and hardened in an acid bath. After that it is pure cellulose again, only in the form of long filaments that can be spun into yarn and knitted into fabric.

Why chemistry is needed at all

Cellulose cannot be melted like plastic. Heat it and it burns instead of turning liquid. It therefore has to be dissolved chemically before it can be formed into new, long fibres. That is true whether the raw material is bamboo, wood or another plant. It is the core of the process behind the fabrics in bamboo sweatshirts for women.

From plant to pure cellulose

First the cellulose must be separated from the rest of the plant. Bamboo or wood is chipped and cooked so that lignin and other substances holding the fibres together are removed. What remains is a white mass of almost pure cellulose, pressed into sheets. These sheets are the raw material for the fibre plant and look like thick, coarse paper.

Making cellulose soluble

The sheets are treated with caustic soda, which makes the cellulose swell and become more reactive. Carbon disulphide is then added, binding to the cellulose and making it soluble. The result is a thick, golden brown liquid that gave viscose its name. The liquid ripens for a while and is filtered before the next step.

What happens in the bath

The solution is pressed through nozzles with many tiny holes into a bath of dilute acid. There the chemicals react, and the cellulose comes out again as long, solid filaments. The filaments are washed thoroughly and dried, and are then ready for spinning. Chemically they are cellulose again, with the molecules arranged in a new way.

From filament to yarn

The long filaments can be used as they are or cut into shorter lengths that are spun into yarn like cotton. Thickness depends on the nozzle holes, length on how the filaments are cut. The yarn is then knitted or woven, dyed and finished. These steps decide the weight, softness and drape of the fabric.

Recovering chemicals

Modern plants recover a large share of the chemicals in a closed system instead of releasing them. That covers caustic soda, sulphur compounds and water. It is one of the most important differences between older and newer production, and it depends on the factory, not the plant species. This also applies to production behind the men's range.

What is left in the finished fabric

After precipitation, washing and finishing, the fibre is cellulose. The chemicals are bound in the process or washed out along the way. The finished fabric is usually tested for residues of harmful substances, which is exactly what schemes like Oeko-Tex check. See the product information in women's most popular styles, and always wash new clothes first.

Lyocell takes another route

Lyocell is a newer method in which cellulose is dissolved directly in an organic solvent without carbon disulphide. The solvent is largely recovered, and the process has fewer steps. The fibre becomes slightly stronger and smoother. Viscose and lyocell both end up as pure cellulose, but the route there is different.

Frequently asked questions

Are there chemical residues in the finished fabric

Fully washed fabric does not contain significant residues. Oeko-Tex tests for exactly this, and a wash before first wear removes what is left from production and transport.

Is lyocell cleaner than viscose

The lyocell process uses a solvent that is largely recovered, and it has fewer steps. How clean a viscose production is depends a great deal on the individual plant.

Why do new clothes sometimes smell

Usually it comes from traces of finishing agents, dye or packaging from storage and transport. The smell normally disappears after the first wash at a normal temperature.