Viscose

Chemically, viscose is cellulose, so it takes the same dyes as cotton. The difference is durability: it loses a large share of its strength when wet, and mechanical action that is normal for cotton turns into damage on viscose.

Why can viscose not be run like cotton?

Viscose is regenerated cellulose. Its cellulose chains are shorter and less ordered than cotton's; the fibre takes up more water, swells, and in the wet state loses roughly half its strength.

In practice this means the same recipe, machine and cycle time give a different result on viscose. Most of the problems, from rope marks through to tearing, come not from the chemistry but from the mechanical action applied to the fabric.

Why are crease and rope marks more common on viscose?

A swollen fibre loses its elasticity, and a fold does not spring back. Viscose running in rope form in a jet passes the same crease line through the same point again and again until the mark is permanent.

Three measures work together: raise the liquor ratio, reduce machine speed, and use an anti-creasing agent. The agent helps the fabric slide over itself; on its own it cannot rescue a wrong machine setting. See the crease marks article.

Dyeing and washing off

Viscose is dyed with reactive and direct dyes. It takes dye up faster than cotton, so levelness control starts earlier and salt is added in stages.

Removing hydrolysed dye after reactive dyeing is just as necessary here, and reactive washing-off agents are formulated for it. Wash temperature and mechanical action are limited by the fibre's wet strength. Method: washing off after reactive dyeing.

Where wet fastness still falls short, direct and reactive dye fixing agents come in.

Is cellulase used on viscose?

It is, but within a narrow window. Cellulase cuts cellulose, and because viscose chains are already short the same dosage costs more strength than it would on cotton.

If the treatment is run, dosage is kept low, time is shortened and the enzyme is always deactivated. The reasoning is in enzyme deactivation. Working conditions are given per product in the anti-pilling enzymes family.

Pre-treatment

Viscose does not need as severe a bleach as cotton; its load of natural colouring matter and pectin is low. Excess alkali and long peroxide exposure weaken the fibre without buying anything. Sequestrant and stabiliser choice again follows water hardness.

Which product groups are used on viscose?

Anti-creasing agents, wetting agents, sequestering agents and stabilisers, washing agents, fixing agents and finishing agents.