How do I strip colour from viscose, modal and lyocell?

Direct answer

Viscose, modal and lyocell are chemically close to cotton, but their wet strength is much lower, especially viscose. The main risk in stripping is not failing to strip the colour; it is damaging the fibre while it is wet and simultaneously exposed to mechanical action and alkali. Using thiourea dioxide here means going mild, short and low-alkali.

1. Three differences from stripping cotton

The conclusion: do not carry over a cotton stripping recipe. Every parameter moves down.

2. Conservative starting point

3. Four operating points

1. Confirm the wet-strength loss first, then check the shade, never the other way round

2. Determine the alkali separately: thiourea dioxide needs alkali to activate, but these fibres tolerate less of it, so the two must be balanced independently

3. Heat and cool slowly: sudden temperature changes make creasing and strength loss worse

4. Neutralise and rinse thoroughly afterwards: residual alkali keeps attacking the fibre

4. When not to use reductive stripping

• Rework fabric whose fibre is already damaged, for example over-mercerised or over-bleached greige
• Cases needing a large depth reduction: reductive stripping has limited reach on heavy shades, and forcing it damages the fibre first
• Blends containing alkali-sensitive components; set the conditions by the most fragile component

Sources

Starting values are the recommended ranges from our technical data sheet and published literature. Wet strength varies widely between regenerated cellulose fibres, so confirm on a bench sample of your own greige before running production.