Dasteck ChemicalsYantai Dasteck Chemicals Co., Ltd.
Direct answer
Thiourea dioxide is a general-purpose reducing agent that covers most processes needing reduction, but how it is applied varies a great deal by dye class: in some it is the main agent, in others it suits stripping only, and in others it must be blended.
Suitability matrix
| Dye class | Process | Suitability | Note |
|---|---|---|---|
| Vat dyes | Vat dyeing | Usable in exhaust dyeing | Pad-steam replacement needs a corrected dye formulation and may shift the hue |
| Sulphur dyes | Dyeing and stripping | Suitable | Common on cotton and cotton blends |
| Indigo | Reduction | Suitable | 80 °C, 1.5 to 3.5 g/L |
| Reactive dyes | Stripping and rework | Suitable | Good on light and medium shades; deep shades need a blend |
| Disperse dyes (polyester) | Reduction clearing after dyeing | Best application | 0.5 to 1.0 g/L, 70 to 95 °C |
| Disperse dyes (polyester) | Stripping | Suitable | Watch for over-reduction shifting the shade |
| Acid and direct dyes (wool, silk) | Stripping | Suitable | Mild alkali, 60 to 80 °C; control strength loss |
| Pigment coloration | - | Not applicable | A reducing agent does not act on pigment particles |
Three general rules
1. Alkali is essential: without adequate pH there is no reduction; add alkali before the product
2. Temperature must be sufficient: full effect above 70 °C; 70 to 95 °C for reduction clearing, boiling for stripping and machine cleaning
3. Blend for deep shades: black and grey stripping at roughly 1:10 (thiourea dioxide : hydrosulfite)
Two cases that need a bench trial
Sources
The above reflects established industry practice and the ranges in our technical data sheet; confirm by bench trial for the specific dye.