How Much Thiourea Dioxide Should I Use Instead of Sodium Hydrosulfite?
Direct Answer
Direct Answer Our technical data sheet gives the substitution relationship as about one third of the sodium dithionite weight for stripping. Actual dosages by process are set out below.
Recommended recipes
| Process | Thiourea dioxide | Caustic soda (38 Be) | Wetting agent / detergent | Liquor ratio | Temperature | Time |
|---|---|---|---|---|---|---|
| Polyester reduction clearing, cross winder | 0.5 to 1.0 g/L | 2.0 to 4.0 ml/L | 1.0 to 2.0 ml/L | 10:1 to 15:1 | 70 to 95 C | 20 to 30 min |
| Polyester reduction clearing, continuous washing line | 2.0 to 3.0 g/L | 5.0 to 7.0 ml/L | 0.3 to 0.5 ml/L | - | 80 to 95 C | 15 to 80 seconds, by depth of shade |
| Stripping of defective dyeings | 2.0 to 3.0 g/L | 8.0 to 15.0 ml/L | - | 10:1 to 15:1 | boiling | 20 to 60 min |
| Machine cleaning | 2.0 to 3.0 g/L | 5.0 ml/L | 0.5 to 1.5 ml/L depending on soiling | - | boiling | 10 to 60 min |
| Bleaching of polyamide | 0.5% on weight of fabric | as per process | - | - | 90 C | 30 min |
Three points on use
- Temperature: the full reducing effect is only developed above 70 C, and running below that badly understates performance
- Alkali: add the caustic soda only shortly before use rather than preparing the bath in advance
- Stripping: with so many dye classes there is no universal formulation, so treat the table as a starting point and run a bench trial
Bottom line
Start stripping at about one third of the hydrosulfite weight; reduction clearing runs at 0.5 to 1.0 g/L and 70 to 95 C, while stripping and machine cleaning run at 2.0 to 3.0 g/L at the boil.
Sources
- 我司产品技术数据表《THIOUREA DIOXIDE Technical Data Sheet》（TDO-TDS，签发日期 2024-05-08）
- US5958184A, Process for producing thiourea dioxide（还原当量质量比、碱中水解式、木浆与脱墨浆等当量漂白实施例），https://patents.google.com/patent/US5958184A/en
- Effective reduction clearing parameters involving alternative reducing agent（2021），DOI 10.54693/piche.04916
- Performance Evaluation of Hydrose and Thiourea Dioxide as Stripping Agents for Reactive Dyes，AJER 7(2), 2018，https://www.ajer.org/papers/Vol-7-issue-2/ZF070201250258.pdf
- Optimization of indigo dyeing with sodium hydrosulfite or thiourea dioxide as reductant（2014）
- 中国棉纺织行业协会《如何用还原染料染棉织物？》(China Cotton Textile Association, How to dye cotton fabric with vat dyes), 2015，http://ccta.org.cn/scytj/rdht/jssj/201503/t20150316_1921005.html
- 我司技术资料《Thiourea Dioxide vs Sodium Hydrosulphite》（2019-07-31）还原电位与用量对比，https://dasteck.com/News/99.html
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