Dasteck ChemicalsYantai Dasteck Chemicals Co., Ltd.
Thiourea dioxide (TDO) is a white crystalline, odourless reducing agent that develops its full reducing power above 70 C in the presence of alkali. In textile processing it replaces sodium hydrosulfite in polyester reduction clearing, dye stripping, machine cleaning and vat dyeing, typically at about one third of the hydrosulfite dosage.
20 questions, grouped by topic
Key data at a glance
| Process | Thiourea dioxide | Caustic soda (38 °Bé) | Auxiliary | Temperature | Time |
|---|---|---|---|---|---|
| Polyester reduction clearing, cross winder or overflow | 0.5–1.0 g/L | 2.0–4.0 ml/L | Wetting agent 1.0–2.0 ml/L | 70–95 °C | 20–30 min |
| Polyester reduction clearing, continuous washing line | 2.0–3.0 g/L | 5.0–7.0 ml/L | Wetting agent 0.3–0.5 ml/L | 80–95 °C | 15–80 s |
| Stripping of defective dyeings | 2.0–3.0 g/L | 8.0–15.0 ml/L | – | boiling | 20–60 min |
| Dyeing-machine cleaning | 2.0–3.0 g/L | 5.0 ml/L | Detergent 0.5–1.5 ml/L | boiling | 10–60 min |
| Polyamide bleaching | 0.5% on weight of fabric | as per process | – | 90 °C | 30 min |
Substitution ratio: about one third of the sodium hydrosulfite weight for stripping; liquor ratio 10:1 to 15:1 for exhaust processes. Source: our technical data sheet.
Product data
| Item | Value |
|---|---|
| Appearance | White crystalline powder, odourless |
| pH value (20 °C, 1% solution) | Approx. 4.5 |
| Solubility in water (20 °C) | 26.7 g/L |
| Bulk weight (20 °C) | Approx. 750 g/L |
| Storage | Sealed, cool and dry, not above 25 °C; at least 6 months |
Can Thiourea Dioxide Really Replace Sodium Hydrosulfite?
Thiourea dioxide replaces sodium hydrosulfite in polyester reduction clearing, stripping and machine cleaning at about one third the dosage, but never weight for weight.
Why Would a Textile Factory Switch from Sodium Hydrosulfite?
Four reasons textile mills switch from sodium hydrosulfite to thiourea dioxide: safer storage, no sulphur odour, better reproducibility and lower cost per tonne of fabric.
Is Thiourea Dioxide Stronger than Sodium Hydrosulfite?
Thiourea dioxide has a reduction potential of about -1230 mV against -1080 mV for hydrosulfite; on equal reducing equivalents 1 kg of hydrosulfite corresponds to about 0.62 kg.
How Much Thiourea Dioxide Should I Use Instead of Sodium Hydrosulfite?
Dose at about one third of the hydrosulfite weight for stripping, or 0.5 to 1.0 g/L at 70 to 95 C for polyester reduction clearing. Full recipe table inside.
Can Thiourea Dioxide Reduce the Chemical Consumption?
Thiourea dioxide cuts reducing-agent consumption to about one third, but caustic demand may not fall. Compare chemical cost per tonne of fabric, not price per kilogram.
What Is the Real Cost Advantage?
Not in unit price. The advantage sits in an effective dose of about one third the hydrosulfite weight, easier storage and transport, a cleaner workshop and fewer reworks.
Does Thiourea Dioxide Work Particularly Well for Polyester Reduction Clearing?
Polyester reduction clearing is thiourea dioxide's strongest application: 0.5 to 1.0 g/L at 70 to 95 C on a cross winder, or 2.0 to 3.0 g/L on a continuous washing line.
Can Thiourea Dioxide Be Used for Color Stripping?
Yes. A typical stripping recipe is 2.0 to 3.0 g/L thiourea dioxide with 8.0 to 15.0 ml/L caustic soda at the boil for 20 to 60 minutes, replacing about one third of the hydrosulfite.
Can Thiourea Dioxide Completely Replace Hydrosulfite in Stripping?
Light and medium shades convert fully; black and grey shades need a 1:10 blend with hydrosulfite, and vat pad-steam replacement requires a corrected dye formulation.
Can Thiourea Dioxide Be Used for Dyeing-Machine Cleaning?
Yes: 2.0 to 3.0 g/L of thiourea dioxide with 5.0 ml/L caustic soda and 0.5 to 1.5 ml/L detergent, circulating at the boil for 10 to 60 minutes, with no sulphur odour.
What Is the Recommended Laboratory Test?
Run a reference plus a dose gradient centred on one third of the hydrosulfite weight, then adjust alkali and temperature, measuring whiteness, stripping efficiency, delta E and fastness.
Can You Provide a Cost Calculation for My Factory?
Yes. Send your hydrosulfite and caustic prices, dosage, liquor ratio, machine type and output, and we return reducing-agent cost, alkali cost and cost per tonne of fabric.
What About Safety and Storage?
The SDS lists acute oral and inhalation toxicity category 4, skin irritation category 2, serious eye damage category 1, STOT single and repeated exposure, and self-reactive Type G.
Does Thiourea Dioxide Have an Odor Problem Like Hydrosulfite?
No. Hydrosulfite releases irritant sulphur dioxide in hot alkali; thiourea dioxide is essentially odourless under normal conditions and needs ventilation only during long high-temperature holding.
Will Thiourea Dioxide Damage Polyester Fabric?
Not under recommended conditions. Damage comes from caustic soda combined with high temperature, not thiourea dioxide. Verify with weight loss below 1% and strength retention above 95%.
Will Thiourea Dioxide Affect the Color Shade?
Less than with hydrosulfite because release is controlled, but overshooting dose, temperature or alkali still shifts the shade. Judge by colour difference, keeping delta E within 0.5.
How Much Thiourea Dioxide Would I Need per Tonne of Fabric?
Polyester reduction clearing uses about 5 to 15 kg per tonne of fabric and stripping about 20 to 45 kg. Set the recipe in g/L first, then convert through the liquor ratio.
Is Thiourea Dioxide Suitable for Pulp and Paper Applications?
Yes. Thiourea dioxide is well established for reductive bleaching of deinked and mechanical pulp without delignification, judged on brightness, ERIC, dirt count and yield.
Can You Provide Free Samples for Testing?
Yes. New customers receive a standard free 200 g sample; existing and large accounts are agreed case by case, and larger needs can be reviewed for reduced sample charge and freight.
How Do I Start a Free Thiourea Dioxide Replacement Trial?
Five steps: send the process data, agree the protocol, take a free 200 g sample for the bench trial, scale up to a works trial and issue the process document.
What is the specification, CAS number and packing of thiourea dioxide?
What transport class is thiourea dioxide, and what does export involve?
How should thiourea dioxide be dissolved and made up?
The dosage is right, so why is thiourea dioxide still not working?
What is the complete process guide for polyester reduction clearing?
How is thiourea dioxide used on wool and silk?
Which dye classes can thiourea dioxide be used with?
How does thiourea dioxide compare with other reducing agents?
How do I handle the common complaints after switching to thiourea dioxide?
How do I calculate the cost of using thiourea dioxide?
How should incoming thiourea dioxide be inspected?
How should the reductive bleaching stage for deinked pulp be designed?