Can Thiourea Dioxide Completely Replace Hydrosulfite in Stripping?

Direct Answer

Direct Answer Not completely, but it covers most of the ground. Our technical data sheet also notes that stripping has to be trialled against the dye system in use.

Where it fully replaces hydrosulfite

Light and medium-depth stripping, first-time stripping, shading correction and rework, and light stripping whose only purpose is to remove unfixed dye. In these cases thiourea dioxide runs on its own at about one third of the hydrosulfite weight, and the working environment improves noticeably.

Where it does not

• Black and grey shade stripping
• Stripping of carbon-black dyed fabric
• Cases where the dyed fabric has to be brought close to its original white

In these situations hydrosulfite remains the stronger stripping agent, and the established practice is a blend of roughly 1 : 10 (thiourea dioxide : hydrosulfite).

A specific note on vat pad-steam dyeing

In the pad-steam process thiourea dioxide can replace sodium dithionite, but hue errors can occur and the dye formulation has to be corrected. A comparative trial is essential before changing the process.

How to decide

In the bench trial, run three arms on the same fabric and dye: thiourea dioxide only, hydrosulfite only, and the 1 : 10 blend. Compare stripping efficiency, shade, strength and handle, and let the data decide rather than relying on experience.

Bottom line

Light and medium shades can be converted. Deep shades and stripping back to white need a blend or hydrosulfite, and a pad-steam conversion requires a corrected formulation.

Sources

1. 我司产品技术数据表《THIOUREA DIOXIDE Technical Data Sheet》（TDO-TDS，签发日期 2024-05-08）
2. 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