Usage & Application in Textile Industry

Sodium Hydrosulphite, also known as Sodium Dithionite, is a powerful reducing agent widely used in the textile industry. It is essential in dyeing, printing, and bleaching processes, especially for vat dyes, sulphur dyes, and indigo.

1. Main Applications

✔ 1. Vat Dyeing (Indigo & Other Vat Dyes)

Sodium hydrosulphite is the primary reducing agent used to convert vat dyes from their insoluble oxidized form to soluble leuco form, enabling dye molecules to penetrate cotton fibers.

Functions:

Reduces vat dyes in dye baths

Ensures full solubilization of dye

Facilitates deep, even dye uptake

Maintains dye bath stability

Used in:

Denim dyeing (Indigo)

Cotton vat dyeing processes

✔ 2. Sulphur Dyeing

Vital for reducing sulphur dyes into their soluble leuco form.

Benefits:

Improves color depth and fixation

Enhances levelness during dyeing

Provides strong shades with excellent wash fastness

✔ 3. Stripping & Color Removal

Used to remove excess dyes from:

Printed fabrics

Faulty dye lots

Over-dyed materials

Applications include:

Stripping reactive dyes

Removing color stains/spots

Correcting dyeing defects

✔ 4. Bleaching of Textiles

Used as a mild reducing bleach, especially for:

Wool

Silk

Polyamide

Delicate fabrics that cannot tolerate oxidative bleaching

Advantages:

Does not damage fiber structure

Effective for removing unwanted tint (e.g., off-shades)

Brightens and cleans sensitive fibers

✔ 5. Cleaning of Machines & Equipment

Sodium hydrosulphite removes:

Rust stains

Iron contamination

Oxidized residues in dyeing machines and pipelines

Often used in machine cleaning cycles (MCC).

✔ 6. After-Treatment of Dyed Fabrics

Used to improve:

Color fastness

Shade brightness

Levelness by reducing unfixed dyes on fabric surface

2. Dosage Guidelines (Industry Range)

Exact dosage varies depending on dye type, shade depth, and process conditions.

Vat dyeing: 2–10 g/L

Sulphur dyeing: 1–8 g/L

Stripping/reactive dye removal: 5–20 g/L

Bleaching delicate fibers: 0.5–2 g/L

Machine cleaning: 1–5 g/L

3. Advantages in Textile Processing

Strong reducing capability

Improves dye solubility and penetration

Produces level, uniform shades

Enhances color fastness

Low fiber damage compared to oxidative methods

4. Safety & Handling

Keep away from moisture and heat

Store in cool, dry, sealed containers

Avoid contact with acids (releases SO₂ gas)

Use gloves, goggles, and protective equipment