Textile Dye Stripping Guide: Methods for Different Dye Types

In textile dyeing and finishing, issues such as shade variation, uneven dyeing, or overly deep color are quite common. In such cases, dye stripping (also known as decolorization or color removal) becomes an essential corrective process.

This article provides a practical overview of dye stripping methods for different dye types, helping you choose the right solution in real production.

What is Dye Stripping?

Dye stripping is a chemical process used to:

Break the bond between dye and fiber, or Destroy the chromophore structure of the dye

As a result, the dye is either removed from the fiber or loses its color, allowing for shade correction or re-dyeing.

It is commonly referred to as:

• Dye Stripping

• Color Removal

• Textile Decolorization

  

Types of Dye Stripping Agents

Dye stripping agents are mainly divided into two categories:

1. Reductive Stripping Agents

Common products:

• Sodium Hydrosulfite

• Rongalite

Mechanism:
These agents reduce the chromophore groups (such as azo bonds –N=N–) into non-colored structures (e.g., amines), resulting in decolorization.

Features:

• Effective for azo dyes

• May be reversible for certain dye structures (e.g., anthraquinone dyes), leading to possible color recovery

2. Oxidative Stripping Agents

Common products:

• Hydrogen Peroxide

• Sodium Hypochlorite

Mechanism:
Oxidation breaks down the dye structure, including:

• Azo bond cleavage

• Amino group oxidation

• Destruction of metal complexes

Features:

• Irreversible reaction

• More complete color removal

• Particularly effective for disperse and anthraquinone dyes

Dye Stripping Processes for Different Dye Types

1. Reactive Dyes

Light Shades:

• NaOH: 2 g/L + Hydrosulfite: 4 g/L

• 95°C × 30 min
  → Hot wash → Rinse

Dark Shades:

• NaOH: 4 g/L + Hydrosulfite: 8 g/L

• 95°C × 40 min
  → Hot wash → Oxidation → Hot wash → Rinse

2. Sulfur Dyes

For slight correction:

• Treat with sodium sulfide (~6 g/L) at high temperature

For severe cases:

• Use sodium hypochlorite or hydrosulfite

Light Shade Process:

• Padding with NaClO (5–6 g/L, 50°C)
  → Steaming (~2 min) → Washing → Drying

Dark Shade Process:

• Oxalic acid (15 g/L, 40°C) → Drying
  → NaClO (6 g/L, 30°C × 15 s)
  → Washing → Drying

Batch Process:

• Sodium sulfide: 5–10 g/L

• Soda ash: 2–5 g/L

• 80–100°C × 15–30 min

3. Acid Dyes

Standard Process:

• Ammonia: 20–30 g/L

• Anionic wetting agent: 1–2 g/L

• Boiling for 30–45 min

Improvement Tip:

• Pre-treatment with hydrosulfite (10–20 g/L at 70°C) enhances stripping

Alternative:

• Oxidative stripping can also be applied

Special Fibers

Silk:

• Sodium carbonate 1 g/L

• Wetting agent 2 g/L

• Hydrosulfite 2–3 g/L

• 60°C × 30–45 min
  → Mordant treatment → Oxidation bleaching

Wool:

• Gradual heating to boil, hold 20–30 min

Nylon:

• NaOH 1–3% + detergents

• 98–100°C × 20–30 min
  → Neutralization with acetic acid

4. Vat Dyes

Reduction system:

• NaOH + Hydrosulfite

• 70–80°C × 30–60 min

Principle:
Re-reduction of dye to soluble form for removal

5. Disperse Dyes (Polyester)

Method 1 (Reductive):

• Rongalite + carrier

• 100–130°C, pH 4–5

Method 2 (Oxidative):

• Sodium chlorite + formic acid

• pH 3.5

Best practice: Combine both methods for optimal results

6. Cationic Dyes (Acrylic)

Typical procedure:

1. Monoethanolamine (5 mL/L) + NaCl (5 g/L), boil 1 hour

2. Oxidation with sodium hypochlorite

3. Reduction or neutralization

Alternative:

• Acid boiling with detergent (pH ~4, 1–2 hours)

7. Insoluble Azo Dyes

• NaOH + Hydrosulfite system

• Anthraquinone used as indicator

 Red color = normal reaction
Yellow/brown = insufficient chemicals

8. Pigments

Pigments are difficult to remove and usually only partially stripped:

• KMnO₄ treatment → Oxalic acid reduction→ Washing → Drying

Important Notes for Dye Stripping

• Always conduct lab trials before bulk production

• Ensure thorough washing (hot and cold) after stripping

• Use short treatment times, repeat if necessary

• Carefully control:

• Temperature

• pH

• Chemical dosage

 Avoid:

• Over-stripping

• Uneven results

• Fabric damage

Conclusion

Dye stripping is a controlled chemical process that requires careful selection based on:

• Dye type (reactive, disperse, vat, etc.)

• Fiber type (cotton, polyester, wool, etc.)

• Shade depth

In practice:

• Reductive stripping → widely used, cost-effective

• Oxidative stripping → stronger, more complete

• Combined methods → most reliable