Reactive Dyes: Classification, Dyeing Mechanism, Application & Stripping

 

Introduction

Reactive dyes are a class of highly versatile dyes known for forming covalent bonds with textile fibers. This chemical bonding ensures vibrant colors, excellent wash fastness, and high durability on a wide range of fabrics—especially cellulosic fibers like cotton.

Their ability to chemically react with fibers makes them distinct and valuable in modern textile dyeing. 

 

Table of Contents

1. • What are Reactive Dyes?

   • Why Are They Called Reactive?

   • History of Reactive Dyes

   • Fibers Dyed with Reactive Dyes

   • Trade Names of Reactive Dyes

   • Characteristics of Reactive Dyes

   • Classification of Reactive Dyes

   • Assistants Used in Reactive Dyeing

   • Dyeing Mechanism of Reactive Dyes

   • Application Methods

   • Stripping of Reactive Dyes

   • Hydrolysis of Reactive Dyes

   • Why Low-Affinity Reactive Dyes Are Preferred

   • Knit Fabric Dyeing Process (Recipe & Curve)
   • Final Thoughts 

2. 1. What Are Reactive Dyes?

   Reactive dyes contain reactive groups that form covalent bonds with –OH groups in cellulosic fibers or –NH₂ groups in wool and polyamides. This reaction integrates the dye into the fiber structure.

   Key Reaction Example: 

   D–SO₂–CH₂–CH₂–OSO₃Na + OH–Cell → D–SO₂–CH₂–CH₂–O–Cell + NaHSO₃
   

    

   2. Why Are They Called Reactive?

   Because they react chemically with fibers, forming covalent bonds rather than attaching through weaker forces like hydrogen bonding. This strong bond makes the dye part of the fiber itself, leading to superior colorfastness.

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   🏛 3. History of Reactive Dyes

   Developed by Stephen and Rattee of ICI UK in 1956 to commemorate 100 years of synthetic dyes.

   🎖️ First Reactive Dyes:

3. Procion Yellow R

4. Procion Brilliant Red 2B

5. Procion Blue 3G

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🧵 4. Fibers Dyed with Reactive Dyes

• Cotton

• Rayon

• Flax

• Wool

• Polyamide (Nylon)

• Silk

• Acetate

   

  

  
  

  5. Characteristics of Reactive Dyes Water-soluble and anionic Excellent light and wash fastness Easy to apply at low temperatures Available in powder, liquid, and paste form Bright shades and moderate rubbing fastness Economical and efficient 6. Classification of Reactive Dyes A. Based on Reactive Group Triazine (Procion, Cibacron) Pyridimine (Reactone) Vinyl Sulphone (Remazol) Vinyl Acrylamide (Primazin) B. Based on Reactivity Low: pH 12–12.5 Medium: pH 11–12 High: pH 10–11 C. Based on Dyeing Temperature Cold Brand: 32–60°C (e.g., Procion M) Medium Brand: 60–71°C (e.g., Remazol) Hot Brand: 72–93°C (e.g., Cibacron)
  7. Assistants Used in Dyeing Assistant Function Salt (NaCl)                                                           Improves dye exhaustion Alkali (NaOH, Na₂CO₃, NaHCO₃)                       Fixes dye by maintaining proper pH Urea                        Helps achieve deep shades Soaping Agent            Enhances wash fastness and removes unfixed dye
  8. Dyeing Mechanism Dye Absorption: Electrolytes like salt help dye penetrate fiber. Fixation: Covalent bonds form between dye and fiber using alkali. Wash-Off: Removes unfixed dye for better fastness. 09. Application Methods A. Discontinuous Methods: Exhaust method Hot critical method B. Continuous Methods: Pad–steam Pad–dry Pad–thermofix C. Semi-continuous Methods: Pad–batch (cold/warm) Pad–jig Pad–roll
  10. Stripping of Reactive Dye Used when uneven dyeing occurs. Partial Stripping: 5–10 parts acetic/formic acid Temp: 70–100°C Full Stripping: Sodium hydrosulfite at boil 1% NaOCl for 30 min at room temperature
  11. Hydrolysis of Reactive Dyes Occurs when dye reacts with water instead of fiber, reducing fixation. Prevention Tips: Use alkali and dye just before dyeing Avoid storing dye-alkali mixtures Maintain temperature below 40°C 🧠 12. Why Low-Affinity Dyes Are Preferred Reduce hydrolysis risk Easier removal of hydrolyzed dye Ensures better wash fastness Optimized dye fixation using salt followed by alkali 13. Knit Fabric Dyeing Process (Hot Brand) 📋 Recipe: Ingredient                                              Quantity Anti-creasing Agent  0.3 g/L Sequestering Agent                                        0.5 g/L Glauber Salt 80 g/L Reactive Dye X% Soda Ash 5 g/L Caustic Soda 1 g/L Acetic Acid 0.75 g/L Soap 0.25 g/L M:L 1:10 Time 60 min Temperature 60–100°C

   Process Flow:

1. Add fabric + anti-creasing + sequestering agent

2. Add salt → wait 5 min

3. Add dye → run 30 min (exhaustion)

4. Add alkali → run 50 min (fixation)

5. After-treatment (hot wash → neutralization → soap wash)   

14. After-Treatment of Reactive Dyeing

• Hot wash at 80°C – 10 min

• Acetic acid wash at 60°C – 10 min

• Soap wash at 95°C – 15 min

Ensures removal of unfixed dye and better fastness.

Final Thoughts

Reactive dyes are essential for modern textile dyeing, offering brilliant shades, strong fiber bonding, and versatility across fiber types. Their chemistry, application methods, and dyeing performance make them the go-to choice for cotton and cellulose-based fabrics in both knit and woven sectors.

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