Reactive dyes: Properties | Classification & Mechanism 

What is Reactive Dye?

▪ Reactive dye contains a reactive group, which makes the covalent bond with fiber & becomes part of the fiber.  

▪ General formula: D-X-Y Here, D= Chromophore, X= Bridge & Y= Functional group. ▪ Reactive dyes make covalent bond with fiber & partially hydrolysis in water: D-X-Y + Cell-OH → D-X-Y-O-Cell 

D-X-Y + H-OH → D-X-Y-OH 

Properties of Reactive Dyes/Why So Popular: 

✔ Water Soluble dyes. 

✔ Makes covalent bonds with the fibers. 

✔ A certain amount of dye is hydrolyzed during dyeing (10-60%) 

✔ Dyeing is carried out in alkaline conditions (PH = 11.5). 

✔ A huge electrolyte is necessary for dyeing with reactive dyes. 

✔ Fastness (wash, light, Rubbing, perspiration) properties are generally good.

✔ Easy applicable to cellulosic as well as protein fibers. 

✔ Very popular and widely used in the wet processing industry in Bangladesh.

✔ Comparatively cheap. 

✔ All kinds of shades are found. 

Classification of Reactive Dyes: 

▪ On the Basis of Reactive group: Two types 

1. Halogenated heterocycles: 
2. Triazine group : Example: Procoin, Cibacron 
3. Pyrimidine group: Example: Reactone 
4. Quinoxaline group: Example: Levafix 
5. Activated Vinyl compounds: 
6. Vinyl Sulphone (D-SO2-CH2-CH2-) Ex: Ramazol. 
7. Vinyl Sulphonamide (D-SO2-NH-CH2-CH2-) Ex. Levafix 
8. Vinyl acrylamide (D-NH CO-CH2-CH2-) Ex: Primazine 

▪ On the Basis of Reactivity: 

1. High reactivity : Ex: Procion M 
2. Moderate reactivity: Ex: Liva fix-E 
3. Low reactivity : Ex: Premazine 

▪ On the Basis of application: 

1. Cold Brand 
2. Hot Brand. 

▪ On the Basis of chemical structure: 

1. Chloro triazinyl Reactive dyes. 
2. Monochloro dyes. 
3. Dichloro/Bifunctional 
4. Trichloro. 
5. Vinyl sulphone Dyes 
6. Heterocyclic halogen containing Reactive dyes

Hydrolysis of Reactive Dye: If the solution of reactive dye is kept for a long time, its concentration drops by reacting with the hydroxyl group of water, which is called Hydrolysis of reactive dye. The reaction is as follows: 

Dye-X-Y + H-OH → Dye-X-Y-OH, Here, X= Bridge & Y= Functional group Example: In case of Triazinyl dyes 

Dye 

C 

HN 

N 

C 

Cl 

N 

+ H-OH Dye 

C 

HN 

N 

C 

OH N 

N C 

Cl 

Dihydroxy group 

N C 

OH 

Dyeing mechanism of reactive dye: 3 stages 

1. Dye absorption: When fiber is immersed in dye liquor, an electrolyte i.e. NaCl is added to assist the exhaustion. This electrolyte neutralizes the negative charge created in the fiber surface and puts extra energy to increase dye absorption. 
2. Fixation: Fixation means the reaction of the reactive group of dye with the terminal –OH or -NH2 group of fiber thus forming a strong covalent bond. This is controlled by maintaining  PH with alkali i.e. caustic soda, soda ash, or NaHCO3. They create proper PH in the dye bath and act as the dye-fixing agent. The reaction that takes place in this stage is shown below: 

D-SO2-CH2-CH2-OSO3Na + OH-Cell → D-SO2-CH2-CH2-O-Cell + NaHSO3 D-SO2-CH2-CH2-OSO3Na + OH-Wool → D-SO2-CH2-CH2-O-Wool + NaHSO3 3. Wash-off: After dyeing, a good wash must be applied to remove unfixed dyes from surface. This is essential for level dyeing and good wash-fastness. It is done by a series of  hot wash, cold wash and soap solution wash. 

Controlling Parameters: 

✔ PH: 10-11.5 

✔ Dyeing time↑→ Hydrolysis ↑, Exhaustion takes place in 20-30 min 

✔ Temp. of dyeing↑→ Hydrolysis↑, 40o-100oC temp. is applied. 

✔ M:L Ratio: 1:5–1:20 

✔ Concentration of electrolyte: Common salt and glauber’s salt, Concentration of salt may be 20-100 g/L depending on the shade (0.1-5.0%) 

Factors To Be Considered: 

✔ Selection of dyeing method: Discontinuous, semi-continuous (pad batch/pad jig method), or continuous (pad steam/pad dry/pad thermo-fix method). 

The selection of the method depends on the:

– Speed of dye diffusion on the fiber 

– Affinity of dye to fiber 

– Reactivity of dyestuff. 

✔ Selection of Brand. 

– Hot brand 

– Medium brand 

– Cold brand 

✔ Cost of dyes. 

✔ Chemical groups. 

✔ Quality of products 

✔ Fastness required. 

✔ Quality of dyes. 

✔ Availability of dyes. 

✔ Reproducibility.

Dyeing With Cold Brand Reactive Dye: 

▪ Recipe: 

Dyestuff: 3% 

Salt: 60 gm/L 

Soda ash: 15 g/L 

M: L= 1:10 

Temp: 600C, Time: 1 hr 

▪ Auxiliaries & water are added in dye bath & after 5 min. mtl & dye is added.  

▪ After 10 min. salt is added & heated to 400-500C, kept 20-30 min. for exhaustion.  

▪ Then alkali is added & heated for 40-60 min at 50-600C for fixation. 

▪ After dyeing, the material is put into 1% acetic acid at 600C for 10 min for neutralizing. Then treated with 1g/l soap solution to remove unfixed dye. Then hot & cold washed. 

Dyeing With Hot Brand Reactive Dye: 

▪ Recipe: 

Dyestuff: 4% 

Salt: 80g/L 

Soda ash: 20g/L 

M: L= 1:15 

Temp: 50-90oC, Time: 1-1.5 hrs 

▪ Dye paste is prepared with cold water, and then prepared for dye solution at 50oC.  

▪ Fabric is dyed for 20 min & raising temp. at 60oC, ½ Salt is added & dyed for 10 min. 

▪ Then rest of ½ salt is added & dyed 30 min.  

▪ Temp. is raised to 90oC & Soda ash is added & dyed for 40-60min.  

▪ Then washing with Cold & Hot water. Then soaping with 2g/l detergent & cold wash. 

Trade Names of Reactive Dyes: 

Dye Chemical Structure Company 

Cl 

N 

1. Procion M 
2. Procion H Cibacron 

D ICI 

HN N 

N 

Cl 

NHR 

N 

DICI 

HN N 

N 

Cl 

3. Remazol D-SO2-CH2CH2-O-SO3Na F Hoechst 
   

N 

Cl 

4. Levafix E 

D OCHNF Bayer 

N 

N 

Cl 

Cl 

5. Procion SP Stripping: 

D HNICI 

N 

N 

Cl 

1. Partial stripping methods: Partial stripping is obtained by treating the dyed fabric with dilute acetic acid (0.5-1%) or formic acid (0.2-1%) at 100oC.  
2. Full stripping: For complete stripping, the goods are firstly treated with Na2S2O4 &  Sodium hydrosulfite at boil temp. Then at room temperature for 30 min.