REACTIVE DYES FOR COTTON

Introduction: 
A dye, which is capable of reacting chemically with a substrate to form a covalent dye substrate linkage, is known as reactive dye.

Here the dye contains a reactive group and this reactive group makes covalent bond with the fibre polymer and act as an integral part of fibre. This covalent bond is formed between the dye molecules and the terminal –OH (hydroxyl) group of cellulosic fibres on between the dye molecules and the terminal –NH2 (amino) group of polyamide or wool fibres.

History: 
Reactive dyes first appeared commercially in 1956, after their invention in1954 by Rattee & Stepheness at the Imperial chemical Industry (ICI). Dyestuffs Divion site in Bleckley, Manchetor. UK.

Usages: 

By reactive dyes the following fibres can be dyed successfully:
1) Cotton, rayon, flax and other cellulosic fibres.
2) Polyamide and wool fibres.
3) Silk and acetate fibres.

Trade names:

Trade name	Manufacturer	Country
Munnactive	Munna Dyechem	India
Ciba cron	Ciba	Switzerland
Remazol	Hoechst	Germany
Levafix	Bayer	Germany
Reactone	Geigy	Switzerland
Primazin	BASF	Germany
Drimarine	Sandoz	Switzerland

Properties of reactive dye: 

1) Reactive dyes are cationic dyes, which are used for dyeing cellulose, protein and polyamide fibres.
2) Reactive dyes are found in power, liquid and print paste form.
3) During dyeing the reactive group of this dye forms covalent bond with fibre polymer and becomes an integral parts of the fibre.
4) Reactive dyes are soluble in water.
5) They have very good light fastness with rating about 6. The dyes have very stable electron arrangement and can protect the degrading effect of ultra-violet ray.
6) Textile materials dyed with reactive dyes have very good wash fastness with rating Reactive dye gives brighter shades and has moderate rubbing fastness.
7) Dyeing method of reactive dyes is easy. It requires less time and low temperature for dyeing.
8) Reactive dyes are comparatively cheap
9) Reactive dyes have good perspiration fastness with rating 4-5.
10) Reactive dyes have good perspiration fastness.

General structure of reactive dyes: 

The general structure of reactive dye is: D-B-G-X.

Chemical structure of reactive dyes

Chemical structure of reactive dyes

Here,

D= dye part or chromogen (color producing part)
Dyes may be direct, acid, disperse, premetallised dye etc.
B = bridging part.
Bridging part may be –NH- group or –NR- group.
G = reactive group bearing part.
X= reactive group.

Classification of reactive dyes: 

Reactive dyes may be classified in various ways as below:

1) On the basis of reactive group: 
a) Halogen (commonly chlorine) derivatives of nitrogen containing heterocycle, like 3 types-
· Triazine group
· Pyridimine group
· Quinoxaline dyes
Example: 
Triazine derivatives: procion, cibacron.
Pyridimine derivatives: reactone
Quinoxaline derivatives: levafix.

b) Activated vinyl compound: 
· Vinyl sulphone
· Vinyl acrylamide
· Vinyl sulphonamide.
Example: 
Vinyl sulphone: Munnactive
Vinyl acrylamide: primazine
Vinyl sulphonamide: levafix.

2) On the basis of reactivity: 
a) Lower reactive dye: Medium reactive dye: here pH is maintained 11-12 by using Na2CO3 in dye bath.
b) Higher reactive dye: here pH is maintained 10-11 by using NaHCO3 in dye bath.

3) On the basis of dyeing temperature:

a) Cold brand: 
These types of dyes contain reactive group of high reactivity. So dyeing can be done in lower temperature i.e. 320-600C.
For example: MUNNACTIVE M, LIVAFIX E.

b) Medium brand: 
This type of dyes contains reactive groups of moderate reactivity. So dyeing is done in higher temperature than that of cold brand dyes i.e. in between 600-710C temperatures.
For example, Munnactive, Livafix are medium brand dyes.

c) Hot brand: 
This type of dye contains reactive groups of least reactivity. So high temperature is required for dyeing i.e. 720-930 C temperature is required for dyeing.
For example MUNNACTIVE H, CIBACRON are hot brand dyes.

Dyeing mechanism of reactive dye: 

The dyeing mechanism of material with reactive dye takes place in 3 stages:-

1. Exhaustion of dye in presence of electrolyte or dye absorption.
2. Fixation under the influence of alkali.
3. wash-off the unfixed dye from material surface.

Now they are mentioned below:

Dye absorption: 
When fibre is immersed in dye liquor, an electrolyte is added to assist the exhaustion of dye. Here NaCl is used as the electrolyte. This electrolyte neutralize absorption. So when the textile material is introduces to dye liquor the dye is exhausted on to the fibre.

Fixation: 
Fixation of dye means the reaction of reactive group of dye with terminal –OH or-NH2 group of fibre and thus forming strong covalent bond with the fibre and thus forming strong covalent bond with the fibre. This is an important phase, which is controlled by maintaining proper pH by adding alkali. The alkali used for this create proper pH in dye bath and do as the dye-fixing agent. The reaction takes place in this stage is shown below: -

1. D-SO₂-CH₂-CH₂-OSO₃Na + OH-Cell   =  D-SO₂-CH₂-CH₂-O-Cell + NaHSO₃

2. D-SO₂-CH₂-CH₂-OSO₃Na + OH-Wool   =   D-SO₂-CH₂-CH₂-O-Wool + NaHSO₃

3. Wash-off: 

As the dyeing is completed, a good wash must be applied to the material to remove extra and unfixed dyes from material surface. This is necessary for level dyeing and good wash-fastness. It is done by a series of hot wash, cold wash and soap solution wash.

Application method: 

These are 3 application procedures available:
1. Discontinuous method-

-Conventional method
-Exhaust or constant temperature method
-High temperature method
-Hot critical method.

2. Cotinuous method-

-Pad-steam method
-Pad dry method
- Pad thermofix method

3. Semi continuous method-

- Pad roll method
- Pad jig method
- Pad batch method.

Stripping of reactive dye: 

The reactive dye cannot be satisfactory stripped from fibre due to covalent bond between dye molecule and fibre. Stripping becomes necessary when uneven dyeing occurs.

Partial stripping: 
Partial stripping is obtained by treating the dyed fabric with dilute acetic acid or formic acid. Here temperature is raised to 70-100°C and treatment is continued until shade is product of hydrolysis. The amount of acid used is as below: -

Glacial acetic acid : 5-10 parts
With water :1000 parts
Or
Formic acid :2.5 to 10 parts
With water :1000 parts
Temperature : 70 - 100°C
Time : until desired shade is obtained.

Different methods of reactive dye application: 

1) Pad-batch method.
Pad batch processes are of two types-

a) Pad (alkali)-batch (cold) process.
b) Pad (alkali)-batch (warm or hot) process.

2) Pad dry method
3) Pad steam method.

Conclusion: By this experiment we came to know the reactive dyes are of the least reactivity because they take more temperature and more time for dyeing.