Name of the experiment:
Dyeing process of cotton fabric with reactive dyes.
A dye, which is capable of reacting chemically with a substrate to form a covalent dye substrate linkage, is known as reactive dye. Nowadays reactive dyes are widely used in dyeing cotton materials. It reacts with fiber in presence of alkali and adheres as a part of fiber.
Here the dye contains a reactive group and this reactive group makes covalent bond with the fiber polymer and act as an integral part of fiber. This covalent bond is formed between the dye molecules and the terminal –OH (hydroxyl) group of cellulosic fibers on between the dye molecules and the terminal –NH2 (amino) group of polyamide or wool fibers.
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.
By reactive dyes the following fibers can be dyed successfully:
- Cotton, rayon, flax and other cellulosic fibers.
- Polyamide and wool fibers.
- Silk and acetate fibers.
Trade names of reactive dyes:
Some trade names of this dye are mentioned:
Properties of reactive dye:
- Reactive dyes are cationic dyes, which are used for dyeing cellulose, protein and polyamide fibers.
- Reactive dyes are found in power, liquid and print paste form.
- During dyeing the reactive group of this dye forms covalent bond with fiber polymer and becomes an integral parts of the fiber.
- Reactive dyes are soluble in water.
- 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.
- Textile materials dyed with reactive dyes have very good wash fastness with rating. Reactive dye gives brighter shades and has moderate rubbing fastness.
- Dyeing method of reactive dyes is easy. It requires less time and low temperature for dyeing.
- Reactive dyes are comparatively cheap
- Reactive dyes have good perspiration fastness with rating 4-5.
- Reactive dyes have good perspiration fastness.
General structure of reactive dyes:
The general structure of reactive dye is: D-B-G-X.
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:
A. On the basis of reactive group:
1. Halogen (commonly chlorine) derivatives of nitrogen containing heterocycle, like 3 types-
- Triazine group
- Pyridimine group
- Quinoxaline dyes
- Triazine derivatives: procion, cibacron.
- Pyridimine derivatives: reactone
- Quinoxaline derivatives: levafix.
2. Activated vinyl compound:
- Vinyl sulphone
- Vinyl acrylamide
- Vinyl sulphonamide.
- Vinyl sulphone: remazol
- Vinyl acrylamide: primazine
- Vinyl sulphonamide: levafix.
B. On the basis of reactivity:
- Lower reactive dye: Here pH is maintained 12-12.5 by using NaOH in bath.
- Medium reactive dye: Here pH is maintained 11-12 by using Na2CO3 in dye bath.
- Higher reactive dye: Here pH is maintained 10-11 by using NaHCO3 in dye bath.
C. On the basis of dyeing temperature:
1. 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: PROCION M, LIVAFIX E.
2. 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, Remazol, Livafix are medium brand dyes.
3. Hot brand:
This type of dye contains reactive groups of least reactivity. So high temperature is required for dyeing i.e. 720-930C temperature is required for dyeing.
For example PRICION H, CIBACRON are hot brand dyes.
Dyeing mechanism of reactive dye:
The dyeing mechanism of material with reactive dye takes place in 3 stages:-
- Exhaustion of dye in presence of electrolyte or dye absorption.
- Fixation under the influence of alkali.
- wash-off the unfixed dye from material surface.
Now they are mentioned below:
1. Dye absorption:
When fiber 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 fiber.
Fixation of dye means the reaction of reactive group of dye with terminal –OH or-NH2 group of fiber and thus forming strong covalent bond with the fiber and thus forming strong covalent bond with the fiber. 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:
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
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.
These are 3 application procedures available:
1. Discontinuous method-
- Conventional method
- Exhaust or constant temperature method
- High temperature method
- Hot critical method.
2. Continuous method-
- Pad-steam method
- Pad dry method
- Pad thermofix method
3. Semi continuous method-
- Pad roll method
- Pad jig method
- Pad batch method.
Typical dyeing recipe:
|SL||Process Parameter||Unit||Dossing||Stock soln:|
Process sequence of cotton dyeing with reactive dyes
Collection of pre-treated sample
Set water level
Add leveling agent
Add dye solution
Add salt solution
Add soda ash solution
Add fabric sample
Raise the temperature to 600C
Run time for 30 minute
Hot wash at 900C for 10 minute
Stripping of reactive dye:
The reactive dye cannot be satisfactory stripped from fiber due to covalent bond between dye molecule and fiber. Stripping becomes necessary when uneven dyeing occurs.
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
- 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:
A. Pad-batch method.
Pad batch processes are of two types-
- Pad (alkali)-batch (cold) process.
- Pad (alkali)-batch (warm or hot) process.
B. Pad dry method
C. Pad steam method.
A. Pad-batch method.
1. Pad (alkali)-batch (cold) process.
2. Pad batch (hot) process:
B. Pad dry method:
C. Pad steam method:
By this experiment we came to know the dyeing of cotton fabric with reactive dyes and reactive dyes are of the least reactivity because they take more temperature and more time for dyeing.
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.