Dyeing Process of Cotton Fabric with Azoic Dyes

Last Updated on 06/03/2021

Name of the experiment:
Dyeing process of cotton fabric with azoic dyes.

Introduction:
The dyes containing insoluble azo group (-N=N-) are known as azoic dyes.

These dyes are not found in ready-made form. Azoic dyes are produced by a reaction between two components. The components are:

Coupling Compound (Naphthol)
Di-azo –compound or diazo base or diazo salt.

The colored substance formed from this colorless compound is insoluble in water and washing fastness of this shade is excellent.

dyeing of cotton with azoic dye — Fig: Dyeing of cotton with azoic dye

Reaction:

Naphtholation:
Naphthols are insoluble in water and they are converted into water soluble compound by treating with alkali.

This salt solution is used for the impregnation of fabric.

Diazotization:
A base containing amino group (-NH2) reacts with the NaNO2 (Sodium Nitrite) to form a solution of diazonium chloride of that base in presence of excess HCl at 0⁰-5⁰C temperature.

Coupling/Developing:
The impregnated material is treated in a bath containing diazonium solution to carry out to coupling and thus color is produced inside the fabric. The PH maintaining is important.

Recipe of dyeing of cotton fabric with azoic dyes:

Naphtholation:

Naphthol = 3%
Glycerine = 1 g/L
Caustic soda = 6 g/L
Common salt = 15 g/L
Time = 20-30 minute.
Temperature = room.
M: L = 1:30

Base solution (for diazotization):

Base color = 3 %
HCl = 3%
NaNO2 = 2%
Acetic acid = 2%
Sodium acetate = 1%
Temperature = 0⁰-5⁰C (with ice)
Time = 20-30 minute.

Procedure:

For making naphthol solution, at first naphthol, glycerine and caustic soda are added in bath.
Then common salt is put in the bath and mixed them well.
Then fabric is immersed into this solution for few minutes.
Then kept for 30 minute at room temperature.
Then for diazotization at first base color, HCl and NaNO₂ are added another bath at 0⁰-5⁰C (with ice). Then sodium acetate and acetic acid is added to maintain proper PH of the solution.
Then the chemicals are mixed properly.
After then the naphthalated fabric is immersed into that solution and color is produced very suddenly.
Finally the fabric is immersed for few minutes. And we got the final shade of color.

After treatment:

After dyeing operation is completed the dye material is put into a bath containing cold wash.
The material is treated with a 1g/L soap solution, which removes the unfixed dye from fabric surface, and makes the surface clean.
Then material is treated with a cold-water bath.
Finally the material is dried in a drier.

Remark:
Our naphtholation process was not so sufficient. So dyeing becomes uneven. But we learn about the dyeing of cotton fabric with azoic dyes.

Conclusion:
Azoic dyes are used for producing bright shade of color such as orange, red, scarlet, navy blue, and black color. By this practical we acquire knowledge about the dyeing process of cotton fabric with azoic dyes. This practical will help us in our study life as well as job life. Especial thanks to our teacher and his assistants for great co-operation.

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Mazharul Islam Kiron

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.