To produce colored Fabric whether dyed or printed needs pre-treatment of those

fabrics of those fabrics before dyeing and printing. The pretreatment operations

involved for cotton fabric are described systematically below:

Singeing

Singeing: It is the process of burning out projecting hairy fibres from surface of

the grey fabric by assigns the fabric through a gas flame. Both sides of the fabric

are burnt out by the flame. It helps in subsequent chemical process of the fabric.

After dyeing or printing of singed fabric, brightness and luster of color and fabric

becomes better.

Singeing is the process of removing the pills and protruding fibers of the fabric

coming from weaving. This operation may either be done at the beginning of the

process or at the end of the finishing operation.

Desizing

Desizing:It is the process of removing starch materials present in the gray fabric.

Generally enzyme is used to degrade and remove the starch present in the grey

fabric. If those size materials are not removed from the grey fabrics, then the

subsequent chemical treatments on the fabric will be irregular, which will cause the

defective dyeing and printing.

Desizing is the second operation after singeing. Desizing of fabric is essential to

remove the sizing materials added during warping to strengthen the warp yarns.

This size if present during subsequent processing will affect the quality of look and

finish. There are many ways to remove the size from the fabric. A few methods are

as below.

a) Acid Desizing - this is an old process of destroying the starch and other size materials

in the presence of acid at elevated temperatures.

b) Oxidative desizing method - desizing with the help of an oxidizing agent such as

Hydrogen peroxide.

c) Enzymatic desizing method - this is a bio degradation method that destroys starch and

other sizing materials in to soluble form that will be washed off during subsequent

washes.

Scouring:It is the process of removing natural impurities present in the cotton

fibre. The natural impurities are pectin’s, pectos, ash, wax, mineral compounds,

etc. if those impurities present in the cotton fibres are not removed, then it will be

difficult to dye or print the fabric uniformly. Normally caustic soda ash is used as

main reagent fro scouring of cotton fabric.

Bleaching:It is the process of removing natural coloring matters present in the

cotton fibre. For his purpose, hydrogen peroxide, bleaching powder or other

bleaching agents are used. Hydrogen peroxide is the best and most commonly used

bleaching agent. If this bleaching treatment is not carried out before dyeing or

printing hen the color yield and shade matching may be a great problem.

Bleaching Process: Bleaching is a process to make the fabric or yarn look brighter

and whiter. This is achieved by oxidizing or reducing the coloring matters in to

colorless

form.

Mostly widely used textile bleaching method is Hydrogen Peroxide bleaching. This

is carried out in an alkaline bath at about 80 to 85°C at a pH of 11.

Mercerization:It is a special chemical pre-treatment on cotton fabric t improves the

properties and performance of cotton fabric. The cotton fabric is treated under

tension in the 20% caustic soda solution which is called mercerization many

properties of cotton fabric is improved, some of them are mentioned below:

1.Increases fabric strength

2.Increases absorbency power

3.Increases fabric luster

4.Increases fabric softness and handle property

5.Reduces dye consumption

6.Reduces chemical consumption in dyeing.