It is the process of removing the Size material from the
warp yarns in woven fabrics to facilitate the process of
weaving. Sizing agents are selected on the basic of type
of fabrics.. Desizing is an essential stage of all textile
processing, in which ‘size’ is removed from fabric before
completing the pre-treatment process, which is necessary
before dyeing, printing and finishing.
3. Objects of Desizing:
1.To remove the starch material from the fabric.
2.To increase the absorbency power of the fabric.
3.To increase the affinity of the fabric on chemicals.
4.To make the fabric suitable for the next process.
5.To increase the luster of the fabric.
4. Where does the size come from?
Before yarn is converted into fabric, the ‘Warp’ yarns
are coated with sizing agents which decreasing
breakages on the loom and improves productivity.
However the sizing agents often resist the dyes and
chemicals commonly used in textile processing, so they
have to be thoroughly removed before any wet
processing can take place.
8. Acid Desizing: Cold solutions of dilute sulfuric
or hydrochloric acids are used to hydrolyze the
starch. however, this has the disadvantage of
affecting the cellulose fiber in cotton fabrics.
9. Enzymatic Desizing:
Enzymatic desizing is the classical desizing process of degrading
starch size on cotton fabrics using enzymes. Enzymes are complex
organic bio-catalysts, formed by living organisms, that catalyze
chemical reaction in biological processes. A small quantity of enzyme is
able to decompose a large quantity of the substance it acts upon.
Enzymes are usually named by the kind of substance. Amylases is the
enzyme that hydrolyses and reduces the molecular weight of amylose
and amylopectin in starch.
10. Desizing on a jigger:
It is a simple method where the fabric from one
roll is processed in a bath and rewound on another
roll. First, the sized fabric is washed in hot water
The desizing liquor is then adjusted to pH 5.5-7.5 .
The amylase is added in an impregnation stage
and degraded the starch in the form of dextrin's.
Then removed by washing two minutes. The jigger
process is a batch process. In the reaction time for
the enzyme may be as little as 15 seconds.
11. Oxidative Desizing:
In oxidative desizing, the risk of damage to the cellulose
fiber is very high, and its use for desizing is increasingly
rare. Oxidative desizing uses sodium or potassium
sulphates or sodium bromite as an oxidizing agent.
12. Factors of Size Removal Efficiency:
The factors on the efficiency of size removal
are as follows:
1.Type and amount of size applied
2.Viscosity of the size in the solution
3.Nature and the amount of the plasticizers
5.Method of desizing
6.Method of washing.
13. Method of testing:
1.The more scientific method is One or two drops of
the solution are put on the desized fabric and rubbed
gently. In a short time the color of the spotted area
changes. The change in color is assessed visually.
2.The weight loss can be used as criteria for testing of
desizing efficiency. The weight loss is of the order of 7-