Desizing
Desizing
is a process by which size materials remove from woven fabric. It is a part of
the pretreatment process in textile wet processing. This is the first wet
processing in the textile finishing process used to remove sized materials from
the warp yarn of woven fabric. This must be done before any subsequent wet
processing of the fabric. Because of this, warp yarns are coated with sizing
elements to reduce their frictional properties, reduce broken yarns on
looms, etc. After de-sizing, the absorption of the fabric increases. As a
result, the fabric can easily absorb chemicals and dye molecules.
Different types of de-sizing process
The
main de-sizing processes are-
i.
Enzymatic de-sizing of starches on cotton fabrics
ii.
Oxidative de-sizing
iii.
Acid de-sizing
iv.
Removal of water-soluble sizes
v.
Alkali de-sizing
Enzymatic de-sizing process
Currently,
enzyme de-sizing is a popular and widely used process. In this process, enzymes
are used to remove starch from the fabric. One of the major advantages of this
is that the starch material is digested with a small number of enzymes but does
not damage the cellulose fiber. However, in this process, temperature and pH
are two big factors, and if not maintained properly, the enzyme does not work
properly, for example, the temperature is 80°C. On top of this, the
effectiveness of the enzyme is deactivated.
Oxidative de-sizing process
In
oxidative de-sizing, the risk of cellulose fiber damage is very high and its use
for de-sizing is increasingly rare. Potassium or sodium persulfate or sodium
bromite is used as an oxidizing agent in oxidative de-sizing. The advantage of
this de-sizing process is that the starch is better removed and the fabric is cleaned.
And the disadvantage is that cellulose fibers are more likely to decay, and the
fabric is more likely to get spots due to the use of harmful chemicals.
Acid de-sizing process
Acid
de-sizing is currently one of the most widely used methods to remove size
material from fabric. Dilute sulfuric acid (H2SO4) or
hydrochloric acid (HCl) is usually used to hydrolyze the size material in this
process. At a temperature of about 40-60°C, it is impregnated 2-3 times in
0.25-0.5% acid solution and stored for 8-12 hours. Then the size material is
removed by washing the fabric with water. This is a very effective process and
is widely used. And the process is done at room temperature and no pH
conditioning is required, so evenly de-sizing is done.
Alkali de-sizing process
In this method, size material is removed from the fabric through alkaline
hydrolysis. It is stored for 8-10 hours in a solution of 0.4-0.6% sodium hydroxide at a temperature of about 60-70°C. Then wash the fabric with water to
remove the size materials. However, care must be taken so that the fabric does not
dry out during de-sizing. It is a very cheap and widely used process.
Removal of water-soluble sizes
This is a very simple, easy, and old method. This method does not require any chemicals to complete the de-sizing. In this case, the fabrics are usually soaked in water at a temperature of 40-60 °C. And within 12-24 hours the existing material in the fabric decomposes. Then the size material is removed by washing it with water. The advantage of this is that no fiber is damaged as there is no need to use any chemical products or enzymes.
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