Desizing in textile

DESIZING
Prepared by
Karamat Ali Saif

Desizing
Introduction:
 Desizing is done in order to removes the size from warp yarn of the
woven fabric. Warp yarn are coated with sizing agents period to
weaving in order to reduce their fractional properties, decrease yarn
breakage in loom and improve weaving productivity by increasing
weft insertion speed.
 The sizing materials present on warp yarn acts as a resist toward
dye and chemicals in textile wet processing. it must therefore be
removed before any subsequent wet processing of the fabric.

Factors on which the desizing
efficiency depends
The factors on which the efficiency of size removal depends are as
follow...
 Type and the amount of size applied
 Viscosity of the size in solution
 Ease of dissolution of the size film on the yarn
 The nature and the amount of the plasticizer
 Fabric construction
 Method of desizing and
 Method of washing off

Objectives of desizing
 The object is to remove from the grey fabric the size that has
been applied during weaving and thus to make the fabric ready
for further processes.
 The main ingredient in size that is not water-soluble is usually
starch.
 Chemically starch is poly-glucopyranose in which straight
chain and branched chain polymers are present.
 .

Objectives of desizing contd
 Both the constituents of starch are insoluble in water but they
can be made soluble by hydrolysis of these long chain
compounds to shorter ones
 Grey cotton fabric contains both natural impurities as well as
‘added matter’.
 The added matter is called ‘size’. It is added by man in a
process called ‘sizing’, as it facilitates weaving.

Mechanism
• The main ingredient in size that is not water-soluble is usually
starch.
• Chemically starch is poly-glucopyranose in which straight chain
and branched chain polymers are present.
• Both the constituents of starch are insoluble in water but they can
be made soluble by hydrolysis of these long chain compounds to
shorter ones.
• Thus, under suitable conditions, the following steps show the
progressive hydrolysis of starch.
• However, in desizing, the hydrolysis of starch is carried out only up
to the soluble dextrin stage, as this can be removed off the desized
fabric by means of an aqueous wash.

Methods of desizing
 Rot steeping
 Enzymatic desizing
 Acidic desizing
 Oxidative desizing

Rot Steep
 This is the oldest and cheapest method of desizing.
 Here no special chemical is used.
 The cloth is first passed through warm water at 40C in a padding
mangle where the cloth is squeezed to about 100% expression.
 The cloth is then allowed to stand for 24 hours.
 The microorganisms, naturally present in water, multiply and
secrete starch-liquefying (hydrolysing) enzymes, which break down
the starch present in the size to w ater-soluble products
 The cloth is then washed to remove these products.

Rot Steeping
Wetting &
squeezing
Steeping Washing

Rot steep
Advantages
 Rot steeping is the cheapest of all the desizing methods.
 No chemicals are required.
Disadvantages
 A large floor space is required for this process.
 The process is slow, so desizing time is long.
 Mildew may attack the cloth during steeping
 and cause stains on the fabric.

Acid Desizing
 —Dilute sulphuric acid or hydrochloric acid may be used to
hydrolyse the starch from the sized fabric.
 —A 0.25% - 0.5 % solution of the acid at room temperature
(30o C) is suitable for this process.
 —The cloth is impregnated with the dilute acid solution in a
two-bowl or three- bowl padding mangle and then stored for 8-
12 hours in a closed concrete pit

Acid Desizing
Advantages
 Acid desizing is an economical process.
 The process is effective and gives fairly uniform desizing, as it
is a chemical- based process. It does not require specific
conditions of pH and can be done at room temperature.
 It is a much quicker process than rot steep desizing.

Acid desizing
Disadvantage
 The main disadvantage of the process is that mineral acid is
harmful to cellulose fibres if proper care is not taken.
 Especially during the storage stage, the acid-wet fabric must
not be allowed to dry.
 This would cause the formation of hydrocellulose, which will
weaken the fibre.

Enzymatic Desizing
• The hydrolysis of starch using enzymes under particular
concentration, temperature and duration is called enzymatic
desizing.
• Enzymatic desizing is the most widely experienced method to
desize the starch.

Enzymatic desizing
Advantages
 Time required for the desizing process is less.
 It is continuous process, so greater production can be
achieved.
 Closely constructed fabric can be easily desized, due to the
effective enzyme action.
 There is no chance for the cellulose to get hydrolysed,
as in acid desizing.

Enzymatic desizing
Disadvantages
 Lower additional cleaning effect towards otherimpurities.
 No effect on certain starches (e.g. tapioca starch)

Oxidative desizing
Desizing with Oxidizing agents
 Though the use of oxidants for desizing of cotton fabric is
widely accepted but their large scale industrial application is
yet to be exploited.
 The most important aspects of oxidizing agents are that they
can be applicable to wide range of fabrics, the size content of
which is often not known.

Oxidative desizing
Advantages
• The advantages of oxidative desizing are supplementary
cleaning effect, effectiveness for tapioca starches but oxidizing
agents may damage to fibres.

Desizing in textile

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