To improve the performance of the yarn in weaving, size is
applied to the yarn and this should be removed from the fabric before it
is taken for processing. If not done so, shall lead to the contamination
of the solution of the other processes and more over the full potential of
the other processes will not be realized in addition to leaving a harsh
handle to the processed goods.
The process of singeing is nothing but
removing the protruding fibers and making the fabric surface smooth
.
Desizing is the process of removing the size applied during weaving.
Gas singeing the fabric by directing a flame on it,
burns the protruding fibers and make the surface of the fabric smooth.
Singeing is done because of the following two reasons.
1. to enhance the appearance of the fabric and make it
2. to make smooth by removing the pills
Desizing: There are basically three type of
desizing methods that are being adopted according the fabric construction,
end use purpose and the economical requirements, viz., 1) acid desizing,
2) basic desizing and 3) enzyme desizing. The last two treatments are
still being followed and the first one has been slowly going out of usage
due to fabric strength loss.
The purpose of desizing is to remove the sizing
ingredients such as starches, gums, PVA etc. The gums and PVA can be
removed by simple hot wash. But starch has to be degraded in to smaller
water soluble molecules by the process of hydrolysis. The
hydrolysis of starch using enzymes under particular concentration,
temperature and duration is called desizing.
The enzyme desizing is carried out by padding the
required concentration of the enzyme under the required pH and allowing
the enzyme to hydrolyze the starch for a required length time. After
allowing the required timings the fabric is taken for hot and cold washed
followed by bleaching, mercerization etc.
Nowadays quick reacting enzymes are available in the
market that can be used for continuous desizing operation without the need
for allowing reaction time after the application of enzyme. Singe - Desize
- Bleach- Mercerize-bleach- dry - is a simple route one can adopt instead
of going for a long route of 8 to 10 hour desizing.
The following parameters are considered to be very
important to obtain a good singeing and desizing.
- Type of fabric - its construction, GSM, fibre content
- Speed of the application machine
- Flame height and intensity
- Brush position
- Bath Concentration, pH and temperature
- Mangle Expression percentage
Some conventional desizing recipes on continuous
processing machine :-
Hydrogen Peroxide desizing (oxidative method/Basic
method) :
Caustic soda 100%
= 40 g/l Temperature
of bath = room temperature
Sandozol HS = 0.3 g/l pH of bath
= 10 to 10.5
Hydrogen Peroxide 50% = 3.3 g/l
pH of the fabric = 8.5
Stabilizer AWNI
= 0.3 g/l Nip Pressure =
2.2.kg/sq.cm; speed = 100 meters/minute
Pick up = 70%
Enzyme Based desizing:
Texsize (enzyme) = 1 gpl
bath temperature = 60 to 70°C - Common salt = 10 gpl pH of bath = 5.5 to
6.5
Deternon = 5 gpl - pH of fabric = 5 to 6 ; Oxalic acid = 0.5 gpl ;
Acetic acid = 1 gpl
Nip Pressure = 2.2 kg/sq cm ; Speed (meters/minute)
= 100 - 120 ; pick up = 70 to 75%
There are so many new products and inventions are coming
up in the market to counter the various needs of textile processors. Right
from desizing at room temperature to boiling temperature and neutral to
alkaline pH are available in the market.
You will see new updates on this topic regularly in this
column.
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