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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.

• to enhance the appearance of the fabric and make it smooth by removing the pills
• to enhance the luster of the fabric after mercerization

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.

1. Type of fabric - its construction, GSM, fibre content
2. Speed of the application machine
3. Flame height and intensity
4. Brush position
5. Bath Concentration, pH and temperature
6. 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.