Fabric that are
formed form natural fiber specially
cotton fabric have to subjected a pre treatment process named scouring to
remove natural & additive impurities such as oil, wax, fat, hand dust, etc.
also to produce a hydrophilic & clean textile material. Scouring is a pre
treatment process. It is one of the vital processes of wet processing. On
cotton fibers, this treatment removes fatty and pectic substances, softening
motes and
preparing the material to absorb the
subsequent treatment agents. Also scouring are done in silk and wool fabric.
Scouring are done to obtain below
advantages
1. To
make the fabric highly hydrophilic.
2. To
remove impurities such as oils, waxes, gum, husks as nearly as possible.
3. To
increase absorbency of fabric or textile materials without physical &
chemical damage.
4. To
produce a clean material by adding alkali.
5. To
make the fabric ready for the next process.
6. To
remove non-cellulosic substance in case of cotton.
Scouring process depends on:
1. The
type of cotton.
2. The
color of cotton.
3. The
cleanliness of cotton.
4. The
twist & count of yarn.
5. The
construction of the fabric.
6. The
shade% & type of shade of finished product.
Chemicals used in Scouring process:
Caustic Soda- Neutralize acidic materials, saponify
glycerides, solubilise silicates.
Surfactants-
Reduce surface tension &
minimize interfacial tension.
Detergents: Emulsify
oil, fats, waxes, & remove oil-borne stains.
Chelating agents: Deactivate
metal ions.
Sodium silicate: Penetrate
& break down lignins.
Soda ash: Maintain
pH.
Sodium silicate: Assist
emulsification by dissolving oily materials
Process that are done in scouring:
There are three main process done in scouring to remove
impurities
i) Saponification : In this process caustic soda are reacted with fats and leads to formation a hydrophilic soaps. That’s how
fats are removed from fiber surface.
ii) Emulsification : Wases are esters of higher fatty acids and can not removed via
saponification. Also mineral oils, lubricants cannot be removed via
saponification. Wax and non saponifiable oils
(Non polar) are removed by emulsification as they are immiscible in water
(Polar). Normal washing soap is used as a emulsifying agent which make
emulsion of them. Soap generated from the saponification process
also act as a emulsifying agent.
iii) Detergency : Finally, After removal of fats and waxes normal dust and dirt particle
have to remove by using a good detergent.
Scouring process:
1. Batch
process.
2. Semi-continuous
process.
3. Discontinuous
process.
4. Modern
process.
Scouring process of cotton:
Generally, there are two principle
of cotton scouring.
1. Discontinuous
(kier boiling process or winch dyeing machine )
2. Continuous
(scouring in ‘J’ or ‘L’ box)
Scouring process of silk:
ʘ Impurities present in silk.
ʘ Sericin up to 30% (main
impurities)
Mineral matter, coloring matter,
traces of waxes & fats =1-1.5%
ʘ the removing of these impurities
in silk are called degumming.
Scouring of jute :(Bast fiber)
ʘ Bast fiber, jute, linen etc.
multicellular fiber, having polygonal shape. The cells are cemented with each
other by lignin which is non-cellulosic unit & is about 11-14%.
ʘ If strong alkali is used for jute
scouring, its strength is reduced as lignin is removed & cells are
separated. So mild alkali is used in jute scouring at low temperature.
Assessment of Scouring:
1.
Drop test:
ʘ In a pipette, a solution of 0.1%
direct red or congo red is taken & droplet of solution put on the different
places of the fabric. Then the absorption time of the fabric is observed.
ʘ The standard time of absorption of
one drop of solution is 0.5-0.8 sec.
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