Scouring Process of Textile Fabric or Yarn (Cotton) | Objects of Scouring and Process Description with Recipe

Posted by Firoz Kabir on Saturday, January 24, 2015 4

Scouring is the process which removes all the natural impurities like oil, wax, fat etc from the surface of the fabric and produce the fabric more hydrophilic, Scouring done by using alkali such as NaoH & Na2Co3.   Natural impurities of cellulosic fabric are normally removed by boiling off in a strong alkaline solution. The  main objective  of  scouring of cotton  fabrics  is to remove  natural  as  well as  added  impurities  to get essentially hydrophobic character as completely as possible and leave the fabric in a highly absorptive condition without undergoing chemical  or physical damage significantly.

    3C17 – COOH + 3NaOH= 3C17H35COONa +3H2O
                      Or   Oil + Caustic =Soap + Glycerine

There are three types of scouring:

• Saponification
• Emulsification
• Detergent

Saponification:
The vegetable oil, which is immiscible with water, is glycerine of fatty acids. When such oils are heated with a solution of sodium hydroxide in water, the oil splits up into its constituents-fatty acid and glycerine. Glycerine is miscible with water easily and the fatty acids reacts with sodium hydroxide present in the solution forming its sodium salt i.e.soap which is also soluble in water. Thus oil is removed.

Emulsification:
Wax and non saponifiable oils are removed by emulsification as they are immiscible in water.  Normal washing soap is used as a emulsifying agent which makes emulsion of them.

Objectives of Scouring Process:

• To make the fabric highly hydrophilic.
• To remove impurities such as oils, waxes, gum, husks as nearly as possible.
• To increase absorbency of fabric or textile materials without physical and chemical damage.
• To produce a clean material by adding alkali.
• To make the fabric ready for next process.
• To remove non-cellulosic substance in case of cotton

The changes occurring of cotton fibers during scouring:

• Saponifiable oils and free fatty acids are converted into soaps.
• Pectin's and pectoses are converted into soluble salts of pectic acid.
• Proteins are degraded to simple soluble amino acids or ammonia.
• Mineral matters are mostly dissolved.
• Non-saponifiable oils are emulsified by the soluble soaps generated from the saponifiable oils.
• Additive dirt's are removed.
• Residual sizing materials are broken down into soluble products

Scouring process depends on:

• The type of cotton.
• The color of cotton.
• The cleanliness of cotton.
• The twist and count of the yarn.
• The construction of the fabric.
•  The shade % and type of shade of finished product.

Forms of Scouring:

Yarn scouring:

• Hank form
• Package form

Continuous sheet warp form.
Fabric scouring:
Open width form :

 Jigger

•  Pad batch
•  Progressive jig
• Rope form

Kier

•  Washer..

Scouring process:
Batch process.
Semi – continuous process.
Discontinuous process.
Modern process.

Scouring methods of Cotton:
Generally, there are two principle methods of cotton scouring.

• Discontinuous (Kier boiling process or winch dyeing machine)
• Continuous (Scouring in J or L box)

Kier boiler process/ Scouring of cotton fabric in Batch process/ discontinuous process:

In this process of cotton scouring, the fabric is scoured in rope form, by alkali liquor.
Kier means specially constructed large cylindrical iron vessel. The kier boiler may be-
a. horizontal(yarn scouring)
b. vertical(fabric scouring).

Kier boiler capacity: maximum 5ton, but in industrially 2-3 ton kier boiler is very popular.


Standard Recipe: The amount of different chemicals used in a kier boiler may vary according to
Hardness of water.
Quality / Quantity of cotton.
Fabric construction/ texture, yarn twist etc.
But in generally, the following amounts of the chemical are used.

Caustic Soda (Strong)→ 2-5% owf
Soda ash (mild)→ 0.3-0.5%
Sequestering agent→0.05-0.5%
Wetting agent→ 0.25-1.0%
M:L→1:4 to1:5
Temp→100˚C-120˚C
Time→12hrs - 4hrs

Main parts of kier boiler:

• Cylindrical vessel
• Mixing tank(liquor prepared according to recipe)
• Multi tubular heat exchanger(heating the liquor)
• Perforated false bottom
• Circular tube(spray liquor on fabric)

Procedure:

• The fabric is loaded in the m/c and kept in rope form.
• The hot liquor is pumped and sprayed by circular tube on to the fabric 
• The liquor passes slowly over the packed cloth and collects at the false bottom of the kier.
• The liquor again pumped into the heater by a centrifugal pump and this cycle is repeated
• After scouring ,the fabric is washed with 800C water to remove impurities on the fabric

Assessment of scouring:/Absorbency test: 

 Drop/Spot test:
 In a pipette a solution of  0.1% direct red or Congo red is taken and droplet of solution put on the different places of the fabric. Then the absorption time of the fabric is observed.
The standard time for the absorption of one drop of solution is 0.5-0.8 sec up to 1 sec.