Cotton fibers contain 4-12% impurities such as proteins, fats, waxes and minerals that must be removed through a scouring process. The classical scouring method uses an aqueous alkaline solution with caustic soda as the alkali to saponify and emulsify impurities. Surfactants and sequesterants are added to the scouring bath to improve wettability, detergency and emulsification and counteract water hardness. Scouring makes cotton fibers highly hydrophilic and responsive to subsequent dyeing and finishing processes.

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SCOURING PROCESS OF COTTON FABRIC
LECTURE – 4
By Robel L.
Faculty of Textile and Fashion Technology
Aksum University
2020
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2. SCOURING
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3. COTTON FIBER IMPURITIES
Cotton fiber is composed of 4-12% impurities
Average (% on dry basis)
Cellulose 88 - 96
Protein matter 1.1 – 1.9
Pectin 0.7 – 1.5
Fats & wax 0.4 – 1.0
Mineral matter {Ash} 0.7 – 1.6
Others * 0.5 – 8.0
Others : Pigments, sugars, organic acids etc
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5.  Oily matter is based on triglycerides
 Proteins are composed of amino acids
 Pectins are salts of polygalacturoic acid
 Ash is a measure of inorganic salts
Characteristics of impurities:
 Either hydrophobic or difficult for removal
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6. SCOURING PROCESS
 The mentioned impurities together with added lubricants are
removed by the so called scouring process.
 In general, scouring removes fat/wax based hydrophobic
impurities & other impurities in association in the fiber.
 Varity of scouring agents can be used for cotton.
 [Alkalis, surfactants, organic solvents]
 The classical scouring method is aqueous alkaline
scouring using caustic soda (NaOH) as alkali.
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 To remove natural as well as added impurities of
essentially hydrophobic character as completely as
possible.
 To increase absorbency of textile materials.
 To leave the fabric in a highly hydrophilic condition
without undergoing physical or chemical treatment or
damage.
 To make the suitable situation for next bleaching, dyeing,
printing, and finishing process.
Objective of scouring
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Method of scouring
 Aqueous scouring
 Solvent scouring
AQUEOUS ALKALINE SCOURING
The process involves treatment of cotton in aqueous alkaline
liquor consisting of sodium hydroxide and scouring bath additives
ALKALINE BOILING OFF + WASHING
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Mechanism of impurity removal
 Saponification
 Emulsification
 Conversion to impurity’s simpler soluble compounds
Responsiveness to subsequent processing
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10.  Saponification of fats/oils by alkali
 Melting and Emulsification of unsaponifiable parts (wax)
 Hydrolysis of protein to amino acid salts
 Conversion of pectin into soluble pectic acid salts
 Dissolution of mineral matter, sugars & oligomeric cellulose
 Swelling of husks
REACTIONS IN SCOURING
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12. SCOURING BATH ADDITIVES
SURFACTANTS SEQUESTERANTS
 In alkaline scouring different auxiliary chemicals are added in
the scouring bath.
 To facilitate the scouring process and for improved efficiency
 For wettability
 For detergency
 For emulsification
 To counteract on hardness of water
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POLAR END NON POLAR END
 Detergents, wetting agents and emulsifiers are based
on surfactants (surface active compounds).
SURFACTANTS
 Surface active compounds have ability to alter the
surface tension between two or more surfaces.
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 Surfactants are characterized by having a
hydrophilic head attached to a hydrophobic
tail.
 Formation of micelle structure and stability in
micellar conformation.
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15.  As wetting agent, enhance wetting and penetration by
chemicals
 As detergent facilitate removal of fatty soils
 As emulsifier form suspension of oily matters
ACTION OF SURFACTANTS
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16. SEQUESTERANTS
 Metal ions in water interfere with smooth alkaline
scouring
 Polyvalent metal ions in water
 Sequesterants are used for removing metal ions
 Complexing or chelating agents remove polyvalent metal
ions from water during scouring process
 Examples: EDTA (Ethylene diamine tetracetic acid),
Polyphosphates
Water Hardness
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Sequestering involves formation of a water soluble complex
between a sequestering agent and a polyvalent metal ion.
EDTA POLYPHOSPHATE
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 Concentration of alkali
 Temperature
Time
 Type and amount of additives
 Machine type [Material liquor ratio, MLR]
AQUEOUS ALKALINE SCORING CONTROLLING PARAMETERS
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20. A. Batch Scouring Procedure
NaOH………………..3% owf
Na2CO3………………1% owf
Wetting agent…………0.2-0.4%
Sequestarant…………..0.1-0.2%
Tem/time………………100 oC/30-45min
Typical Recipes and Process Conditions
B. Continuous Scouring Procedure
NaOH…………….….30-40 g/l
Na2CO3 ……………….10 g/l
Wetting Agent………....2 g/l
Sequestarant……………1 g/l
Eg. In J-Box machine
1. Saturate fabric with chemicals
2. Steaming fabric one hour at 100
oC in j-box or steamer.
3. Rinse thoroughly with cold and
hot water at 60 oC
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Solvent Scouring
 Solvent scouring is the treatments of fabrics in organic solvent
medium to remove impurities such as lubricating oils and spin
finishes.
 Certain organic solvents will readily dissolve oils fats and waxes
and these solvents can be used to purify textiles.
 Removal of impurities by dissolution is called Extraction.
 It is found that waxes are removed by solvents like chloroform,
benzene, carbon tetra chloride
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Provide adequate wettability and absorbency so as to obtain level
and reproducible results in the subsequent dyeing and finishing
operations.
Solvent Properties
Boiling Point: Temperature at which solvent is converted from liquid
to a gas.
Specific Heat: The amount of energy needed to raise one gram of
solvent in one degree centigrade (Calories/gram/ oC).
Latent Heat of Evaporation: The amount of energy needed to
vaporize one gram of solvent (Calories/gram).
Why Scouring?
Cont.…
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23. TEST FOR SCOURING EFFICIENCY
 Scouring efficiency is measured by absorbency
Drop test
Capillary action in fixed time
Sinking test
 A drop of water is placed on fabric and the time it takes for the
drop to penetrate fabric is recorded.
 The faster the wetting time, the more absorbent the
fabric.
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END
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