Scouring

Total Textile Process at a Glance

Scouring:• Scouring is the process by which all

natural and additive impurities such as oil, wax, fat, hand dust etc. are removed to produce hydrophilic and clean textile material. It is one of the vital processes of wet processing.

Objects of Scouring: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.

Composition of cotton• Natural impurities

Constituent %

Cellulose 88

Oils, Fats and Waxes

0.5

Pectins 0.7

Proteins 1.1

Colouring matter 0.5

Mineral Matter 1.0

Moisture 8.0

Fats and Waxes

• Fatty acids• Stearic acid• Palmitic acid• Oleic acid• Fatty alcohols• Gossipyl alcohol (C30H61OH)• Ceryl alcohol (C26H53OH)• Montanyl alcohol (C28H57OH)

Pectins • Derivatives of pectic acid • Polymer of high molecular weight• Composed of Galactouronic acid

Some COOH groups are present as Ca and Mg salts

Free acid and Ca and Mg salts are insoluble in water

Proteins• Nitrogenous compounds• Present in primary wall and Lumen• Some of the amino acids identified are• Leucine• Valine• Proline, • Alanine etc.• Yellowish (Creamish) colour of cotton is related to Proteins

and • Colouring matter

Colouring matter

• Colour pigments present are• 3,5,7,2’, 4’ Penta hydroxy flavone (Morrin)

• 3,5,7,8,3’,4’ Hexa hydroxy flavone (Gossypetine)

Mineral Matter

• Depends on soil composition• Can be determined by ash analysis

Potassium carbonate 44.8

Potassium chloride 9.9

Potassium sulphate 9.3

Calcium sulphate 9.0

Calcium carbonte 10.3

Magnesium sulphate 8.4

Ferric oxide 3.0

Aluminium oxide 5.0

Chemicals used in scouring process:Main chemicals Use

Caustic soda Neutralize acidic materials, saponify glycerides (waxes and oil),solubilise silicates

Surfactants Reduce surface tension & minimize interfacial tension.

Detergents Emulsify oil, fats, waxes and remove oil-borne stains.

Chelating agent Deactivate metal ions.

Sodium silicate Penetrate & break drown lignin's.

Soda ash Maintain pH.

Solvent Assist emulsification by dissolving oily materials.

General recipe for scouring for Kier boiler process:

•Alkali (NaOH) - 2 to 5 gm per Litre. •Soda ash - x gm per Litre to adjust PH (PH required for scouring is 10.5). •Wetting agent - 1 gm per Litre. •Sequestering agent - 1 gm per Litre. •Detergent - 1 to 2 gm per Litre. •Temperature – 100 0c. •Time - 6 hours (close vessel) and 8 hours (open vessel) •M : L - 1 : 10

Teknologi dan Rekayasa

Reaction that happened at scouring of cotton is :

Reaction with caustic soda:R – COO – H + Na OH R – COO – Na + H2O

soap of sodium dissolve easy in water.

Reaction with soda ash(sodium carbonat)2R – COO – H + Na2 CO3 2R – COO – Na + H2O + CO2

Fat


Reaction with mixture of lime water and soda ash2R – COO – H + Ca (OH)2 (RCOO)2 Ca + 2 H2O

insoluble calcium soap in water.

(RCOO)2 Ca + 2HCl Ca Cl2 + 2 RCOOHFat2RCOOH + Na2 CO3 2R – COO – Na + H2O + CO2

Soap of sodium

Scouring Process

There are two types of textile scouring processes – 1. Conventional scouring process: • Kier boiling (discontinuous) scouring. • Scouring in J or L box (continuous). • Exhaust method

2. Special scouring process: • Solvent scouring process. • Vapor lock scouring proces


Procedure- Materials and chemical agents weigh as according to calculation of recipe - Water and chemical agent prepared as according to liquor ratio at recipe - Fabric done at solution process with temperature 95oC,then stir to flatten during 60 minute - Afterwards cloth cleaned by hot water ,then cleaned to be chill water - Materials dried is later,then weigh and perceived, do test of fabric absorpsion.


Schema Process

TemperatureoC

60oC

30oC

NaOHNa 2CO3

Scouring

0 15 75 minute Time(minute)

Shema of scouring process of cotton with Na2CO3 and NaOH used exhaustion methode

Rinsed by Hot Water And chill water

Form 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(Rope Form) Winch (Rope Form)

Jet machine (Rope form) Jigger (Open width

form)

• 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)

• Process: The working process in J-box can be divided into four units. There are– Impragnaion box– Pre – heater.– J – box.– Washing unit.

Good scouring

Uniform scouring

Uneven scouring

Added Impurities

• Sizing agents:

• Agents used to give protective coating to warp threads

• Minimize the breaking of warp threads during weaving

• Improve weaving productvity.

• The operation is known as sizing.

• Starch is one of the most important sizing agent for cotton

PREPARATORY PROCESSES

Purpose• To remove added and natural impurities from textile

material

• Removal impurities to the maximum extent possible with minimum effect on fibre strength.

• To impart desirable properties to textile material

Principle of preparatory processes

• The impurity is insoluble in water

• Conversion of water insoluble impurity to its water soluble

form.

• Chemical reactions involved are

• Hydrolysis

• Oxidation

• The choice of chemicals depends on chemical nature of

impurity.

Description and Working Principle of Scouring Process:

Kier boiler is a long mild steel or cast iron cylindrical vessel provided with two perforated tube sheets (disc with a number of holes). One is placed at the bottom and another is top. These discs are connected by a number of tunes which carry the liquor from the bottom compartment to the upper one. In the middle compartment steam is passed. Thus the tubes carrying the liquor are surrounded by steam which heats them.

The hot liquor from the multitublar heater is sprayed over the cloth, packed in the kier, through a hollow perforated ring. The liquid passes slowly over the packed cloth, collects below the false bottom, from where it is pumped into the auxiliary heater by a centrifugal pump and the cycle repeats.

Figure scouring process

Desizing • Process of removal of size is known as desizing• Facilitates penetration of chemicals and dyes applied during subsequent

processing operations • Starch is the main ingredient for sizing of cotton warp• Chemically starch is

Chemically it is

Amylose: Linear polymer of low mol. Wt.

Amylopectin: High molecular wt. Branched polymer Water insoluble

SCOURINGTREATMENT OF COTTON WITH ALKALINE SOLUTION

PURPOSE

• REMOVE NATURAL IMPURITIES : FATS AND WAXES, PECTIC SUBSTANCES, PROTINES

• REMOVE ADDED IMPURITY : OIL STAINS

• SEED COAT FRAGMENTS

• IMPROVE WATER ABSORBENCY FOR UNIFORM DYEING, PRINTING AND FINISHING.

PRINCIPLE• Hydrolysis of impurities

INDUSTRIAL PRACTICES EQUIPMENT USED

BATCH WISE OPERATION1. KIER ( ROPE FORM )2. JIGGER (OPEN WIDTH )3. WINCH (ROPE FORM, PARTICULARLY FOR KNITS )4. JET DYING (ROPE FORM, PARTICULARLY FOR KNITS )

CONTINUOUS1. J – BOX ( ROPE FORM )2. VARIOUS PAD STEAM PROCESSES (OPEN WIDTH )

SEMI-CONTINUOUS1. PAD – ROLL (OPEN WIDTH)

Continuous Processing

J-Box (Rope Form)

Continuous (Open width)

Saturator, Steamer, Washer.

Semi-Continuous

Pad-Batch (Open Width form)

Scouring

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