PREPARATORY PROCESSES

FOR COTTON

R.B.CHAVAN

Department of Textile Technology

Indian Institute of Technology

Hauz-Khas, New Delhi 110016

E-mail rbchavan@hotmail.com

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

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.

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

Desizing methods

• Starch solubilization• Hydrolysis

Oxidation

Ref: http://www3.itv-denkendorf.de/itv2/downloads/d0003602/WG3BarcPosner.pdf

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

BLEACHING

• Removal of colouring matters by Oxidation

• BLEACHING AGENTS

• sodium and calcium hypochlorite

• Hydrogen peroxide

• Sodium Hypochlorite

• Peracetic acid

• HYDROGEN PEROXIDE MOST POPULAR ON INDUSTRIAL SCALE

• It is environment friendly

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)

Kier(Rope Form) Winch (Rope Form)

Jet machine (Rope form) Jigger (Open width

form)

Continuous Processing

J-Box (Rope Form)

Continuous (Open width)

Saturator, Steamer, Washer.

Semi-Continuous

Pad-Batch (Open Width form)

PRESENT PRACTICE

COMBINED (OPEN WIDTH)

• DESIZING - SCOURING

• SCOURING – BLEACHING

• DESIZING – SCOURING – BLEACHING

EQUIPMENT

SATURATOR – PADDER – STEAMER - WASHER

ENVIRONMENTAL ISSUES

DESIZING

the wash water from desizing may contain up to 70 % of the total COD load in the final effluent,

Neither enzymatic nor oxidative desizing allows size recovery.

H2O2 BLEACHING

• H2O2 decomposition forms water and oxygen

• some stabilzers may from complexes with metal in the effluent, releasing them in the receiving waters

• effluents containing inorganic chlorides (e.g. NaCI from dyeing can be oxidised to their chlorites/hypochlorites when they are mixed with hydrogen peroxide bleach waste water.

• In this way AOX may be found in waste water even if bleaching is carried out without chlorine-based bleaching agents.