Composition of cotton

• Natural impurities•

Constituent %

Cellulose 88

Oils and Waxes 0.5

Pectins 0.7

Proteins 1.1

Colouring matter 0.5

Mineral Matter 1.0

Moisture 8.0

Fats and Waxes

• These are

• Readily saponifiable triglycerides of fatty acids

• Waxes which are saponified with difficulty

• Free fatty acids

• Traces of soaps

• Free fatty acids and fatty alcohols identified in cotton are

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

Purpose

• 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 (Cotton)

• 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

Amylopectin

Desizing methods

• Starch solubilization• Hydrolysis

Oxidation

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

Hydrolytic desizing

• Rot steeping

• Acid Desizing

• Enzyme Desizing

Acid desizing • Treatment with sulphuric or hydrocjloric acid (5-10 g/l)• Room temperature• 3-4 hours• Hydrolysis of starch with the formation of small water soluble

polymer chain segments.• Precautions• Cloth should be totally submerged in the acid solution• Danger of cotton degradation at the dried portions due to

increase in acid concentration• Higher temperature increases the rate of starch hydrolysis• Chances of cotton degradation also increase• After desizing wash and neutralize to remove acid completely• Advantages• Economical method provided precautions are taken to prevent

fibre degradation• Also removes mineral matters.

Enzyme Desizing

• Enzymes• Proteins of high molecular weight.• Catalyse the specific reaction• Also known as biocatalyst • Specific in reaction• Active under narrow temperature and pH conditions• Nomeclature according to substrate attacked

Amylase Amylose

Cellulase Cellulose

Protease Protein

Types of enzymes

• Malt Enzymes• Obtained from fermentation of barley (Grain)• Pancreatic enzymes• Obtained from pancreas (Digestive glands) of

slaughtered animals• Malt and pancreatic enzyme composition is not easily

controlled• Limited use on industrial scale desizing • Bacterial enzymes• Prepared from the growth of microorganisms under

controlled conditions.• Used on industrial scale

Application conditions

Enzyme pH Temp. Deg.C

Malt 4.6-5.2 55-65

Pancreatic 6.8-7 40-55

Bacterial 5-7 60-70

Enzyme desizing process

• In textile industry enzymes desizing was first used in 1857. cloth was steeped for several hours in water containing Barley

• 1n 1900 Malt enzyme

• In 1912 Bacterial enzymes were introduced

• Presently bacterial enzymes are most popular

• Some bacterial enzymes are stable upto 100 deg.C

Industrial methods

• Fabric form• Rope• Open width

• Processes• Batch wise• Semi continuous• Continuous

Equipments

• Batch wise operation• Fabric in rope form• Kier• Fabric in open width form• Jigger

• Semi continous• Pad – batch• Saturate-Store in a pit or wagan• Continuous• Pad-steam-Wash• Pad-Store in J box-Wash

Fabric in open width form

Continuous desizing in J-Box