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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