lecture 2 preparatory processes
TRANSCRIPT
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PREPARATORY PROCESSES
FOR COTTON
R.B.CHAVAN
Department of Textile Technology
Indian Institute of Technology
Hauz-Khas, New Delhi 110016
E-mail [email protected]
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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
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Fats and Waxes
• Fatty acids
• Stearic acid
• Palmitic acid
• Oleic acid
• Fatty alcohols
• Gossipyl alcohol (C30H61OH)
• Ceryl alcohol (C26H53OH)
• Montanyl alcohol (C28H57OH)
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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
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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
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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)
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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
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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
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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
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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.
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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
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Desizing methods
• Starch solubilization• Hydrolysis
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Oxidation
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Ref: http://www3.itv-denkendorf.de/itv2/downloads/d0003602/WG3BarcPosner.pdf
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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
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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
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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)
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Kier(Rope Form) Winch (Rope Form)
Jet machine (Rope form) Jigger (Open width
form)
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Continuous Processing
J-Box (Rope Form)
Continuous (Open width)
Saturator, Steamer, Washer.
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Semi-Continuous
Pad-Batch (Open Width form)
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PRESENT PRACTICE
COMBINED (OPEN WIDTH)
• DESIZING - SCOURING
• SCOURING – BLEACHING
• DESIZING – SCOURING – BLEACHING
EQUIPMENT
SATURATOR – PADDER – STEAMER - WASHER
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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.