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Lecture 2 preparatory processes


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Lecture 2 preparatory processes

  1. 1. PREPARATORY PROCESSES FOR COTTON R.B.CHAVAN Department of Textile Technology Indian Institute of Technology Hauz-Khas, New Delhi 110016 E-mail
  2. 2. Composition of cotton <ul><li>Natural impurities </li></ul>8.0 Moisture 1.0 Mineral Matter 0.5 Colouring matter 1.1 Proteins 0.7 Pectins 0.5 Oils, Fats and Waxes 88 Cellulose % Constituent
  3. 3. Fats and Waxes <ul><li>Fatty acids </li></ul><ul><li>Stearic acid </li></ul><ul><li>Palmitic acid </li></ul><ul><li>Oleic acid </li></ul><ul><li>Fatty alcohols </li></ul><ul><li>Gossipyl alcohol (C30H61OH) </li></ul><ul><li>Ceryl alcohol (C26H53OH) </li></ul><ul><li>Montanyl alcohol (C28H57OH) </li></ul>
  4. 4. Pectins <ul><li>Derivatives of pectic acid </li></ul><ul><li>Polymer of high molecular weight </li></ul><ul><li>Composed of Galactouronic acid </li></ul>Some COOH groups are present as Ca and Mg salts Free acid and Ca and Mg salts are insoluble in water
  5. 5. Proteins <ul><li>Nitrogenous compounds </li></ul><ul><li>Present in primary wall and Lumen </li></ul><ul><li>Some of the amino acids identified are </li></ul><ul><li>Leucine </li></ul><ul><li>Valine </li></ul><ul><li>Proline, </li></ul><ul><li>Alanine etc. </li></ul><ul><li>Yellowish (Creamish) colour of cotton is related to Proteins and </li></ul><ul><li>Colouring matter </li></ul>
  6. 6. Colouring matter <ul><li>Colour pigments present are </li></ul><ul><li>3,5,7,2’, 4’ Penta hydroxy flavone (Morrin) </li></ul><ul><li>3,5,7,8,3’,4’ Hexa hydroxy flavone (Gossypetine) </li></ul>
  7. 7. Mineral Matter <ul><li>Depends on soil composition </li></ul><ul><li>Can be determined by ash analysis </li></ul>5.0 Aluminium oxide 3.0 Ferric oxide 8.4 Magnesium sulphate 10.3 Calcium carbonte 9.0 Calcium sulphate 9.3 Potassium sulphate 9.9 Potassium chloride 44.8 Potassium carbonate
  8. 8. Added Impurities <ul><li>Sizing agents: </li></ul><ul><li>Agents used to give protective coating to warp threads </li></ul><ul><li>Minimize the breaking of warp threads during weaving </li></ul><ul><li>Improve weaving productvity. </li></ul><ul><li>The operation is known as sizing. </li></ul><ul><li>Starch is one of the most important sizing agent for cotton </li></ul>
  9. 9. PREPARATORY PROCESSES <ul><li>Purpose </li></ul><ul><li>To remove added and natural impurities from textile material </li></ul><ul><li>Removal impurities to the maximum extent possible with minimum effect on fibre strength. </li></ul><ul><li>To impart desirable properties to textile material </li></ul>
  10. 10. Principle of preparatory processes <ul><li>The impurity is insoluble in water </li></ul><ul><li>Conversion of water insoluble impurity to its water soluble form. </li></ul><ul><li>Chemical reactions involved are </li></ul><ul><li>Hydrolysis </li></ul><ul><li>Oxidation </li></ul><ul><li>The choice of chemicals depends on chemical nature of impurity. </li></ul>
  11. 11. Desizing <ul><li>Process of removal of size is known as desizing </li></ul><ul><li>Facilitates penetration of chemicals and dyes applied during subsequent processing operations </li></ul><ul><li>Starch is the main ingredient for sizing of cotton warp </li></ul><ul><li>Chemically starch is </li></ul>Chemically it is Amylose: Linear polymer of low mol. Wt. Amylopectin: High molecular wt. Branched polymer Water insoluble
  12. 12. Desizing methods <ul><li>Starch solubilization </li></ul><ul><li>Hydrolysis </li></ul>
  13. 13. Oxidation
  14. 14. Ref:
  15. 15. SCOURING TREATMENT OF COTTON WITH ALKALINE SOLUTION <ul><li>PURPOSE </li></ul><ul><li>REMOVE NATURAL IMPURITIES : FATS AND WAXES, </li></ul><ul><li>PECTIC SUBSTANCES, PROTINES </li></ul><ul><li>REMOVE ADDED IMPURITY : OIL STAINS </li></ul><ul><li>SEED COAT FRAGMENTS </li></ul><ul><li>IMPROVE WATER ABSORBENCY FOR UNIFORM DYEING, </li></ul><ul><li>PRINTING AND FINISHING . </li></ul><ul><li>PRINCIPLE </li></ul><ul><li>Hydrolysis of impurities </li></ul>
  16. 16. <ul><li>BLEACHING </li></ul><ul><li>Removal of colouring matters by Oxidation </li></ul><ul><li>BLEACHING AGENTS </li></ul><ul><li>sodium and calcium hypochlorite </li></ul><ul><li>Hydrogen peroxide </li></ul><ul><li>Sodium Hypochlorite </li></ul><ul><li>Peracetic acid </li></ul><ul><li>HYDROGEN PEROXIDE MOST POPULAR ON INDUSTRIAL SCALE </li></ul><ul><li>It is environment friendly </li></ul>
  17. 17. INDUSTRIAL PRACTICES EQUIPMENT USED <ul><li>BATCH WISE OPERATION </li></ul><ul><li>KIER ( ROPE FORM ) </li></ul><ul><li>JIGGER (OPEN WIDTH ) </li></ul><ul><li>WINCH (ROPE FORM, PARTICULARLY FOR KNITS ) </li></ul><ul><li>JET DYING (ROPE FORM, PARTICULARLY FOR KNITS ) </li></ul><ul><li>CONTINUOUS </li></ul><ul><li>J – BOX ( ROPE FORM ) </li></ul><ul><li>VARIOUS PAD STEAM PROCESSES (OPEN WIDTH ) </li></ul><ul><li>SEMI-CONTINUOUS </li></ul><ul><li>1. PAD – ROLL (OPEN WIDTH) </li></ul>
  18. 18. Kier(Rope Form) Winch (Rope Form) Jet machine (Rope form) Jigger (Open width form)
  19. 19. Continuous Processing J-Box (Rope Form) Continuous (Open width) Saturator, Steamer, Washer.
  20. 20. Semi-Continuous Pad-Batch (Open Width form)
  21. 21. <ul><li>PRESENT PRACTICE </li></ul><ul><li>COMBINED (OPEN WIDTH) </li></ul><ul><li>DESIZING - SCOURING </li></ul><ul><li>SCOURING – BLEACHING </li></ul><ul><li>DESIZING – SCOURING – BLEACHING </li></ul><ul><li>EQUIPMENT </li></ul><ul><li>SATURATOR – PADDER – STEAMER - WASHER </li></ul>
  22. 22. ENVIRONMENTAL ISSUES <ul><li>DESIZING </li></ul><ul><li>the wash water from desizing may contain up to 70 % of the total COD load in the final effluent , </li></ul><ul><li>Neither enzymatic nor oxidative desizing allows size recovery . </li></ul><ul><li>H2O2 BLEACHING </li></ul><ul><li>H2O2 decomposition forms water and oxygen </li></ul><ul><li>some stabilzers may from complexes with metal in the effluent, releasing them in the receiving waters </li></ul><ul><li>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. </li></ul><ul><li>In this way AOX may be found in waste water even if bleaching is carried out without chlorine-based bleaching agents. </li></ul>