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Bleaching slides

  1. 1. BLEACHING OF COTTON <ul><li>CREAM COLOUR OF COTTON AFTER SCOURING </li></ul><ul><li>PRESENCE OF FLAVAONE PIGMENTS ( MORRIN AND GOSSYPETIN ) </li></ul><ul><li>CLIMATE AND SOIL CAUSE VARIOUS DEGREE OF YELLOWNESS </li></ul><ul><li>TIPS OF LEAVES COMING IN CONTACT WITH MOIST COTTON BOLL CAUSE YELLOW SPOTS </li></ul><ul><li>DISCOLORATION DUE TO DIRT/DUST, INSECTS OIL STAINS FROM HARVESTING MACHINERY . </li></ul>
  2. 2. OBJECT OF BLEACHING <ul><li>TO PRODUCE WHITE FABRIC BYE DESTROYING COLOURING MATTER WITH MINIMUM FIBRE DEGRIDATION. </li></ul><ul><li>FURTHER IMPROVEMENT OF WHITENESS BY TREATMENT WITH OPTICAL WHITENESS AGENTS. </li></ul>
  3. 3. NINE MAIOR BREAK THROUGH IN COTTON PROCESSING <ul><li>SULPHURIC ACID SOUR 1756 </li></ul><ul><li>CHLORINE BLEACH 1790 </li></ul><ul><li>SODA ASH BOIL 1791 </li></ul><ul><li>HIGH PRESSURE KIER 1815 </li></ul><ul><li>ROPE WASHER 1830 </li></ul><ul><li>ENZYME DESIZING 1900 </li></ul><ul><li>PEROXIDE BLEACHING 1925/1935 </li></ul><ul><li>CONTINUOUS H2O2 BLEACHING 1939 </li></ul><ul><li>OPTICAL WHITNESS 1950 </li></ul>
  4. 4. CLASSIFICATION OF BLEACHING AGENT <ul><li>OXIDIZING BLEACHING AGENT </li></ul><ul><li>CHLORINE SYSTEM </li></ul><ul><li>PEROXIDE SYSTEM </li></ul>
  5. 5. CHLORINE SYSTEM <ul><li>BLEACHING POWDER </li></ul><ul><li>SODIUM HYPOCHLORITE </li></ul><ul><li>SODIUM CHLORITE </li></ul><ul><li>PEROXIDE SYSTEM </li></ul><ul><li>HYDROGEN PEROXIDE </li></ul><ul><li>PER ACETIC ACID </li></ul><ul><li>SODIUM PERBORATE </li></ul><ul><li>POTASSIUM PERMANGANATE </li></ul>
  6. 6. REDUCTIVE BLEACHING AGENT <ul><li>SULPHUR DIOXIDE </li></ul><ul><li>SODIUM HYDROSULPHITE </li></ul><ul><li>SODIUM SULPHOXYLATE FORMALDEHYDE </li></ul><ul><li>SODIUM BISULPHATE </li></ul><ul><li>MAINLY USED FOR BLEACHING OF WOOL </li></ul>
  7. 7. BLEACHING POWDER MANUFACTURE <ul><li>RAW MATERIALS </li></ul><ul><li>SLAKED LIME ( Ca(OH) 2 ), CHLORINE GAS </li></ul><ul><li>SPREAD LIME IN CLOSED CHAMBER WITH GLASS WINDOW </li></ul><ul><li>AS SOON YELLOW COLOR DISAPPEARS, ADD MORE Cl2 GAS </li></ul><ul><li>TURN LIME UPSIDE DOWN </li></ul><ul><li>REPEAT THE PROCESS TILL PERMANENT COLOUR IN THE CHAMBER </li></ul><ul><li>ADD FRESH LIME TO ABSORB RESIDUAL CHLORINE </li></ul>
  8. 8. PROPERTIES <ul><li>SOLID WITH AMORPHOUS POWDER </li></ul><ul><li>HYGROSCOPIC </li></ul><ul><li>DECOMPOSES WHEN EXPOSED TO AIR </li></ul><ul><li>Ca( OCL ) 2 SOLUBLE IN WATER </li></ul><ul><li>DUE TO PRESENCE OF FREE LIME, CLEAR SOLUTION IS NOT OBTAINED </li></ul><ul><li>AN STANDING CaCO3 SETTLES AS SLUDGE AT BOTTOM </li></ul>
  9. 9. DISSOLUTION OF BLEACHING POWDER <ul><li>SPECIAL PROCEDURE FOR DISSOLUTION OF BLEACHING POWDER </li></ul><ul><li>TWO TANKS KEPT AT DIFFERENT HEIGHTS AND CONNECTED TO EACH OTHER </li></ul><ul><li>TAKE BLEACHING POWDER IN TANK KEPT AT HIGHER HEIGHT </li></ul><ul><li>ADD WATER TO GET DESIRED AVAILABLE CHLORINE </li></ul><ul><li>MIX THOROUGHLY </li></ul><ul><li>KEEP STANDING </li></ul><ul><li>DURING THIS PERIOD INSOLUBLE Ca(OH) 2 AND CaCO 3 SETTLES </li></ul><ul><li>THE CLEAR SUPERNATANT LIQUOR IS DRAWN OFF FROM STOP AND COLLECTED INTO TANK BELOW </li></ul><ul><li>CONCENTRATION OF CLEAR SOLUTION ADJUSTED TO DESIRED CONCENTRATION </li></ul><ul><li>USED FOR BLEACHING </li></ul>
  10. 10. SODIUM HYPOCHLORITE <ul><li>VIRTUALLY REPLACED BLEACHING POWDER </li></ul><ul><li>MORE CONSTANT IN COMPOSITION </li></ul><ul><li>AVAILABLE IN LIQUID FORM </li></ul><ul><li>MANUFACTURE </li></ul><ul><li>PASSAGE OF Cl2 GAS IN NAOH SOLUTION (3-4%) </li></ul><ul><li>2 NaOH + Cl 2 = NaOCl + NaCl +H 2 O </li></ul><ul><li>QUANTITY OF Cl 2 ABSORBED 14-15% </li></ul>
  11. 11. AVAILABLE CHLORINE <ul><li>STENGTH OF BLEACHING POWDER OR NaOCl ISEXPRESSED AS AV. Cl2/l </li></ul><ul><li>COMPOSITION OF BLEACHING POWDER IS NOT CONSTANT </li></ul><ul><li>SODIUM HYPOCHLORITE DECOMPOSE ON STORAGE, EXPOSURE TO LIGHT AND HOT WEATHER </li></ul><ul><li>NECESSARY TO ESTIMATE STRENGTH IN TERMS OF AVAILABLE CHLORINE </li></ul><ul><li>ESTIMATION BASED ON QUANTITATIVE LIBERATION OF IODINE FROM POTASSIUM IODIDE IN ACIDIFIED SOLUTION </li></ul><ul><li>LIBRATED IODINE TITRATED WITH N/10 THIOSULPHATE USING STARCH INDICATOR </li></ul><ul><li>1ML N/10 THIOSULPHATE =0.00355g CHLORINE </li></ul>
  12. 12. EFFECT OF pH <ul><li>DURING BLEACHING WITH NAOCL OR Ca(OCl)2 THREE ACTIVE BLEACHING SPECIES DEPENDING ON pH </li></ul><ul><li>NaOCl = OCl + Na pH 10 and above </li></ul><ul><li>NaOCl + H2O = HOCl + NaOH pH 5-8.5 </li></ul><ul><li>HOCl + HCl = Cl 2 + H 2 O </li></ul><ul><li>THUS COMPOSITION OF NAOCL OR BLEACHING POWDER CHANGES WITH pH </li></ul>
  13. 13. FORMATION OF HOCl AND OCl WITH pH <ul><li>MOST ACTIVE SPECIES IN COMPLEX OF HOCL AND OCl WHICH IS MAXIMUMM AT pH 7 </li></ul><ul><li>pH7 IS CONSIDERED AS DANGER ZONE </li></ul><ul><li>MAXIMUM BLEACHING ACTION </li></ul><ul><li>DANGER OF FIBRE DEGRADATION WITH THE FORMATION OF OXY CELLULOSE </li></ul><ul><li>DURING REACTION WITH CELLULOSE HOCL FIRST REACT WITH PRIMARY OH GROUPS WHICH THEN LOSES HCL WITH FORMATION OF (-CHO, ALDEHYDE), (C=O, KETO) OR (-COOH CARBOXYL ) GROUPS ON CELLULOSE CHAIN </li></ul><ul><li>THE REACTION PRODUCTS ARE KNOWN AS OXY CELLULOSE </li></ul>
  14. 14. COMPARISON AT VARIOUS pH
  15. 15. DEGRADATION OF COTTON
  16. 16. SUGGESTIONS <ul><li>AVOID DANGER ZONE pH 7 </li></ul><ul><li>ACID ZONE IS NOT DESIRABLE </li></ul><ul><li>CARRY BLEACHING UNDER ALKALINE pH 10-11 </li></ul><ul><li>MAXIMUM CELLULOSE DEGRADATION AT pH 7 </li></ul><ul><li>PLOT FLUIDITY VS pH </li></ul>
  17. 17. EFFECT OF TEMPERATURE <ul><li>HIGH TEMPERATURE </li></ul><ul><li>INCREASE IN RATE OF BLEACHING </li></ul><ul><li>INCREASE IN RATE OF CELLULOSE DEGRADATION </li></ul><ul><li>NaOCl SOLUTION STABLE AT HIGH TEMP. AT pH > 11 </li></ul><ul><li>DECOMPOSE RAPIDLY AT LOWER pH </li></ul><ul><li>CHLORINE FORMATION, HAS NO BLEACHING ACTION </li></ul><ul><li>IF BUFFERED TO pH 11 RATE OF BLEACHING INCREASED BY FACTOR OF 2.3 FOR EVERY 10 0 C TEMP. RISE </li></ul><ul><li>POSSIBLE TO BLEACH AT pH 11 IN 7 MIN . AT 60 0 C </li></ul><ul><li>AFFECT UNIFORMITY OF BLEACHING </li></ul><ul><li>DIFFICULT TO CONTROL FIBRE DEGRADATION </li></ul>
  18. 18. EFFECT OF CONCENTRATION <ul><li>GENERAL BLEACHING BATH CONCENTRATION IS 2-3 g/l AVILABLE CHLORINE </li></ul><ul><li>ACTUAL CONCENTRATION DEPENDS ON </li></ul><ul><li>DEGREE OF COTTON YELLOWING, </li></ul><ul><li>TIME AND </li></ul><ul><li>TEMPERATURE OF BLEACHING </li></ul>
  19. 19. ACCELERATED BLEACHING <ul><li>NaOCl REACTS WITH H 2 O 2 FORMING HO 2 ( PER HYDROXYL RADICAL ) </li></ul><ul><li>H 2 O 2 + OCl = HO 2 + Cl + OH </li></ul><ul><li>IN ACTUAL PRACTICE FIRST BLEACH WITH NaOCl AT ROOM TEMP. THEN </li></ul><ul><li>WITHOUT WASHING BLEACH WITH H 2 O 2 </li></ul><ul><li>NaOCl TREATMENT CAN BE CARRIED OUT IN J-BOX AT ROOM TEMP FOR 15 MIN. </li></ul><ul><li>WITHOUT RINSING TREAT FABRIC IN ANOTHER J-BOX WITH H 2 O 2 AT HIGH TEMP. </li></ul><ul><li>TOTAL BLEACHING TIME REDUCED WITH GOOD WHITENESS </li></ul><ul><li>H 2 O 2 ALSO ACT AS ANTICHLOR </li></ul>
  20. 20. ADVANTAGE OF NAOCL OVER BLEACHING POWDER <ul><li>NaOCl HAS REPLACED BLEACHING POWDER </li></ul><ul><li>BLEACHING POWDER MIXTURE OF Ca HYPOCHLORITE WITH LIME </li></ul><ul><li>CaCO 3 SETTLES ON FABRIC DURING BLEACHING </li></ul><ul><li>NaOCl IS FREE FROM THIS PROBLEM </li></ul><ul><li>BLEACHING POWDER IN SOLID FORM PARTIALLY SOLUBLE IN WATER </li></ul><ul><li>NaOCl IN LIQUID FORM TOTALLY MISCIBLE IN WATER </li></ul><ul><li>SOURING IS ABSOLUTELY NECESSARY IN CASE OF BLEACHING POWDER FOR THE REMOVAL OF INSOLUBLE CaCO 3 FROM FABRIC </li></ul><ul><li>NaOCl PENETRATES INTO FABRIC MORE THOROUGHLY COMPARED TO BLEACHING POWDER : </li></ul><ul><li>REQUIRES LESS BLEACHING TIME </li></ul>
  21. 21. DISADVANTAGES <ul><li>YELLOWING ON STORAGE </li></ul><ul><li>pH SENSITIVE </li></ul><ul><li>DANGER OF FIBRE DEGRADATION AT pH 7 </li></ul><ul><li>NOT SUITABLE FOR SYNTHETIC FIBRES, WOOL AND SILK </li></ul><ul><li>CORROSION OF EQUIPMENT </li></ul><ul><li>UNPLEASANT ODOUR OF Cl2 IN WORK AREA </li></ul><ul><li>HARMFUL TO SKIN IN CONCENTRATED FORM </li></ul><ul><li>FORMATION OF HIGHLY TOXIC CHLORINATED ORGANIC BYPRODUCTS KNOWN AS AOX ( ADSORBALE ORGANIC HALOGEN ) </li></ul><ul><li>AOX NOT REMOVED DURING EFFLUENT TREATMENT </li></ul><ul><li>NON-ENVIRONMENT FRIENDLY </li></ul><ul><li>NOT RECOMMENDED FOR EXPORT MARKET </li></ul>
  22. 22. INDUSTRIAL BLEACHING OPERATION <ul><li>SCOURED FABRIC MUST BE THOROUGHLY RINSED AND SQUEEZED TO REMOVE EXCESS WATER </li></ul><ul><li>SATURATE WITH BLEACH LIQUOR ( 0.5-3g/l AVAILABLE CHLORINE pH 10-11) IN ROPE FORM </li></ul><ul><li>SQUEEZE TO REMOVE EXCESS WATER </li></ul><ul><li>PILE IN RECTANGULAR TILED CEMENT OR STAINLESS STEEL TANK </li></ul><ul><li>TANK HAS PERFORATED FALSE BOTTOM WITH AN OUTLET TO SUMP UP OF EQUAL CAPACITY </li></ul>
  23. 23. Cont.. <ul><li>PREPARE BLEACHING POWDER OR NaOCl SOLUTION OF DESIRED CONCENTRATED IN SUMP TANK </li></ul><ul><li>PUMP AND SPRAY ONTO PILED COTTON FABRIC THROUGH WHICH IT PERCOLATES AND GETS ACCUMULATED INTO SUMP </li></ul><ul><li>CARRY TREATMENT FOR 2-4 HOURS </li></ul><ul><li>AFTER BLEACHING SOUR WITH 5 G/L HCL TO REMOVE RESIDUAL CHLORINE, DISSOLVE CaCO 3 ( IN CASE OF BLEACHING POWDER ), ALSO REMOVE IRON STAINS. </li></ul>
  24. 24. HYPOCHLORITE BLEACHING UNIT
  25. 25. BLEACHING IN J-BOX <ul><li>CONTINUOUS BLEACHING IN J-BOX POSSIBLE </li></ul><ul><li>SATURATE CLOTH IN ROPE FORM WITH NAOCL SOLUTION </li></ul><ul><li>STORE IN J-BOX FOR 1 HOUR </li></ul><ul><li>WASH, ANTICHLOR, WASH </li></ul><ul><li>CLOTH FIRST FEED I IS FIRST OUT IN J-BOX </li></ul><ul><li>WHEREAS IN PIT CLOTH FIRST FED IS LAST OUT, NON UNIFORM TIME OF TRETMENT </li></ul>

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