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Bleaching slides
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Bleaching slides

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

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