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Bleaching slides
 

Bleaching slides

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    Bleaching slides Bleaching slides Presentation Transcript

    • 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 .
    • 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.
    • 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
    • CLASSIFICATION OF BLEACHING AGENT
      • OXIDIZING BLEACHING AGENT
      • CHLORINE SYSTEM
      • PEROXIDE SYSTEM
    • CHLORINE SYSTEM
      • BLEACHING POWDER
      • SODIUM HYPOCHLORITE
      • SODIUM CHLORITE
      • PEROXIDE SYSTEM
      • HYDROGEN PEROXIDE
      • PER ACETIC ACID
      • SODIUM PERBORATE
      • POTASSIUM PERMANGANATE
    • REDUCTIVE BLEACHING AGENT
      • SULPHUR DIOXIDE
      • SODIUM HYDROSULPHITE
      • SODIUM SULPHOXYLATE FORMALDEHYDE
      • SODIUM BISULPHATE
      • MAINLY USED FOR BLEACHING OF WOOL
    • 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
    • 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
    • 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
    • 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%
    • 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
    • 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
    • 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
    • COMPARISON AT VARIOUS pH
    • DEGRADATION OF COTTON
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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.
    • HYPOCHLORITE BLEACHING UNIT
    • 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