The document discusses the bleaching of cotton fabric using chlorine-based bleaching agents such as bleaching powder and sodium hypochlorite. It explains that the objective of bleaching is to produce a white fabric by destroying color compounds while minimizing fiber degradation. It then describes the manufacturing process for bleaching powder and sodium hypochlorite, and compares their properties and effects on bleaching cotton at different pH levels, temperatures, and concentrations. Finally, it outlines the typical industrial bleaching operation process.

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