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Lecture 5 dyeing of cotton with reactive dyes
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  • 1. REACTIVE DYES
    • DISCOVERED IN 1956: BRITISH CHEMIST RATTEE AND STEPHEN, ICI NOW ZENECA COLOURS
    • AFTER 100 YEARS OF DISCOVERY OF FIRST SYNTHETIC DYE, PERKINS, BRITISH CHEMIST
    • CHEMICAL REACTION BETWEEN DYE AND FIBRE
    • COVALENT BOND FORMATION
    • NAMED AS REACTIVE DYES
  • 2. MODE OF REACTION
    • STRUCTURAL FEATURES
    • S-D-B-X
    • S SOLUBILIZING GROUP
    • C CHROMOPHORE
    • B BRIDGING GROUP
    • X REACTIVE GROUP
  • 3. REACTIVE DYES BASED ON TRIAZINE
  • 4. SCHEMATIC REPRESENTATION OF TRIZINE REACTIVE DYES
  • 5. REACTIVE DYES BASED ON VINYL SULPHONE
  • 6. CLASSIFICATION
    • MONO-FUNCTIONAL REACTIVE DYES
    • BI-FUNCTIONAL REACTIVE DYES
    • MONO-FUNCTIONAL REACTIVE DYES
    • PRESENCE OF REACTIVE GROUP (ONE OR TWO) AT A SINGLE LOCATION ON DYE MOLECULE
    • REACTIVE DYES DEVELOPED AT EARLY STAGES WERE MONO-FUNCTIONAL
    • TYPICAL EXAMPLES ARE
    • MONOCHLORO TRIAZINE
    • DICHLORO TRIAZINE (TWO REACTIVE GROUPS LOCATED ON THE SAME TRIAZINE RING)
    • VINYL SULPHONE
  • 7. MONO FUNCTIONAL REACTIVE DYES
    • REACTIVE GROUP ATTACHED TO A SINGLE CHROMOPHORE
    • NO SEPARATION OF REACIVE GROUPS FROM EACH OTHER
  • 8. Typical mono functional reactive groups
  • 9. CLASSIFICATION
    • BIFUNCTIONAL REACTIVE DYES
    • RECENTLY INTRODUCED
    • PRESENCE OF TWO REACTIVE GROUPS OF SAME TYPE (MONO OR DIDCHLORO TRIAZINE) OR DIFFERENT TYPES (MONOCHLORO TRIAZINE AND VINYL SULPHONE
    • AT TWO DIFFERENT LOCATIONS IN THE DYE MOLECULE.
    • THESE DYES ALSO CALLED AS HE DYES
    • SHOW HIGH EXHAUSTION, HIGH FIXATION
    • BETTER COLOUR YIELD
    • REDUCED POLLUTION: LESS DYE IN EFFLUENT
    • VERY POPULAR FOR EXHAUST DYEING.
    • HIGH EXHAUSTION IS DUE TO HIGH MOLECULAR WEIGHT SIMILAR TO DIRECT DYES, HIGH AFFINITY TO COTTON
    • REACT WITH CELLULOSE WITH CROSS LINK FORMATION.
  • 10. BIFUNCTIONAL REACTIVE DYES CHROMOPH-ORE CHROMOPHORE BRID-GE REACT-IVE GROUP REACT-IVE GROUP
  • 11. Homo and Hetrobifunctional reactive dyes
  • 12. DYEING METHODS
    • Batch dyeing
    • THREE STAGES
    • EXHAUSTION FROM AQUEOUS BATH CONTAINING ELECTROLYTE, UNDER NEUTRAL CONDITION
    • ADDITION OF ALKALI TO PROMOTE FURTHER UPTAKE AND DYE FIBRE REACTION AT OPTIMAL pH AND TEMP.
    • RINSING AND SOAPING AT BOIL TO REMOVE ELECTROLYTE, ALKALI AND UNREACTED DYE.
    • FOLLOW DYE MANUFACTURERS RECOMMENDTIONS FOR DYEING
  • 13. DYEING CONDITIONS
    • REACTIVE GROUP DYEING COMMON SODA
    • TEMP.0 0 SALT (g/l) ASH g/l
    • DICHLORO 30 25-55 2-15
    • TRIAZINE
    • MONOCHLORO 80-85 30-90 10-20
    • TRIAZINE
    • VINYL SULPHONE 70-80 30-80 10-20
    • BIFUNTIONAL 80-85 30-60 10-20
  • 14. DYEING CYCLE
  • 15. WASHING OFF AFTER DYEING
    • EFFECTIVE WASHING AFTER DYEING IS VERY ESSENTIAL FOR THE COMPLETE REMOVAL OF UNREACTED DYE
    • UNREACTED DYE IF NOT REMOVED GIVES FALSE INDICATION OF LOW WASH FASTNESS
    • RINSE 2-3 TIMES WITH FRESH WATER AT 50-60 0 C
    • SOAP AT BOIL FOR 15-30 MIN. USING EASILY RINSABLE DETERGENT
    • RINSE WITH COLD WATER UNTILL THE RINSED WATER IS COLOURLESS OR SLIGHTLY TINTED
  • 16. AFTER TREATMENT
    • IN THE DYEING OF DEEP SHADES OR INEFFICIENT WASHING EQUIPMENT THERE MAY BE INCOMPLETE REMOVAL OF UNFIXED DYE
    • AFTER TREATMENT WITH CATIONIC DYE FIXING AGENT
    • INSOUBILIZES UNFIXED DYE
    • IMPROVE WASH FASTNESS
    • TREAT WITH 5-10 g/l CATIONIC DYE FIXING AGENT AT 50-60 0 C FOR 15-30 MIN.
    • FINAL RINSE IS NOT ESSENTIAL.
    • TREATMENT WITH DYE FIXING AGENT SHULD NEVER BE REGARDED AS A SUBSTITUTE FOR THE MOST EFFICIENT WASHING OFF PROCESS
  • 17. SEMI CONTINUOUS DYEING
    • KNOWN AS PAD-BATCH DYEING
    • ABLE TO DYE FABRIC LENGTH OF 1000-2000 METERS PER SHADE AT ECONOMICAL COST.
    • PAD-BATCH DYEING
    • SATURATION OF FABRIC WITH DYE AND ALKALI AT ROOM TEMP.
    • UNIFORM SQUEEZING OF SURPLUS LIQUOR WITH THE HELP OF PADDING MANGLE
    • WRAPPING OF THE BATCHED ROLL OF WET FABRIC IN POLYTHENE FILM AND STORAGE AT AMBIENT TEMP. FOR 2-24 hr. DEPENDING ON DYE REACTIVITY AND pH
    • WASHING AND SOAPING
    • DRYING
  • 18. PAD-BATCH METHOD
  • 19. MERITS
    • SIMPLE PROCESS
    • LOW CAPITAL COST OF EQUIPMENT
    • LOW ENERGY AND WATER CONSUMPTION
    • EXCELLENT REPRODUCIBILITY
    • BATCH LENGTHS OF 1000-10,000 m PER COLOUR.
    • HIGH REACTIVITY DYES PREFERRED FOR LOW BATCHING TIME (2-4 hr)
    • LOW REACTIVITY DYES ARE PREFERRED FOR WITH LONGER BATCHING TIME (6-24 hr)
    • DEMERITS
    • WITH MODERATE AND HIGH REACTIVITY DYES IT IS NECESSARY TO HAVE DYE ALKAI MIXER FOR IMPROVED BATH STABILITY
    • TAILING EFFECTS DURING PADDING DUE TO DYE AFFINITY TO FIBRE
    • TAILING CAN BE AVOIDED BY CONTINUOUS FEEDING OF CALCULATED CONC. OF DYE SOLUTION IN PADDING TROUGH
    • LIMITED DYEBATH STABILITY IN PREENCE OF ALKALI
  • 20. CONTINUOUS METHODS
    • HIGH PRODUCTIVITY
    • DYE FIXATION ACHIEVED IN FEW SECONDS OR MINUTES BY HEATING AT HIGH TEMPERATURE
    • HIGH CAPITAL COST
    • METHODS
    • PAD-DRY
    • PAD-DRY-BAKE
    • PAD-STEAM
    • PAD-WET FIXATION (alkali Boil)
  • 21. PAD-DRY METHOD
    • SUITABLE FOR HIGHLY REACTIVE PROCION M DYES
    • PROCESS ORIGINALLY DEVELOPED FOR PROCION M DYES TOGETHER WITH 10 g/l SODIUM BICARBONATE
    • UREA MAY BE ADDED TO IMPROVE DYE SOLUBILITY
    • SODIUM ALGINATE IN SMALL CONC. ADDED TO MINIMIZE DYE MIGRATION DURING DRYING.
    • LOWER THE DYE SUBSTANTIVITY AND REACTIVITY OF DYE HIGHER IS MIGRATION
    • HIGH SUBSTANTIVE DYES WITH HIGH REACTIVITY ARE PREFERRED.
    • HIGH REACTIVTY ALSO INCREASE THE CHANCES OF DYE HYDROLYSIS IN BATH RESULTING IN LOW DYEBATH SATBILITY
    • PROCESS NOT SUITABLE FOR DYES WITH LOW REATIVITY LIKE PROCION H OR REMAZOL
  • 22. PAD-DRY METHOD
  • 23. PAD-DRY-BAKE METHOD
    • PAD-DRY-BAKE PROCESS SUITBLE FOR PROCION H DYES
    • GOOD DYEBATH STABILITY IN PRESENCE OF ALKALI AT ROOM TEMP.
    • PAD-BATH COMPOSITION
    • DYE 10-30 g/l, SODIUM BICARBONATE 10-20 g/l,
    • UREA 100-200 g/l
    • PAD-DRY (90-100 0 C - BAKE AT 150 0 C FOR 3-5 MIN.
    • WASH-SOAP-DRY
    • ROLE OF UREA
    • IMPROVE DYE SOLUBILITY
    • MELT AT 132 0 C,
    • FORMS MOLTEN BATH
    • DYE SOLUBILITY IN MOLTEN BATH AND FIBRE SWELLING
    • DYE DIFFUSION AND DYE RECTION WITH FIBRE
  • 24. DYEING OF COTTON WITH REACTIVE DYES WORLD FIBRE CONSUMPTION (X1000 tonne) Dye consumption (Tonne) 48500 20500 42% 2200 2400 23400 49% 2000 42600 17300 41% 2000 2500 20700 49% 1996 39300 14900 39% 2000 2700 18700 49% 1990 Total Synthetic wool Regenerated Cotton Year 354 000 290 000 300 000 Total 178 000 109 000 60 000 Reactive 13 000 18 000 28 000 Azoic 12 000 12 000 12 000 Indigo 22 000 21 000 36 000 Vat 68 000 60 000 74 000 Direct 70 000 70 000 90 000 Sulphur 2004 1995 1988 Dye class
  • 25. SALIENT STATISTICS
    • The total world-wide production of cotton is estimated at 23 x10 6 te p.a. (metric tonnes per annum ).
    • The corresponding amount of reactive dye used for cotton coloration is estimated to be 120,000 te p.a. Of this about two thirds is dyed by exhaust technology.
    • Salient statistics, which follow from these figures, include:
    • 4 x 106 te p.a. of cotton is exhaust dyed with reactive dyes;
    •  4 x 108 te p.a. of fresh water is used in the overall process, and all of this is ultimately discarded in a contaminated state;
    • 2.8 x 106 te p.a. of salt is used in the process; and all of this is ultimately discarded in the aqueous effluent;
    •  8 x 104 te p.a. of reactive dye is applied, with an average fixation yield of 70%, thus:
    • 2.4 x 104 te p.a. of dye is discarded in the aqueous effluent.