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
MODE OF REACTION
• STRUCTURAL FEATURES
• S-D-B-X• S SOLUBILIZING GROUP• C CHROMOPHORE• B BRIDGING GROUP• X REACTIVE GROUP
REACTIVE DYES BASED ON TRIAZINE
SCHEMATIC REPRESENTATION OF TRIZINE REACTIVE DYES
REACTIVE DYES BASED ON VINYL SULPHONE
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
MONO FUNCTIONAL REACTIVE DYES
• REACTIVE GROUP ATTACHED TO A SINGLE CHROMOPHORE
• NO SEPARATION OF REACIVE GROUPS FROM EACH OTHER
Typical mono functional reactive groups
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.
BIFUNCTIONAL REACTIVE DYES
CHROMOPH-ORE
CHROMOPHORE
BRID-GE
REACT-IVE
GROUP
REACT-IVE
GROUP
Homo and Hetrobifunctional reactive dyes
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
DYEING CONDITIONS
• REACTIVE GROUP DYEING COMMONSODA
TEMP.00 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
DYEING CYCLE
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 50-600C • SOAP AT BOIL FOR 15-30 MIN. USING EASILY
RINSABLE DETERGENT• RINSE WITH COLD WATER UNTILL THE RINSED
WATER IS COLOURLESS OR SLIGHTLY TINTED
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 50-600C 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
SEMI CONTINUOUS DYEING
• KNOWN AS PAD-BATCH DYEING• ABLE TO DYE FABRIC LENGTH OF 1000-2000 METERS PER
SHADE AT ECONOMICAL COST.
• PAD-BATCH DYEING1. SATURATION OF FABRIC WITH DYE AND ALKALI AT ROOM
TEMP.
2. UNIFORM SQUEEZING OF SURPLUS LIQUOR WITH THE HELP OF PADDING MANGLE
3. 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
4. WASHING AND SOAPING
5. DRYING
PAD-BATCH METHOD
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
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)
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
PAD-DRY METHOD
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 0C - BAKE AT 150 0C FOR 3-5 MIN. • WASH-SOAP-DRY• ROLE OF UREA• IMPROVE DYE SOLUBILITY• MELT AT 132 0C, • FORMS MOLTEN BATH• DYE SOLUBILITY IN MOLTEN BATH AND FIBRE SWELLING• DYE DIFFUSION AND DYE RECTION WITH FIBRE
DYEING OF COTTON WITH REACTIVE DYES
WORLD FIBRE CONSUMPTION (X1000 tonne)
Year Cotton Regenerated
wool Synthetic Total
1990 1870049%
2700 2000 1490039%
39300
1996 2070049%
2500 2000 1730041%
42600
2000 2340049%
2400 2200 2050042%
48500
Dye consumption (Tonne)
Dye class 1988 1995 2004
Sulphur 90 000 70 000 70 000
Direct 74 000 60 000 68 000
Vat 36 000 21 000 22 000
Indigo 12 000 12 000 12 000
Azoic 28 000 18 000 13 000
Reactive 60 000 109 000 178 000
Total 300 000 290 000 354 000
SALIENT STATISTICS
• The total world-wide production of cotton is estimated at 23 x106 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.