lecture 5 dyeing of cotton with reactive dyes

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.