DYE CONSUMPTION (TONNE) DYE CLASS 1988a 1992 2004b SULPHUR 90 000 70 000 DIRECT 74 000 60 000 68 000 VAT 36 000 21 000 22 000 INDIGO 12 000 AZOIC 28 000 18 000 13 000 REACTIVE 109 000 178 000 TOTAL 300 000 290 000 354 000

WORD FIBRE CONSUMPTION CONSUMPTION (1000 TONNE) YEAR COTTON REGENERATED WOOL SYNTHETIC TOTAL 1990 18700 (49%) 2700 2000 14900 (39%) 39300 1995 20700 2500 17300 (41%) 42600 23400 2400 2200 20500 (42%) 48500

DYEING OF COTTON WITH DIRECT DYES TYPICAL DYE STRUCTURE CONGO RED N NH2 Na2SO3

DIRECT DYES FEATURES PRESENCE OF SULPHONIC ACID GROUPS WATER SOLUBLE ANIONIC IN NATURE SUBSTANTIVITY/AFFINITY TO COTTON APPLIED FROM AQUEOUS DYEBATH CONTAINING ELECTROLYTE SIMPLE DYEING OPERATION LOW WASH FASTNESS WASH FASTNESS IMPROVED TO SOME EXTENT AFTER TREATMENT WITH CATIONIC DYE FIXING AGENT WASH FASTNESS STILL NOT ADEQUATE COMPARED TO OTHER DYE CLASSES SUCH AS REACTIVE DYES

DIRECT DYES USES USED FOR DYEING OF LOW PRICED COTTON OR VISCOSE FABRIC, CUTAIN, FURNISHING OR CARPETS WITH GOOD LIGHT FASTNESS AND MODERATE WASH FASTNESS CHEAP COTTON DRESSING GOWNS AND BED SPREADS WHICH ARE NOT WASHED REGULARLY DUE TO LOW WASH FASTNESS, LIMITED USE. BEING REPLACED TO GREAT EXTENT WITH REACTIVE DYES WHICH HAVE BETTER WASH FASTNESS AND PRODUCE BRIGHT SHADES.

CLASSIFICATION CLASS A SELF LEVELLING CLASS B SALT CONTROLLABLE CLASSIFIED ACCORDING TO DYEING BEHAVIOUR CLASS A SELF LEVELLING DYES WITH GOOD MIGRATION OR LEVELLING PROPERTIES i.e. DYES WHICH PRODUCE UNIFORM SHADE. NOT SENSITIVE TO DYEING CONDITIONS. CLASS B SALT CONTROLLABLE UNIFORM SHADE PRODUCD ON CONTROLLED ADDITION OF SALT DURING DYEING CLASS C TEMPERATURE CONTROLLABLE UNIFORM SHADE PRODUCED ON CAREFUL CONTROL OF DYEING TEMPERATURE AND SALT ADDITION

EFFECT OF VARIOUS PARAMETERS ON DYEING TEMPERATURE RATE OF DYEING AND PENETRATION INCREASES TEMPERATURE. DYES BEING HIGH MOLECULAR WEIGHT DYEING CARRIED OUT AT BOIL FOR GOOD PENETRATION. DYEING TIME PRODUCTION OF LEVEL AND WELL PENETRATED DYEING IS FAVOURED BY INCREASED DYEING TIME. HOWEVER, PROLONGED BOILING CAUSES DECOMPOSITION OF MANY DIRECT DYES. THE DYEING TIME IS USUALLY 1 hr. AT BOIL LIQUOR RATIO DYEBATH EXHAUSTION IS USUALLY DECREASED WITH INCREASE IN M:L RATIO. HOWEVER, UNIFORMITY OF DYEING IS IMPROVED.

EFFECT OF VARIOUS PARAMETERS ON DYEING ELECTROLYTE ELECTROLYTE IS ESSENTIAL FOR DYEING WITH DIRECT DYES COMMON ELECTROLYTE USED COMMON SALT (NaCl) OR GLAUBER’S SALT (Na2SO4) CONCENTRATION OF ELECTROLYTE IS GOVERNED DYE CONCENTRATION: LESS SALT FOR LOW DYE CONCENTRATION No OF SULPHONIC ACID GROUPS IN DYE MOLECULE: HIGH SALT WITH MORE No. OF SULPHONIC ACID GROUPS

ROLE OF ELECTROLYTE COTTON IN WATER : NEGATIVE SURFACE POTENTIAL ANIONIC DYES DISSOLVED IN WATER : NEGATIVE CHARGE DUE TO IONOIZATION OF WATER SOLUBILIZING SO3Na GROUPS DUE TO SIMILAR CHARGES: REPULSION BETWEEN DYE AND FIBRE SURFACE FOR THE DYE TO GO ON FIBRE: NECESSARY TO REDUCE –Ve CHARGE OF FIBRE ACHIEVED BY ADDITION OF ELECTROLYTE ELECTROLYTE DISSOCIATE IN WATER, RELEASE +Ve CHARGE Na+ Na+ ACCUMULATE AT THE –Ve CHARGED FIBRE SURFACE NEUTRALIZE –Ve SURFACE POTENTIAL OF FIBRE FACILITATE –Ve DYE MOLECULE ATTRACTION/ADSORPTION ON FIBRE

BATCHWISE DYEING OF COTTON DYE DISSOLUTION USE SOFT WATER FOR DYE DISSOLUTION AND DYEING. PASTE WITH COLD WATER. ADD SUFFICIENT QUANTITY OF BOILING WATER. STIRR. FILTR TO REMOVE ANY INSOLUBLE DYE PARTCLES ADDITION OF 0.5-1 g/l WETTING AGENT HELPS TO WET OUT THE FIBRE DURING DYEING. GENERAL DYEING PROCEDURE CLASS A DYES THE DISSOLVED DYE IS ADDED TO DYEING MACHINE MAKE TO TOTAL VOLUME ACCORDING TO M:L RATIO IF DYE IS SENSITIVE TO HARDNESS OF WATER, ADD 1-2 g/l SODIUM HEXAMETA PHOSPHATE OR SODA ASH ADD SODIUM CHLORIDE, FOR PALE SHADE 5% OWM, MEDIUM SHADE 10%OWM AND HEAVY SHADE 20% OWM. ENTER THE FABRIC AT 40-500C RAISE THE TEMPERATURE TO BOIL IN 30-40 MIN. CONTINUE DYEING AT BOIL FOR 30-45 MIN RINSE WITH COLD WATER AFTER TREAT WITH CATIONIC DYE FIXING AGENT. DRY WITHOUT RINSING.

CLASS B DYES SALT SENSITIVE DYES ADD SALT IN INSTALMENTS DURING RAISING THE TEMP. TO BOIL IF DESIRED SALT ADDITION MAY BE CONTINUED AFTER THE DYEBATH HAS REACHED TO BOIL. ADDITION OF DISSOLVED SALT BY DRIP FEED METHOD IS PREFERRED

CLASS C DYES TEMPERATURE SENSITIVE DYES LOW ELECTROLYTE CONC. ADDED AT THE START RAISE TEMP TO BOIL AT VERY LOW RATE DYEING CONTINUED AT BOIL FOR 45-60 MIN. SALT ADDITION SHOULD BE DONE IN INSTALMENTS AT BOIL. COMPOUND SHADES PRODUCED BY USING TWO OR THREE DYES TAKEN TOGETHER TAKE MIX DYES BELONGING TO THE SAME CLASS DYES IN MIXTURE SHOULD HAVE SIMILAR RATE OF EXHAUSTION DYE MANUFACTURER SHADE CARD GIVES INFORMATION ON DYE CLASS AND DYEING CONDITIONS FOLLOW THE INSTRUCTIONS CAREFULLY AND FAITHFLLY.

AFTER TREATMENT INADEQUATE WASH AND PERSPIRATION FASTNESS OF DIRECT DYES CAN BE IMPROVED BY AFTERTREATMENT AFTER DYEING DIAZOTIZATION AND DEVELOPMENT COPPER SULPHATE AND POTASSIUM DICHROMATE TREATMENT FORMALDEHYDE TREATMENT CATIONIC DYE FIXING AGENT: MOST POPULAR FORMS COMPLEX WITH ANIONIC DYE. DECREASE IN DYE SOLUBILITY TRETMENT CARRIED OUT USING 1-3%OWM CATIONIC AGENT AT 600C FOR 30 MIN AT pH 5 WITH ACETIC ACID. NO RISING AFTER TREATMENT

CATIONIC DYE FIXING AGENT