1. 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
TOTAL

2. 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

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

4. 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

5. 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.

6. 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

7. 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.

8. 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

9. 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

10. 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 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 C
RAISE THE TEMPERATURE TO BOIL IN MIN.
CONTINUE DYEING AT BOIL FOR MIN
RINSE WITH COLD WATER
AFTER TREAT WITH CATIONIC DYE FIXING AGENT.
DRY WITHOUT RINSING.

11. 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

12. 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 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.

13. 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

14. CATIONIC DYE FIXING AGENT