Transcript LECTURE 2, DIRECT DYEING OF COTTON

DYE CONSUMPTION (TONNE)
DYE CLASS
1988a
1992
2004b
SULPHUR
INDIGO
AZOIC
90 000
74 000
36 000
12 000
28 000
70 000
60 000
21 000
12 000
18 000
70 000
68 000
22 000
12 000
13 000
REACTIVE
60 000
109 000
178 000
TOTAL
300 000
290 000
354 000
DIRECT
VAT
WORD FIBRE CONSUMPTION
CONSUMPTION (1000 TONNE)
YEAR
COTTON
1990
18700 2700
(49%)
20700 2500
(49%)
23400 2400
(49%)
1995
2000
REGENERATED
WOOL
SYNTHETIC
TOTAL
2000
14900
(39%)
17300
(41%)
20500
(42%)
39300
2000
2200
42600
48500
DYEING OF COTTON WITH DIRECT
DYES
• TYPICAL DYE STRUCTURE
NH2
NH2
N
N
N
N
Na2SO3
Na2SO3
CONGO RED
DIRECT DYES
FEATURES
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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
• 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
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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
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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
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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