Innovations in dyeing of cotton with indigo
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INNOVATIONS IN DYEING OF COTTON WITH INDIGO
R.B.CHAVAN, S.JAHAN,
J.N.CHAKRABORTYDepartment of Textile Technology
Indian Institute of Technology
Hauz-Khas, New Delhi 110016
FUNDAMENTALS
• SOLUBILIZED IN PRESENCE OF NaOH AND Na2S2O4
• VERY LOW AFFINITY INDIGO• OLDEST NATURAL DYE, BELOGNS TO VAT DYE
CLASS• SUNTHETIC INDIGO COMMERCIALLY
MANUFACTURED IN 1897• PRESENTLY MAJOR INDIGO PRODUCTION USED
FOR DYEING OF DENIM
PROPERTIES• WATER INSOLUBLE• APPLICATION TROUGH MULTIPLE DIPS AND NIPS
WITH INTERDEDIATE AIR OXIDATION
pH EFFECT
• FIG
TWO INDIGO FORMSMONO-PHENOLATE HAS HIGH AFFINITY THAN BI-PHENOLATE FORM
ADVANTAGESTECHNICAL • LESS –VE CHARGE ON FIBRE, LESS DYE REPULSION
• HIGH STRIKE RATE• RING DYEING• BETTER WASH DOWN EFFECTS
ENVIRONMENTAL• BETTER COLOUR YIELD• LESS DYE IN EFFLUENT• LOW EFFLUENT LOAD• SAVING IN DYE CONSUMPTION• LOW DYEING COST
MATERIALS
• COMMERCIAL SYNTHETIC INDIGO
ALKALI• NaOH• ORGANIC ALKALIES – I, II, III, IV
(ALIPHATIC AMINES)
• SODIUM HYDROSULPHITE
• COTTON FABRIC
EXPERIMENTAL
INDIGO REDUCTIONSTOCK VAT
INDIGO 2 gmALKALI X gm*Na2S2O4 1.5 gmWATER 100 ml
VATTING AT ROOM TEMP., 10 MIN.
DILUTED TO 657 ml WITH DILUTION LIQUOR
*ALKAINaOH 1 gmORGANIC ALKAI I 2.43 gmORGANIC ALKALI II 3.81 gmORGANIC ALKALI II 2.24 gmORGANIC ALKALI IV 2.94 gm
DYE BATHDILUTION LIQUOR
ALKALI x g/l*
Na2S2O4 1.5 g/l
*NaOH 1.35 g/l
ORGANIC ALKALI AS PER NaOH EQUIVALENCE
PAD BATH
INDIGO 3 g/l
Na2S2O4 3.55 g/l
ALKALI x g/l*
*NaOH 2.67 g/l
ORGANIC ALKALI AS PER NaOH EQUIVALENCE
DYEING
COTTON FABRIC PADDING WITH INDIGO SOLUTION (3 g/l), ROOM TEMPERATURE
• DIPPING TIME 30 sec• AIR OXIDATION 60 sec• EXPRESSION 80%• 6 DIP – 6 NIP
WASHING• SEVERAL COLD WATER RINSING• SOAP 2 g/l LISSAPOL D , 600C, 10 min.• COLD WATER RINSE
INDIGO ON FABRIC
COLOUR DEPTH• K/S DETERMINATION AT 640 nm
WAVELENGTH
%YIELD• K/S (NaOH) AS 100%
NaOH EQUIVALENCE OF ORGANIC ALKALI
TITRATION WITH 0.1N H2SO4
PHENOPHTHALEIN INDICATOR
RESULTS IN TERMS OF gm OF ORGANIC ALKALI EQUIVALENT TO 1 gm NaOH
ALKALI CONCENTRATION IN DYE BATH
10 ml DYE LIQUOR,
TITRATE WITH 0.1 N H2SO4 UNTIL THE DROP OF DYE LIQUOR PLACED ON PHELOLPHTHALEIN PAPER DOES NOT SHOW RED COLOUR
NA2S2O4 CONCENTRATION IN DYEBATH
10 ml DYE LIQUOR
ADD1 ml FORMALDEHYDE, 5 ml ACETIC ACID
TITRATE: 0.1 n IODINE SOLUTION
SPOT TITRATED LIQUOR ON STARCH PAPER
CONTINUE TITRATION TILLLIQUOR DROP PRODUCE DARK BLUE (Black) SPOT SURROUNDED BY VIOLET RING
DETERMINE Na2S2O4 FROM IODINE CONSUMED
NaOH Equivalence of Organic Alkalis
Organic Alkali NaOH Equivalence (1gm)
Organic Alkali I
Organic Alkali II
Organic Alkali III
Organic Alkali IV
2.43
3.81
2.24
2.94
DYEBATH STABILITY AND COLOUR BUILD UP
• DURING DYEING THERE IS CONSUMPTION OF Na2S2O4 AND ALKALI
• ORGANIC ALKLIS BEING WEAK, THERE IS POSSIBILITY OF THEIR RAPID CONSUMPTION AFFECTING DYE-BATH STABILITY AND COLOUR YIELD
• DYE-BATH STABILITY AND COLOUR YIELD WERE TESTED BY CARRYING OUT DYEING (6DIP-6 NIP) AFTER STORAGE OF LEUCO VAT FOR DIFFERENT INTERVALS OF TIME.
Effect of Different Alkalis on Indigo Dye bath Stability and Colour Build up
Alkali 0hrs 2hrs 4hrs 6hrs 8hrs
NaOH
Organic Alkali I
Organic Alkali II
Organic Alkali III
Organic Alkali IV
100/13
128
142
131
139
100/13
133
155
133.6
143.1
100/14
118.6
148.5
140.1
146.1
100/14
121.1
-
137.5
155.8
100/15
110.0
63.5
104.6
124.4
OBSERVATIONS
• ALL ORGANIC ALKALIS SHOWED HIGHER COLOUR YIELD THAN NaOH
• ALL LEUCO INDIGO SOLUTIONS WERE STABLE EXCEPT ORGANIC ALKALI II
• AFTER 24 hrs. NO ALKALI INCLUDING NaOH WAS ABLE TO MAINTAIN INDIGO IN LEUCO FORM
THE HIGHER COLUR YIELD IN CASE OF ORGANIC ALKALI MAY BE RELATED TO pH OF INDIGO BATH
CHANGE OF pH WITH TIME BEFORE PADDING
Alkali 0hr 2hr 4hr 6hr 8hr
NaOH
Organic Alkali I
Organic Alkali II
Organic Alkali III
Organic Alkali IV
12.3
10.8
10.6
10.8
10.8
11.6
10.7
10.5
10.7
10.6
11.5
10.6
10.3
10.5
10.5
11.4
10.5
10.0
10.4
10.5
11.4
10.3
9.6
10.1
10.2
OBSERVATIONS
• NaOH STRONGER ALKAI SHOWED pH 12.3• ORGANIC ALKALIS SHOWED pH 10.8
ACCORDING TO LITERATURE• INDIGO SHOWS MAX. COLOUR YIELD AT pH 10.5-
11.5• INDIGO IN MONO-PHENOLATE FORM• HIGH AFFINITY TO COTTON• BETTER COLOUR YIELD COMPARED TO NaOH• IN CASE OF NaOH, INDIGO IN BI-PHENOLATE
FORM• LOW AFFINITY
Effect of Number of dips on Alkali Consumption
Alkali
% Consumption of alkali after each dip
1 2 3 4 5 6
NaOH
Organic Alkali I
Organic Alkali III
Organic Alkali IV
10
7.9
6.9
12.5
11.2
9.2
7.8
18.7
12.5
11.8
8.7
21.8
15.0
13.1
9.5
20.5
16.2
14.3
12.2
28.1
17.5
15.8
14.8
29.9
ALKALI CONSUMPTION
• NEUTRALIZATION BY NaHSO3 FORMED BY OXIDATION OF Na2S2O4
• NEUTRALIZATION BY ATMOSPHERIC CO2
• ADSORPTION BY COTTON
ALKALI CONSUMPTION TO AN EXTENT OF 15-17% EXCEPT ORGANIC ALKALI IV (30%)
Alkali % Consumption of Na2S2O4
1 2 3 4 5 6
NaOH
Organic Alkali I
Organic Alkali III
Organic Alkali IV
48.2
52.0
40.3
37.5
53.5
67.2
61.5
53.6
60.7
74.5
67.3
58.9
67.8
80.0
73.1
67.8
78.5
80.8
79.8
76.7
89.2
89.0
81.7
83.0
Effect of Number of dips on Na2S2O4 Consumption
Na2S2O4 CONSUMPTION
• OXIDATION DUE TO ATMOSPHERIC OXYGEN
• CONSUMPTION DURING 1st DIP IS HIGH• INTRODUCTION OF OCCLUDED AIR BY
COTTON
• AT THE END OF 6 DIPS Na2S2O4 CONSUMPTION IS 80-90%
• HIGH Na2S2O4 CONSUMPTION IS THE MAIN CAUSE FOR DYE BATH INSTABILITY
SIMULATION OF COMMERCIAL DYEING PRACTICE
• RESIDUAL DYE-BATH USED SEVERAL TIMES IN COMMERCIAL PRACTICE AFTER REPLENISHING WITH ALKALI AND Na2S2O4
• THE DYEINGS OF 1st DAY AND 7th DAY ARE
ALMOST IDENTICAL
SIMULATION OF COMMERCIAL DYEING PRACTICE
Alkali Sample of the
1st day
Sample of the
7th day
K/S pH K/S pH
NaOH
Organic Alkali I
16.7
20.7
12.3
10.9
16.3
19.7
11.9
10.7
CONCLUSION
• ORGANIC ALKALIS SHOWED HIGHER COLOUR YIELD OF INDIGO COMPARED TO NaOH
• IN PRESENCE OF ORGANIC ALKALI, LEUCO INDIGO IS IN MONO-PHENOLATE FORM
• NaOH MAY BE SUBSTITUTED BY ORGANIC ALKALI.
• ESSENTIAL TO ESTABLISH ON THE BASIS OF BULK SCALE TRIALS AND COSTING
IRON (II) SALT COMPLEXES
PROBLEMS WITH Na2S2O4
• DECOPOSE OXIDATIVELY AND THERMALLY TO SEVERAL BY-PRODUCTS
• ONLY A PORTION IS AVAILABLE FOR DYE REDUCTION
• SOME BY-PRODUCTS ARE ACIDIC• ABOUT 3 TIMES MORE NaOH AND Na2S2O4 OVER
STOICHOMETRIC REQUIREMENT BY-PRODUCTS• Na2S AND NaHS: POLLUTE ATMOSPHERE,
FORMATION OF H2S• Na2SO3, NaHSO4, Na2SO4, Na2S2O3: CONTAMINATE
SEWAGE, CORRODE CEMENT PIPES
ALTERNATIVE ECO-FRIENDLY REDUCING AGENTS
• ELECTROCHEMICAL REDUCTION
• HYDROXY ACETONE
• IRON PENTACARBONYL COMPOUNDS
• IRON (II) SALT COMPLEXES
IRON (II) SALT COMPLEXES
FeSO4 AND Ca(OH)2 OLDEST METHOD• BULKY SEDIMENTS, POOR SOLUBILITY OF Fe(OH)2
• NON-REPRODUCIBLE RSULTS
• MODERN APPROACH• SLUBILIZATION OF Fe(OH)2 THROUGH COMPLEX
FORMATION
• GLUCONIC ACID AS LIGAND HAS BEEN INVESTIGATED IN GERMAN LITERATURE (1995)
Fe(OH)2 AS REDUCING AGENT
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