1. INNOVATIONS IN DYEING OF COTTON WITH INDIGO
R.B.CHAVAN, S.JAHAN,
J.N.CHAKRABORTY
Department of Textile Technology
Indian Institute of Technology
Hauz-Khas, New Delhi

2. 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

3. pH EFFECT
FIG

4. TWO INDIGO FORMS
MONO-PHENOLATE HAS HIGH AFFINITY THAN BI-PHENOLATE FORM
ADVANTAGES
TECHNICAL
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

5. MATERIALS ALKALI COMMERCIAL SYNTHETIC INDIGO NaOH
ORGANIC ALKALIES – I, II, III, IV
(ALIPHATIC AMINES)
SODIUM HYDROSULPHITE
COTTON FABRIC

6. EXPERIMENTAL INDIGO REDUCTION STOCK VAT INDIGO 2 gm
ALKALI X gm*
Na2S2O gm
WATER 100 ml
VATTING AT ROOM TEMP., 10 MIN.
DILUTED TO 657 ml WITH DILUTION LIQUOR
*ALKAI
NaOH 1 gm
ORGANIC ALKAI I 2.43 gm
ORGANIC ALKALI II 3.81 gm
ORGANIC ALKALI II 2.24 gm
ORGANIC ALKALI IV 2.94 gm

7. DYE BATH DILUTION LIQUOR ALKALI x g/l* PAD BATH INDIGO 3 g/l
Na2S2O4 1.5 g/l
*NaOH 1.35 g/l
ORGANIC ALKALI AS PER NaOH EQUIVALENCE
PAD BATH
INDIGO 3 g/l
Na2S2O g/l
*NaOH 2.67 g/l
ORGANIC ALKALI AS PER NaOH EQUIVALENCE

8. 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

9. INDIGO ON FABRIC COLOUR DEPTH K/S DETERMINATION AT 640 nm WAVELENGTH
%YIELD
K/S (NaOH) AS 100%

10. 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

11. 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

12. NA2S2O4 CONCENTRATION IN DYEBATH
10 ml DYE LIQUOR
ADD
1 ml FORMALDEHYDE, 5 ml ACETIC ACID
TITRATE: 0.1 n IODINE SOLUTION
SPOT TITRATED LIQUOR ON STARCH PAPER
CONTINUE TITRATION TILL
LIQUOR DROP PRODUCE DARK BLUE (Black) SPOT SURROUNDED BY VIOLET RING
DETERMINE Na2S2O4 FROM IODINE CONSUMED

13. NaOH Equivalence of Organic Alkalis
NaOH Equivalence (1gm)
Organic Alkali I
Organic Alkali II
Organic Alkali III
Organic Alkali IV
2.43
3.81
2.24
2.94

14. 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.

15. Effect of Different Alkalis on Indigo Dye bath Stability and Colour Build up
0hrs
2hrs
4hrs
6hrs
8hrs
NaOH
Organic Alkali I
Organic Alkali II
Organic Alkali III
Organic Alkali IV
100/13
128
142
131
139
133
155
133.6
143.1
100/14
118.6
148.5
140.1
146.1
121.1 -
137.5
155.8
100/15
110.0
63.5
104.6
124.4

16. 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

17. 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
11.6
10.7
10.5
11.5
10.3
11.4
10.0
10.4
9.6
10.1
10.2

18. OBSERVATIONS ACCORDING TO LITERATURE
NaOH STRONGER ALKAI SHOWED pH 12.3
ORGANIC ALKALIS SHOWED pH 10.8
ACCORDING TO LITERATURE
INDIGO SHOWS MAX. COLOUR YIELD AT pH
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

19. Effect of Number of dips on Alkali Consumption
% 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
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

20. 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%)

21. Effect of Number of dips on Na2S2O4 Consumption
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
78.5
80.8
79.8
76.7
89.2
89.0
81.7
83.0

22. 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

23. 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

24. SIMULATION OF COMMERCIAL DYEING PRACTICE
Alkali
Sample of the
1st day
7th day
K/S pH
NaOH
Organic Alkali I
16.7
20.7
12.3
10.9
16.3
19.7
11.9
10.7

25. 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

26. 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

27. ALTERNATIVE ECO-FRIENDLY REDUCING AGENTS
ELECTROCHEMICAL REDUCTION
HYDROXY ACETONE
IRON PENTACARBONYL COMPOUNDS
IRON (II) SALT COMPLEXES

28. 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)

29. Fe(OH)2 AS REDUCING AGENT