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