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 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 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

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

EXPERIMENTAL INDIGO REDUCTION STOCK VAT INDIGO 2 gm ALKALI X gm* Na2S2O4 1.5 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

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 Na2S2O4 3.55 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 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

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

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 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

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 11.6 10.7 10.5 11.5 10.3 11.4 10.0 10.4 9.6 10.1 10.2

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 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 % 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

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%)

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

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 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

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