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Aatcc revised paper final

  1. 1. REVISED PAPER Dyeing of Cotton with Vat Dyes using Iron(II) Salt Complexes J N Chakraborty, Department of Textile Technology, National Institute of Technology, Jalandhar-144011 R B Chavan, Department of Textile Technology, Indian Institute of Technology, New Delhi -110016, IndiaABSTRACTSodium hydrosulfite is universally used reducing agent for dyeing of cotton with vat dyes.However it forms various decomposition products containing sulfur, which go into wastewatercreating environmental problems. Search is therefore on for alternative reducing systems for vatdyeing. In the present work, the use of the co-ordination complexes of Fe(II) salts with suitableligands is reported.Key TermsHydrosulfite, Dye Strength, Fe(II) salt, Ligand,Vat colors possess pairs of carbonyl (C=O) groups in their structure and are water insoluble.These are converted to water soluble form in presence of strong reducing agent and alkali whichonly then exhibit affinity for cellulosics1,2. Sodium hydrosulfite is universally used reducingagent for dyeing of cotton with vat dyes. However, there are certain drawbacks associated withuse of sodium hydrosulfite viz. reduction and dyeing both are performed at different temperaturefor different classes of vat dyes2 ; wastage of sodium hydrosulfite due to its thermal andoxidative decomposition in bath, which is compensated by means of adding it in excess3,4 (a costfactor), as well as formation of various decomposition products containing sulfur, which go intowaste-water creating environmental problems5,6 .
  2. 2. Various alternative eco-friendly reducing systems viz. hydroxy acetone7,8, glucose-NaOH9,electrochemical reduction10-11 are reported in the literature. Fe(OH)2, though a strong reducingagent, its reducing capacity is not revealed due to its poor water solubility. In order to useFe(OH)2 as reducing agent it is necessary to keep it in solution. This is possible by the formationof co-ordination complexes of Fe(II) salts with suitable ligands in presence of alkali like NaOH.It was reported that gluconic acid co-ordinates with Fe(II), improves its water solubility togenerate reduction potential for vat dye reduction and subsequent dyeing of cotton at 60oC5. Inour previous work, we had shown that Fe(II) salts can be successfully complexed with tartaricacid, citric acid or triethanolamine in presence of NaOH12. These co-ordination complexes weretermed as single ligand complexes or single ligand systems. These Fe(II)–single ligandcomplexed reduction baths were turbid due to incomplete solubilisation of Fe(OH)2 ; thougheffective for reduction of indigo were ineffective for other vat dyes12 .The present paper aims at the use of co-ordination complexes of Fe(II) salts with two ligands(viz. citric acid and triethanolamine or tartaric acid and triethanol amine, termed as two ligandsystems) along with NaOH for reduction and application of vat dyes other than indigo on cottonat room temperature. Fe(II) complexed with gluconic acid was also used for dyeing at 60oC asreported in literature5 to compare with the dyeing efficiency of our system.EXPERIMENTALMaterials (with specifications), determination of alkali equivalence of ligands, calculation oftotal NaOH requirement, measurement of color strength of samples, measurement of reductionpotential, estimation of iron in dyed samples, estimation of ferric iron, estimation of soluble ironin dyebath were reported in earlier paper12. Commercial vat dyes were used. C.I.Generic namesare reported in this paper13. 2
  3. 3. Preparation of Reduction BathSingle Ligand System2.16g of tartaric acid or 3.0g of citric acid or 5.6ml of gluconic acid (50%) or 1.92ml oftriethanolamine was dissolved in 100 ml water in a glass beaker in open air ; 2 g of FeSO4 wasdissolved in this bath ( FeSO4 : ligand = 1 : 2 molar ) followed by addition of NaOH ( 1.47g,2.62g or 1.21g for tartaric, citric or gluconic acid system respectively ). All the baths were turbid.Quantity of dye required to get 1% shade was then added. Vatting and dyeing were carried outat room temperature, except gluconic acid bath which was heated up at 60oC as reported inliterature12.Double Ligand System3.78g of tartaric or 6g of citric acid was dissolved in 50 ml water in a glass beaker in open airfollowed by addition of 2g of FeSO4 with constant stirring till the latter gets completelydissolved. Triethanolamine was added in this solution (1ml in tartaric and 1.5ml in citric acidsystem) and stirred well to ensure thorough mixing. In another beaker, desired weight of NaOH( 3.09g for tartaric and 4.3g for citric acid system ) was dissolved in 50 ml water followed byaddition of this NaOH solution to the previously prepared FeSO4, tartaric (or citric) acid andtriethanolamine mixture. A clear solution was obtained. Quantity of dye required to get 1%shade was added to this bath. Instantaneous reduction of dye occurs (though 10 minutes wereallowed to ensure complete reduction). The vatting and dyeing were carried out at roomtemperature at material to liquor ratio of 1:20Sodium hydrosulfite systemConcentrations of hydrosulfite, NaOH and vatting and dyeing conditions were as follows1,2 : 3
  4. 4. IK IW IN IN special Temperature of vatting 35-40oC 45-50oC 55-60oC ≥ 60oC Temperature of dyeing 35oC 45oC 50-55oC ≥60oC Hydrosulfite (g/l) 8 10 12 15 NaOH (g/l) 8 10 12 15Dyeing of SamplesCotton fabric samples were dyed in open air in glass beakers for 1 hr. at room temperature insingle and double ligand reducing systems separately, at 60oC in gluconic acid system and atspecific temperature range in hydrosulfite system. Dyed samples were air oxidized, rinsed withwater, soaped at boil with anionic detergent (5g/l) for 15 minutes followed by thorough washing.Wash and light fastness were determined as per standard procedure reported in Bureau of IndianStandards( Test methods IS: 764 : 1979 and IS 2454 : 1985 respectively)14. Color strength wasmeasured in Datacolor Color Matching Instrument.RESULTS AND DISCUSSIONFor the simplicity of understanding the co-ordination complex system essentially consisting ofFe(II) salt like FeSO4, NaOH and ligands like citric acid, tartaric acid or triethanolamine eitheralone (single ligands) or tartaric acid and citric acid separately in combination withtriethanolamine (two ligands), it is envisaged that FeSO4 reacts with NaOH with formation ofFe(OH)2 of poor water solubility. Its water solubility is improved when Fe(II) forms co- 4
  5. 5. ordination complex with single ligand or two ligands as mentioned above. In the followingparagraphs such co-ordination complexes are referred as single ligand or two ligand systems.Dyeing of Cotton with Anthraquinoid Vat DyeSingle Ligand SystemReducing systems based on Fe(OH)2 complexed with single ligand though worked successfullyfor dyeing of cotton with indigo12, showed their inability to reduce anthraquinoid vat dyes exceptgluconic acid system. Table 1 shows values of pH, reduction potential, complexed iron and dyestrength of samples. It was observed that no dye reduction took place from FeSO 4 + NaOH aswell as FeSO4 + NaOH + triethanolamine systems, hence no dye yield. In case of tartaric andcitric acid systems, partial reduction of dye was visually observed, however there was no dyeing,whereas in case of gluconic acid system dye reduction and dyeing took place, though thereduction potential at all stages of dyeing was highest in triethanolamine system.Different ligands showed varying amounts of complexed Fe(II) in bath before dye addition, asshown in Table I. Complexed Fe(II) was least in FeSO4 + NaOH system and highest in gluconicacid system. Thus it appears that the amount of complexed Fe(II) in triethanolamine system wasnot adequate for vat dye reduction and therefore no dyeing took place. Complexed Fe(II)washigher in case of tartaric and citric acid systems ; thus when dye was added to these reducingsystems, partial reduction of vat dye was observed but no dyeing took place. In contrast, ingluconic acid system complexed Fe(II) was highest causing complete reduction of vat dye andgood dyeing. Failure of anthraquinoid vat dye reduction and its subsequent dyeing in spite ofhigh reduction potential and pH of baths at different stages of dyeing clearly indicated that it wasnot only the reduction potential but also amount of complexed Fe(II) in bath was equallyimportant for dye reduction and to keep the dye in reduced form during dyeing. 5
  6. 6. Chemically vat dyes can be classified in two types - indigoid and anthraquinoid. Indigoid vat dyecan be reduced and maintained in reduced condition at low reduction potential (-700 mV)compared to anthraquinoid vat dyes -(850-900)mV. Therefore a single ligand system wascapable of reducing indigo and keeping it in reduced condition giving good dyeing of cotton 12but the same systems failed to reduce anthraquinoid vat dyes. This analysis made it clear that thedyeing of cotton with vat dye did not occur from co-ordination complexes of Fe(II) with singleligand systems (except gluconic acid) due to inadequate complexion of Fe(II). It was thereforethought to use two ligand systems for vat dyeing.Chakraborty replace the words highlighted with unstable co-ordination complex of Fe(II)Two Ligand SystemsLimited complexion of Fe(II) in presence of single ligand like tartaric or citric acid might be dueto formation of weak co-ordination linkages with limited stability. It was thought that a secondligand like triethanolamine may enter along with tartaric and citric acid in co-ordination linkagewith Fe(II), resulting in more stable complex. Based on this assumption, reduction bathsconsisting of FeSO4-tartaric acid-triethanolamine-NaOH or FeSO4 -citric acid - triethanolamine -NaOH ( FeSO4 -25 g/l, Tartaric acid or Citric acid-15 g/l, Triethanolamine - 40 ml/l andNaOH-50 g/l) were prepared so as to get colorless, clear reduction baths indicating completecomplexion of Fe(II). In these formulations, molar ratio of FeSO4 with triethanolamine was 1: 3,that with tartaric acid 1: 1.5 and with citric acid 1 : 1. Dyeing with few randomly selected vatdyes was carried out in 1% shade at room temperature and were compared with those obtainedfrom hydrosulfite system. Results are shown in Table II. Except C.I. Vat Blue 7 and C.I. VatViolet 1, the dyeings were comparable to sodium hydrosulfite system. 6
  7. 7. This observation gave support to our hypothesis that for satisfactory dyeing with vat dyes, it wasnot only the reduction potential at different stages of dyeing but also maximum complexion ofFe(II) are very important.Chakraborty Replace the highlighted portion by: the formation of stable co-ordination complexof Fe(II) is importantOptimisation of Dyebath Recipe for Double Ligand Systems Replace double by twoThe above experiment gave the clue for successful dyeing of cotton with vat dyes using Fe(II)complexes as reducing agent. Subsequently, concentration of each component in double ligand (replace by two) reducing systems was optimized. Concentration of total NaOH required andalkali equivalence of acidic ligands was explained in earlier paper12. Criteria for optimizedconcentrations were those that produced clear solutions having maximum efficiency for dyereduction and showing maximum dye uptake on cotton.In FeSO4 - tartaric acid - triethanolamine - NaOH reducing system, the optimized reduction bathcomposition was FeSO4-20 g/l, Tartaric acid-37.8 g/l (FeSO4: tartaric acid =1:3.5 molar),Triethanolamine - 10 ml/l (FeSO4 : triethanolamine = 1: 0.7 molar) and NaOH-30.9 g/l ;whereas in FeSO4-citric acid - triethanolamine - NaOH reducing system, the optimized reductionbath composition was FeSO4 - 20 g/l, Citric acid - 60 g/l ( FeSO4 : citric acid =1 : 4.5 molar),Triethanolamine - 15 ml/l (FeSO4 : triethanolamine = 1: 1.1 molar) and NaOH - 43 g/l . Therecipes stated in experimental section are based on these optimized concentrations.Stability of Reduction BathsReduction baths with optimized concentration of chemicals were prepared in absence andpresence of dye and were stored in open air at room temperature for different intervals of time up 7
  8. 8. to 24 hours. Reduction potential was measured at definite intervals and is shown in Fig.1. Allthe reduction baths remained fairly stable up to 4 hours, beyond which drop in reductionpotential started taking place. After storing for 24 hours, the drop in reduction potential wassubstantial in all cases. The dyeability of reduction baths after storage for definite intervals wasstudied by carrying out dyeing of cotton with C.I. Vat Green 1 (4% owf). Dye strength valuesare shown in Fig. 2, which also indicated that baths remained stable up to 4 hours, beyond whichthe stability went on decreasing. Comparison of dye strength indicated the bath stability in thefollowing orderHydrosulfite < Citric acid, triethanolamine ligands ≃ Tartaric acid, triethanolamine ligands< Gluconic acid ligand systemsDyeing with different Vat DyesIn order to establish the feasibility of new reducing systems for application of vat dyes, dyeing ofcotton with a wide range of vat dyes belonging to I K, IW, IN and IN special classes was carried outfor 4% shades. For comparison purpose, respective standards were prepared in hydrosulfite andNaOH system. Dyeings were also carried out in gluconic acid system at 60oC using FeSO4:gluconic acid (1: 2 molar) as reported in literature5 to compare efficiency of our systems. In caseof C.I. Vat Green 9 (Black BB), dyeings were carried out for 10% shades. Results obtained areshown in Ttable III.Dye belonging to IK class showed better color strength in two ligand systems compared tohydrosulfite and gluconic acid systems. In case of IW, IN and IN special classes, no definite trend wasobserved. Hydrosulfite and gluconic acid systems produced good black shades with Black BB,whereas two ligand systems produced deep olive green shade instead of a black 8
  9. 9. From these observations it may be concluded that two ligand systems (tartaric, triethanol amineand citric acid, triethanol amine) investigated in the present work in principle were suitable formost of the vat dyestuffs. Few dyes particularly blues showed less color strength probably due toover-reduction problem associated with structure of these dyes (indanthrone type) and black BBdid not give black shade.Fastness Properties of Dyed SamplesWash and light fastness tests were carried out on few selected dyed samples to confirm ifpresence of iron interferes in their fastness properties. While wash fastness properties remainedunaffected for all dyed samples in all reducing systems, light fastness in case of C.I. Vat Brown 3was lowered in case of Fe(II) complexes, might be due to presence of iron, which showedcatalytic action on dyed samples (table IV). In order to confirm this, estimation of residual ironwas carried out on dyed samples. It was found that negligible amount of iron was deposited ondyed sample in gluconic acid system whereas higher amounts were deposited on samples dyedfrom tartaric and citric acid systems (table V). Presence of iron on dyeing might show catalyticaction in presence of light, but this problem is restricted to certain red, yellow and brown dyesonly1.CONCLUSIONSReducing systems based on Fe(II) complexes with single ligand such as tartaric acid, citric acidor triethanolamine were not suitable for dyeing with vat dyes. However, Fe(II) complexes withtwo ligands produced dyeing comparable to sodium hydrosulfite system with few exceptions.Blue vat dyes with indanthrone structure produced weaker dyeing due to over reduction, whereasC.I. Vat Green 9 produced deep olive green shade instead of black. Wash fastness of five vat 9
  10. 10. dyes under investigation was comparable to literature values, whereas there was deterioration inlight fastness in case of C.I. Vat Brown 3.References1. M. R. Fox, Vat Dyestuffs and Vat Dyeing, 1st edition, Chapman & Hall Ltd, London, 1948, pp97 - 100.2. S.V.Gokhale, and R.C.Shah, Cotton piece Dyeing, 1st edition, Ahmedabad Textile Industries Research Association, India, 1974, pp30-35.3. G. P. Nair and S. S. Trivedi, Colourage, Vol. 17, No. 27, December 1970, pp19-21.4. F. Shadov, M. Korchagin and A. Matetsky, Chemical Technology of Fibrous Materials, Revised English Translation, Mir Publishers, Moscow, 1978, pp428-433.5. B. Semet, B. Sackingen and G. E. Gurninger, Melliand Textilberichte, Vol. 76, No.3, March 1995, pp161-164.6. D. Fiebig and K. Konig, Textile Praxis International, May 1977, pp 577- 586.7. E. Marte, Textil Praxis, Vol. 44 , No. 7, July 1989, pp737-738.8. U. Baumgarte, Melliand Textilberichte, Vol. 68, No. 3, March 1987 , pp189- 195.9 N. Nowack, H. Brocher, U. Gering and T. Stockhorst, Melliand Textilberichte, Vol. 63, No. 2, February 1982, pp134-136.10. T.Bechtold, E. Burtscher, D. Gmeiner and O. Bobleter, Melliand Textilberichte, Vol. 72, No.1, January 1991, pp50-54.11. T.Bechtold, E. Burtscher, G. Kuhnel and O. Bobleter, Journal of the Society of Dyers & Colourists, Vol. 113, No. 4, April 1997, pp135-144.12. R. B. Chavan and J. N. Chakraborty, Coloration Technology, Vol. 117, No.2, February 2001, pp88-94.13. Colour Index International, 3rd edition (3rd revision), Society of Dyers & Colourists, Bradford, 1987.14. Handbook of Textile Testing, Part-4, 1st Revision, Bureau of Indian Standards, New Delhi, 1988, pp115-119 & 141-142.Authors Address:Dr. J.N Chakraborty, NIT, Jalandhar, India Dr. R.B. Chavan, IIT, New Delhi, India 10
  11. 11. E-Mail –chakrabortyjn@hotmail.com E-Mail - rbchavan@hotmail.comTel : 95-181-2690301-2, Ext. 221 Tel : 95-11-26591406Fax: 95-181- 2690320 Fax: 95-11-26581103 11