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Comment on Sustainable Cotton Dyeing in Nonaqueous Medium Applying Protic Ionic Liquids

Comment on Sustainable Cotton Dyeing in Nonaqueous Medium Applying Protic Ionic Liquids
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  Comment on  “ Sustainable Cotton Dyeing in Nonaqueous MediumApplying Protic Ionic Liquids ”  Ju             ̈ rgen Andreaus *  and La í s Feltrin Sidou Departamento de Química, Universidade Regional de Blumenau, 89030-903 Blumenau, SC, Brazil  ACS Sustainable Chem. Eng.  2017  ,  5  (10), 8756 − 8765. DOI: 10.1021/acssuschemeng.7b01555  ACS Sustainable Chem. Eng.  2019  ,  7   (9). DOI: 10.1021/acssuschemeng.9b01809 O ne way to approach sustainability in industrial processessuch as textile dyeing can be the selection of adequatealternative green solvents. Andrade et al. 7 reported the use of protic ionic liquids as promising nonaqueous solvents for thedyeing of cotton textiles. A critical analysis of the resultspresented in their article was made and leads to the conclusionthat the proposed alternative dyeing procedure did not lead tosatisfactory dyeing results and is not viable.The textile industry relies on several relatively harsh wetprocesses that have a negative impact on the environment  not only because of the amount of consumed water but also because of the generated wastewater contaminated withchemicals. Ionic liquids (ILs), organic salts with interestingproperties such as negligible vapor pressure, high solvationpower, and thermostability, have gained increasing interest asindustrial sol v ents and been investigated for di ff  erent textileapplications, 1 − 3  but little has been reported on their use intextile dyeing. 4 − 6 In the article  “ Sustainable Cotton Dyeing inNonaqueous Medium Applying Protic Ionic Liquids ”  , Andradeet al. 7 describe the application of 13 di ff  erent protic ionicliquids (PILs) as solvents in cotton reactive dyeing, evaluatingcolor yield (K S − 1 ), change in L * a *  b *  color coordinates,tensile strength, and surface morphology of the dyed fabrics.The authors claim that their alternative exhaustion dyeingprocess uses only dye and solvent, but no additional chemicalssuch as alkali or salt, and allows the recycling of the dyeing bath without appreciable loss of e ffi ciency since the un 󿬁  xeddye remains reactive and can be reused in another dyeingprocess.Detailed analyses of the presented spectrophotometric dataand the claims reveal some critical issues:(i) K S − 1  values are very low, which means that attainedcolor intensities are too low for acceptable dyeings.(ii) Values for a *  and b *  are too low and not distinguishablefrom gray.(iii) Dyeing results with PILs were not compared to standarddyeing procedures with water as solvent and alkali asauxiliary.(iv) No results on the reuse of the spent dyeing baths werepresented.In this Letter to the Editor, we intend to discuss these issuesusing available data from the literature in order to contribute tothe original work and open a dialogue with the researchcommunity.Color intensities (K S − 1  values) obtained by Andrade et al. 7 after dyeing at 60  ° C for 60 min and postwashing with anaqueous standard detergent solution (1 g L − 1 ) for 30 min at 25 ° C (cold washing) and 57  ° C (hot washing) were lower than0.07, which means that fabrics remained practically uncolored,and di ff  erences between the di ff  erent dyeings using water orPILs are insigni 󿬁 cant. It is also surprising that the authors donot present standard deviations for color measurements. Thereference value used by the authors is that from a dyeing withonly water without the addition of alkali, which is expected tolead to almost zero dye  󿬁  xation.Color yield or strength obtained with a speci 󿬁 c dye throughdyeing is related to the dye concentration in the bath or dyequantity used per fabric, usually expressed as % owf (on weightfabric; g dye/100 g fabric). The correlation between thequantity of applied dye and the resulting color strength iscommonly used in textile industries for calibration anddevelopment of di ff  erent colors. According to Broadbent, 8 reactive dyes with maximum absorptions at 580 and 620 nm,applied at concentrations between 0.1% and 0.4% owf yieldedK S − 1  values between 1 to above 4 and 2 to above 8,respectively. Since Andrade et. al used an initial dyeconcentration of 2% owf, much higher K S − 1  values thanthose reported by Broadbent should be expected. As the K S − 1  values obtained for all the tested PILs were not greater than0.07, it can be concluded that very little dye was  󿬁  xed to thecotton fabrics, and probably (the K S − 1  values before washingare not shown in the srcinal paper) most of the dye, if initially on the fabric, was washed o ff   during the washing processes. Although some ionic liquids tested granted a higher K S − 1  value than the control process (using water) like 2-HEAPr and2-HEAAd, the obtained K S − 1  value is still too low for asatisfactory and viable dyeing process. In addition, the authorsdid not show any photos of the dyed fabrics. According to the available literature about the CIE L * a *  b * color space, a *  and b *  coordinate values between  − 10 and 10can be read as gray colored and/or without a distinguishablecolor. 8 ,9 In the work of Andrade et al., 7 all the a *  and b *  valuesfall under this spectrum, which indicate a great loss of colorafter the washing process. Broadbent 8 indicates that a CIEL * a *  b *  color di ff  erence greater than 5.8 points between beforeand after washing corresponds to a fastness grade of 2 or lowerin standard color fastness tests, which indicates poor  󿬁  xation of the dye to the fabric. Another debatable point is the fact that the authors did notcompare their results to a standard dyed sample using alkali. Asthoroughly explored by many authors, 8 ,10 − 12 the  󿬁  xation of  Received:  February 26, 2019 Published:  April 17, 2019 Letter to the Editor Cite This:  ACS Sustainable Chem. Eng.  2019, 7, 7999 − 8000 © 2019 American Chemical Society  7999  DOI:10.1021/acssuschemeng.9b01112  ACS Sustainable Chem. Eng.  2019, 7, 7999 − 8000    D  o  w  n   l  o  a   d  e   d   b  y   I   N   S   T   F   E   D   E   D   U   C   I   E   N   C   I   A   E   T   E   C   H   C   E   A   R   A  a   t   0   5  :   5   5  :   1   1  :   8   5   6  o  n   J  u   l  y   0   2 ,   2   0   1   9   f  r  o  m    h   t   t  p  s  :   /   /  p  u   b  s .  a  c  s .  o  r  g   /   d  o   i   /   1   0 .   1   0   2   1   /  a  c  s  s  u  s  c   h  e  m  e  n  g .   9   b   0   1   1   1   2 .  reactive dyes on cellulosic  󿬁  bers is only possible throughnucleophilic substitution and addition reactions, in which thealkali causes acidic dissociation of the hydroxyl groups on thesurface of cellulose molecules, forming cellulosate ions thatreact with the dye.The dye used by Andrade et al., 7 Marinho Sidercron, has a very similar structure to the widely used C.I. Reactive Black 5, with two reactive groups of the sulfatoethylsulfone type. Dye 󿬁  xation occurs through a nucleophilic addition reaction, but 󿬁 rst, the sulfatoethylsulfone groups need to be activated by alkali, generating a vinylsulfone group, consuming one mole of hydroxyl ions and releasing one mole of sulfate ions per moleof reactive group.It appears therefore to be quite unlikely that one part of thedye molecules in the dyeing bath are activated to form the vinyl intermediate and react with the cotton cellulose, whilethe other part remains in the sulfatoethylsulfone form, so thatit can be reused. Conventional reactive cotton dyeing leads toexhausted dyeing baths containing un 󿬁  xed hydrolyzed dyemolecules, which cannot be reused in another reactive dyeingprocedure. Despite their claim for reuse of the exhausteddyeing baths, the authors did not present any related results.The di ff  erences in the K S − 1  values obtained after the two washing procedures (25 and 57  ° C) have been also discussed by the authors. They attributed the lower K S − 1  values of thehot washed water-dyed fabrics to the higher solubility of thedye in the hot detergent solution. On the other hand, they argued that some of the hot washed PIL-dyed fabrics (2-HEAAd, 2-HDEASa, and 2-HDEAPr) revealed higher K S − 1  values because of an additional  󿬁  xation of the dye due to thee ff  ect of the PILs on the cellulose structure and an improved 󿬁  xation. We consider this very unlikely since there are noreports in the literature of signi 󿬁 cant structure changes incellulose due to PIL treatment at low temperatures (60  ° C). 13 Furthermore, di ff  erences are quite small, and without standarddeviation, it is impossible to verify the statistical signi 󿬁 cance of these di ff  erences. It is also not clear from the presented data if the ionic liquids were completely removed from the cottonfabrics through the washing procedures. Residual PILs canhave an in 󿬂 uence on some of the evaluated fabric properties.From the above presented analyses and discussions of thedata presented by Andrade et al., 7  we conclude that none of the 13 PILs investigated by Andrade et al. serves as a promisingsolvent for reactive cotton dyeing and that results of new alternative dyeing processes have to be compared toconventional dyeing results, otherwise erroneous conclusionsmay be drawn. ■  AUTHOR INFORMATION Corresponding Author * E-mail: ORCID  Ju             ̈ rgen Andreaus:  0000-0001-8124-6528 ■  ACKNOWLEDGMENTS The authors are grateful to National Council for Scienti 󿬁 c andTechnological Development (CNPq) for  󿬁 nancing Project461555/2014-0 and wish to thank CNPq for Grant 313458/2017-0 of JA and CAPES (Coordination for the Improvementof Higher Education Personnel) for the scholarship of L.F.S. ■  REFERENCES (1) De Silva, R. D.; Wang, X.; Byrne, N. Recycling Textiles: The Useof Ionic Liquids in the Separation of Cotton Polyester Blends.  RSC Adv.  2014  ,  4  (55), 29094 − 29098.(2) Kantouch, A.; Khalil, E. M.; Mowafi, S.; El-Sayed, H. Antimicrobial Finishing of Wool Fabric Using Ionic Liquids.  J. Text. Inst.  2013  ,  104  (4), 363 − 369.(3) Tavanaie, M. A. Ionic Liquids as New Solvents for Textile FiberFormation and Modification.  Chem. Eng. Technol.  2013  ,  36   (11),1823 − 1837.(4) Knittel, D.; Schollmeyer, E. Ionic Liquids for Textile Finishing,Part 1: Dyeing of Textiles.  Melliand Textilberichte Int. Text. Rep.  2007  , 88  (1/2), E14.(5) Bianchini, R.; Cevasco, G.; Chiappe, C.; Pomelli, C. S.;Rodríguez Douton, M. J. Ionic Liquids Can Significantly ImproveTextile Dyeing: An Innovative Application Assuring Economic andEnvironmental Benefits.  ACS Sustainable Chem. Eng.  2015  ,  3  (9),2303 − 2308.(6) Earle, M.; Seddon, K. Dyeing Process in Ionic Liquid Solvents.Patent WO/2009/024766, February 27, 2009.(7) Andrade, R. S.; Torres, D.; Ribeiro, F. R.; Chiari-Andre            ́ o, B. G.;Oshiro Junior, J. A.; Iglesias, M. Sustainable Cotton Dyeing inNonaqueous Medium Applying Protic Ionic Liquids.  ACS SustainableChem. Eng.  2017  ,  5  (10), 8756 − 8765.(8) Broadbent, A. D.  Basic Principles of Textile Coloration ; Society of Dyers and Colourists: Bradford, West Yorkshire, England, 2001.(9) Schanda, J. Colorimetry: Understanding the CIE System ; Wiley:Hoboken, NJ, 2007.(10)  The Theory of Coloration of Textiles  , 2nd ed.; Johnson, A., Ed.;Society of Dyers and Colourists: Bradford, West Yorkshire, England,1995.(11) Mahapatra, N. N.  Textile Dyes and Dyeing  ; WoodheadPublishing India in Textiles; CRC Press, 2016.(12) Burkinshaw, S. M.  Physico-Chemical Aspects of TextileColoration ; Wiley: Hoboken, NJ, 2016.(13) Pinkert, A.; Marsh, K. N.; Pang, S. Alkanolamine Ionic Liquidsand Their Inability To Dissolve Crystalline Cellulose.  Ind. Eng. Chem.Res.  2010  ,  49  (22), 11809 − 11813. ACS Sustainable Chemistry & Engineering  Letter to the Editor DOI:10.1021/acssuschemeng.9b01112  ACS Sustainable Chem. Eng.  2019, 7, 7999 − 8000 8000

ZMSI 97 (1)

Oct 13, 2019
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