Radical mechanism of azo cleavage for monoazo reactive dyes, a QSPR study : the similarity between photoreduction on polyamide substrates and thermal reduction in aqueous dithionite solutions / Yasuyo Okada in COLORATION TECHNOLOGY, Vol. 132, N° 4 (08/2016)  

[article]  inCOLORATION TECHNOLOGY > Vol. 132, N° 4 (08/2016) . - p. 327-343 Titre : Radical mechanism of azo cleavage for monoazo reactive dyes, a QSPR study : the similarity between photoreduction on polyamide substrates and thermal reduction in aqueous dithionite solutions Type de document : texte imprimé Auteurs : Yasuyo Okada, Auteur ; Toshio Hihara, Auteur ; Zenzo Morita, Auteur Année de publication : 2016 Article en page(s) : p. 327-343 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Colorants azoïques Colorants réactifs Dithionite de sodium Polyamide 6 Réduction (chimie) Solutions aqueuses (chimie) Thermochimie Index. décimale : 667.3 Teinture et impression des tissus Résumé : The same radical mechanism occurs in reductive azo cleavage via monohydrogenated radicals generated as the starting reactants in photo- and thermal (by dithionite) reduction on a nylon 6 substrate and in aqueous and alcoholic solutions. The rates of photo- and thermal azo cleavage in the solid and liquid phases have been thermochemically analysed by calculating the heats of formation of the reactants, intermediates, and products for (1) intramolecular hydrogen transfer (self-decomposition via rearrangement) in the photo- and radically induced hydrazinyl radicals as well as for (2) the disproportionation (redox reaction) between the radicals via a molecular orbital method. The rates of reductive fading (or azo cleavage) are controlled by the heats of reaction via reaction pathways (1) and (2) as well as by rearrangement, depending on the reaction system. Photoreduction of these dyes on polyamide generated the same end products – diazo components and iminooxoquinones from the coupling component – as the products of thermal reduction in aqueous sodium dithionite and of photoreduction in the liquid phase. Photofading on polyamide substrates owing to continuous irradiation is controlled by three factors: the quantum yield of photoinduced hydrazinyl radicals, its rearrangement processes, and the heats of reaction for the thermal azo cleavage reactions via the two pathways. These factors may become molecular descriptors that correlate the rates of fading with molecular structures. The present study may become an introductory trial to construct quantitative structure–property relationship modelling for reduction-fast azo dyes. Note de contenu : - EXPERIMENTAL : Dyes used - Parameters used for the analysis - Materials : dyeing and exposure - RESULTS AND DISCUSSION : Formation of the (MHN) moiety - Thermochemical analysis for the rates of thermal reduction of food azo dyes - Rates of photoreduction for model azo dyes in an alcoholic aqueous solution - Photoreduction of reactive azo dyes on PA substrates DOI : 10.1111/cote.12223 En ligne : https://onlinelibrary.wiley.com/doi/epdf/10.1111/cote.12223 Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=26735 [article]

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The clearing of dyed polyester. Part 1. A comparison of traditional reduction clearing with treatments using organic reducing agents / Anwar ul Aleem in COLORATION TECHNOLOGY, Vol. 132, N° 4 (08/2016)  

[article]  inCOLORATION TECHNOLOGY > Vol. 132, N° 4 (08/2016) . - p. 280-296 Titre : The clearing of dyed polyester. Part 1. A comparison of traditional reduction clearing with treatments using organic reducing agents Type de document : texte imprimé Auteurs : Anwar ul Aleem, Auteur ; Robert M. Christie, Auteur Année de publication : 2016 Article en page(s) : p. 280-296 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Colorants Dioxyde de thiourée Agent réducteur, de blanchiment ou de décoloration utilisé dans l'industrie textile, l'industrie des pâtes et papier et les procédés photographiques. Dithionite de sodium Hydroxyacétone Polyesters Réduction (chimie) Solutions aqueuses (chimie) Teinture -- Fibres textiles synthétiques Index. décimale : 667.3 Teinture et impression des tissus Résumé : Reduction clearing using aqueous sodium dithionite under alkaline conditions at elevated temperatures is commonly carried out as an aftertreatment to remove deposits of disperse dye and other impurity residues from the surface of dyed polyester. In this paper, the effect of conventional reduction clearing on the colour and fastness properties of polyester dyed with a series of selected commercial disperse dyes at a range of depths of shade is established, and an understanding of the scientific principles is developed. The results correlate closely with an assessment of surface dye removal by cold acetone extraction of the dyed samples. Because of certain environmental, technological, and economic disadvantages associated with traditional reduction clearing using sodium dithionite, there is industrial interest in alternatives. Thus, this paper also describes a study of the use of two organic reducing agents, thiourea dioxide and hydroxyacetone, and the relative merits of the three processes are discussed. The outcome of clearing varies with the particular dye. Mechanistic explanations are proposed, based on individual characteristics of the molecular structures of the dyes. Scanning electron microscopic investigations of the surface of dyed samples before and after reduction clearing were qualitatively consistent with the assessments of the technical performance. This paper is the first in a series in which we will subsequently report further comparative studies, based on similar methodology, exploring alternative clearing processes. Note de contenu : - EXPERIMENTAL : Materials - Dyeing - Reduction clearing with sodium dithionite - Reduction clearing with TUDO/FAS and hydroxyacetone - Assessment of surface dye removal - Assessment of fastness properties - Colour measurement - Scanning electron microscopy - Redox potential - BOD/COD - RESULTS AND DISCUSSION : General principles - Conventional reduction clearing with sodium dithionite - Clearing with the organic reducing agents DOI : 10.1111/cote.12217 En ligne : https://onlinelibrary.wiley.com/doi/epdf/10.1111/cote.12217 Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=26730 [article]

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