Paper Acid Dyes

Acid Dyes. These water-soluble anionic dyes ate appHed to nylon, wool, sUk, and modified acryHcs. They ate also used to some extent for paper, leather, food, and cosmetics. The original members of this class aU had one or mote sulfonic or catboxyHc acid groups in thein molecules. This characteristic probably gave the class its name. Chemically, the acid dyes consist of azo (including preformed metal complexes), anthraquiaone, and ttiaryHnethane compounds with a few azHie, xanthene, ketone imine, nitro, nitroso, and quHiophthalone compounds. 

In a series of papers (175) comparing chlorination and o2oni2ation, reactive and acid dyes were readily destroyed, but direct and disperse dyes reacted more slowly o2one was more effective in some instances. Although chlorination is cheaper than o2oni2ation, the possible formation of chlorinated compounds such as dioxin and its environmental impact caimotbe overlooked (see Chlorocarbonsandchlorohydrocarbons, TOXIC AROMATICS). 

In this work hybrid method is suggested to determine cationic surfactants in water. It is based on preconcentration of cationic surfactants in the some of ion associates with acidic dyes on the paper filter and measurement of color intensity by solid-phase specdophotomenic method or visual comparison. 

The first acid dye, Orange I (1.53 Cl Acid Orange 20), was discovered in 1876. All but a handful of the acid dyes developed since then were evaluated initially with wool dyeing in mind. In terms of adaptability to the coloration of other substrates, however, acid dyes have proved pre-eminent. This is the main reason for their number and variety. As well as the dyeing and printing of nylon and protein fibres, acid dyes are important for the coloration of leather, paper, jute, wood and anodised aluminium. Most of the permitted dyes for food and... 

The nomenclature given for these componnds is a nniversally recognised system for the naming of dyestuffs devised by the Society of Dyers and Colourists as part of their Colour Index (Cl). The Cl Generic Name is made up of the application class, the hne and a nnmber. Acid dyes are nsed on wool and polyamide, direct dyes on cel-lulosic fibres, paper and leather, disperse dyes on polyester fibres, reactive dyes on cellnlosic fibres and basic dyes on polyacrylonitrile and paper. 

Freeman, H.S., Sokolowska-Gajda, J. and Reife, A. (1993) Premetallized acid dyes based on environmental considerations. In Book of Papers, International Conference of American Association of Textile Chemists and Colorists pp. 254—259 Chem. Abstr., 121, 159353. 

Acid Dyes. These water-soluble anionic dyes are applied to nylon, wool, silk, and modified acrylics. They are also used to some extent for paper, leather, ink-jet printing, food, and cosmetics. 

Numerous cationic azo dyes are prepared by the action of /V-hydroxymcthyl-chloroacetamide on azo dyes in sulfuric acid medium, followed by displacement of the reactive chloro substituent by pyridine or trialkylamine. Of special significance for dyeing paper are dyes that are prepared by coupling of diazotized 2-(4 -aminophenyl)-5-methylbenzothiazole to acetoacetaiylides, pyrazolones, naphthols [143], or barbituric acid derivatives [144], followed by reaction with N-hydroxymethylchloro-acetamide and pyridine. The azo dye obtained by oxidative dimerization of 2-(4 -aminophenyl)-5-methylbenzothiazole may also be subjected to this conversion [145], Dye 51 colors paper yellow. 

For this reason many, and above all the older, acid dyes have lost all importance for the dyeing of wool and are used today only for the coloring of paper, soaps, food, and cosmetics. 

Naphthols and Naphtholsulfonic Acids as Coupling Components. This series includes two important acid dyes with very similar structures C.I. Acid Red 88 (see Section 3.9.3), derived from diazotized naphthionic acid and 2-naphthol, and C.I. Acid Red 13, 16045 [2302-96-7] (2), from naphthionic acid and Schaffer s acid. Both are all-purpose dyes which, because of their attractive red shades, are still in use today in many areas of textile dyeing and also for leather and paper dyes. Wool dyeings produced with these dyes exhibit moderate fastness levels. 

Acid dyes derive their name from their insolubility in acid baths. They are used for dyeing protein fibers such as wool, silk, and nylon also leather and paper. 

A solution of a basic compound, such as Fixanol, which is essentially cetyl pyridinium bromide and cetyl trimethylammonium bromide, is added to the acid dye sample solution to precipitate the acid dye. The end point of the titration is reached when the colour of a drop of the titrated solution on filter paper is different from that of the precipitate. The drawback of this method is that the end point determination is difficult, which could lead to titration errors. A few repeated titrations may reduce the error level. 

Anthosin . [BASF AG] Based on acid dyes for paper coloring in papermaking. 

Activated carbon is one of the most commonly used meda for dye removal [95]. It very effectively adsorbs cationic, mordant, and acid dyes while the adsorption of dispersed, direct, pigment, and reactive dyes is lower. Because the effectiveness of axdivated carbon in adsorption of dyes depends on the cliaracteristics of the waste water, in certain cases carbon adsorption can be ineffective [5]. Other examples of carbon filtration in waste water treatments include an effective controlling of perfluorocarbons (PFCs) emissions from the semiconductor manufecturing processes, purification of waste waters in the paper industry, etc [96-97]. 

Molecular structures of the above mentioned dyes are presented in Figure 5. The dyes were purchased from Sigma-Aldrich (Germany) and used witliout further purification. These dyes were selected for the studies because they are extensively used in the textile industry. C.I. Acid Orange 7 is applied for fibers such as silk, wool and nylon using neutral to acid dye baths. Direct Blue 71 is used for cotton, paper, leather, wool, silk and nylon dyeing. Reactive dyes, e.g. RB5, are by far the best choice for dyeing of cotton and other cellulose fibers. 

One of the true arts, still practised in papermaking, is the colouration of paper. Chapter 10 covers this subject with great delicacy. Explanations are given of how colour is perceived by the human eye and how differences in shade are distinguished. The chemistry of various chromophores is discussed as well as the conditions under which these chemicals are best used e.g. acid dye use in crepe paper, basic dyes in newsprint and direct dyes in printing and writing papers. 

Acid dyes are generally small molecules, with a molecular weight of 350-500, and a small conjugated double bond system (Fig. 10.2), with no attractive forces. As such they have very little afOnity for cellulose fibres. They do, however, have extremely high solubility and normally produce very bright shades. They can be apphed at the surface and they are generally restricted to papers which have a limited use, i.e. crepe paper. 

Uses Antistatic finish for polyester fibers flocculant, coagulant for industrial process water treatment flocculant for min. recovery, ion exchange resins, adhesives, acid dye receptivity, electrostatic coatings on wood retention aid for paper food-contact paper/paperboard Reguiatory FDA 21CFR 176,170... 

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