Paper Anionic Direct Dyes

Substantive anionic direct dyes can be repolarized by incorporating an excess of cationic groups [11] without impairing the substantive properties. Several dyes of this kind have been developed for the paper industry, e.g., C.I. Basic Red 111, [118658-98-3] (25). 

Anionic direct dyes are the most widely used colourant within the tissue, printing and writing paper sectors. Having a typical molecular weight of 550-2,000, they produce a wide range of shades, although certain bright shades cannot be achieved... 

These retain the planar molecular structure of acid direct dyes, but cationic groups have been incorporated in the structure. This is to increase their affinity to paper fibers. They are moderately adsorbed on bleached Hgnin-containing stocks, and even in the case of deep shades, alum or a fixative is usually not required. These dyes produce fairly good bleed fastness. Combination dyeing with anionic direct dyes can be carried out to improve the fixation of the dyes on the paper machine... 

These are defined as anionic dyes with substantivity for cellulosic fibres applied from an aqueous dyebath containing an electrolyte. The forces that operate between a direct dye and cellulose include hydrogen bonding, dipolar forces and non-specific hydrophobic interaction, depending on the chemical structure and polarity of the dye. Apparently multiple attachments are important, since linearity and coplanarity of molecular structure seem to be desirable features (section 3.2.1). The sorption process is reversible and numerous attempts have been made to minimise desorption by suitable aftertreatments (section 10.9.5). The two most significant non-textile outlets for direct dyes are the batchwise dyeing of leather and the continuous coloration of paper. 

Direct Dyes. These water-soluble anionic dyes, when dyed from aqueous solution in the presence of electrolytes, are substantive to, i.e., have high affinity for, cellu-losic fibers. Their principal use is the dyeing of cotton and regenerated cellulose, paper, leather, and, to a lesser extent, nylon. Most of the dyes in this class are polyazo compounds, along with some stilbenes, phthalocyanines, and oxazines. Aftertreatments, frequently applied to the dyed material to improve washfastness properties, include chelation with salts of metals (usually copper or chromium), and treatment with formaldehyde or a cationic dye-complexing resin. 

Taking into account high capacity and selectivity of ion exchange resins for different dyes, they seem to be proper materials for dyes sorption from textile effluents. Applicability of the anion exchange resins in the removal of acid, reactive, direct dyes widely used in the textile industry, from aqueous solutions and wastewaters, was confirmed in some papers [2,15, 20, 23, 25-28]. 

Certain products, particularly anionic direct violet dyes, are affected by the moisture content of the dried sheet. Paper containing these products will change... 

In the paper, the results of the sorption of three textile dyes such as C.I. Acid Orange 7, C.I. Reactive Black 5 and C.I. Direct Blue 71 on the commercially available anion exchangers are summarized and discussed based on the data presented in papers [2,15, 20, 23, 25-31]. 

A recent study reports the solvation dynamics of coumarin 153 and 6-propionyl-2-dimethylaminon-aphthalene (PRODAN) in [emim][BF4] and [bmim] [BF4]. The fluorescence decay profiles showed biphasic solvation dynamics as was observed for molten tetraalkylammonium salts.- The results were interpreted as indicating a short-lived component resulting from the motion of the anion, followed by a longer-lived component resulting from the motion of both the anion and the cation. In the same papers, estimates of the value of (30) were made for these solvents based on comparisons of the values for each probe molecule in conventional solvents. The values obtained (48.9 from coumarin 153 and 47.1 kcal mol" from PRODAN for [bmim][BF4]) were somewhat lower than those measured directly using Reichardt s dye.- ... 

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