Paper Cationic Direct Dyes

Dyeing of paper has been traditionally carried out with acid, direct and basic dyes, whilst newer systems are based on cationic direct dyes. These cationic direct dyes are related structurally to reactive dyes with the labile chlorines replaced by pendant cationic groups, e.g. (2.50). 

Since the early 1970s a new class of colorants called cationic direct dyes has become important for coloring paper. These dyes combine the molecular shape and geometry of direct... 

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. 

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). 

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... 

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]. 

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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