Cotton dyeing

Cotton dyes Cotton fabric Cotton gin trash Cotton linters... 

Phthalocyanine sulfonic acids, which can be used as direct cotton dyes (1), are obtained by heating the metal phthalocyanines in oleum. One to four sulfo groups can be introduced in the 4-position by varying concentration, temperature, and reaction time (103). Sulfonyl chlorides, which are important intermediates, can be prepared from chlorosulfonic acid and phthalocyanines (104). The positions of the sulfonyl chloride groups are the same as those of the sulfonic acids (103). Other derivatives, eg, chlormethylphthalocyanines (105—107), / /f-butyl (108—111), amino (112), ethers (109,110,113—116), thioethers (117,118), carboxyl acids (119—122), esters (123), cyanides (112,124—127), and nitrocompounds (126), can be synthesized. 

Fig. 4. Carbocychc azo dyes. Disperse Yellow 3 [2832-40-8] (Cl 11855) (26) is used to dye polyester Reactive Orange 1 [6522-74-3] (Cl 17907) (27) is a cotton dye Direct Orange 26 [25188-23-2] (Cl 29150) (28) is a dye for paper Synacril Fast Red 2G [48222-26-0] (Cl 11085) (29) dyes acrylic fibers Acid...

Ligands like (222) are useful analytical reagents for Cu(II) (64HC(20)l), whilst ligands (223) and (224) are used as dyes (Section 4.04.4.1.3). In dyes such as (223), which are applied to wool, the usual metal employed is chromium for cotton dyes like (224) it is more common to use copper. 

Another comprehensive evaluation of cotton dyeing parameters has been carried out for eighteen isomeric monoazo H acid red dyes containing aminochlorotriazine and... 

Congo red is the prototype of the substantive cotton dyes of the benzidine group. The tinctorially valuable property of dyeing cotton directly (i.e. without a mordant) is doubtless to he attributed to the intimate adsorption of the colloidal particles of the dye on the fibre. 

It is this action alone which enables a relatively small number of dyes, the so-called substantive cotton dyes, to be absorbed directly by the unmordanted vegetable fibre. The most important of these dyes are the bis-azo dyes, such as Congo-red and related compounds, which are derived from doubly diazotised benzidine. In aqueous solution they are present as sols and are colloidally adsorbed by the fibres as irreversible gels. 

Mukheijee, A.K. Bhuvanesh, G. Chowdhury, S.M.S. Separation dyes from cotton dyeing effluent using cationic polyelectrolytes. Am. Dyest. Rep. 1999, 88, 25-28. 

In two-bath processes either the cotton or the acry lic can be dyed first. Heavy shades are best dyed by first dyeing the acrylic and then dyeing the cotton under alkaline conditions. In order to prevent desorption of the cationic dye the dyeing temperature for the cotton dyeing must be below ihe glass-transition temperature for the acrylic of 80V. 

Phthalocyanine sulfonic acids, which can he used as direct cotton dyes, are obtained by heating the metal phthalocyamnes in oleum. 

Compared to direct azo dyes, the direct anthraquinone dyes have lower tinctorial strengths and are therefore far less economical to use. They have lost most of their importance. Only a few special green dyes have retained their importance. Direct green cotton dyes can be produced by coupling a blue bromamine acid dye and a yellow azo dye via ureido or diaminotriazine bridges. 

With the increasing popularity of the continuous method of dyeing in the paper industry, new direct dyes were developed with particularly good cold-water solubility without any impairment to the substantivity. Improvements of this kind with regard to substantivity and solubility can be seen in the further development of the widely used, but only moderately soluble, cotton dye C.I. Direct Red 81, 28160 [2610-11-9] (4). 

Direct dyes are anionic colorants that have affinity for cellulosic fibers.17 They were the first dyes that could be used to dye cotton in the absence of a mordanting agent, giving rise to the term direct-cotton dyes. Like acid dyes, direct dyes contain one or more -SOjNa groups, making them water-soluble. Unlike acid dyes, they interact with cellulose (Cell-OH) chains via secondary valency forces (e.g., H-bonding and dipole-dipole interactions), as illustrated in... 

The 1,6- and 1,7-naphthylaminesulfonic acids have long been very important as components for azo dyes, particularly as the middle component in polyazo dyes. They are used in the preparation of the important black cotton dyes of the type of Columbia black FF, and also of a whole series of developed dyes, such as the important naphthogene blue, Zambesi black V, and others. Sulfonic acids of this type are also frequently used in preparing dyes of the Sirius blue series (Bayer). 

Sulfonation of l-naphthylamine-8-sulfonic acid with oleum gives, depending on the conditions, either the di- or trisulfonic acid of naphthylamine (as well as the naphthsultamdisulfonic acid ). Alkali fusion of these compounds yields the corresponding aminonaphtholsulfonic acids (III and IV), which are starting materials for wool and cotton dyes. 

The tint of the dye prepared by this method is decidedly purer and stronger. The separation of the diazo compound is especially important when cotton dyes are to be prepared from it, since impurities are especially detrimental in subsequent steps. For example, an extremely light fast cotton dye of the Sirius blue type is prepared by coupling the diazo compound with m-amino-p-cresol ether and subsequently coupling this product with J acid ... 

Compounds 14 to 2-3 are all used as end or middle components for substantive cotton dyes. 

Reduction of these dyes leads to tints which are appreciably more reddish, going as far as reddish oranges. If, for example, the dye prepared above is only partly neutralized and reduced directly after the condensation with 40 grams of crystalline sodium sulfide (I hour at 75°G.), followed by acidification as described above. Mikado orange R is obtained. This is a very good, light-fast cotton dye. 

Cotton dyeing and finishing operations can expose workers to formaldehyde in concentrations that exceed the U.S. OSHA workplace PEL for formaldehyde of 0.75 ppm of air as an 8 h time weighted average concentration and 2 ppm of air as a 15-min short-term exposure limit (STEL) [645]. 

Reactive dyes, in Cotton Dyeing and Finishing A Technical Guide, Cotton Incorporated, Cary, NC, 1996, pp. 76-92. 

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