Aqueous Dye Baths

Articles made of pure PES fibers are dyed almost exclusively in exhaustion processes. Disperse dyes are most stable at a pH of 4-5 (acetic acid). A dispersing agent is also added to the dyebath. Dyes sensitive to heavy metals (e.g., anthra-quinoid red products) are dyed in the presence of a complexing agent (EDTA type). 

12 Disperse Dyes on Polyester and Other Man-Made Fibers 

---

The dyeing of fiber from an aqueous dye bath depends on the dye-fiber interaction. Depending on the nature of dye and the nature of fiber, the dye is fixed onto the fiber chemically or physically. Table 8.1 shows the methods of apphcation for various dye classes and principal substrates [7]. 

Cotton and rayon are dyed readily with dyes that are soluble in the aqueous dye-bath such as the class of direct dyes. The apparent reason for the success of water-soluble dyes with cotton or rayon is that cellulose swells appreciably in the aqueous dye-bath, thereby enhancing diffusion of the large dye molecules into the interior of the fibers. Cellulose exhausts the dye from the bath rapidly, resulting in deep eolor shades for cotton and rayon. For the most part, the classes of soluble dyes are not applicable to the more hydrophobic cellulose acetate and triacetate fibers and fabrics [37,71]. 

The preferred dyes for cellulose acetate and triacetate are the disperse dyes. These consist mainly of azo, anthraquinonoid, and nitrodiphenylamine dyes that are insoluble or at best slightly soluble in hot aqueous dye-bath systems. These crystalline dyes must be ground to a very small particle size, e.g., 2 pm. They are then pasted with water and a wetting agent and added to the dye-bath through a fine mesh screen. A dispersing agent and a carrier or accelerant may be present in the dye-bath to enhance diffusion of the dye molecules into... 

DuPont [63] claimed a process for stabilisation of dyed poly(trimethylene terephthalate) fibres by adding a speciality benzotriazole in the dye bath (Cibafast USM Ciba). The structure of this additive was not revealed, but it most probably features extra substituents in the form of sulfonic acid(s) or derivatives thereof, which would allow the additive to be dispersed or dissolved in the aqueous dye bath. 

Direct dyes are anionic dyes that are substantive to cellulose when applied from an aqueous dye bath containing an electrolyte. Although anionic, they are not classificated as acid dyes because the acidic substituent is not the means of attachment to the fiber. 

Commercial Disperse Azo Dyes. The first proposal to use insoluble dyes in suspension in an aqueous foam bath, ie, disperse dyes, to dye cellulose acetate was in 1921 (60). Commercialization of disperse dyes began in 1924 with the introduction of the Duranol dyes by British Dyestuffs Corporation (61) and the SRA dyes by British Celanese Company (62). In contrast to the acid monoazo dyes, derivatives of benzene rather than of naphthalene are of the greatest importance as coupling components. Among these components mono- and dialkylariifines (especially A/-P-hydroxyethyl-and A/-(3-acetoxyethylanifine derivatives) are widely used couplers. Nitrodiazobenzenes are widely used as diazo components. A typical example is CeUiton Scarlet B [2872-52-8] (91) (Cl Disperse Red 1 Cl 11110). 

Contrary to other synthetic fiber materials, polypropylene fibers cannot be colored by contacting them with an aqueous solution or dispersion of organic dyes. Due to its highly apolar nature, polypropylene is not able to interact with conventional dye molecules, so that it cannot take up any dye from the dye bath. 

Commercially sold rabbit hair (Joseph Galler Inc.) and milkweed fibers that had been collected by the researcher in 2004 were each colored with aqueous solutions of lab grade hematite (Fe203) as a substitute for ochre and copper sulfate. Additionally, rabbit hair from a breeder (Jennings, T.), commercially produced rabbit yam, and milkweed fibers were also colored in an aqueous bloodroot dye bath that did not contain any dyeing aids. 

The process of dyeing may be carried out in batches or on a continuous basis. The fiber may be dyed as stock, yam, or fabric. However, no matter how the dyeing is done, the process is always fundamentally the same dye must be transferred from a bath—usually aqueous—to the fiber itself. The basic operations of dyeing include (1) preparation of the fiber, (2) preparation of the dye bath, (3) application of the... 

The appearance of the fabric can be restored by a dye treatment. Highly fibrillated areas of cloth can be placed in an aqueous bath at Basic Yellow 40. The materials is contacted with the aqueous dye solution for 30 minutes followed by a treatment of a 10% detergent solution of hexylene glycol at 60°C for 10 minutes. Finally, the materials are rinsed thoroughly with water and dried. ... 

Direct dyes provide the simplest means of coloring cellulosic fibers, normally being applied from neutral or slightly alkaline dye baths, with the addition of sodium chloride or sodium sulfate salts. The purpose of the salt is to counteract the slight negative charge that cellulosics have in aqueous conditions because it would repel an anionic dye. 

Direct dyes are defined as anionic dyes substantive to ceUulosic fibers (cotton, viscose, etc), when applied from an aqueous bath containing an electrolyte. Before the discovery of Congo Red in 1884, only mordanted cotton could be dyed. Congo Red [573-58-0] (62) (Cl Direct Red 28 Cl 22120) a primary symmetrical disazo dye, which is made readily from bisdiazotized benzidine and naphthionic acid [84-86-6] (4-arnino-l-naphthalenesulfonic acid), was the precursor of a most important line of dyes, including all shades, derived from benzidine and its homologues. Today, no benzidine dye is produced because benzidine is carcinogenic. 

Cl Sulphur Black 1, which is produced from the relatively simple intermediate 2,4-dinitrophenol and aqueous sodium polysulphide. A similar product (Cl Sulphur Black 2) is obtained from a mixture of 2,4-dinitrophenol and either picric acid (6.148 X = N02) or picramic acid (6.148 X = NH2). A black dye possessing superior fastness to chlorine when on the fibre (Cl Sulphur Black 11) can be made from the naphthalene intermediate 6.149 by heating it in a solution of sodium polysulphide in butanol. An equivalent reaction using the carbazole intermediate 6.150 gives rise to the reddish blue Cl Vat Blue 43 (Hydron blue). This important compound, which also possesses superior fastness properties, is classified as a sulphurised vat dye because it is normally applied from an alkaline sodium dithionite bath. Interestingly, inclusion of copper(II) sulphate in the sulphurisation of intermediate 6.150 leads to the formation of the bluish black Cl Sulphur Black 4. 

Method I.—50 gms. dimethylaniline, 20 gms. of benzaldehyde and 20 gms. of pulverised anhydrous zinc chloride (see p. 509) are heated in a porcelain dish, with frequent stirring, on a water bath for 4 hours. The mass is then melted by the addition of hot water and transferred to a large flask, where it is steam distilled until no more dimethylaniline passes over. The leuco-base of the dye remains in a viscous form on the sides of the flask after cooling the aqueous solution is decanted and the base washed a few times by decantation with cold water. The base is dissolved in boiling alcohol, the solution filtered hot, and the filtrate left overnight in an ice chest. Colourless crystals separate, which are collected and dried in air on filter paper. A second crop may be obtained by concentrating the mother liquor. If the base separates as an oil, instead of crystals, more alcohol should be added, and heat applied until the oil redissolves. 

If the aqueous solution is Orange yellow if it assumes a fuchsine-red colour on treatment with HC1 if it gives a violet colour when evaporated to dryness and then taken up with concentrated sulphuric add if this sulphuric acid solution changes to fuchsine-red on dilution if it dyes wool in an acid bath... 

Exhaustion dyeing from an aqueous bath with dyes that have an affinity for... 

In the case of faulty dyeing, the dye can be largely stripped by treatment at 120°C with benzyl alcohol in an aqueous bath or with a carrier and a retarder which has a leveling effect in the presence of hydrosulfite in an alkaline liquor. 

---