Coloration Dyeing and Printing

Color may be imparted to various forms of textile substrates, including direct incorporation of color into the polymer, or dyeing of stock, yarn, fabric, garment, hosiery, carpet, and the like. Typically the application of dyes comprises several steps, that is, surface sorption, diffusive penetration into fibers, fixation, and washing. This is true of various classes of dyes shown in Table 7.27. 

Pigment coloration may be done during fiber formation or later by surface application in which there is little or no penetration into the fiber, and the attachment of color to the substrate is primarily through the use of binders, such as latex. 

Fixation levels vary between dye classes, substrates, dyeing machines, and procedures. Table 7.28 shows typical dye fixation for some common situations. The unfixed dye is washed out and causes colored wastewater [1]. 

In considering the environmental impact of textile wet processing, it is important to recognize the nature of the textile supply chain. It is not unusual to see fibers handled by 5-10 different companies during the manufacturing process, between the fibrous state and the end-use product. This places severe constraints on the abilities of manufacturers to address environmental issues. 

Acid Wool (hair) Acetic add Affinity by ionic Color 

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These dyes have affinity for one or, usually, more types of hydrophobic fibre and they are normally applied by exhaustion from fine aqueous dispersion. Although pure disperse dyes have extremely low solubility in cold water, such dyes nevertheless do dissolve to a limited extent in aqueous surfactant solutions at typical dyeing temperatures. The fibre is believed to sorb dye from this dilute aqueous solution phase, which is continuously replenished by rapid dissolution of particles from suspension. Alternatively, hydrophobic fibres can absorb disperse dyes from the vapour phase. This mechanism is the basis of many continuous dyeing and printing methods of application of these dyes. The requirements and limitations of disperse dyes on cellulose acetate, triacetate, polyester, nylon and other synthetic fibres will be discussed more fully in Chapter 3. Similar products have been employed in the surface coloration of certain thermoplastics, including cellulose acetate, poly(methyl methacrylate) and polystyrene. 

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... 

Arsenic pentoxide is used to make colored glass in fungicide formulations in adhesive for metals in wood preservatives in dyeing and printing and to prepare arsenates. 

In addition to the dyeing and printing of natural and acrylic fibers, triarylmethane dyes are suitable for the coloration of other substrates such as paper, ceramics, leather, fur, anodized aluminium, waxes, polishes, soaps, plastics, drugs, and cosmetics. Several triarylmethane dyes are used as food colorants and aie manufactured under stringent processing controls. 

Use Arsenates, insecticides, dyeing and printing, weed killer, colored glass, metal adhesives. 

The analysis of dyes and pigments for textile applications is really a very broad subject because it usually involves many different types of analyses and the use of many sophisticated instruments. It is difficult to provide a detailed coverage in a short section here. Therefore, only some basic and simple analyses are introduced. Readers who want to know more can access the books published elsewhere. - Analysis of colorants can also mean many different things. Identification of colorants on textile materials is an important aspect of forensic analysis and also very useful for textile dyers. Characterisation of colorants is critical for colour chemists to know what chemical structures the colorant has. Determination of dye classes has its practical significance in making up dyeing and printing recipes as well as in the analysis of historical textiles. 

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