The Application of Dyes

The nature of substrate selects the type of dye needed, and methods of dye application. The development of new substrates led to new dyes and dyeing methods and influenced the dyeing technology in a fundamental manner. The dyeing of any substance (e.g., textile fiber) is based on a physico-chemical equilibrium process, namely diffusion and sorption of dye molecules or ions. These processes may be followed by chemical reactions in the substrate, for example, in the application of vat, reactive, azoic, and chrome dyes [9]. 

The process of dye application involves the transfer of dye from a solution in a dye bath to the fiber, the dye preferentially adsorbs onto and diffuses into the fiber. The driving force for this adsorption process is the difference in chemical potential between the dye in the solution phase and the dye in the fiber phase. In order for a dye to move from 

The methods of apphcation of dyes in textile dyeing and printing have undergone several modifications to meet the requirements of the new synthetic fibers and their blends with the natural fibers and new classes of dyes. However, the basic operations of dyeing remain the same and include the following  

Fiber preparation ordinarily involves scouring to remove foreign material and ensure even access to dye hquor from the dye bath. The textile material generally needs a pretreatment before dyeing. Wool must be washed to remove wax and dirt and sometimes bleached. Cotton must be boiled and bleached to remove pectins and cotton seeds and is mercerized. Sizes and spinning oils must be eliminated [7]. 

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]. 

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In Chapters 3-6, the commercially important chemical classes of dyes and pigments are discussed in terms of their essential structural features and the principles of their synthesis. The reader will encounter further examples of these individual chemical classes of colorants throughout Chapters 7 10 which, as a complement to the content of the earlier chapters, deal with the chemistry of their application. Chapters 7, 8 and 10 are concerned essentially with the application of dyes, whereas Chapter 9 is devoted to pigments. The distinction between these two types of colorants has been made previously in Chapter 2. Dyes are used in the coloration of a wide range of substrates, including paper, leather and plastics, but by far their most important outlet is on textiles. Textile materials are used in a wide variety of products, including clothing of all types, curtains, upholstery and carpets. This chapter deals with the chemical principles of the main application classes of dyes that may be applied to textile fibres, except for reactive dyes, which are dealt with exclusively in Chapter 8. 

In this section the types of dye lasers, the mechanism of lasing as applied to dyes, structural types of laser dyes and a few of the applications of dye lasers will be dis-cussed. ... 

The reactions which will be discussed here are basic in the application of dyes as sensitizer for photographic materials like silver halides, zinc oxide and others. Model experiments can be performed at electrodes of such materials which help to understand the mechanism of spectral sensitization in photography. 

In the application of dyes three techniques are used the dye liquor is moved as the material is held stationary, the textile material is moved without mechanical movement of the liquor, or bolh move. 

The application of dyestuffs to textile fibres has been dealt with rather more fully than in the earlier work, but not at a greater length than is in accordance with the character of the hook. To technologists requiring further details of the application of dye-stufis I can recommend Hummel s excellent work on The Dyeing of Textile Fabrics. ... 

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. 

It is possible to modify the interfaces between liquids with specific additives. This was discovered by andent and medieval investigators and applied in the form of soaps, and later in food technology and in the application of dyes. The mechanisms of these additives only came to be realized in about 1900. Such additives are generally molecules with hydrophobic and hydrophilic sedions that align along interfaces between the two liquid phases. They reduce interfadal tension and stabilize phase morphology to smaller dispersed phase sites. This phenomenon was realized by IG Farbenindustrie chemists who applied it in the late 1920s in emulsion polymerization that they used to produce synthetic rubber. 

Alkyl sulfonate, sulfate, and fatty amine are usually tested by using dye-reagent complex formation and counter ion titration. The applications of dye-reagent complex formation and counter ion titration are mainly introduced by the following. 

Very recently, the application of dye-clay intercalation compounds for the removal of toxic substances from water has been examined (291-293). Organic modification of clays with aliphatic or simple aromatic ammonium or pyridinium ions has been conducted to control the adsorptive properties of dyes for this purpose (294,295). Such dye-clay intercalation compounds therefore can be considered as a new class of adsorbents with additional functions, such as sensing and photoresponsive adsorptive properties. 

The usefulness of these chlorotriazinyl dyes in binding to textiles had been recognized in the 1950 s. However, optimal binding procedures of these dyes to polysaccharide matrices were developed more recently.The application of dye - ligand chromatography to protein purification has been reviewed recently. ... 

The SVET was utilized for the initiation of stress corrosion cracking of sensitized type 304 stainless steel in dilute thiosulfate solution (Isaacs, 1988 a). The method of potential monitoring to identify the onset of cracking was combined with the in situ measurement of local currents by means of the SVET. After solution annealing at 1100°C, the samples were sensitized at 600°C for 24 h and polished afterwards. The specimen were loaded, exposed to the electrolyte, and afterwards the potential and the spatial distribution of current were measured. Since the exposed surface area was very small, the connection and disconnection of a platinum foil were used to vary the area for cathodic reduction and thereby the corrosion potential of the specimen. By connecting and discoimecting the platinum foil, cracking could be initiated and anodic currents were observed at the respective sites, as afterwards confirmed by the application of dye penetrant. 

Textile fabrics receive a number of chemical and physical treatments before they are made into a final product. From formaldehyde finishes to improve crease resistance to flame-retardant treatment and dyeing of many types of fabrics, the possibilities for the application of dyeing and finishing processes to change the characteristics of textile materials are almost endless. Recent advances in nanomaterials have led to the development of treatments based on metallic nanoparticles for making textiles more resistant to water, stains, wrinkles, and pathogens such as bacteria and fungi. 

Haynes, American Chemical Industry, 4 233-35 Metz quotation found in Metz Explains Grasselli Agreement, DCM 17 (November 18, 1925) 1395 Kuttroff, Pickhardt Joins General Dyestuff Combination, DCM 17 (December 30, 1925) 1803 Ludwig s technical specialty was the application of dyes. Ludwig Elected National Aniline Head, Chemical Markets 21 (August 1930) 167. 

Other techniques used in vitro have included the application of dyes (Mahadevan et al., 1979) or radioisotopes (Wallace, 1983) to label the test proteins to quantify their breakdown from release of these labels in incubations with mixed ruminal organisms or proteases. These methods worked well for soluble proteins, but proved unreliable with insoluble proteins due to non-homogeneous labeling (Broderick et al., 1988). 

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