Sulfur Dyeing Techniques

Examples for such techniques are found in sulfur dyeing for black shades and in a special form in indigo dyeing for denim, where a continuous replenishment of the dyebath is performed for a long period of production. 

Insolubilization. Insolubilization of compounds within textiles parallels the history of humanity the direct dyeing techniques for cotton were highly advanced in the Bronze Age. With the exception of fiber-reactive dyes discussed earlier, other cotton dyes, ie, vat and sulfur, are insolubilized within the fiber after an oxidization step. Insoluble metal oxides have been used to flameproof cotton, and zirconium compounds have been insolubilized on cotton to render the fabric microbial resistant (135) or mildew resistant (136) via a mineral dyeing process (see Textile Finishing). 

Metallic Dyes. MetaUic dyes are among the older hair color materials known. Commercial products are based on a 1% solution of lead acetate in an aqueous, slightly acidic, alcohoHc medium. Precipitated sulfur appears to be essential. The convenience aspect is stressed by the leave-in appHcation method. Actually, the color development is so slow, taking about a week to ten days, that there is no alternative to this technique. Daily appHcation is needed at first. 

The essential oxidation rate steps in the environment involve reactive species such as free radicals (RO2RO, HO ), ozone, and 02 (singlet oxygen). For predictive purposes, it is important to identify the important oxidants and their concentrations in the environmental compartments. Values of many oxidation rate constants are known reliably (Hendry etal, 1974). In the atmosphere, oxidation by the OH radical is significant, whereas ozone is important in the oxidation of some olefins and possibly some sulfur or phosphorus compounds. The RO2 radical can be important in sunlight photolysis in natural waters. Competitive kinetic techniques could be used to evaluate the relative loss of two chemicals, one of which is a standard of known reactivity to a specific oxidant (Mill etal., 1978). Azo compounds could be used to generate RO2 radical in water, nitrous acid to form the HO radical in air, and a dye to generate 02 in water. 

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