Dyeing processes for apparel fabrics

This section explores the practice and technology used to apply dye to the principal apparel fibers. This leads to Section 5.6, which provides an overview of sustainability issues arising from commercial practice in the dyeing of apparel fabrics. 

Direct dyes have an inherent substantivity for cellulose fibers. The dyebath is gradually heated and electrolyte added to promote exhaustion and diffusion. The most attractive feature is the simplicity of the dyeing process. However, a cationic after-treatment is necessary for most direct dyeings to enhance washing fastness (Cook, 1982 Shore, 1995b). The wash fastness of the apparel item, even with an aftertreate-ment, is only satisfactory for pale and some selected medium shades. Consequently direct dyes have been largely replaced by reactive dyes. 

Sulfur and vat dyes are insoluble in water. They are chemically reduced using sodium sulfide or sodium hydrosulfite to produce their water soluble leuco form before apphcation (Gobi and Vilensky, 1983). Once soluble, the dyes are appUed to cotton in a way similar to dyeing with anionic dyes. Immediately after application, the fabric is oxidized to return the dye to its insoluble form. Thus, the dye molecules become physically trapped within the fiber. At the end of dyeing, washing off is carried out to remove unfixed dye. In such dyeing methods, reduction and oxidation steps pose sustainability issues due to their impact on dyeing effluent. 

3 Dyeing wooi, nyion, and silk with acid dyes 

Like dyeing protein with acid dyes, the dyeing of polyacrylic fibers with cationic dyes is based on the ionic attraction and bonding between the dye molecule and the 

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