ABSTRACT
At present a great number of direct dyes are known which give a full range of colours and find wide use to cellulosic textiles, natural proteins, paper and leather. The chromophore in direct dyes includes azo (disazo, trisazo and polyazo dyes), stillbene, oxazine and phthalocyanine, with some thiazole and copper complex azo dyes. Dyes containing cyclic imide system, e.g. imidazolone, quinoxilinedione or benzoaxazolone show significant affinity to cellulose, even in cases where the dye has a relatively small molecular size. Direct dyes contain one or more sulphonic acid groups to impart solubility. Direct dyes are also called substantative colors because cellulosic fibres have strong affinity for them. Solubility decreases with increase in molecular weight of dye. While a major portion of the production of direct dyes goes for coloration of paper, leather and other uses. Direct dyes are water-soluble and can be applied to cotton and other cellulosic fibres such as viscose, linen, jute, hemp and ramie.
