ABSTRACT
Abstract: Denim is exclusively dyed with indigo to produce brilliant blue shades with desired wash-down effect. Although indigo is a member of vat dye class, it possesses no affinity for cellulosics in reduced and solubilised form unlike other vat dyes. Exhaust dyeing does not show any such dye uptake forcing to introduce a multi-dip-nip padding technique with intermediate airing for gradual build-up of shade. Among various dyeing parameters, pH is the most crucial to achieve surface intense ring dyeing effect allowing to develop bio-polishing effect. Extent of indigo uptake may also be synergised through different pretreatment of denim. DMSO is the right solvent to extract indigo with ease. Eco-friendly alternate reducing systems have also been developed.
