Comparison of the thermal fixation of reactive dyes on cotton using infrared radiation or hot air

A 100% cotton fabric was impregnated with an alkaline solution of a reactive dye and reaction with the cellulose achieved by heating using electric infrared emitters or hot air. The conditions gave temporal variations of fabric humidity and temperature that were similar for each heating method. Fixation yields and color strengths for the dyed fabrics were measured as a function of heating time. Infrared dye fixation yields were higher, and obtained in much shorter times, than those for dyeings produced by heating in air, particularly for dyes of lower reactivity. When using hot air for fixation, evaporation of water at the yarn surfaces during the initial phase of drying causes dye solution migration to the surface and an increased color yield of the final dyeing. The lower color yields of dyeings produced by infrared fixation were interpreted in terms of the suppression of this type of migration. Reaction of dye with the cotton at room temperature, under conditions preventing any drying, was assumed to occur without any migration of the initially unfixed dye. Fully continuous dyeing trials showed that the infrared fixation process gave high fixation yields with no visible color variation. Infrared fixation of reactive dyes on cotton could be valuable for reducing the environmental impact of unfixed dyes and dyeing assistants in the dyehouse effluent.