reactivedye

Reactive dye is a class of textile dye that forms covalent bonds with the fibers it dyes, producing permanent coloration. The defining feature is a reactive group in the dye molecule that engages in a chemical reaction with the fiber, typically cellulose. Common reactive groups include chlorotriazine and vinyl sulfone chemistries, which bond to hydroxyl groups in cellulose during dyeing. The dyeing process generally requires an alkaline bath to activate the fiber and promote bond formation. Once fixed, the dye is covalently bound to the fiber, yielding high washfastness and bright colors.

Used primarily on cellulose fibers such as cotton and cotton blends, reactive dyes can be applied by exhaust dyeing, pad-dyeing, or printing with suitable binders and auxiliaries. Typical dyeing temperatures range from moderate to high, often around 50–80°C, followed by thorough washing to remove unfixed dye and byproducts. After-treatment steps may include neutralization and additional washing to ensure full removal of residual dye and chemicals.

Advantages of reactive dyes include a broad color range, strong wash and light fastness, and relatively low dyeing cost. Limitations include the need for alkaline dyeing conditions, significant water and salt usage, and the requirement for effluent treatment to remove unfixed dye and reactive byproducts. Process control is important to ensure uniform fixation and color strength, particularly in large-scale operations.

Environmental and safety considerations emphasize reducing dye bath volumes, improving fixation efficiency, and treating wastewater to remove residual dyes and reactive chemicals before discharge. Reactive dyes have had a substantial impact on cotton dyeing since their mid‑20th century development, enabling durable, vivid colors on cellulose fibers.