Reactive dyes

Reactive dyes are a dye class introduced by ICI in 1956 (Procion) that carry a reactive anchor group such as monochlorotriazine, dichlorotriazine or vinyl sulphone. These anchor groups react under alkaline conditions with the hydroxyl groups of cellulose to form a covalent ether bond. The covalent bond is the key to their exceptional wash fastness and makes reactive dyeing first choice for cotton and viscose goods that are washed frequently.

The most important trade names are Procion (Dystar, formerly ICI), Cibacron (Huntsman/Ciba), Remazol (Dystar) and Drimarene (Clariant). For wool and polyamide there are special reactive dyes like Lanasol (Huntsman) that bond under acidic conditions via alpha-bromoacrylamide to the amino and thiol groups of wool. Silk can also be dyed reactively.

The colour range covers thousands of shades from soft pastels to intense blacks. Downside is salt dependence of classic reactive dyes: 60-100 g salt per litre are common to raise dye affinity. Low-salt systems (Avitera SE, Cibacron LS) have cut salt and water use by up to 60 percent over the last 15 years.