Reactive dye
Also searched as: fiber-reactive dye, fibre-reactive dye, reactive dyes, vinyl sulfone dye, vinyl sulphone dye, triazine dye, dichlorotriazine, monochlorotriazine, bifunctional reactive dye
A reactive dye is a colorant carrying a chemical group that forms a covalent bond with the fiber, most importantly with hydroxyl groups of cellulose in cotton and viscose.
In detail
A reactive dye has a chromophore, water-solubilizing sulfonate groups, and one or more reactive groups such as a halotriazine or vinyl sulfone. In an exhaust process, salt drives dye onto cellulose, and alkali then ionizes cellulose hydroxyls so they attack the reactive group, fixing the dye by covalent bond. The same alkali also lets water compete, hydrolyzing some dye so it can no longer react. That hydrolyzed dye must be washed off thoroughly or it bleeds in later washing.
The science and numbers
Two reaction types dominate. Halotriazine dyes react by nucleophilic substitution: the cellulosate anion displaces chloride or fluoride on the triazine ring. Vinyl sulfone dyes, formed from a sulfatoethylsulfone precursor under alkali, react by nucleophilic addition across the double bond. Hydroxide in the bath competes with cellulosate, so fixation efficiency is always below 100 percent. Bifunctional dyes with two reactive groups aim to raise fixation. A review of fiber-dye chemistry notes that cellulose's relative inertness toward dyes necessitates chemical auxiliaries, and that effluent contains unreacted dye and high salt loads. Research dyes with vinyl sulfone centers show fixation varying strongly with pH, temperature and time. Because reactive-dyed cotton fibers look morphologically alike, forensic laboratories identify them by extracting and analyzing the dye.
A practical example
A dyehouse colors cotton jersey bright turquoise. Fixation leaves part of the dye hydrolyzed in the bath and loosely held in the fabric. If rinsing and soaping are cut short to save water, the garment may pass the lab dye check yet stain a white shirt in its first home wash. The dye chemistry was sound; the removal of unfixed dye was not.
What to distinguish
Covalent fixation gives good wash fastness but does not guarantee lightfastness or chlorine resistance, which depend on the chromophore. Reactive dyeing uses large amounts of salt and alkali and leaves colored effluent from hydrolyzed dye. Reactive is a dye class, not a sustainability claim, and dyes marketed as low-salt or high-fixation are producer claims to check.
Origins and history
Reactive dyes are a comparatively recent class. Earlier dyes for cellulose, such as direct and vat dyes, relied on physical affinity or insolubilization in the fiber rather than a chemical bond. Commercial dyes designed to bond covalently with cellulose arrived in the mid twentieth century and became a leading route for bright cotton shades. This edition could not verify the specific inventors and launch dates, so they are omitted.
Related terms
Sources & further reading
- Polymers: Environmental impact of textile materials, challenges in fiber-dye chemistry (Negi, 2025)
- Molecules: Identification of cotton fibers dyed with reactive dyes for forensic purposes (Smigiel-Kaminska et al., 2020)
- Scientific Reports: Nano-disperse reactive dyes with vinyl sulfone and triazine centers (Rizk et al., 2026)
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.