Reactive dyes or Fibre reactive dyes are basically a class of highly coloured organic substances. Reactive dyes uses a chromophore that contains a substituent that is quite capable of a direct reaction with a fibre substrate. It is the covalent bonds Which the reactive dyes form with the substrates that are responsible for attaching the reactive dye to natural fibers. These bonds makes reactive dyes among the most permanent of dyes. Cold reactive dyes, like Cibacron F, Procion MX, and Drimarene K, are very easy to use as they can be applied at room temperature. Reactive dyes are the best bet for dyeing cotton and other cellulose fibers. They are primarily used for tinting textiles.

Of late, fibre Reactive Dyes have also been developed for dyeing other fibres but there is not much commercial success.

Permanency of the colour- Fibre Reactive Dyes can be easily said to be the most permanent of all dye types. This is because of an unique quality, unlike other dyes, it can actually form a covalent bond with the Substrate (cellulose or protein molecule). After the formation of the bond, there is only one molecule, as the molecule of the is now part of the cellulose fiber molecule.

Easy washing- The fibres that are dyed with reactive dyes can be safely dyed even with white garments without the danger of colouring it.

Chemical Binding- The chemical bonds as explained above significantly improves the product's colour stability and washability. Thus, no doubt reactive dying of cotton is presently the most popular textile dying process in the world.

There are mainly three types of reactive dyes. They are:

Vinylsulphone Dye (VS)- Vinylsulphone Dyes are moderately reactive. The dyeing temperature is generally 600C and pH is 11.5 that gets applied by utilising a mixture of soda ash and caustic soda. These dyes show excellent fixation properties under proper alkaline condition. A typical example is the Remazol Black B (CI Reactive Black 5)

Monochlorotriazine Dye (MCT)- Normally these dyes are less reactive than vinylsulphone dyes. Reaction can take place in more energetic reaction conditions. That is typically 800C and pH value of 10.5, are essential for a proper fixation on cellulosic fibres. A typical monochlorotriazine dye is shown here.


(Monochloro-s-triazine dye (Procion Red H-3B, C.I. Reactive Red 3)
Bi-functional Dye- A Bi-functional dye is a form of reactive dye that shows more than one type of reactive group in the molecule. These reactive dyes are designed in such a manner to have the capacity to react with the fibre in more than a single way.