Reactive dyes are introduced to the market by ICI in 1956. These dyes
form a covalent bond between the dye and fiber. They are basically a class
of highly colored organic substances. They show improved fastness
properties. They are primarily used for tinting textiles.
Mechanism of Reactive Dye Fixation
- Utilizes dichlorotriazine as reactive linker
- Nucleophilic aromatic substitution
- Allows for a wide variety of chromophores to be used
Advantages of the Reactive Dyes
Chemical Binding- The chemical bonds as
explained above significantly improves the product's color stability and
washability. Thus, no doubt reactive dying of cotton is presently the most
popular textile dying process in the world.
Permanency of the color- 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).
Easy washing- The fibres that are dyed with reactive dyes can be
safely dyed even with white garments without the danger of coloring it.
Types of Reactive Dyes
Vinyl sulfone dyes are moderately reactive. The dyeing
temperature is generally 60 degree C 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).
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.
Monochlorotriazine Dye (MCT)-
Normally these dyes are less reactive
than Vinyl sulfone dyes. Reaction can take place in more energetic reaction
conditions. That is typically 80 degree C and pH value of 10.5, are
essential for a proper fixation on cellulosic fibres. A typical
monochlorotriazine dye is shown here.