Dyeing mechanism of reactive dye

Dyeing mechanism

The dyeing mechanism of material with reactive dye takes place in 3 stages:-

A.    Exhaustion of dye in presence of electrolyte or dye absorption.

B.    Fixation under the influence of alkali.

C.    wash-off the unfixed dye from material surface.

Now they are mentioned below:

A.    Dye absorption:

When fibre is immersed in dye liquor, an electrolyte is added to assist the exhaustion of dye. Here NaCl is used as the electrolyte. This electrolyte neutralize the negative charge formed in the fibre surface and puts extra energy to increase dye absorption. So when the textile material is introduces to dye liquor the dye is exhausted on to the fibre.

B.    Fixation:

  Fixation of dye means the reaction of reactive group of dye with terminal –OH or-NH₂ group of fibre and thus forming strong covalent bond with the fibre and thus forming strong covalent bond with the fibre. This is an important phase, which is controlled by maintaining proper pH by adding alkali. The alkali used for this purpose depends on brand of dye and dyeing temperature. Here generally caustic soda, soda ash or NaHCO₃ is used as alkali depending upon reactivity of dye. They create proper pH in dye bath and do as the dye-fixing agent. The reaction takes place in this stage is shown below: -

1. D-SO₂-CH₂-CH₂-OSO₃Na + OH-Cell  ⟶ D-SO₂-CH₂-CH₂-O-Cell + NaHSO₃ 

2. D-SO₂-CH₂-CH₂-OSO₃Na + OH-Wool ⟶ D-SO₂-CH₂-CH₂-O-Wool + NaHSO₃

3.

 

C. Wash-off: 

As the dyeing is completed, a good wash must be applied to the material to remove extra and unfixed dyes from material surface. This is necessary for level dyeing and good wash-fastness. It is done by a series of hot wash, cold wash and soap solution wash.