Assistants used for dyeing with reactive dyes

The following assistants are used in dye bath for dyeing with reactive dyes.

1)    Salt:

  As a salt NaCl is used widely. The salts do the following things-

-        Salts are used to increase the affinity of dye to fibre.

-        It decreases the hydrolysis rate of dyes.

-        It neutralizes the electro negativity of fibre surface when immersed in solution.

-        It puts extra energy to push the dye inside the fibre polymer i.e. increase absorption of dye.

           The amount of salt and used depends upon the shade to be produced.

                   For light shade – 10gm/ L salt is used.

                   For medium shade – 20 gm/ L salt is used.

                   For dark shade – 30gm/L salt is used.

2)    Alkali:

 Alkali is used for the following purposes:

-        Alkali is used to maintain proper pH in dye bath and thus to create alkaline condition.

-        Alkali is used as a dye-fixing agent.

-        Without alkali no dyeing take place.

-        The strength of alkali used depends on the reactivity of dyes.

-        As strong alkali caustic soda is used to create pH 12.5-12.

-        As medium alkali soda ash (Na2CO3) is used to create pH 11-12 when dye is of medium reactivity.

-        As weak alkali NaHCO₃ is used to create pH 10-11 when dye is highly reactive.

 3. Urea:    Urea is used in continuous method of dying. It helps to get required shade of dye.   To get dark shade more urea is used and to get light shade less amount of urea is used.

     

     4. Soaping:   By soaping, the extra color is removed from fibre surface. Thus  washing fastness is improved. Soaping increases the brightness and stability of the dye.