Stripping Process of Reactive Dye

The reactive dye cannot be satisfactory stripped from fibre due to covalent bond between dye molecule and fibre. Stripping becomes necessary when uneven dyeing occurs. By stripping azo group (—N=N—) from the dye is removed. 

Now the stripping processes are described:-

1. Partial stripping:

Partial stripping is obtained by treating the dyed fabric with dilute acetic acid or formic acid. Here temperature is raised to 70-100°C and treatment is continued until shade is removed by desired amount. After that a through washing is necessary to remove the product of hydrolysis. 

The amount of acid used is as below: -

Glacial acetic acid  : 5-10 parts
With water :1000 parts
Or
Formic acid :2.5 to 10 parts
With water :1000 parts
Temperature  : 70 - 100°C
Time  : until desired shade is obtained.

2. Full stripping:

For complete stripping the goods are first treated with sodium hydrosulphite (hydrose) at boil then washed off and bleached with 1% sodium hypochlorite (NaOCl) at room temperature. This is carried out for 30 min.

The recipe is as below: -

Na-hypochlorite : 1% at room temperature
Na-hydrosulpite: at boil.
Time  : 30 min