Stripping
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
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