Thursday, November 13, 2008

Stripping and Shade correction of dyed materials

There are possible occasions arise for the correction of the dyed shade. According the substrate(fabric/yarn)
quality and the dyestuff used for dyeing, the following methods may be considered useful:

A) Cellulose:

1) Direct dyes are best removed by an alkaline reduction strip. Some
dyestuffs may require a non-ionic boil off.

2) Vat dyes are very difficult to remove, usually a strong reduction strip
with caustic and hydros and strong organic stripping agent (leveling/dispersing agents).
are required. Mostly the treatment has to be done at 80°C or more.

3) Sulfur dyes can be removed partially in depth by treating the fabric
with sodium sulfide at 80°C or with caustic and hydros. You can make a judicial
combination of 2 treatments to strip off maximum color by treating the
fabric with sodium hypochlorite 3 to 5 g/l followed by a reduction strip
with caustic and hydros.

4) Naphthols: Either oxidizing agents (hypo) or reducing agent would
work as stripping agents. But case to case this would defer. Lab trial
is essential before finalizing anything on bulk treatment.

5) Reactive: Either hypochlorite or hydros or caustic hydros would
work. Before doing bulk stripping one has to test the suitability. Most
2 treatments are required. Hypo treatment followed by caustic hydros or
Caustic hydros treatment followed by hypo treatment would work.

B) Polyamide (nylon) stripping:

A reduction stripping in alkaline medium with a non-ionic dispresing agent
yields better result.

Light shades may be stripped by a mild boil off in the presence of
a non-ionic dispersing agent.

Deep shades and pre-metalized dyes may be stripped by an oxidizing
bleach with sodium chlorite in acid medium.

C) Polyester:

Disperse dyes may be stripped by boiling off with a suitable carrier
and dispersing agent.

Azo type disperse dyes may be stripped off by reduction method (caustic
and hydros).

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