Technical Tuesday

REF:TT/ Apr 2012/ WK 5
Testing the purity of Peroxide killer

What is a peroxide killer?

·  After bleaching the cellulosic fiber with hydrogen peroxide, the fiber is subjected a thorough hot wash, cold wash and neutralization processes These operations would remove all superficially available chemicals that were used in bleaching process

·  However in practice it is found that the core alkali i.e. the alkali due to the use of caustic soda or soda ash and hydrogen peroxide, wetting agents and other auxiliaries would remain in the core of the fiber processed even after 2 or 3 washes. These residual chemicals like alkali's and peroxide are detrimental to the production of uniform flawless fabric production.

·  The core residual alkali would lead to immature hydrolisation of the reactive dyes and results in streaky and uneven dyeing. The residual peroxide present in the fiber will oxidize the reactive dyes' chromophore that contain the metal ions and lead to tonal variation and sometimes uneven dyeing

·  In some cases the chromophore itself is getting destroyed into a colorless product and lead to pale or white

·  Hence the removal residual alkali and peroxide are very much essential before starting a good dyeing operation.

·  So any chemical that kills the residual peroxide in the fiber is called a peroxide killer. Again we should note that excess presence of reducing agent in the fiber also lead to destruction of dyestuff molecule.

·  Hence a careful selection of a peroxide killer is important; now in the market there are many enzymatic peroxide killers available that will remove the residual peroxide and die-off during subsequent dyeing operations at higher temperatures

Testing the adulteration in Enzymatic Peroxide Killers:

·  Generally enzymatic killers are Catalyze enzymes diluted in different concentrations. Catalyze is the natural enzyme that specifically search and consume hydrogen peroxide and does not react with cellulose. This specific property of selective reaction is made use of to scavenger the residual peroxide in hydrogen peroxide.

·  Nowadays, cheap products are available in the market with the name 'enzymatic

Peroxide killers'. These products not only kill peroxide at lower dosages. But they may not be of pure enzyme or even sometimes, not enzyme at all.

·  Any inorganic reducing agent such as Sodium bisulphite, Sodium thiosulphite, etc., can

easily remove residual peroxide. But the residue of these products may inturn affect

dyeing process. So to find out whether the product that you are using is an enzyme or not

there is a simple test.

Testing Procedure:

·  Take 250ml conical flask. Add 100 ml distilled water; to this add 3 drops of 0.1 N iodine solution. You can get a light yellow color solution.

·  Add a drop of your peroxide killer. If the yellow color disappears immediately, then your product is not an enzyme; it may be either a mixture of sodium bisulphite and catalase enzyme or a pure inorganic salt solution.

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