Hydrogen peroxide bleaching action

Borax is used in laundry detergents and bleaches. It releases hydrogen peroxide when it reacts with water. Hydrogen peroxide acts as a bleach, and its action is aided by the alkaline solution also produced by the reaction. 

In the context of peracid bleaching it is worthwhile recalling the reaction outlined in Scheme 10.30, in which peracetic acid is produced in situ by the action of the activator tetra-acetylethylenediamine (10.86) on hydrogen peroxide [244]. 

The most intensive bleaching action is achieved with paste bleaches, which are prepared before use by mixing hydrogen peroxide solution (6-12 vol%) with a bleach powder. The powder consists of a peroxodisulfate, an alkalizing agent, stabilizers, thickeners, and other additives. Sodium, potassium, or ammonium peroxodisulfate is used. The ammonium salt is most effective when combined with an alkalizing component such as sodium carbonate or silicate, ammonia is formed. 

The base readily penetrates the hair and promotes bleaching. The addition of stabilizers such as sodium pyrophosphate or sodium oxalate [16,17] retards the decomposition of hydrogen peroxide in the alkaline preparation and thus enhances the bleaching action. The same holds for complexing agents (seques-trants) such as ethylenediaminetetraacetic acid, which hinder decomposition due to traces of heavy metals. Thickening additives include carboxymethyl celluloses, xanthine derivatives, and synthetic polymers. Certain dyes can also be added. 

Permanent hair colors can be achieved with tint shampoos. The shampoo base is adjusted to an alkaline pH and contains oxidation dye intermediates. Before application, it is mixed with hydrogen peroxide or a hydrogen peroxide addition compound. In comparison with oxidation hair dyes, tint shampoos employ lower concentrations of base and oxidant. This suppresses the simultaneous bleaching process that occurs during dyeing (see Section 5.4.2). As a result, damage to the keratin in hair is diminished, but the uniform coloring action is lost. 

Hydrogen peroxide has the chemical formula H202 and consists of two linked oxygen atoms each with a hydrogen atom attached. It has a powerful oxidising action and is used as a bleaching agent. See also urea. 

In solution, sodium perborate monohydrate is similar in action to that of hydrogen peroxide. At elevated temperatures, active oxygen is released and has a bleaching effect but does not affect animal, vegetable, and synthetic fibers [3, 4]. 

Biocides are used widely in industry. There are at least three main classes of industrial chemical biocides. The first class includes the oxidizing and bleaching agents, such as chlorine dioxide, hydrogen peroxide, and sodium hypochlorite. The oxidizing action may directly kill bacteria or fungi or weaken the cell walls so that they are more susceptible to other classes of biocides (see below). Sodium... 

Though hydrogen peroxide is stable in acidic medium, but bleaching occurs by the addition of alkali or by increased temperature. Hydrogen peroxide liberates perhydroxyl ion (HO ) in aqueous medium and chemically behaves like a weak dibasic acid. The perhydroxyl is highly unstable and in the presence of oxidisable substance (coloured impurities in cotton), it is decomposed and thus bleaching action takes place. Sodium hydroxide activates hydrogen peroxide because ion is neutralised by alkali which is favourable for liberation of HO. ... 

In the second stage, bleaching is carried out in alkaline condition of hydrogen peroxide. Iron that settles on the surface and inside the fibre acts as a catalyser and brings about enhanced bleaching action by extremely reactive radicals (HO ... 

Bleaching of wool is necessary for the enhancement of whiteness and lustre. Using proteolytic enzymes alone [99] or in combination with peroxide [100], the degree of whiteness and hydrophilicity of the fibres are increased, comjjared with the oxidative treatment alone [99]. Serine protease stable to hydrogen peroxide is active in an alkaline medium and its activity increases with increasing peroxide level [94]. Higher whiteness index is caused by the decolourising action of the enzyme on natural colorants present in the wool fibre [100]. 

Hydrogen peroxide is virtually the only bleaching agent available for protein fibres and it is also used very extensively for the cellulosic fibres. It was at one time thought that its oxidizing action depended upon the fact that it readily underwent decomposition with the liberation of oxygen ... 

This explanation, however, is no longer tenable. There is no absolute certainty about the nature of the bleaching action but it is believed that the perhydroxyl ion is the active species. These ions are formed when hydrogen peroxide dissociates in the following manner ... 

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