Bleaching with peroxides

Hydrogen peroxide was discovered in 1818 and its use in bleaching textiles was first suggested in 1866. However, its high cost limited its use in cotton bleaching until 1935. The problem was partially solved by the process using barium peroxide and phosphoric acid. In 1926 hydrogen peroxide was manufactured by an electrolytic process based on the decomposition of persulphuric acid (H SOj) [15]. 

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The advantages favouring the pre-eminence of hydrogen peroxide (over 90% of cotton goods are bleached with peroxide) include [143,225] ... 

Most cotton is bleached with peroxide, by far the greater proportion by continuous methods. Synthetic fibres seldom require bleaching, but where it is necessary either peroxide or chlorite bleaches are recommended. Most regenerated cellulosic fabrics are only bleached... 

Dyeing cotton yarn with selected direct dyes and simultaneous bleaching with peroxide. It is claimed that the peroxide also increases the colour yield [324]... 

For satisfactory whiteness on wool, it is essential for the fibre to be well scoured and bleached, either oxidatively with hydrogen peroxide or by reduction using stabilised sodium dithionite. Brightener is usually applied together with the dithionite bleach. To achieve the highest possible whiteness, the wool should first be scoured to remove natural waxes and other contaminants, then bleached with peroxide and finally treated with FBA during a second bleach with dithionite. 

Developments since 1920 include multistage bleaching of kraft bleaching with peroxides, chlorine dioxide, and sodium hypochlorite use of synthetic resins for wet-strength paper for bags, maps, etc. and use of soluble bases for sulfite pulping, which allow the use of more species of wood. 

Mechanical pulps are bleached by procedures that preserve lignin, but eliminate most coloured groups. Most mechanical pulps can be bleached to brightness levels of 75-80%, that are suitable for uncoated and coated papers. The principal bleaching procedures for mechanical pulps are reductive bleaching with sodium dithionite (hydrosulphite), and oxidative bleaching with peroxide under alkaline conditions. 

The alkali earth elements represents a major variable in cotton fibre (Table 4.2) and mainly comes from cotton seed husks. Further the use of hard water can precipitate alkali earth metal phosphates on the fibre instead of eliminating them [2]. The reason for reddish shade after bleaching with peroxide is the high content of manganese, Mn -> colourless but Mn violet. The contents of Fe, Mn, Ca and... 

Leary and Giampaolo [70] found that unbleached softwood TMP behaved differently upon alkali treatment than peroxide-bleached TMP. Unbleached softwood TMP was bleached with peroxide (4% charge) to an ISO brightness of 78% however, alkali-darkened pulp could only be bleached to 68% with the same peroxide charge. Borohydride reduction of the pulp before the alkali treatment inhibited the darkening and almost fully restored its bleachability. The absorption maximum for alkali darkening of unbleached pulp appeared at 420 nm, but was shifted to 360 nm if the pulp was pretreated with borohydride. 

In a separate study, Pero and Deuce [52] also found methoxy-l,4-benzoquinone difficult to bleach with peroxide. They postulated that both hydroxy-quinone and quinone condensation products were formed. 

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