Peroxide bleaching conditions

W. C. Eroass, Interactions of Calcium, Magnesium and Silicate Under Peroxide Bleaching Conditions, M.S. Dissertation, SUNY College of Environmental Science and Eorestry, Syracuse, N.Y., June, 1991. 

This indicates alkaline conditions for peroxide bleaching. However, an upper pH limit exists as a result of competing, nonreversible reactions ... 

In fastness to peroxide bleaching, ISO 10S-N02, the specimen is immersed ia a standard bleaching solution containing hydrogen peroxide (or sodium peroxide for viscose) where the composition of the bleaching Hquor is dependent on the fibers used ia the test specimen as are the pH and time of exposure (1—2 h). The objective of the test is to assess the colorfastness usiag typical bulk bleaching conditions for the fiber under test. 

In an optimally controlled process free from transition-metal ions hydrogen peroxide bleaching is remarkably safe, there being no reported detrimental effects of bleaching at around 100 °C or for more than several hours [143]. Under such conditions, most of the peroxide appears to be consumed in the oxidation of chain end units of the cellulose macromolecule. The other major effect on the substrate is oxidation of secondary hydroxy to keto groups, accompanied by the formation of very few aldehyde or carboxyl groups [235]. 

Table 10.14 Recommended conditions for batchwise peroxide bleaching [143]...

Table 10.16 Recommended conditions for cold pad-batch peroxide bleaching...

Table 10.17 Recommended conditions for TAED-activated peroxide bleaching [244]...

Oxidative bleaching of wool is invariably carried out with hydrogen peroxide. The active species involved is likely to be the same as on cellulosic substrates but specific reactions with wool amino acid residues must be considered. The primary reaction is oxidation of cystine disulphide bonds leading to the formation of cysteic acid residues (Scheme 10.41). The rupture of disulphide crosslinks, with attendant increase in urea-bisulphite and alkali solubility values, adversely affects fibre properties. As the severity of bleaching conditions increases, the urea-bisulphite solubility remains little changed but the relationships between alkali solubility and cysteic acid (Figure 10.36) and between cystine and cysteic acid (Figure... 

Table 10.27 Recommended conditions for the peroxide bleaching of wool [259]...

The adverse effects of alkali on wool cause reduction in its dry strength only after fiber solubilization and considerable loss in its cystine content (105). Because of its sensitivity to alkali, wool is preferentially given a peroxide bleach with added formic acid silk does not degrade nearly so much under alkaline conditions and may be bleached at pH 10 with peroxide, using stabilizers such as sodium silicate (98). 

The traditional conditions for alkaline hydrogen peroxide bleaching have called for modest temperatures in the region of 70-80 °C, but temperatures as... 

It is very difficult to specify strict guidelines for optimum bleaching conditions for hydrogen peroxide as the operation is normally affected by the nature and quality of the goods to be bleached, the amount of bleaching required and on the equipment available. However, the following general variables are considered to be important ... 

Alkaline hydrogen peroxide bleaching is the most preferred system for polyester/ cotton blends and bleaching can be carried out on various equipment using batchwise, semi-continuous and continuous method. Table 6.9 shows conditions for bleaching... 

PJ Wright and J Abbot. Kinetic Models for Peroxide Bleaching under Alkaline Conditions. Part 1. One and Two Chromophore Models. J. Wood Chem. Technol. 11 349-371, 1991. 

In summary, there is abundant evidence that alkaline peroxide reacts with lignin to form hydroquinones, some of which are not oxidized further under the bleaching conditions. It seems likely that the p-quinones detected in bleached TMP have been formed by subsequent oxidation by air. 

Plexene . [Sylron] Chdating agents for eing, peroxide bleaching sequester-ir% agent fhard water conditions. 

Plexene . [Sybron] Chdating agents for dyeing, peroxide bleaching sequester-ii agent for Ca and Mg unda hard water conditions. 

Oxidative depolymerization of cellulose occurs during the bleaching of wood pulp under alkaline conditions (alkali-oxygen and alkali-peroxide bleaching processes) leading to losses in pulp strength and involve the reactions outlined above. The oxidation at the C-2, -3 or -6 hydrot ls usually is initiated by hydroxyl radicals... 

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