Oxygen bleaching

Earlier formulations contained mainly chlorine bleach, metasiUcates, triphosphate, and nonionic surfactants. Modem manufacturers have switched to more compHcated formulations with disiUcates, phosphates or citrate, phosphonates, polycarboxylates, nonionic surfactants, oxygen bleach, bleach activator, and enzymes. The replacement of metasiUcates by disilicates lowers pH from approximately 12 to 10.5, at 1 g ADD/L water. The combined effect of decreased pH, the absence of hypochlorite, and the trend toward lower wash temperatures has paved the way for the introduction of enzymes into ADDs. Most ADD brands in Europe are part of the new generation of ADD products with enzymes. The new formulations are described in the patent hterature (55—57). 

Oxygen predelignification, oxygen bleaching, displacement bleaching... 

Laundry bleaches fall into two categories. The first is what are called chlorine bleaches. The second is oxygen bleaches. 

Oxygen bleaches such as sodium carbonate peroxide (also called sodium percarbonate), sodium peroxide, or sodium perborate are made by reacting molecules with hydrogen peroxide. When the result is added to water, the hydrogen peroxide is released. 

Most oxygen bleaches work best in hot water. Additives such as tetra acetyl ethylene diamine allow the hydrogen peroxide to work in warm water (50°C). 

Choose oxygen bleach over chlorine bleach if the product contains enzymes or perfumes. 

Chlorine bleaches react with more chromophores than oxygen bleaches. They react irreversibly with aldehydes, alcohols, ketones, carbon-carbon double bonds, acidic carbon-hydrogen bonds, nitrogen compounds, sulfur compounds, and aromatic compounds. 

O. Samuelson Suppression of undesirable reactions during oxygen bleaching of wood pulp... 

Fig. 8-16. Depolymerization of cellulose (viscosity decrease) during oxygen bleaching of pine kraft pulp. Dotted line, no inhibitor addition full line, inhibitor added (Mg salt).

Fig. 8-17. Yield in oxygen bleaching. Full line, inhibitor added dotted line, no inhibitor addition, (a) Spruce sulfite (b and c) pine kraft (d) spruce sulfite pulps (reducing end groups have been eliminated by NaBH4 reduction).

Malinen, R., and Sjostrom, E. (1972). Studies on the reactions of carbohydrates during oxygen bleaching. Part I. Oxidative alkaline degradation of cellobiose. Pap. Puu 54, 451 -468. 

There have been many investigations on the oxidation of sodium hydroxide-alkalized cellulose for the preparation of rayon and lacquers, for the oxygen bleaching of fiber, and for the oxygen pulping of wood chips. 

However, given the presence of these complexing agents in oxygen bleaching, what is required to prevent catalyzed oxidation is a stronger, stable complex that will not permit participation of the transition metals in the radical-redox reactions. This appears to be the most plausible role to ascribe to magnesium. 

Retardation of Cellulose Degradation during Oxygen Bleaching, TAPP I (1973) 56 (6) 95-99. 

Gaspar, A., Evtuguin, D. V, and Neto, C. P., Oxygen bleaching of kraft pulp catalysed by Mn(III)-substituted polyoxometalates. Appl Catalysis A-General 2003, 239 (1-2), 157-168. 

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