Bleaching of Chemical Pulps

Cleavage of Carbon—Carbon Bonds. Under appropriate conditions, the propanoid side chain in lignin maybe mptured to form three-, two-, or one-carbon fragments. This carbon—carbon fragmentation occurs in a variety of laboratory treatments and technical processes such as in bleaching of chemical pulps with CI2, CIO2, and O2, in microbial degradation (15), and in photooxidation (16). 

The carboxyl contents of different lignins are shown in Table 7.5.1. In the case of lignins isolated or modified without recourse to strong oxidation procedures, the carboxyl content is generally less than 10%. However, when lignin is subjected to the action of strong oxidants, as is the case, for example, in the bleaching of chemical pulps, the carboxyl content may substantially exceed this value. 

D da Silva Perez, A Castellan, S Grelier, MGH Terrones, AEH Machado, R Ruggiero, and AL VUarinho. Photochemical Bleaching of Chemical Pulps Catalyzed by Titanium Dioxide. J. Photochem. Photobiol. A Chem. 115 73-80, 1998. 

In the bleaching of chemical pulp, oxidation reactions result in the formation of carboxyl groups iu the liguiu that uuder alkaline conditions will ionize and, thns. 

Bleaching remains the principal use for sodium peroxide. Today its largest market is in the paper industry. In this field, its original use was in the bleaching of ground wood pulp, and in recent years it has become firmly established for the bleaching of chemical pulps. Some textiles and certain flours such as tapioca also employ sodium peroxide bleaches. 

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