A Survey of Oxidative Modifications

Due to the 3 hydroxyl groups available for oxidation within one anhydroglucose unit and due to the polymeric character of the cellulose a great variety of structural modifications and combinations is possible. As with other types of chemical changes at the cellulose molecule also in this case the oxidation can affect different structural levels differently. Depending on the oxidative stress imposed on the cellulose, the individual hydroxyls within the AGU and within the polymer chain are involved to varying extent and may respond to further treatment and reactions in a specific way. Despite their low concentration in the imol/g range, oxidative functionalities are one of the prime factors to determine macroscopic properties and chemical behavior of cellulosic materials (Fig. 1). 

The main causes for the formation of carbonyl and carboxyl groups in cellulose are isolation and purification procedures besides natural aging. This applies in particular to cellulosic pulps from wood, which has undergone a number of processing steps to be freed from lignin, hemicelluloses, and extractives. 

Although we are far away from being able to fully analyze an oxidized cellulose with all these different possibilities of oxidative modifications with regard to their type and exact location, cellulose chemists have taken major steps towards developing methodology to address those problems. Major obstacles on the way to a comprehensive analysis of oxidized functionalities are certainly the low concentration of these structures in cellulosic materials, the characterization of their position within the molecular weight distribu- 

This review summarizes the generation, nature and determination of oxidized structures in celluloses as well as recent developments in their analytics. 

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