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You are here : Home > Training > EFPG Days > 12-  Different ways to create carboxyl groups on cellulose. Effect of paper properties (abstract)
        Last update : December 12, 2005
 
                  Fourth session - Fiber chemical modification              
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            12 - Different ways to create carboxyl groups on cellulose.
Effect of paper properties
           
Gérard Mortha (EFPG)

Site Web de l'EFPGOne way to improve the economy balance of wood pulp production is to find attractive new issues for making chemical modification of cellulose pulps that give new functionalities to the pulp. It would be even better if such chemical treatments could be carried out as post-treatments in the pulp mill. 

Chemical treatments such as oxidation of alcoholic groups lead to deep modifications of the pulp in its bulk structure, i.e. at the fiber wall level or molecular level. Change in physical properties such as aspect, colour, stiffness, brittleness, strength resistance, wettability, brightness reversion and yellowing, DP of cellulose, resistance to chemical oxidants such as hypochlorite can be encountered. Some new properties of the pulp are beneficial and others detrimental.

In this presentation, we will summarize the different ways of creating chemical oxidation of cellulose functional groups, i.e alcoholic functions. The discussion will be focused on carboxyl group creation and the chemical mechanism involved.

Then some experiments carried out at EFPG on cellulose modification using catalysed oxygenated bleaching agents will be presented. The latter can be applied as post-treatments after bleaching on the mill site. The use of non-chlorine agents is also an advantage.
The effect of the applied oxidative treatment was to enrich the pulp in a limited number of carboxyl groups. Simultaneously the best conditions were found to minimize the DP degradation. Anyway, in this case this had little consequence on the final strength properties of the pulp, because of the cross-linking reactions that take place after drying.
Cross linking properties were actually developed by a specific thermal treatment at 90-120°C. The latter created new linkages by esterification reactions between alcohols and acid groups in the cellulose.
If the reaction occurs on fiber surfaces, inter-fiber linkages are only created. They are resistant to moisture and increase the wet resistance of paper. This is the case of cotton linters fibers which were not much penetrated by the reagents.
In the case of wood fibers the bulk structure of fiber walls were penetrated by reagents and the accessibility to cellulose chains was better. Some physical properties of the pulp were significantly modified like stiffness, tear resistance, wet strenfth and permeability after rewetting.

As concluding remark, it can be said that the issues of cellulose modification are promising and far to be fully explored. Modifications at mill-site by using an easy-to apply chemistry should be possible to give specific properties to pulps and set up new markets for pulp mills.

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