Modification of softwood kraft pulp fibres using hydrogen peroxide at acidic conditions
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ORIGINAL RESEARCH
Modification of softwood kraft pulp fibres using hydrogen peroxide at acidic conditions Axel Martinsson
. Merima Hasani
. Antje Potthast
. Hans Theliander
Received: 27 January 2020 / Accepted: 18 May 2020 Ó The Author(s) 2020
Abstract The aim of this work was to provide softwood kraft pulp fibres with new functionalities by the introduction of carbonyl groups. Carbonyl groups are known to affect properties such as wet strength through the formation of covalent bonds, i.e. hemiacetals. The method developed involves oxidation using hydrogen peroxide at mildly acidic conditions. It was found that the carbonyl group content increased with both increasing temperature and residence time when oxidized at acidic conditions. The number of carboxylic groups, however, remained approximately constant. There was virtually no increase in carbonyl groups when oxidation was performed at alkaline conditions. The maximum increase in carbonyl groups was found at a residence time of 90 min, a reaction temperature of 85 °C and a pH of 4. These conditions resulted in an increase in carbonyl groups from 30 to
A. Martinsson M. Hasani (&) H. Theliander Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 412 96 Gothenburg, Sweden e-mail: [email protected] M. Hasani H. Theliander Wallenberg Wood Science Center, The Royal Institute of Technology, Chalmers University of Technology, 10044 Stockholm, Sweden A. Potthast Division of Chemistry of Renewables, Department of Chemistry, University of Natural Resources and Life Sciences Vienna, Muthgasse 18, 1190 Vienna, Austria
122 lmol/g. When formed into a sheet, the pulp oxidized at acidic conditions proved to maintain its structural integrity at aqueous conditions. This indicates the formation of hemiacetal bonds between the introduced carbonyl groups and the hydroxyl groups on the carbohydrate chains. Thus, a possible application for the method could be fibre modification during the final bleaching stage of softwood kraft pulp, where the wet strength of the pulp could be increased. Keywords Hydrogen peroxide Cellulose oxidation Carbonyl groups Wet strength Bleaching
Introduction Wet strength is an important property in some paperbased products, e.g. various packaging and absorbing applications. It is not easily achieved, however, because when a paper material is wetted, the interfibre hydrogen bonds that keep the material together are broken; the strength of the material is reduced by more than 90% (Dunlop-Jones 1991). Although techniques such as wet pressing and refining have been implemented to overcome this and reduce the loss in strength, they nevertheless have a very limited effect on the wet strength. Wet strength agents are therefore commonly added to increase the wet strength further, after which between 10 and 30% of the initial strength
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Cellulose
can be maintained under wet conditions. These additives can be expensive and have negative environmental impac
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