Structural changes during swelling of highly charged cellulose fibres
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Structural changes of fibrils and fibril aggregates in the fibre wall were studied after oxidation of the cellulose by 2,2,6,6-tetramethyl-1-piperidinyloxy to high charge densities (highest charge density: 1300 μeq/g). The increase in pore volume was measured by mini-WRV at two different pH levels, and the supramolecular structure in the fibre wall in terms of aggregate size, specific surface area and average pore size was measured by solid state NMR, DVS desorption and BET N2 gas adsorption. A structural change in the arrangement of the fibrils inside the fibril aggregates was observed although the oxidation did not lead to a complete liberation of individual fibrils, i.e. they still exist as an aggregated structure after oxidation. Theoretical estimates suggest that the electrostatic repulsion energy connected with the increase in surface charge of the fibrils can be sufficient to gradually separate the fibrils enough to expose all fibril surfaces to oxidation chemicals.
KeywordsCellulose fibres Nano structure TEMPO oxidation Fibril Fibril aggregates CNF Cellulose nano fibrils Specific surface area
Domsjö Fabriker AB is acknowledged for kindly supplying the pulp used in this work. The authors would like to acknowledge Anne-Mari Olsson at Innventia for the help with desorption measurements. Wallenberg Wood Science Center is acknowledged for financial support. Dr Anthony Bristow is thanked for linguistic revision of the manuscript.
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