A new, robust method for measuring average fibre wall pore sizes in cellulose I rich plant fibre walls
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A new, robust method for measuring the average pore size of water-swollen, cellulose I rich fibres is presented. This method is based on the results of solid-state NMR, which measures the specific surface area (area/solids mass) of water-swollen samples, and of the fibre saturation point (FSP) method, which measures the pore volume (water mass/solids mass) of water-swollen samples. These results are suitable to combine since they are both recorded on water-swollen fibres in excess water, and neither requires the assumption of any particular pore geometry. The new method was used for three model samples and reasonable average pore size measurements were obtained for all of them. The structural characterization of water-swollen samples was compared with the dry structure of fibres as revealed using BET nitrogen gas adsorption after a liquid exchange procedure and careful drying. It was concluded that the structure of the water-swollen fibres sets an upper limit on what is obtainable in the dry state.
KeywordsCellulose I CP/MAS 13C-NMR Fibre saturation point (FSP) Water retention value (WRV) BET Pore size
Dr. Derek Weightman at Sappi Saiccor in South Africa is kindly acknowledged for supplying samples of the eucalyptus dissolving pulp. Domsjö Fabriker AB is acknowledged for supplying the softwood dissolving pulp. Thanks are expressed to German Salazar-Alvarez at the Department of Material and Environmental Chemistry, Stockholm University, Stockholm, for help with the BET nitrogen gas adsorption measurements.
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