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Swelling and mechanical properties of cellulose hydrogels. IV. Kinetics of swelling in liquid water

, : Swelling and mechanical properties of cellulose hydrogels. IV. Kinetics of swelling in liquid water. Journal of applied polymer science 26(8): 2561-2572

The swelling kinetics of cellulose hydrogels have been studied in experiments where partially dried gels were reswollen to equilibrium in liquid water. The swelling interval studied was from the dry state to 3.6 g water/g dry gel, and the temperature range was from 15 to 65°C. The experimental arrangement and the theoretical analysis was based on the unidimensional, unsteady sorption of water into a swelling sheet. The effects of sheet thickness, temperature and the initial degree of swelling were investigated. The integral sorption curves obtained were sigmoid in shape when plotted as the sorbed amount of water versus the square root of time. These anomalous, non-Fickian sorption curves were analyzed under the assumption that the anomalous behavior is due to a slow establishment of concentration equilibrium at the boundary surfaces. Each sorption curve can then be described by a combination of a mutual diffusion coefficient and a surface relaxation rate. The sigmoidicity of the sorption curves is accordingly determined by the ratio of a characteristic diffusion time to a characteristic surface relaxation time. More classical, Fickian-type behavior is then explained by an increase in this ratio. The experimental sorption curves were found to become more nearly classical as the sheet thickness, the temperature and/or the initial degree of swelling was increased. The relaxation process was found to be associated with a higher apparent activation energy than the diffusion process.


DOI: 10.1002/app.1981.070260806

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