To obtain a successful utilization of cellulose as a component in new materials a fundamental knowledge about their interaction with moist air or condensed water is necessary. There is a need to be able to predetermine the change in materials properties under various environmental conditions. Cellulose fibres are however difficult to study due to the variety of the fibres both regarding chemistry and morphology and there is therefore a need to develop a model cellulose material that can be studied regarding the water sorption and the irreversible change in swelling upon drying of the material.<br/>To solve this problem macroscopic spherical cellulose-based hydrogel beads with a diameter of 2-3 mm were produced using cellulose-rich pulp dissolved in the DMAc/LiCl-system followed by a special precipitation step. A carboxymethylation of the pulp was performed to introduce charges in the final gel beads. By using NMR and X-ray scattering it was shown that the water swollen gel beads consist of a non-crystalline cellulose network where the scattering objects are coil-like entities of around 20 nm in diameter. By exposing the gel beads to different pH and ionic strengths it was also shown that they behave like a polyelectrolyte gel in the same manner as the plant fiber wall i.e. the swelling is affected when changing the pH and/or adding salt.<br/>The gel beads have also proven to be an excellent model material for studying the non-ionic contribution to the water uptake in cellulose-rich substrates. Despite a considerable work on clarifying the ion-induced swelling of cellulose hydrogels, there is still a very limited knowledge about the factors controlling the non-ionic swelling of the hydrogels which in fact is the dominating factor controlling the swelling. The non-ionic water retaining ability of the cellulosic network was studied by placing the gel beads in solutions with high molecular weight dextran at different concentrations. The increase in concentration of the dextran created an increased osmotic stress on the gel beads which in turn induced a change in structure leading to a draining of water at around 17 KPa. However the gel beads were not fully drained until an osmotic pressure of approx. 4.9 MPa was applied. In an attempt of further separating this water retaining ability in an ionic, a non-ionic and a mechanical network strength contribution the water activity of gel beads with different charge densities and concentrations of cellulose have been studied.

Cellulose-based gel beads for quantifying the swelling behavior of plant fibers

255th National Meeting (2018)

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