Abstract
Cellulose-based model materials in the form of fibrillar networks and macromolecular hydrogels were used to investigate the ion-induced swelling in relation to the elasticity and structure of the network. Both networks were charged by the introduction of carboxyl groups onto the cellulose surface, and the dimensions of the networks in aqueous solution were measured as a function of pH. The use of cellulose-model materials that contained either noncrystalline cellulose or cellulose I fibrils made it possible to model the effect of the ion-induced osmotic pressure of a delignified wood fiber wall. The noncrystalline hydrogels represented the noncrystalline domains of the fiber wall and the fibrillar network represented the supramolecular network of cellulose I fibrils of the fiber wall. The experimental results were compared to swelling potentials computed using the Donnan theory, and it was found that the ion-induced water uptake within the cellulose networks followed the theoretical predictions to a large extent. However, fibrillar networks were found to plastically deform upon swelling and deviated from the ideal Donnan theory for polyelectrolyte gel networks. Upon addition of salt to the aqueous phase surrounding the cellulose materials, both hydrogels and fibrillar networks deviated from the Donnan theory predictions, suggesting that structural differences between the networks impact their swelling.
Highlights
The interest in forest-based raw materials has grown as the demand for biobased fossil-free products has increased
The modulus of the gel beads was found to decrease with increasing charge density and ranged from 13 to 120 kPa depending on the method of measurement
Average pKa values for the carboxyl groups, and the initial increase in water uptake began at a lower pH when NaCl
Summary
The interest in forest-based raw materials has grown as the demand for biobased fossil-free products has increased. While native materials have excellent properties, to more efficiently utilize the wood-based materials, different chemical modifications are often performed, to alter properties or provide different functional groups for further processing. CNFs from wood cellulose are high-aspect-ratio particles with widths of approximately 3− 5 nm and lengths on the order of several micrometers.[3] CNFs have received great interest due to their high strength, high stiffness, and comparatively low weight.[3,4] CNFs have been used in, for example, nanocomposites,[5,6] barrier films,[7] flameretardant materials, and improved paper products.[8,9] CNFs are often prepared by disintegrating oxidized fibers using a highpressure homogenizer, and it has been shown that oxidation of fibers facilitates the liberation of nanofibrils via an increased fiber wall swelling.[10]
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