Abstract
Cellulose-based hydrogels were prepared by dissolving cellulose in aqueous sodium hydroxide (NaOH)/urea solutions and casting it into complex shapes by the use of sacrificial templates followed by thermal gelation of the solution. Both the gelling temperatures used (40–80 °C), as well as the method of heating by either induction in the form of a water bath and hot press or radiation by microwaves could be shown to have a significant effect on the compressive strength and modulus of the prepared hydrogels. Lower gelling temperatures and shorter heating times were found to result in stronger and stiffer gels. Both the effect of physical cross-linking via the introduction of additional non-dissolving cellulosic material, as well as chemical cross-linking by the introduction of epichlorohydrin (ECH), and a combination of both applied during the gelation process could be shown to affect both the mechanical properties and microstructure of the hydrogels. The added cellulose acts as a physical-cross-linking agent strengthening the hydrogen-bond network as well as a reinforcing phase improving the mechanical properties. However, chemical cross-linking of an unreinforced gel leads to unfavourable bonding and cellulose network formation, resulting in drastically increased pore sizes and reduced mechanical properties. In both cases, chemical cross-linking leads to larger internal pores.
Highlights
Hydrogels are three-dimensional polymer networks capable of trapping large amounts of water
The method employed not produce a visible change in the microstructure of other the Thegelling produced hydrogels showdid a competitive range of mechanical properties compared to hydrogels, exemplarily shown for the gels prepared without chemical or physical cross-linker in similar cross‐linked hydrogels, especially when cross‐linked by ECH [34]
Cellulose hydrogels can be produced by temperature induced gelling and the used temperature and corresponding gelling time could be shown to have a strong influence on the mechanical properties of the gels
Summary
Hydrogels are three-dimensional polymer networks capable of trapping large amounts of water. Epichlorohydrin (ECH) is commonly used to cross-link polysaccharides and has been employed for the cross-linking of cellulose hydrogels from NaOH/urea solutions [28,29,30,31], but can be used in an additional post-processing step after the cellulose has been regenerated from the solvent [32] Both physical and chemical cross-linking of cellulose in cellulose hydrogels has been analysed before, but their combined effects have not been thoroughly characterised [29,32,33,34]. In this work the effects of gelling conditions such as temperature and method of heating on the mechanical properties of cellulose based hydrogels prepared by thermal gelling prior to regeneration will be characterised It will be analysed how strength and stiffness of the gels can further be improved by addition of cellulose powder acting as physical cross-linker and reinforcing agent. This work, aiming to characterize thermally set cellulose hydrogels will allow us to assess their potential for applications in the form of 3D printed porous media, for use as a liquid chromatography stationary phase or 3D printing of vascular soft tissue scaffolds [35,36]
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