Nanopapers prepared from oxidized cellulose nanofibrils swell dramatically in deionized water due to the osmotic pressure generated by the charged groups on the fibril surface. This is in many aspects considered as a disadvantage and something to prevent in order to utilize the mechanical properties of CNF in future materials. In this work we take an opposite approach and try to utilize the impressive swelling of charged CNF films in order to create ideal networks that are hard to reach by traditional methods. Due to the ionic repulsion between the fibrils and between the fibrils and added highly charged anionic polyelectrolytes it is possible to create highly dynamic networks also at rather high CNF concentrations. These dynamic networks are used to tune the material properties of hydrogels and the subsequent freeze dried aerogels. The incorporation of small amounts of anionic polyelectrolytes, in this case alginate, also makes it possible to further enhance the swelling ability and to introduce a way to lock the desired hydrogel or to make the aerogel water resistant. The presented approach provides the possibility to tailor the dry content, density, mechanical properties as well as the shape and size of the hydrogels and aerogels with high accuracy. Furthermore, we study solvent exchange of the prepared hydrogels to create a platform for chemical modifications in different solvents or to enable critical or ambient drying to produce aerogels without lyophilization. In conclusion, we present different tunable materials from cellulose nanofibrils to be used as a foundation for advanced functional materials such as electrically or biomedically interactive devices.

Dynamic networks of cellulose nanofibrils as a platform for tunable hydrogels, aerogels, and chemical modifications

255th National Meeting (2018)

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