Aerogels made from nanocellulose have attracted great attention during recent years. One initial shortcoming of nanocellulose-based aerogels was their lack of mechanical integrity when exposed to liquid water, in which they easily disintegrate. This issue has been addressed by several researchers and several methods to chemically crosslink nanocellulose structures have been reported. A common crosslinking procedure involves addition of crosslinking agents to the nanocellulose before the fabrication of the dry material together with a curing step, although crosslinking have also been reported in the wet state by using, for example, aldehyde-containing nanocellulose and amine-containing crosslinkers. Another method to produce crosslinked cellulosic structures is to induce a significant amount of aldehydes in the cellulose backbone, for example by periodate oxidation, that induces inter-molecular and inter–fibrillar hemiacetals through a reaction with adjacent cellulose hydroxyls. Recently, a method was reported for producing wet-stable CNF aerogels by simply freezing and thawing dispersions of these modified nanofibrils, i.e. a method without energy and time consuming freeze-drying and thermal activation of the crosslinker (J. Erlandsson et al., <i>Applied Materials Today</i>, 5, 2016, p246). However, in this initial investigation the focus was on presenting the new method and little attention was on the properties of the aldehyde-containing CNFs and the influence of their properties on the final properties of the aerogel. This also means that no dedicated experiments were performed to clarify the mechanism of formation of the structure, the crosslinking reaction or the influence of critical parameters of the aerogel preparation. This work aims to shed some light on the mechanism(s) behind this freeze-induced crosslinking and the ability to form crosslinked networks in the form of aerogels. Besides characterisation of the aerogels formed, a large attention was on the use of colloidal probe AFM measurements to study the origin of the bonds involved in the cross-linking reaction between the cellulose fibrils.

On the mechanism of freeze-induced crosslinking of aerogels made from periodate-oxidised cellulose nanofibrils

255th National Meeting (2018)

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