Fabrication of aerogels based on low-aspect-ratio cellulose nanocrystals

We have introduced a new protocol for the fabrication of aerogels based on low-aspect-ratio cellulose nanocrystals.

In this project cellulose nanocrystals (CNCs), which can be isolated from a variety of bio-sources, are used as the basis for aerogels. While aerogels made from high-aspect-ratio CNCs have been shown to exhibit attractive properties, low-aspect-ratio CNCs, which can be isolated from wood or cotton and are much more amenable for commercial exploitation, have been little explored in this context. We recently produced new aerogels by freeze-drying mixtures of CNCs extracted from cotton with poly(vinyl alcohol) (PVOH) in water. While materials made by adapting literature protocols displayed poor mechanical coherence, judiciously chosen processing conditions afforded mechanically coherent aerogels whose mechanical properties are comparable to those of aerogels made from higher-aspect-ratio CNCs. The origin of these desirable characteristics appears to be the formation of porous structures with a pore size of around 5 μm, in which leave-like compacted PVOH/CNC sheets provide stress transfer in three dimensions. We discovered that annealing such PVOH/CNC aerogels at elevated temperature renders them insoluble in water. The possibility to create water-borne, water-insoluble aerogels based on natural nanofibers is very intriguing from a sustainability point of view.

Adolphe Merkle Institute - Chemin des Verdiers 4 - CH-1700 Fribourg - Phone +41 26 300 9254