Microstructure of a cellulose aerogel wiht high strength nano-fibrils.
Many biopolymers like cellulose, chitin, carrageenan can be processed to yield a completely new class of aerogels, which look at the nanoscale like a nanofelt: Nanosized fibers, fibrils, are randomly interwoven in 3D and at their contact points they are covalently bonded or with hydrogen bonds (this is different to felts at the macroscale, which are typically interwoven and linked only mechanically). Wet gels are produced by dissolution of the biopolymers in suitable ionic liquids or salt-hydrate melts and the gel forms on cooling to room temperature. Aerogels of any shape can easily be produced, even as filaments by an extrusion or spinning process, which then allows to make felts of nanostructured fibers or even woven fabrics. Biopolymeric aerogels always have to be dried supercritically. Possible applications are filters to regulate humidity, the carbondioxide content and the microbiological climate in cars, trains, airplanes and spacecrafts. Since these aerogel class posses interesting mechanical properties, they can be used as cores in sandwich structures with additional functionality. These aerogels are extremely lightweight: they can be made just a bit denser than air.