Cellulose-Silica Aerogel Composites

Abstract

Cellulose is the most abundant naturally occurring polymer and given this accessibility it is a highly promising resource in sustainable aerogel developments. Silica aerogels are characterized by a low thermal conductivity but still show insufficient mechanical properties like low stiffness and high brittleness. In the view of improving both the thermal properties of cellulose aerogels and the mechanical properties of silica aerogels, hybrids or composites are of a special interest. In that context, our present work deals with the development of cellulose-silica aerogel composites which were prepared using a "one-pot" process. Cellulose was dissolved using a salt hydrate melt based on cheap zinc chloride tetrahydrate and mixed with a silica sol based on tetraethylsilicate. The gelled cellulose-silica samples were regenerated in ethanol, dried with supercritical CO2 and characterized with respect to shrinkage, density, surface area, mechanical and thermal properties as well as micro-structure via SEM. The monolithic cellulose-silica composites are white in colour and apparently homogeneous. On visual examination the composites seem to get more robust, they feel stiffer and are easier to handle compared with the pure silica aerogels. The silica phase was shown to have a reinforcing effect on the cellulose aerogel by effectively increasing its Young's modulus. Furthermore, the resulting composites yield densities the range of 0.10–0.20 g/cm and specific surface areas in between 600 and 1000 m*m/g outlining an excellent combination of both original aerogels.