Cellulose–silica composite aerogels from “one-pot” synthesis

Abstract

Cellulose-silica composite aerogels were prepared via "one-pot" process: aqueous solutions of cellulose-8 wt% NaOH and sodium silicate were mixed, coagulated and dried with supercritical CO2. The system was studied both in the fluid and solid (dry) states. Cellulose and sodium silicate solutions were mixed at different temperatures and concentrations; mixture properties were monitored using dynamic rheology. The gelation time of the mixture was strongly reduced as compared to that of cellulose-NaOH solutions; we interpret this phenomenon as cellulose self-aggregation inducing partial coagulation due to competition for the solvent with sodium silicate. The gelled cellulose/sodium silicate samples were placed in aqueous acid solution which completed cellulose coagulation and led to in situ formation of sub-micronic silica particles trapped in a porous cellulose matrix. After drying with supercritical CO2, an organic-inorganic aerogel composite was formed. The densities obtained were in the range of 0.10-0.25 g/cm3 and the specific surface area was between 100 and 200 m2/g. The silica phase was shown to have a reinforcing effect on the cellulose aerogel, increasing its Young's modulus