Cellulose-based aerogels

New organic aerogels were prepared using cellulose derivatives as precursors. The elaboration process and the structural characterisations of these porous cellulose-based materials are described in the present study. Series of monolithic gels were synthesised in acetone by crosslinking cellulose acetate with a non-toxic isocyanate via sol-gel route, using tin-based catalyst. Gelation times (ranging from 15 to 150 min) were significantly dependent on reagents' nature and concentration. Low-density materials (from 0.25 cm(3)/g to 0.85 cm(3)/g) were obtained after supercritical carbon dioxide drying. These newly developed nanostructured materials were characterised using mercury porosimetry, nitrogen adsorption and scanning electron microscopy. All the prepared materials have shown both a nanostructured solid network (specific surface areas between 140 and 250 m(2)/g) and a nanoporous network (characteristic pore sizes between 13 and 25 nm) together with specific porous volumes as large as 3.30 cm(3)/g. Influence of sol-gel synthesis parameters as crosslinker content and cellulose degree of polymerisation or concentration was investigated. First empirical correlations between synthesis parameters and final material properties were obtained. A special attention was dedicated to the different shrinkages occurring during the elaboration process. In particular, the important shrinkage occurring during the supercritical drying step was studied in terms of affinity between the crosslinked polymeric network and carbon dioxide. In parallel, first thermo-mechanical properties were presented in terms of bulk modulus and effective thermal conductivity. (c) 2006 Elsevier Ltd. All rights reserved.