Preparation of polyurethane-based aerogels and xerogels for thermal superinsulation

Previous work has demonstrated the feasibility of synthesizing low-density polyurethane- and polyisocyanurate-based aerogels that exhibit low effective thermal conductivity. On the basis of this literature, the present study synthesized and characterized nanostructured polyurethane aerogel-like materials processed via subcritical drying routes. Two families of polyurethane gels were studied. Wet gels were synthesized with two polyols of different functionality. The influence of the composition of the reaction media is discussed. Depending on the solubility of the precursors, macroporous foam-like or mesoporous aerogel-like materials can be obtained as observed by scanning electron microscopy coupled with mercury porosimetry. Prior to drying, specific washing steps were performed. Preliminary results obtained by evaporative and freeze-drying were then compared to reference aerogel materials dried through a direct supercritical route. Only a slight density increase was observed. Effective thermal conductivities were also measured and discussed. (C) 2004 Elsevier B.V. All rights reserved.