Abstract
Less fragile lightweight nanostructured polyurea based organic aerogels were prepared via a simple sol–gel processing and supercritical drying method. The uniform polyurea wet gels were first prepared at room temperature and atmospheric pressure by reacting different isocyanates with polyamines using a tertiary amine (triethylamine) catalyst. Gelation kinetics, uniformity of wet gel, and properties of aerogel products were significantly affected by both target density (i.e., solid content) and equivalent weight (EW) ratio of the isocyanate resin and polyamine hardener. A supercritical carbon dioxide (CO2) drying method was used to extract solvent from wet polyurea gels to afford nanoporous aerogels. The thermal conductivity values of polyurea based aerogel were measured at pressures from ambient to 0.075 torr and at temperatures from room temperature to −120 °C under a pressure of 8 torr. The polyurea based aerogel samples demonstrated high porosities, low thermal conductivity values, hydrophobicity properties, relatively high thermal decomposition temperature (~270 °C) and low degassing property and were less dusty than silica aerogels. We found that the low thermal conductivities of polyurea based aerogels were associated with their small pore sizes. These polyurea based aerogels are very promising candidates for cryogenic insulation applications and as a thermal insulation component of spacesuits.
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Acknowledgment
This work was conducted by the financial support of the United States National Aeronautics and Space Administration (NASA), SBIR Contract No. NNJ04JA22C. The authors are grateful to Mr. Max Mesham, Ms. Geeta Bhakhari, and Mr. Nathan Bhobho for their helps in preparing samples and also, to Ms. Sara Rosenberg, Dr. Jenifer Marchesi, and Dr. Shannon White for their valuable helps. The authors would like to thank Ms. Evelyn S. Orndoff and Mr. Luis A. Trevino of NASA for their continuous supports for this work. The authors are also grateful to TPRL for thermal conductivity measurement at different pressures and temperatures and Dow Corning Analytical Lab for SEM measurement.
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Lee, J.K., Gould, G.L. & Rhine, W. Polyurea based aerogel for a high performance thermal insulation material. J Sol-Gel Sci Technol 49, 209–220 (2009). https://doi.org/10.1007/s10971-008-1861-6
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DOI: https://doi.org/10.1007/s10971-008-1861-6