Bio-based aerogels: a new generation of thermal super-insulating materials
Résumé
Aerogels are highly porous, ultra-light (density around 0.1 g/cm3) nanostructured materials. One of their most extraordinary properties is thermal super-insulation, i.e. thermal conductivity below that of the air: 0.015 vs 0.025 W/(m.K) in room conditions. However, classical silica aerogels are extremely fragile and organic/synthetic (resorcinol-formaldehyde) aerogels may include toxic components, which hinders their wide application. Bio-aerogels are a new generation of aerogels made from biomass-based polymers, mainly polysaccharides. We prepared aerogels from cellulose (“aerocellulose” /1, 2/) and pectin (“aeropectin” /3/) via polymer dissolution, coagulation and drying with super-critical CO2. Their density varies from 0.05 to 0.2 g/cm3 and specific surface area is around 200-300 m2/g. Bio-aerogels are mechanically strong, with Young’s moduli from 1-2 to 20-30 MPa and plastic deformation up to 60-70% strain before the pore walls collapse. Aeropectin thermal conductivity turned to be around 0.015 – 0.020 W/(m.K) making it the first reported thermal super-insulating fully biomass-based aerogel. The thermal conductivity of aerocellulose is rather “high”, around 0.030-0.035 W/(m.K), due to the presence of large macropores. We demonstrate that by using polysaccharide functionalization and making polymer-silica aerogel hybrids it is possible to vary specific surface area (increase to 800-900 m2/g) and decrease aerogel thermal conductivity below that of the air.