(Encadrant : Tatiana Budtova)
Decreasing the energy consumption is currently one of the most important global concerns. For example, buildings are responsible of more than 25% CO~2~ emissions and 45% of energy consumption. These emissions are mainly linked to limited thermal insulation. To change this dramatic situation it is necessary to find new generation of thermal insulation materials. One way is thedevelopment of high performance thermal insulating materials. These are the innovative thermal super-insulating materials, i.e. with thermal conductivity below that of air (0.025 W/(m.K)) in ambient conditions.
There are two families of super-insulating materials and components:
1) One is Vacuum Insulation Panels, which are mature enough (Technology Readiness Level index, TRL = 8-9) with very low conductivity (around 0.007 W/(m.K) for the whole life effective conductivity); however, they are rather brittle and difficult to install.
2) The second is the Super-Insulation at Atmospheric Pressure materials. They are exclusively represented by aerogels, which are “intrinsically” super-insulating at the atmospheric pressure due to their mesoporosity (Knudsen effect), their low density and nanostructured solid backbone. Typical aerogels are made of silica and their composites, with TRL = 5-8 and conductivity around 0.015 W/(m.K) /1/. Their main drawbacks are high brittleness and also their significant dust emission. For the time being, they remain rather expensive (around 2000 euros/m^3^) and thus used only in niche markets. Organic (polyurethane) aerogels are under industrial development with strong advancements made by BASF (Slentite™ with thermal conductivity around 0.016 W/(m.K)). However, polyurethane chemistry is harsh.
At the beginning of the 21st century a new generation of aerogels appeared: bio-aerogels (based on polysaccharides). They are finely structured (specific surface area of 200-600 m^2^/g), mechanically strong (with a large plastic deformation region till 60-80% strain before pore collapse) and are thus a very promising alternative to silica and synthetic polymer based aerogels. Large amount of literature reports on thermal super-insulating properties of silica aerogels and ways of improving their mechanical properties /1/. Bio-aerogels are in the very early state: their use is suggested as matrices for drug delivery and their carbons for catalysis and electrode materials. It is only recently that some bio-aerogels were reported to be thermal super-insulating materials with conductivities around 0.016 – 0.020 W/(m.K) /2-4/.
The goal of this project the possibilities, for bio-aerogels, to compete with classical inorganic and synthetic polymer aerogels in terms of performance and price, the latter including the price of materials and processing?
References:
M. Koebel, A. Rigacci,P. Achard, “Aerogel-based thermal superinsulation: an overview”, J. Sol-Gel Sci. Technol. 63, 315 (2012)
S. Zhao, W. J. Malfait, A. Demilecamps, Y. Zhang, S. Brunner, L. Huber, P. Tingaut, A. Rigacci, T. Budtova, M. Koebel “Strong, thermally superinsulating biopolymer-silica aerogel hybrids by cogelation of silicic acid with pectin” Angew Chem Int Ed 54, 14282 (2015)
L. Druel, R. Bardl, W. Vorwerg, T. Budtova “Starch aerogels: a member of the family of thermal super-insulating materials”, Biomacromolecules 18 (12), 4232–4239 (2017)
S. Groult, T. Budtova “Thermal conductivity/structure correlations in thermal super-insulating pectin aerogels”, Carbohydrate Polymers, 196, 73–81 (2018)