Matériaux isolants: Développement d'un produit expansé à base de cellulose

National audienceInsulation board market is largely dominated by mineral and iol based sources and presente a constant increase. Foamed products are expected to rise in the near future thanks to high performance products. However, the environmental impact is bad. As a consequence, WoTIM European project, funded by WoodWisdom–Net Research Program 2014, aims at developing insulation products based on cellulose obtained from wood. Two products are proposed: expending cellulose foam competing with polyurethane foams to be sprayed and boards of various dimensions. Thanks to highly porous and low density network, insulation performances are high. As an exemple, thermal conductivity as low as 0.035 W/K.m is obtained on under optimization products. During project, economic and environmental performance of products will be evaluated to propose competitive solutions. Partners are VTT in Finland; Holmen and Innventia in Sweden; Soprema and FCBA in France.Les matériaux d'isolation à base minérales ou issus de pétroressources sont actuellement les plus largement utilisés dans le monde et en croissance constante. Une augmentation est attendue dans le secteur de l'isolation à base de mousse plastique à cause de leurs hautes performances. Toutefois, d'un point de vue environnemental et durabilité, cette tendance est problématique. WoTIM, projet européen WoodWisdom–Net Research Programme 2014, propose de développer des matériaux d'isolation, à base de cellulose issue du bois, sous forme de mousses expansives ou panneaux. Grace à cette structure de très faible densité, les propriétés d'isolation sont augmentées en créant des espaces d'air dans une matrice. Le meilleur de ces démonstrateurs, en cours d'optimisation, présente une conductivité thermique de 0.035 W/K.m, illustrant ainsi la bonne performance de ces nouveaux produits d'isolation cellulosiques qui rivalise avec les produits courants issus de laine minérale

Low-density, water-repellent, and thermally insulating cellulose-mycelium foams

This work explored whether partial cellulose bioconversion with fungal mycelium can improve the properties of cellulose fibre-based materials. We demonstrate an efficient approach for producing cellulose-mycelium composites utilizing several cellulosic matrices and show that these materials can match fossil-derived polymeric foams on water contact angle, compression strength, thermal conductivity, and exhibit selective antimicrobial properties. Fossil-based polymeric foams commonly used for these applications are highly carbon positive, persist in soils and water, and are challenging to recycle. Bio-based alternatives to synthetic polymers could reduce GHG emissions, store carbon, and decrease plastic pollution. We explored several fungal species for the biofabrication of three kinds of cellulosic-mycelium composites and characterized the resulting materials for density, microstructure, compression strength, thermal conductivity, water contact angle, and antimicrobial properties. Foamed mycelium-cellulose samples had low densities (0.058 – 0.077 g/cm3), low thermal conductivity (0.03 – 0.06 W/m∙K at + 10 °C), and high water contact angle (118 – 140°). The recovery from compression of all samples was not affected by the mycelium addition and varied between 70 and 85%. In addition, an antiviral property against active MS-2 viruses was observed. These findings show that the biofabrication process using mycelium can provide water repellency and antiviral properties to cellulose foam materials while retaining their low density and good thermal insulation properties. Graphical Abstract: (Figure presented.

Starspots due to large-scale vortices in rotating turbulent convection

We study the generation of large-scale vortices in rotating turbulent convection by means of Cartesian direct numerical simulations. We find that for sufficiently rapid rotation, cyclonic structures on a scale large in comparison to that of the convective eddies, emerge, provided that the fluid Reynolds number exceeds a critical value. For slower rotation, cool cyclonic vortices are preferred, whereas for rapid rotation, warm anti-cyclonic vortices are favored. In some runs in the intermediate regime both types of cyclones co-exist for thousands of convective turnover times. The temperature contrast between the vortices and the surrounding atmosphere is of the order of five per cent. We relate the simulation results to observations of rapidly rotating late-type stars that are known to exhibit large high-latitude spots from Doppler imaging. In many cases, cool spots are accompanied with spotted regions with temperatures higher than the average. In this paper, we investigate a scenario according to which the spots observed in the temperature maps could have a non-magnetic origin due to large-scale vortices in the convection zones of the stars.Comment: 8 pages, 8 figures, version published in ApJ. Version with higher resolution figures can be found at http://www.helsinki.fi/~kapyla/publ.htm