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uni'wissen 02-2012 ENG

cess wood and see whether we can produce something worthwhile from the waste.” The pro- cessing of byproducts like bark is another link in the value chain of wood – and is thus financially attractive for the industry. As far as insulating properties are concerned, biofoams can stand comparison with convention- al foams. In a study conducted by a group of sci- entists including Laborie, it was shown that foams made of tannin, a compound found in tree bark, insulates every bit as well as synthetic insulating material. They achieve a thermal conductivity of 0.033 watts per meter Kelvin. This means that at a temperature difference of one degree Celsius, one ten-centimeter thick square meter of wall made of this material allows 0.33 joules of energy per second to pass from inside to outside. Typical insulating material used today reaches a value of 0.035 watts per meter Kelvin. As a comparison: Concrete allows around 2.3 watts per meter Kel- vin to pass through, 70 times as much. Foam As a Life Saver Another advantage of the foam is its flame re- sistance – a potentially life-saving factor in a house. In addition, if one wishes to insulate an existing house there’s no need to tear down the facade in order to apply the insulating material. The foam can be injected directly into hollow spaces in the walls, where it self-inflates to fill the empty space: All one needs to do is set off the chemical reaction that leads to the creation of the foam, and it does the rest on its own. The biofoam will even be useful after it is no longer needed as an insulating material: It will be con- verted into biofuel – a further goal of the project. Last but not least, it is also environmentally friendly since it replaces synthetic foams pro- duced with the limited resource petroleum. The idea of producing insulating foams from bark is not new. It is based on research on or- ganic tanning agents, the tannins. The distin- guishing feature of tannins is that they bond with proteins upon contact and change their proper- ties, dehydrating them and making them resis- tant to decomposition by microorganisms and heat. This explains the properties of the insulat- ing foams they can be used to produce. However, there are many different kinds of tannins. The The micro-tomographic image (left) shows the inner structure of the foam being developed by the teams of Marie-Pierre Laborie, Prof Dr. Antonio Pizzi, and Prof. Dr. Alain Celzard, Université de Lorraine, France, as well as Milan Šernek, University of Ljubljana, Slovenia (right). Since the microstructure can be manipulated, the researchers can influence properties of the foam like thermal insulation, sound absorption, and stability. Image: b-cube AG, Switzerland; Photo: Kunz “We go to the companies that process wood and see whether we can produce something worthwhile from the waste” 0.000 [mm] 1.700 1.0 mm 30