Jul 6 2012
Homeowners who don't want to insulate their walls with environmentally harmful foams will soon have an ecological alternative: hard foams made of tannin, a compound found in tree bark.
They are being developed by a team led by Prof. Dr. Marie-Pierre Laborie at the Freiburg Materials Research Center and the Institute of Forest Utilization and Work Science of the University of Freiburg. Tannin is extracted from tree bark, which is typically left over as a waste product in the lumber industry. "This allows us to recycle the bark and thus enhance the value of wood," says Ricarda Böhm, a doctoral candidate in Laborie's research group.
Foams made of tannin have been around for some time, but until now the tannin was procured from the wood of the mimosa and other tropical plants. Böhm and her team are experimenting with producing the same foams out of European woods like spruce and pine. These woods have a very different chemical structure than tropical woods and are among the most important suppliers of raw material for the European lumber industry. Böhm's colleague Danny Garcia-Marrero is working on synthesizing the foams, Böhm herself on characterizing them. The foam they produce in the lab is created in a chemical reaction and is self-inflating. The ingredients include tannin, furfuryl alcohol, formaldehyde, and a solvent, such as diethyl ether. Formaldehyde serves as a cross-linking agent, as a kind of glue between the tannin and the alcohol. "We are still looking for a less environmentally harmful, natural cross-linking agent to replace formaldehyde in the future," says Böhm. The scientists are trying to use exclusively natural raw materials, ideally waste products that don't need to be produced expressly for research purposes.. One interesting candidate is aldehyde furfural, which can be produced from sawdust. Böhm and her colleagues are also using natural additives that prevent the foam from crumbling too much. The foams can also be modified with nanocellulose to improve their mechanical stability.
Since the foams have good insulating and flame resistant properties, they will be used predominantly as insulating material for buildings and molded automobile parts. Foams made of tannin can seal almost as well as polyurethane foams but do not contain any poisonous isocyanates. "The goal is to establish our environmentally friendly foams on the market as an alternative to conventional foams," says Böhm. When they are no longer usable, they are converted into synthesis gas. The biomass released in the process can be used, for instance, to power a water turbine. The team also hopes that the foams will one day be used as catalysts or filters for heavy metals and as a replacement for packaging materials like styrofoam.
The European Union-funded project "Biofoambark" is coordinated by Marie-Pierre Laborie, who also initiated the project in February 2012. Besides the University of Freiburg, the institutions collaborating on the project include the Fraunhofer Institute for Solar Energy Systems and scientific partners and companies in Italy, Spain, Finland, Slovenia, and France.