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.