The lignin was obtained from residual beech wood and wheat straw using two environmentally friendly digestion processes.
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Researchers at the Technical University of Hamburg-Harburg (TU HH) have successfully produced aerogels consisting primarily of lignin, and processed these into insulation boards, among other things. Aerogels are robust, highly porous materials with low density and thermal conductivity. Currently, the production of aerogels consisting purely of lignin is impossible. A team led by Professor Irina Smirnova at TU HH, however, is said to have come one step closer to achieving this goal. The scientists used lignin, which they obtained from residual beech wood and wheat straw with the help of the environmentally friendly organosolv and aquasolv digestion processes. Using five different gelling strategies, they then converted the lignins into aerogels.
The most successful of these attempts yielded hybrid lignin-polyurethane aerogels with an adjustable density ranging from 50 to 250 kg/m3. Their mass-related lignin content was measured at 78 percent; the process has been rescaled for use in pilot plants. Insulation boards of this aerogel type achieve a thermal conductivity of 24 mW/m-K, significantly exceeding the insulating properties of polystyrene or rock wool. In addition to this type, lignin-based resorcinol-formaldehyde aerogels with surfaces of 500 m2/g and a very broad spectrum of modifiable properties, could also be promising. These can have a lignin content of up to 70 percent. In the future, two spin-off companies of the TU HH will dedicate themselves to lignin-based aerogels: BioMP, which collects expertise in the field of hot water hydrolysis and production of lignin for sampling and further processing, and Aerogelex, which produces various types of organic aerogels and offers lignin-polyurethane aerogel plates for industrial tests.
The "Material Use of Lignin: Nanoporous Materials" project was sponsored by the German Federal Ministry of Food and Agriculture (BMEL) through its lead partner, the Agency for Renewable Resources (FNR, Fachagentur Nachwachsende Rohstoffe e. V.). Alongside the TU HH, several other institutions such as the Fraunhofer Center for Chemical-Biotechnological Processes (CBP), the University of Natural Resources and Life Sciences Vienna, the Bavarian Center for Applied Energy Research (ZAE Bavaria), and the companies Dräger Safety and Loick Biowertstoffe were also involved in the project.