Wood foam - a new lightweight material (lecture only accessible in German)
Dr Steffen Sydow - Fraunhofer-Institut für Holzforschung

A process has been developed at the Fraunhofer WKI to produce foams from wood particles. First, wood is ground into fine particles at a high water content (disintegration) until a wood fiber suspension is formed. This suspension is then foamed chemically or physically with the aid of internal or external gas generators, such as CO2. In a subsequent step, the mass is cured at temperatures of approx. 70 °C. The strength of the foam is due to the wood fiber suspension. The strength of the foam is due to the wood's own bonding forces, which means that synthetic adhesives can be dispensed with. There is therefore no potential health risk from emissions from adhesives. The result of this development is a lightweight material with a porous, open-cell structure and a low bulk density. For example, foams can be produced specifically in a density range between 60 kg/m³ and max. 200 kg/m³. The wood foams developed can be processed like other wood-based materials.

One area of application for wood foams is in the field of insulating materials. Although wood-based insulating materials already exist, they have the disadvantage of being less dimensionally stable than insulating materials made of plastics. The foam products developed have already been tested according to applicable insulation standards. Promising results have been obtained for both the thermal-insulating and the physical-technological properties. Compressive strengths at 10% compression range from 20 kPa to 600 kPa, depending on the density.

The thermal conductivities are also density-dependent and are below 0.04 W/mk at low densities and are thus comparable to the values of polystyrene and wood fiber insulation boards. Thickness swelling after 24 hours of water storage is < 2 percent, and the foams remain dimensionally stable. Fire behavior is similar to that of natural fiber insulation materials. They burn and smolder, and the flame partially extinguishes by itself. Any additives required for flame retardancy can be easily and efficiently mixed with the fibrous materials in the manufacturing process. Due to its open-pored structure, wood foam exhibits high sound absorption. Furthermore, it should be possible to recycle the wood foam without any problems. Further areas of application can therefore be sandwich core elements, also in combination with textile concrete or metal and decorative cover layers, or packaging materials.