Flexible wood-fiber mats are ideally suited for thermal insulation in buildings, for example as between-rafter insulation or as a filler for thermal-insulation bricks. Wood-fiber insulation materials are currently produced primarily from softwood. However, as a result of climate change, the resulting forest damage, and the associated forest restructuring, the supply of raw materials is constantly changing. Softwood is not always available. Beechwood, in contrast, is available in large quantities. The researchers therefore set out to determine whether wood-fiber insulation materials could also be produced from beechwood fibers.

“In order to ensure a reliable supply of raw resources for wood-fiber insulation materials in the construction industry, we have developed, in collaboration with Loick Biowertstoffe GmbH, insulation mats and innovative wood-foam granules made from beechwood fibers. In cooperation with Ziegelwerk Bellenberg Wiest GmbH & Co. KG., we have tested the filling of vertically perforated bricks. Pilot-scale implementation was carried out at a rented facility at the University of Göttingen. In collaboration with Japes GmbH, a final concept for the construction of a pilot plant has been developed. With our project, we have created a sustainable solution for the construction industry as well as a high-value application possibility for beechwood,” reported Dr. Nina Ritter, Group Leader at the Fraunhofer WKI.

The researchers conducted investigations into which processes could be used to break down the beechwood into fibrous materials for the production of insulation mats and wood foam or wood-foam granulate. Among other things, low-value damaged wood was used for this purpose. The team developed insulation mats with bulk densities of 50-100 kg/m³ from beechwood fibers in combination with bicomponent fibers. Various fiber-production processes were thereby tested. Due to the flexible adjustability of the fiber geometry, the refiner proved to be the technically preferable process. With the aid of an optimized spiking roller, it was possible to considerably reduce the addition of bicomponent fibers and to significantly improve the blending of wood and plastic fibers. An additional aspect of the research work was the further development of fiber laying. The fibers are dispersed by aligning them as a flow. This allows the thermal conductivity to be controlled and a good insulating effect to be achieved. The researchers discovered that the thermal performance capabilities of the mats are competitive compared to established insulation materials.

In addition to this, the scientists also evaluated fire retardants. It was found that the addition of ammonium sulphate is a suitable standard. Investigations into mechanical, hygric and fire-protection properties confirm the fundamental suitability of beechwood insulation materials for application in filled vertically perforated bricks and on the construction site.

As a specific application example within this project, the scientists tested the filling of vertically perforated bricks in cooperation with brick manufacturer Ziegelwerk Bellenberg Wiest GmbH & Co. KG. The researchers found that a homogeneous stiffness and uniform thickness of the mats is the key factor for a stable, industrially feasible filling process. Hole-pattern-dependent bricks were filled with mats, while hole-pattern-independent bricks were filled with wood-foam granules and wood-fiber suspensions. Practical testing was then performed.

One particular focus of the project was on recycling. The project partners were able to prove that the filled bricks can be mechanically broken down following deconstruction. The filler materials can be separated from the brick material by wet or airstream sorting systems. The recovered insulation mats can be pressed into dense wood-based panels (> 1,000 kg/m³) at higher temperatures. As a result, a second utilization cycle and a recycling-compatible overall system are created that can, in principle, be integrated into established construction-material recycling streams.

Through the utilization of beechwood for the production of wood-fiber insulation materials, an economically attractive solution is being made available for the quantities of beechwood that will accrue in the future. This is an important step towards securing and broadening the raw-material base in view of climate-change-related forest restructuring. In order to exploit the resource “beechwood” even more efficiently, it would also be conceivable to utilize the new wood-foam granulate as a filler for transport packaging.