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Bio-based resin for stable timber construction materials.

To reduce its dependency on fossil raw materials, Covestro is looking to manufacture a growing number of products and their associated precursors from renewable raw materials. Working with four partners,1 the company is aiming to develop bio-based reinforcing layers for solid wood construction materials to replace the petrochemical products used to date. 

The polyurethane system, which is reinforced with cellulose fibers, is to be more than 90 percent bio-based, contain zero additives and exhibit excellent flame retardance and weathering resistance. The project is being supported by the German Federal Ministry of Food and Agriculture (BMEL) through the project sponsor, Fachagentur Nachwachsende Rohstoffe e.V. (Agency for Renewable Resources, FNR). 

State-of-the-art solid timber construction techniques are increasingly coming to dominate our urban spaces. The main materials used to manufacture construction elements are cross-laminated timber and glued-laminated timber. Both materials consist of alternate layers of wood and thinly spread polyurethane resin. If aramid, glass or carbon fibers are embedded into the layers of resin, they create reinforcing segments that further enhance the stability of the construction elements.

Bio-based alternatives
Over the course of the recently launched project, the researchers want to find bio-based alternatives to the fossil-based resins and fibers that have been used to date. They are pursuing a combination of biogenous, aliphatic polyisocyanates and polyols based on vegetable oils. The resultant polyurethanes should exhibit low flammability and good weathering resistance, so that no special additives are needed to enhance either property. 

When it comes to reinforcement, the scientists favor cellulose fibers such as those extracted from regenerated cellulose. "At the end of this process, we will have the first ever reinforcing materials for use in timber construction that are made up of at least 90 percent renewable raw materials," says Dr. Paul Heinz from Covestro, who is coordinating the research project. This, he claims, will make state-of-the-art timber construction with cross-laminated and glued-laminated timber even more sustainable. 

Continuous production by pultrusion
When it comes to manufacturing the construction elements, the project partners have opted for pultrusion, a continuous industrial production process for highly filled, continuous fiber-reinforced composite profiles. Pilot facilities run by the Fraunhofer Institute are being used to manufacture flat profiles for testing and optimizing the necessary tools and process parameters. 

During the project, Sortimo will produce an industry-standard model component that will then be used to evaluate the technical, economic and ecological potential of the new material and production process for the construction industry. Beech wood is being used for the component, as this material is becoming available in growing volumes due to forest restructuring.