Wood is a good lightweight-construction material. By nature, it has a low bulk density and high stability. The tensile strength in the direction of the fibers (in relation to the bulk density) is greater than that of steel. Compared to modern lightweight-construction materials such as fiber-reinforced PU foams or plastics (CFRP/GFRP), wood-based materials are, however, often still relatively heavy when the mechanical requirements are fulfilled. Or they are light and possess good heat-insulating properties, but are mechanically less resilient.
Project goal: Materials, components and manufacturing process
This is where the project idea comes into play: Bio-based polymer fibers (“bioplastics”) or particle foams are to be combined with wood (plus agricultural residues such as straw, husks, etc., or paludi biomass) and processed to form extremely lightweight, stable components by means of an automated molding machine.
Two approaches are thereby being pursued:
- The development of hybrid materials from particulate raw materials such as wood fibers or chips and polymer fibers or foam beads
- The development of reinforced hybrid materials: Particle foam or particle/particle hybrids with inserted reinforcing component (e.g. veneers, square timber, wood-based material) and/or with cover layers (e.g. molded veneer, fabric, films)
Until now, automated molding machines have been used exclusively for particle-foam processing. More precisely, pre-expanded thermoplastic polymer beads are bonded to the finished molded part within a very short time (a few seconds) using a short burst of hot steam or by means of energy from electro-magnetic waves (HF technology). Within the framework of the project, this technology will be used in order to develop a new processing technology (bonding and pressing) for novel bio-hybrid materials.
The polymer particles thereby act as an adhesive. Bioplastics with low melting points (< 130 °C) are particularly well suited for the project. In the molding machine, an astonishingly good adhesion between the surface-melted polymer and the wood or agricultural residue is created through the application of a very short, hot burst of steam, or energy in the form of electro-magnetic waves. The focus in this project is directed in particular at commercially available, bio-based polylactides (PLA) and polyamides (PA).
Planned technology demonstrators fpr the following application areas:
- Thermal insulation of buildings: molding machine and insulation element in commercial format
- Furniture construction: molding machine and furniture element
Recycling
Recycling possibilities and recycling potentials should be incorporated into the development from the outset (design for recycling). The recycling of PLA, for example, is not yet economical and is still in its infancy. Possible recycling concepts and advantages are therefore to be investigated.
Tasks of the Fraunhofer WKI
The primary tasks of the Fraunhofer WKI in the project (in addition to the coordination of the joint project) are:
- Production and supply of wood particles
- Investigation of various lignocellulosic materials and bioplastics with regard to bonding ability/adhesion to one another
- Handling and mixing of wood fibers and other lignocellulose-based particles with polymer fibers
- Production of reinforcing components for the manufacture of hybrid molded parts for furniture construction
- Characterization of hybrid materials for the application areas of thermal insulation and furniture construction
- Investigation of recyclability:
- Production of wood-based materials such as particle board or MDF using the shredded hybrid material
- Tests on the separability of the components
Fraunhofer Institute for Wood Research 
