Wood-based materials such as particle board, OSB, plywood or fiber materials (MDF, HDF) are climate-friendly, resource-saving and can be used in a variety of applications. Until now, they have been used primarily as a sustainable building material for structural timber engineering, the interior finishing of buildings, vans and mobile homes, and for furniture construction. In further developed form, they could play a major role in further areas of application in the future - for example in the production of functional and decorative components in vehicle interiors, or structural components in exterior applications (e.g. car bodies).
For the production of wood-based materials, different wood layers or particles are bonded together. So-called condensation resins are frequently utilized as adhesives. These include phenol-formaldehyde resins (PF resins).
Phenol is toxic and is suspected of having a mutagenic effect. In addition, it is primarily extracted from petroleum. Lignin, a possible substitute, is a major component of wood and poses no health risk. Lignin is produced in large quantities during the manufacture of pulp (incl. paper production) and has until now been used mainly for energetic purposes, i.e. incinerated. Furthermore, residues from the forestry and agricultural industries (e.g. sawdust, wheat straw) could be used for the extraction of lignin.
Formaldehyde is classified as carcinogenic under EU law. For this reason, products made from wood-based materials for indoor use are subject to strict regulations with regard to their formaldehyde emissions. The official guideline value is 0.1 mg/m3. The majority of formaldehyde emissions from wood-based materials result from the adhesives used. Hydroxymethylfurfural (HMF) is a promising, more health-friendly alternative to formaldehyde. As it is produced from sugar polymers such as starch or cellulose, it can be extracted from residual materials which contain sugar. In a previous project, we collaborated with the University of Hohenheim on the development of a process that enables HMF to be produced from old bakery products such as bread, rolls or cakes.
The lignin-HMF resins could also replace other petrochemical and formaldehyde condensation resins used for the production of wood-based materials - in particular, urea-formaldehyde resins (UF resins) and melamine-urea-formaldehyde resins (MUF resins).
As a result of the health-endangering effects of formaldehyde, wood-based materials manufactured using PMDI binders (polymeric diphenylmethane diisocyanate) are increasingly being launched on the market. They belong to the group of PU adhesives. Although these are formaldehyde-free, they are nevertheless also made from petroleum, and the isocyanates thereby utilized are harmful to health. In addition, wood-based material production using PMDI binders is generally more cost-intensive than with condensation resins. The lignin-HMF resins developed in the project are therefore also a promising alternative to PMDI binders.