Open-plan architecture with glass fa？ades and large window fronts that allow plenty of natural light into the house are very popular – just like the desire for ecological and natural living. However, when it comes to protecting wooden surfaces indoors, it has been difficult to combine both requirements: without a coating, UV light with a wavelength of 330 to 380 nanometres can interact with wooden surfaces and lead to discolouration and damage due to photo-oxidation. However, the transparent protective coatings currently available on the market contain chemical additives such as benzophenones, benzotriazoles or phenyltriazine derivatives as UV blockers, which are harmful to health. It is particularly critical that these volatile substances can enter the body directly via the respiratory system, for example during the drying process. To date, all bio-based alternatives for protecting wood from ageing caused by sunlight are coloured and therefore impermeable to light.

Proteins for binding, plant extracts for UV protection

Against this background, the idea of developing a solution to this problem arose in the collaboration between the Fraunhofer IVV and Naturhaus Naturfarben GmbH. With the task of finding suitable plant-based components for a natural wood coating that protects the material from UV radiation while leaving its structure visible, the Fraunhofer IVV began work on the “ProTann” project in 2021. The scientists tapped into a completely new area of research: “We at the Fraunhofer IVV have been using proteins very successfully for a long time for natural bonding in coating systems,” explains Melanie Platzer, research associate in the Process Development of Plant Raw Materials department. “What was new for us was the combination with secondary plant substances, which were to serve as UV protection for a water-based coating.” One of the project objectives was therefore to work out the resulting cross-linking between proteins and secondary plant substances in the coating and ultimately to ensure that the two substances bonded firmly together.

Challenging development process

The development process for the coating was organised in several stages. First, the researchers tested their initial formulation idea, which was based on a preliminary project at the Fraunhofer IVV, with several proteins, for example from peas or soya. Melanie Platzer: “The decisive factor for us in this phase was: Does the resulting coating adhere to wood? Is it absorbed? And can it be removed so that the UV-blocking effect can be measured at all?” The project team then selected two proteins and added various secondary plant substances that offer good protection against UV radiation. One of the challenges here was the pH range, as wood varnishes must have a certain pH value in order to protect the material. The addition of the plant extracts themselves was also a crucial point for the research team, as it was almost impossible to predict in advance how well the different extracts would dissolve, whether they would interact with the proteins and how the colour of the resulting coating would change throughout the process.