Open-plan architecture with glass façades 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 discoloration and damage due to photo-oxidation.

Researchers at the Fraunhofer Institute for Process Engineering and Packaging found that the transparent protective coatings currently available on the market contain chemical additives, such as benzo-phenones, benzo-triazoles, or phenyl-triazine derivatives as UV blockers, which are harmful to health.

It is particularly critical as 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 aging caused by sunlight are coloured and therefore impermeable to light.

Against this background, the idea of developing a solution to this problem arose in the collaboration between Fraunhofer 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 began work on the “ProTann” project in 2021.

Plant proteins

The scientists tapped into a completely new area of research– they had been using proteins very successfully for a long time for natural bonding in coating systems. What was new for them 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.

The development process for the coating was organized in several stages. First, the researchers tested their initial formulation idea, which was based on a preliminary project at the Fraunhofer, with several proteins, for example, from peas or soya.

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 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 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.

During the approximately two-year project period, the scientists tested many combinations and worked very successfully with mixtures of different secondary plant substances.

All the options found are harmless: direct contact or inhalation does not harm humans or animals. The selected model formula is now undergoing further development at Naturhaus Naturfarben.

The aim is to adapt the composition so that it can be produced on a larger scale to ultimately open a new market in the field of natural wood preservatives. In application, the water-based formula could then be applied in several layers and sealed with another natural varnish to provide long-lasting protection for parquet and furniture.

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