Natural sun protection for parquet and furniture

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 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.

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Which composition is best suited?

During the approximately two-year project period, the scientists tested many combinations and also worked very successfully with mixtures of different secondary plant substances: “In the end, we had many hits in terms of possible protein-additive combinations for the UV protective coating and were able to address the question of which formulation makes sense when thinking in terms of production – also in terms of the regionality and availability of the raw materials used,” summarises Melanie Platzer. “Where possible, we include leftovers from the agricultural and food industry in our development work, such as peelings from apple juice production or pomace from wine production.” All of the options found are harmless: direct contact or inhalation does not harm humans or animals.

Further development not only for wood preservation

The selected model formula is now undergoing further development at Naturhaus Naturfarben GmbH. The aim is to adapt the composition so that it can be produced on a larger scale in order to ultimately open up 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. A follow-up project has already been initiated at the Fraunhofer IVV to further develop the many research results from ProTann and realise their potential: Further possible applications for the UV-repellent protein-plant substance combinations could be in packaging coatings or skin protection, for example.