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Effective sunscreen for wood

After several years of testing, the results are finally in. And they are positive. By formulating nanoparticles and an organic UV absorbent in clear coat, it has been possible to produce a surface protection that can prolong the durability of wood for several years.

These results open up a number of opportunities for utilising the aesthetic benefits of natural wood in applications from facades and furniture to detailing and timber floors that are exposed to sunlight, whether indoors or out.

The surface protection has been developed and field tested as part of the Woodlife project. Commencing in 2010 and coordinated by RISE, this three-year project was part of the EU Seventh Framework Programme, the purpose of which was to improve the durability of wood materials.

Although wood is an excellent renewable building material, it is susceptible to degradation when exposed to direct sunlight. Among other things, the project has focused on developing water-based clear coating systems with improved UV protection properties. The goal of this improved surface protection was to make the wood more durable and thereby reduce the need for and cost of maintenance.

"Lignin is the component in wood that makes it so sensitive to sunlight. When wood is exposed to solar UV rays, lignin is released from the surface and the wood is weathered grey. This deterioration occurs rapidly. So, in order to obtain a long-lasting surface treatment, the release of lignin must be prevented,” explains Anders Larsson, senior researcher at RISE.

After a number of years of testing, it appears that the combination of nanoparticles and organic UV absorbent in clear coat is the key.

“All organic matter is broken down by sunlight, even UV absorbents. Clear coat containing UV absorbents offers good protection; however, when nanoparticles where added to the formula, the results revealed a significant increase in durability,” says Anders Larsson.

Must meet requirements

The particles in the formula in question have been developed by the British company Energenics, a partner in the project. The challenge with the formula has been to adapt the nanoparticles to work in a water-based clear coat and to ensure that they are disseminated in the coating. If they clump together or otherwise react with the clear coat and UV absorbent, the coating will become matt and may even become difficult to apply.

"The formula also needs to be stable, both in the tin and once applied to the wood,” says Anders Larsson.

The method can of course be used for coating systems other than the one tested in the Woodlife project; however, Anders Larsson emphasises that this is no panacea or quick-fix solution. The formula must be adapted to the raw materials in each system, meaning that each individual product must be tested to ensure that the formula remains stable.

Maximum sunlight

In addition to working on the formula, RISE has also developed and prepared samples for laboratory and field tests, which were conducted in accordance with EU standard EN 927-3:2012. Paints and varnishes. Coating materials and coating systems for exterior wood. Natural weathering test. According to the standard, testing must continue for one year. For research purposes and in order to ensure the accuracy of test results, the Woodlife project chose a longer test period.

“We have applied the surface treatment to a flat wood panel of pine with a  planed specified in the standard. Test samples were installed at a 45° angle facing south, in order to expose them to the maximum amount of sunlight, a test method that ensures an accelerated aging process,” explains RISE senior researcher Stig Bardage.

Considerably greater durability

This accelerated aging means that the process of degradation is significantly longer in practice. Given the extended test period, one can draw the conclusion that the surface coating has considerable greater durability. Samples were tested in parallel in Sweden and the UK in order to compare results.

"The results where equally long lasting in both countries,” says Stig Bardage.

The applications for this type of UV-protective surface treatment are not limited to wood. Both Anders Larsson and Stig Bardage see potential uses in other organic polymer materials. Various types of plastic surfaces, as well as textiles for awnings and tarpaulins, are only some examples of other areas of application.

Considerable customer benefits

The long-term effect of the project was that one of the participating companies, Energenics, was able to develop a product portfolio of UV absorbents.

"The Woodlife project provided Energenics with the opportunity to develop a unique series of UV absorbents, something that would not have happened without this project,” says Mike Attfield, CEO of Energenics Europe Limited.

Published: 2019-02-26