Wood products have to endure ultra violet (UV) light, temperature changes, precipitation, air pollution, mechanical and chemical challenges. In addition, coatings, which are often used to protect and enhance the look of wood, have to be resistant enough to protect the wood for several years. Their performance is therefore critical for wood to compete with alternative building materials that claim to have low maintenance requirements.
Over the years, FPInnovations has investigated a number of issues related to interior and exterior wood finishing.
One of the goals of research into exterior finishes has been to enhance the performance of transparent and semi-transparent coatings. Initial studies on these coatings recorded the effect of adding ultraviolet absorbers (UVA) and hindered amine light stabilizers (HALS) in the formulation. One study showed that early failure of semi-transparent wood coatings was due to the colonization of the wood-coating interface by black stain fungi before the UV protection offered by the coatings had failed.
Research results identified biocide combinations most effective against black stain, and demonstrated that black stain can be controlled by applying thicker coating layers, and by using efficient UV-visible protective pre-coats. It was also demonstrated that new preservative systems are compatible with several existing commercial coatings, and that nano-size UV absorbers, when they were well dispersed, could limit discoloration.
Water-based fluoro-acrylic coatings for wood products containing 70% polyvinylidene fluoride (PVDF) were developed and applied to different wood species. The photo degradation resistance of these products was tested and results have shown that the presence of a fluoropolymer, such as PVDF, significantly slows down the resin’s degradation. As a result, colour retention was found to be better for the semi-transparent as well as the opaque coatings tested.
IR-reflective coatings for wood products were also prepared and tested. These coatings are currently used in warm regions such as California and Greece where raising coating reflectivity from the current 10-20% to about 60% can reduce cooling-energy use in buildings by 20%. Cool coatings also result in a lower ambient temperature that further decreases the need for air conditioning and reduces smog formation. These products could also help prevent resin exudation and crack formation caused by heat accumulation or temperature differentials.
Investigation into interior finishes were particularly dedicated to the development of nano-composite coatings that showed greater surface performance, the improvement of wood surface preparation when using water-based coatings, and more recently the development of smart coatings (self-healing, self-cleaning and easy-to-clean finishes) for the kitchen and furniture industries. These studies addressed the challenges facing finished wood products manufacturers such as furniture, flooring, millwork, kitchen cabinets and others, and opened up new market possibilities for wood products manufacturers.
Research was also performed on water-based wood coatings. Grain raising was studied and was found to be strongly relate to the quality of the surface preparation and the wood species selected. The performance of wood coatings was also assessed and compared with solvent-based coatings. It was found that the quality of water-based coatings varies significantly from one company to another, but in general, water-based coatings were found to yellow less than solvent-based coatings.
Self-healing solvent-based polyurethane coatings were also prepared and tested. These coatings can be repaired by applying heat (ex. hair dryer for 10 minutes) to their surface for a short period of time. Once heat was applied, the depth and width of the scratches was found to decrease significantly while the gloss came close to the initial gloss (before scratching).
To improve anti-dirt and anti-stain performance, wood coatings with siloxane and fluoro-surfactant additives were developed. High solid UV coatings prepared with ZnO nanoparticles and a water-based wood coating formulated with TiO2 nanoparticles have also shown easy-to-clean properties. For wood surfaces that do not lie flat during use, the addition of nano particles with a photo-catalytic effect can impart self-cleaning qualities that can increase the range of wood products.
For more information on this article, or further details on the various studies, contact Paul Morris (paul.morris@fpinnovations.ca), or Véronic Landry (veronic.landry@fpinnovations.ca).
FPInnovations is a world leader that specializes in the creation of scientific solutions in support of the Canadian forest sector’s global competitiveness. For more information about FPInnovations, visit: www.fpinnovations.ca • ® FPInnovations, its marks and logos are registered trademarks of FPInnovations.
References
• Blanchard, V., Stirling, R. 2013. Plasma pre-treatment enhances field performance of exterior wood coatings. Wood Fiber Sci. 45(2): 228-231.
• Landry, V., Blanchet, P., Zotig, L., Martel, T. 2012. Performance of Exterior Semitransparent PVDF-Acrylic Coatings, J. Coat. Technol. Res. 1-10.
• Landry, V., Blanchet, P. 2012 Weathering resistance of opaque PVDF-acrylic coatings applied on wood substrates, Progr. Org. Coat., 75(4): 494-507
• Morris, P.I., McFarling, S. 2006. Enhancing the performance of transparent coatings by UV protective pre-treatments. International Research Group on Wood Protection. Document No. IRG/WP/06-30399. 10p. IRGWP, Stockholm, Sweden.
• Morris, P.I., Wang, J., Ingram, J.I. 2008. Ability of transparent coatings to retard leaching of borates in a Weather-Ometer test. JCT Coatings Tech. 5(3): 44-47.
• Sharpe, P.R., Dickinson, D.J. 1993. Blue stain in service on wood surfaces. Part 3. The nutritional capability of Aureobasidium pullulans compared to other fungi commonly isolated from wood surface coatings. IRG/WP/93-10035. International Research Group on Wood Preservation, Stockholm. 10 pp.
• Stirling, R. 2011. Compatibility of coatings and carbon-based wood preservatives. American Wood Protection Association Annual Meeting. 107: 46-51.
• Stirling, R. Morse, B., Morris, P.I., 2006. The effect of various coatings on western redcedar extractive retention. Proceedings Canadian Wood Preservation Association. 27: 10p.
• Stirling, R., Morris, P.I. 2013. Performance of Coatings on Wood Treated with Carbon-Based Preservatives. International Research Group on Wood Protection. IRGWP, Stockholm, Sweden. In press. 11p.
• Stirling, R., Uzunovic, A., Morris, P.I. 2011. Control of black stain fungi with biocides in semi-transparent wood coatings. Forest Prod. J. 61(5): 359-364.
• Vlad Cristea, M., Riedl, B., Blanchet, P. 2010. Enhancing the performance of exterior waterborne coatings for wood by inorganic nanosized UV absorbers. Progr. in Org. Coatings. 69: 432-441.
• Vlad Cristea, M., Riedl, B., Blanchet P. 2012. Nanocharacterization techniques for investigating the durability of wood coatings. Eur. Polym. J. 48(3): 441-453.
