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Natural weathering of wood in a sunny climate effects on surface chemistry and paint adhesion
1997 - IRG/WP 97-20109
Radiata pine veneers and blocks were exposed to natural weathering under Australian summer conditions over a period of 30 days. Infrared spectroscopy revealed that there was perceptible surface delignification after 4 hours exposure, substantial surface delignification after 3 days exposure and almost complete surface delignification after 6 days. Viscometry determinations on holocellulose samples from weathered veneers and unweathered controls indicated significant depolymerisation of cellulose after short periods of weathering. A tape test was used to assess the adhesion of acrylic latex primers to weathered blocks. The adhesion of exterior acrylic primers decreased on weathered wood surfaces and was significantly lower on specimens that were weathered for 5 to 10 days. An oil-modified acrylic primer showed greater adhesion to weathered wood surfaces. Primer adhesion was lower on weathered radial surfaces than on similarly exposed tangential surfaces. The practical implications of these findings for the coating of exterior wood with acrylic latex primers and the development of photoprotective treatments for wood are discussed briefly.
P D Evans, P D Thay, K J Schmalzl

Effect of CCA and Tanalith E on the performance of surface finishing
2008 - IRG/WP 08-40405
Effect of CCA and Tanalith E treatment on the performance of surface finishing properties was the objectives of this study. Sapwood of scots pine, (Pinus sylvestris L.) and oriental beech (Fagus orientalis Lipsk.) specimens (300 x 100 x 15 mm along the grain) were impregnated with aqueous solution of CCA 2% and Tanalith E 2%. Surface roughness, dry film thickness, adhesion strength, gloss measurement, scratch and abrasion resistance were determined according to related standards for treated and untreated samples. Results indicated that surface roughness and adhesion strength depend on wood species and the chemical composition of preservatives. Wood preservatives did not affect the scratch resistance because it depends on properties of the coating. Treatments with CCA and Tanalith E affected only the abrasion test for beech samples. The highest gloss value was determined on untreated (control) pine samples while there was no clear difference on gloss values between CCA and Tanalith E treatment.
T Ozdemir, A Temiz, I Aydin

Wet and dry adhesion of coatings on modified and unmodified wood: comparison of the pull-off test and the cross-cut test
2010 - IRG/WP 10-40524
The objective of this paper is to study the influence of several types of modification (acetylation, furfurylation, thermal modification) on coatings adhesion and to compare two methods of assessing the adhesion: the cross-cut test and the pull-off test both tested in dry and wet conditions. The study also investigates the effect of other parameters of the wood substrates on adhesion like the ring orientation, the density, the surface preparation and conventional preservatives treatments. It has been shown that the pull-off test is more sensitive than the cross-cut test and gives more information about the influence of the substrate. For both tests wet adhesion is lower than dry adhesion. Compared to the reference, there is no improvement in the dry adhesion due to the different modifications, treatments or variations of the substrates. For some coatings a decrease in dry adhesion is observed on furfurylated and thermally modified wood.
L Podgorski, G Grüll, M Truskaller, J D Lanvin, V Georges, S Bollmus

Wet and dry adhesion of coatings on modified and unmodified wood: influence of 18 months of natural weathering on the pull-off test and cross-cut test results
2011 - IRG/WP 11-40569
The objective of this paper is to study the influence of several types of modification (acetylation, furfurylation, heat treatment) on coatings adhesion after 18 months of natural weathering according to EN 927-3 in Vienna (Austria). The paper compares two methods for assessing the adhesion: the cross-cut test (EN ISO 2409) which is the conventional method used and recommended in EN 927-3 and the pull-off test specified in ISO 4624. The influence of the test condition (dry or wet) is also investigated. Results are part of the WoodExter project funded by the Woodwisdom-net and complete document IRG/WP 10-40524 which presented adhesion results before weathering.
L Podgorski, G Grüll, M Truskaller, J D Lanvin, S Bollmus

Copper Coating on Wood: a New Way of Protecting Wood
2013 - IRG/WP 13-30617
Thermal spray metal coating technology was used to apply a thin layer of copper on the surfaces of a number of wood species. The adhesion of metal coating to mahogany, oak, soft maple, spruce, white pine and medium density fibreboard (MDF) was evaluated by pull off adhesion test. The resistance of copper coated wood samples to mildew were assessed in the lab. Also, the decay resitance and water repellency of Cu-coated white pine wood samples were tested. The water immersion tests were designed to measure the performance of coating in reducing water–uptake from wood, and then to calculate the rate of water vapour transmission during drying time as a measure of coating permeability. The adhesion of copper coating to both hardwoods and softwoods were very good. The adhesion of Cu-coating to MDF was greater than the cohesion of MDF layers. The Cu-coated samples had significantly lower weight loss than uncoated wood after decay test. Also, there were no sign of mildew growth on the coated surfaces of wood samples exposed to mildew test. Overall, thermal spray metal coating on wood proved to be a very useful technique to protect the surface of wood from decay and mildew.
M Nejad, R Shafaghi, L Pershin, J Mostaghimi, P Cooper

Investigation of Dimensional Stability and Coating Performance of Different Heat-Treated Poplar Wood Before and After Accelerated Aging
2015 - IRG/WP 15-40702
In this investigation, coating performance of heat-treated poplar wood (Populus tremuloioes) in different environments, before and after accelerated aging was studied. Specimens with 150×100×20 mm and 20×20×20 mm in dimensions were prepared. Heat treatments were performed in air, steam and linseed oil media. Specimens were coated by alkyd based stain. Adhesion strength before and after aging, long term water absorption and volumetric swelling were studied and analyzed statistically. The results showed that heat treatment increases the adhesion strength (especially in air and steam). By increasing the temperature, all specimens showed increases in adhesion strength, except adhesion strength before aging in oil-heat treated specimens. OHT increased adhesion strength of coating after accelerated aging. Heat treatment reduced the rate of water absorption and thereby improved the dimensional stability of the samples.
A Talaei, D Ansari Movahed, G Rassam

Bacterial adhesion to selected wood finishes
2017 - IRG/WP 17-40793
A new generation of furniture, including antibacterial surfaces, should adjust to the changing needs of an ageing population. Respectively, determination of bacterial adhesion on wooden surfaces, finished with various wood finishes or coating is an important topic. The main aims of our work were of a preliminary character. We wanted to state if the existing methods for testing of bacterial adhesion on different surfaces could be implemented on wooden surfaces coated with some common surface finishes. It was shown that wood coatings and finishes on wood could be tested for adhesion of bacteria, when the established procedures are adapted for wood as a specific substrate material. It seems that Pseudomonas aeruginosa adhesion level was different on selected finishes. Our preliminary results showed that the lowest one was on the hydrophobic and olephobic silane formulation treated laminated beech wood and the highest one on linseed oil. This tentative indication should be confirmed with extensive experiments in future.
M Petrič, D Kekec, J Žigon, K Godič Torkar, K Bohinc

Adhesion durability of the thinnest CLT in Japan treated by solvent recovery system
2019 - IRG/WP 19-40882
The purpose of this study is to clarify the adhesion durability of the thinnest CLT (36 mm thickness) in Japan impregnated with preservatives (azole neonicotinoid compounds (AZN)) under solvent recovery system so called “dry pressure process” for long-term durability. The adhesion durability tests were conducted in accordance with the Japanese Agricultural Standard (JAS) of Cross-Laminated-Timber (2013), and the peeling tests and the block shear tests were performed. As a result, the AZN treated CLT retained sufficient adhesion durability.
K Kawakami, W Ohmura

Silicate coatings for wood substrates
2020 - IRG/WP 20-40906
Silicate coatings are surface finishing products containing alkali metal silicates or ethyl silicates as main binders. They are traditionally designed and well established for mineral substrates or corrosion protection of steel. The interest for these coatings in wood field is growing because of the benefits they could provide such as high durability, weathering resistance and fireproofing and sustainability. Contrary to conventional substrates (concrete, stones, steel), wood is organic, a highly dimensionally instable material. So, a durable coating for wood must meet a compromise between adhesion, liquid water and water vapour permeability and its flexibility. This is essential to accommodate surface strains developed, when wood swells and shrinks, to avoid cracking and debonding. Appropriate formulation combining painstakingly inorganic and organic components with eventually surface pre-treatments could overcome the adhesion and flexibility drawbacks related to wood finishing and weathering. Few silicate-based products for wood are already in the markets, but scientific literature in the field remains not significant and inaccurate. This poster paper presents an ongoing research project financially supported by The Slovenian National Research Agency (ARSS) under the frame of EU Marie Curie “Seal of excellence” and the University of Ljubljana. The project will provide outstanding basic-knowledge correlating formulations-coating properties–weathering and potential improvements for development of new products and application processes.
A M Cheumani Yona, M Pavlič, M Petrič

Comparative study of the properties of silicate coatings with different mineral pigments (titanium dioxide, iron (III) oxide, copper (II) oxide) on the surface of wood
2022 - IRG/WP 22-40936
Silicate coatings are attractive alternatives to conventional organic-based coatings for wood protection. In this work, silicate coatings were prepared with a potassium silicate binder modified with a methyl siliconate solution, and three types of mineral pigments titanium dioxide, iron (III) oxide and copper (II) oxide. The coatings were applied on beech wood and cured under ambient conditions. The colour, surface roughness, adhesion strength, and resistance to cold liquids of the cured coatings were determined and reactions to fire of the coatings were compared using single flame source tests. The surface of wood was well masked by the coatings and the colour of the coatings was a function of the pigments. The coating layers were rough with arithmetic average roughness values Sa between 3 μm and 5 μm and maximum peak-to-valley height between 45 μm and 48 μm. The adhesion of the coatings was comparable, and sufficiently high (> 3 MPa) for application of the coatings to the surface of wood without a primer. The coatings were not considerably affected by the cold liquids. The single flame source tests showed that coatings containing titanium dioxide and copper (II) oxide reduced the charred area of the wood underneath, while coating with iron (III) oxide increased the charred area compared to the uncoated reference. A pigment such as iron (III) oxide which promotes the formation of char could produce an early layer of char at the surface of wood decreasing the spread of the fire within the wood. Further studies are planned to completely describe the fire behaviour of the coatings and extend the work to other pigments.
A M Cheumani Yona, M Petrič

Premature adhesion failure of exterior wood coatings – The influence of substrate temperature at coating application and moisture accumulation during storage
2022 - IRG/WP 22-40937
The present study aimed at extending the knowledge about premature coating failures of industrially finished wood cladding. Two potential factors were studied: the influence of substrate temperature at coating application and moisture accumulation during storage on the adhesion of waterborne coating systems. In the first experiment, 4 batches of wood specimens were submitted to 4 different temperatures (-25°C, 0°C, 10°C, 20°C) before coating. In the second experiment, coated wood specimens were divided into two batches. One batch was conditioned to 12% moisture content, the other one to 27%. Both batches were then exposed to IR- and UV-radaition in a chamber, simulating intense solar radiation causing intense warming of the cladding boards after being installed on a façade. None of the two studied factors were found to affect coating adhesion. The results suggest that the risk of adhesion defects due to sub-zero substrate temperatures and moisture accumulation during storage is low and that other parameters, especially drying conditions, are of significantly greater importance in quality control of industrially finished cladding.
U Hundhausen