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- Kymäläinen, Maija, et al.
(författare)
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Artificial Weathering of Contact-Charred Wood : The Effect of Modification Duration, Wood Species and Material Density
- 2022
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 15:11
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Tidskriftsartikel (refereegranskat)abstract
- A relevant issue with charred exteriors is the inconsistency of the result, which makes service life predictions complicated. Contact charring enables the creation of a very evenly modified surface with accurate control of temperature and modification time, but the weathering properties are questionable. This paper evaluated the effect of the modification time relative to char layer and transition zone thickness, wood species and material density in an artificial weathering test. The results revealed higher color stability in connection to longer modification time, but also an increase in the cracked surface area. Cracking was heavily dependent on the modification regime and increased with increasing char and transition zone thicknesses. Dense spruce had the highest color stability with the most severe modification regime, but char layer thickness varied more than on other wood types. Furthermore, species-dependent cracking patterns affected the final result as the small-scale flaking experienced by birch increased the washing off of char. It is likely an even higher modification temperature with a shorter modification time is needed to produce sufficient weathering resistance suitable for exterior uses.
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| 2. |
- Kymäläinen, Maija, et al.
(författare)
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Surface modification of solid wood by charring
- 2017
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 52:10, s. 6111-6119
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Tidskriftsartikel (refereegranskat)abstract
- Most wooden structures for outdoor applications require repetitive maintenance operations to protect the surfaces from adverse effects of weathering. One-sided surface modification of boards with a relatively fast charring process has the potential to increase the durability and service life of wooden claddings. To assess some weathering-related effects on surface charred wood, spruce and pine sapwood were subjected to a series of long charring processes (30–120 min) at a moderate temperature of 250 °C and to a short one (30 s) at a high temperature of 400 °C. The wettability and contact angles of treated samples were investigated, and the heat transfer was measured along with the micromorphological changes taking place in the material. The result revealed an increased moisture resistance of charred spruce sapwood and an increased water uptake of pine sapwood. The contact angles of both wood species improved compared to references. Heat conduction measurement revealed that only a thin section of the wood was thermally modified. Some micromorphological changes were recorded, especially on the inside walls of the lumina. The results show that spruce sapwood has an improved resistance towards moisture-induced weathering, but more studies are needed to unlock the potential of surface charred wood.
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