Wood is economically important material, which has to be protected if used in outdoor applications. For this purpose biocidal protection can be used, meaning that wood is impregnated with chemicals that are toxic or repellent to fungi and insects. Copper ethanolamine based preservatives are currently the most important group of preservatives for wood protection in the third and fourth use class. In addition to the effectiveness of the preservative, leaching of preservatives is the most important criterion for the selection of biocidal products. Leaching of active ingredients is a negative phenomenon, which reduces the effectiveness and has a negative impact on the environment as well. Leaching cannot be completely avoided, but it may be influenced to some extent, if we know the factors which affect leaching. We prepared 900 samples from three different wood species, and impregnated by four different procedures. Impregnated samples were soaked in distilled water and leached for eleven weeks. Some samples were also exposed to fluctuations in temperature. After three, five, seven, nine and eleven weeks, the amount of residual copper in the wood was determined. These data enabled calculation of leaching curves. It turns out that leaching is most intense during the first few weeks, but it then slows down. The uptake of preservative was from about 100 kg/m3 when dipping, to about 600 kg/m3 when deeply impregnated. Between 25 % - 40 % of copper compounds were leached out in 11 weeks, about 30 % for spruce.
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