Thermal modification is one of the commercially most successful modification processes. One of the main parameters of quality of thermally modified wood is the loss of mass during the process, which is a function of time and temperature. We examined which parameter has more influence on wood resistance to fungus decay. Samples of beech were thermally modified at temperatures 180 °C and 220 °C for 1; 1,5; 2; 3; 4; 6; 8; 16; 36 hours, and exposed to Trametes versicolor. Samples of spruce were thermally modified at the same temperatures for 1; 1,5; 2; 3; 4; 6; 10; 16; 36; 72 hours, and exposed to Gloeophyllum trabeum. After 16 weeks of exposure to the fungi, the loss of mass was determined with a gravimetric method, and compared to the loss of mass caused by thermal modification process. The resistance of wood against decay caused by fungi is linearly correlated with the loss of mass due to thermal modification. It is not important how mass loss during the thermal modification is obtained (longer time and lower temperature or shorter time and higher temperature) the resistance to fungi being comparable. Using thermal modification at lower temperature (180 °C) we cannot achieve adequate modification to sufficiently protect the wood against fungi. The effect of thermal modification processes on short term absorption of water was determined with tensiometer; the samples with a higher level of modification were more hydrophobic.
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