Thermal modification of wood is one of the most perspective procedures to protect wood. The use of this procedure is expanding from year to year. The process is environmentally friendly as it runs without any added chemicals. Wood is modified at temperatures from 170 °C to 240 °C in special chambers, without the presence of oxygen. By relationship between the duration of modification and the temperature of modification, the desired level of protection is achieved. Higher temperature makes the timber more resistant, but at the same time, it reduces mechanical properties. Most researchers have been done on the important industrial wood species; less used timber species are less researched. Four different, less commercially important timber species (larch, poplar, alder and ash), were tested at different temperatures and different duration. The samples were determined by weight loss, modified using four different fungi (Trametes versicolor, Pleurotus ostreatus, Gloeophyllum trabeum, Antrodia vaillanti), and placed for 16 weeks in an incubator. From gravimetrically determined weight loss, we found out that the resistance of wood against fungi is in linear relation to the weight loss during the thermal modification. Lower temperature (up to 190 °C) is in no case sufficient for complete protection, while higher temperature (up to 215 °C) already proves to be effective, but not against all types of wood fungi.
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