Wood modification is increasing the resistance against wood destroying fungi. The protective mechanism is most likely associated with its hydrophobic character and increased moisture performance, but still not fully understood. The different modification processes aim on keeping wood moisture below conditions favourable for decay organisms. However, measurements on thermally modified, furfurylated, and acetylated timber showed considerably increased moisture content (MC) compared to untreated wood in outdoor exposure, which might be explained by high capillary water uptake. The fact that it is still controversially discussed, to which extent decay is influenced by the presence of liquid water in cell lumens, needs consideration when estimating decay risks of modified wood based on MC measurements. Therefore this laboratory study aimed on determining physiological threshold values for wood decay fungi with respect to modified timber. In total 4200 specimens made from acetylated, furfurylated and thermally modified beech and Scots pine sapwood specimens were exposed to Coniophora puteana and Trametes versicolor. Piles consisting of 50 small specimens were incubated above malt agar in Erlenmeyer flasks for 16 weeks. Generally, pile upwards mass loss and wood MC decreased. Threshold values for fungal growth and decay (mass loss > 2%) were determined. Surprisingly, T. versicolor was able to degrade untreated beech wood at a minimum of 15 % MC; growth was possible at 13% MC. In contrast, untreated pine sapwood was decayed by C. puteana not below 29 % MC. As an overall finding it was observed that the minimum MC for fungal decay was slightly below fibre saturation for the majority of the materials.
Keywords: acetylated wood, furfurylated wood, thermally modified wood, moisture performance, resistance
Authors
Meyer L.
Inst. of Vocational Sciences in the Building Trade (IBW), Faculty of Architecture and Landscape Sciences, Leibniz University Hannover, Hannover
Brischke C.
Inst. of Vocational Sciences in the Building Trade (IBW), Faculty of Architecture and Landscape Sciences, Leibniz University Hannover, Hannover
Treu A.
Norwegian Forest and Landscape Institute, Ås
Larsson-Brelid P.
SP Technical Research Institute of Sweden, Borås
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