Abstract
The biological durability of wood is frequently determined in laboratory tests with monocultures of different decay fungi under ideal conditions for fungal growth. To avoid contamination with mould and inhibition of fungal growth, wood specimens need to be sterilized using different methods. To determine the mass loss of wood blocks during incubation, the initial total dry mass is needed but should be determined without oven-drying to avoid the loss of volatile compounds of the tested wood. In this study the effect of different sterilization techniques in combination with different methods of determining the oven-dry weight on mass loss (MLF) in agar plate wood block tests was investigated. No significant MLF differences were observed between sterilization through gamma radiation, steam, autoclaving, ethanol dipping and oven-drying. Solely, non-sterilized specimens showed reduced MLF, since the test fungus was inhibited by mould growth. Oven-drying of wood species that contain volatile and resistance-affecting compounds such as Scots pine (Pinus sylvestris) led to reduced biological durability and should either be avoided or adapted to kiln-drying temperatures usually applied in practice.
Highlights
The biological durability of wood is frequently determined in laboratory tests with monocultures of different decay fungi under ideal conditions for fungal growth (EN 113-2 2021; AWPA E 10 2015)
Grinda (1984) observed no negative effect of gamma radiation on fungal resistance of wood compared to steam-sterilized wood blocks, but applied a radiation dosage of 30 kGy, which was the lowest of the different dosages applied by Hasan et al (2008)
Oven-drying for determining the absolute dry weight of Scots pine sapwood and heartwood specimens led to higher MLF compared to specimens which had been conditioned in normal climate
Summary
The biological durability of wood is frequently determined in laboratory tests with monocultures of different decay fungi under ideal conditions for fungal growth (EN 113-2 2021; AWPA E 10 2015). Similar test setups can be used for determining the efficiency of wood preservatives (EN 113-1 2021; ASTM D1413-05b 2005). These experiments are rather fast, reproducible, and allow to distinguish between the effect of different decay types and even fungal species on wood degradation. To assure that (1) decay is caused by the selected test fungus exclusively, and (2) growth and decay activity of the test fungus are not inhibited by antagonistic effects caused by other organisms, it is important and requested according to different standards (e.g. EN 113-1 2021; EN 113-2 2021) that the wood test specimens are sterilized before incubation. The profile of requirements for sterilization techniques comprises the following:
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