Acetylated Southern yellow pine (SYP) panels were exposed at a test field outside Stockholm, Sweden. After 7 months outdoors exposure at 45° facing south and 90° facing north, panels with different acetyl contents became disfigured by fungi. Since panels facing north also became stained by fungi it is believed that UV degradation may have minor importance for the establishment of fungi on the surface of these panels. It is believed that water dynamics may play a more important roll.
Histological studies showed acetylated SYP wood to contain starch, fats and triglycerides and that these extractives have been redistributed to some extent in the wood structure. The presence of such extractives in acetylated SYP wood is the most probable primary source of nutrients for invading fungi.
The content of free acetic acid in acetylated panels may influence the establishment of fungi on panel surfaces exposed outdoors. The effect of acetic acid on fungal growth was studied in laboratory trials. Fungal spores and starved growing mycelia were exposed to acetic acid in solid agar media. Results show toxicity effects of acetic acid on fungi which are related to acid concentration. The limit concentration of acetic acid that totally prevents the growth of Aureobasidium pullulans was studied on liquid cultures. Results revealed the limit acid concentration to be in the range of 0.1 %.
Keywords: Acetylation, acetic acid, extractives, disfigurement, fungi
Authors
Bardage S.L.
SP Trätek, Stockholm, Sweden
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