Resistance of acetylated wood to biological degradation

Abstract

Acetylated pine wood samples were tested in ground contact (stake test) at two test sites, one located in Simla Êngsdalen, Sweden, and one in Viikki, Finland, according to European standard EN 252. The test stakes were inspected annually and their condition was compared with that of untreated controls and of stakes treated with two reference CCA preservatives. The use of untreated controls and preservative treated wood gave a measure of the aggressiveness of the fungal decay at the individual test sites. The resistance to fungal decay of acetylated wood with an acetyl content of about 20% is of the same magnitude as for CCA treated wood at a high retention level (10.3 kg/m 3 ).Exposure of acetylated mini stakes to three different unsterile soils in the laboratory showed that decay was signi®cantly reduced at acetyl contents of 15.1%. An acetyl content of 18.5% prevented most attack by brown, white and soft rot fungi. Acetyl levels above 20.9% were required to eliminate attack by tunneling bacteria.Acetylated wood samples were also tested in seawater on the Swedish West Coast for their resistance to marine borers (EN 275). Results show that the acetylation of wood gives only minor protection against marine borers, although the degree of attack is lowered with increased acetyl content. Resistenz von acetyliertem Holz gegen biologischen Abbau Acetylierte Holzproben wurden an zwei verschiedenenStandorten einem Bodentest nach EN 252 unterworfen. Die Holzpfa Èhle wurden ja Èhrlich untersucht und mit unbehandelten Kontrollen verglichen. Zum weiteren Vergleich dienten Proben, die mit zwei CCA-Schutzmitteln behandelt waren. Diese lieferten ein Maû fu Èr die Aggressivita Èt des Pilzabbaus an den zwei Standorten. Die Resistenz des acetylierten Holzes mit einem Acetylgehalt von 20% entspricht der einer CCA-Behandlung mit 10,3 kg/m 3 . Labortests an Kleinproben in unsteriler Erde ergaben, daû der Abbau schon bei einem Acetylgehalt von 15,1% deutlich verringert ist. Ein Gehalt von 18,5% verhindert weitgehend den Angriff von Braun, Weiû-und Rotfa Èulepilzen. Ein Acetylgehalt von 20,9% ist erforderlich, um das Eindringen von Tunnel-Bakterien auszuschlieûen. Acetyliertes Holz wurde auch in Meerwasser an der schwedischen Westku Èste gegen den Angriff von Bohrmuscheln nach EN 275 gepru Èft. Der Angriff ist zwar mit steigendem Acetylgehalt verringert; dennoch verleiht die Acetylierung nur einen geringen Schutz gegen Bohrmuscheln.

Chemical modification of wood: A short review

“…This fungal cellar test was continued for an additional 5 years, with no attack at 17.9 WPG, which provides additional evidence that the moisture content of the cell wall is critical to fungal attack . Acetylated solid wood and flakeboards have been subjected to in-ground tests (Hadi et al, 1996;Rowell et al, 1997;Larsson-Brelid et al, 2000) throughout the world. In the United States, Sweden, and New Zealand, specimens showed little or no attack after 10 years of exposure.…”

Efficacy of Hydrophobic Coatings in Protecting Oak Wood Surfaces during Accelerated Weathering

“…Modification in the form of hydrophobization can increase the natural durability of wood against biotic and abiotic damages on its exterior [8,9]. Modifications changing the properties of wood in its entire volume, such as thermal treatment or acetylation, are a frequent treatment method [10,11]. For exposures without ground contact (Class 3 according to EN 350 [1]), it is possible to use hydrophobization in the form of a coating [12].…”

Testing common hornbeam (Carpinus betulus L.) acetylated with the Accoya method under industrial conditions

“…It cannot be extrapolated which WPG is sufficient against any biological attack in wood species, but it can be concluded that the higher the level of acetylation, the higher the durability will be. Multiple scientific papers have proven a direct link between acetyl content and wood durability (Peterson & Thomas 1978, Imamura & Nishimoto 1987, Beckers et al 1994, Ohkoshi et al 1999, Suttie et al 1999, Larsson et al 2000, but there are also other influential factors like water uptake, density, anatomy, etc. According to Militz (1991b), beech resisted brown and white rot fungi at 20% WPG.…”