Meyer-Veltrup et al.: The combined effect of wetting ability and durability on outdoor performance of wood -development and verification of a new prediction approach Abstract Comprehensive approaches to predict performance of wood products are requested by international standards and the first attempts have been made in the frame of European research projects. However, there is still an imminent need for a methodology to implement the durability and moisture performance of wood in an engineering design method and performance classification system. The aim of this study was therefore to establish an approach to predict service life of wood above ground taking into account the combined effect of wetting ability and durability data. A comprehensive data set was obtained from laboratory durability tests and still ongoing field trials in Norway, Germany, and Sweden. Supplementary, four different wetting ability tests were performed with the same material. Based on a dose-response concept decay rates for specimens exposed above ground were predicted implementing various indicating factors. A model was developed and optimised taking into account the resistance of wood against soft, white and brown rot as well as relevant types of water uptake and release. Decay rates from above ground field tests at different test sites in Norway were predicted with the model. In a second step the model was validated using data from lab and field tests performed in Germany and Sweden. The model was found to be fairly reliable and it has the advantage to get implemented into existing engineering design guidelines. The approach at hand might furthermore be used for implementing wetting ability data into performance classification as requested by European standardisation bodies.

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.

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Microwave energy has been used as a heat source the for acetylation of wood with acetic anhydride. Process parameters for the proper acetylation of wood in timber dimensions were investigated using a lab-scale microwave reactor. A high degree of reproducibility and a uniform acetylation was obtained when spruce wood samples (10.5´9.7´16 cm; r´t´l) of the same origin were acetylated separately, but under the same conditions in the microwave reactor. The variation in acetyl content both within and between the samples was less than 2% units. In general, a somewhat higher acetyl content was obtained in the middle of the acetylated wood than in the outer part of it. Microwave energy was also shown to be ef®cient in the removal of excess acetic anhydride and by-product acetic acid by evaporation under vacuum. During the vacuum step, about 70% of the chemicals could be removed within the ®rst 30 minutes. Pine and spruce wood samples acetylated for 2 hours at 130°C followed by a vacuum step for two hours at 120°C, obtained an acetyl content of about 17% and the content of residual chemicals was about 3% calculated on a basis of dry acetylated wood. The temperature in the wood samples could be maintained at about 130°C even at very low contents of residual excess chemicals without any formation of hot spots. Acetylieren von Massivholz durch Erhitzen mit Mikrowellen Teil 2. Experimente im LabormaûstabMikrowellen wurden als Wa Èrmequelle fu Èr die Acetylierung von Holz verwendet. Die Reaktionsparameter fu Èr eine ausreichende Acetylierung von Schnittholz wurden mit Hilfe eines Mikrowellenreaktors im Labormaûstab untersucht. Ein hohes Maû an Reproduzierbarkeit und Gleichfo Èrmigkeit der Acetylierung wurde erreicht, wenn Fichtenproben (10,5´9,7´16 cm; r´t´l) vom gleichen Ursprung nacheinander und unter gleichen Bedingungen acetyliert wurden. Die Variation des Acetylgehaltes lag sowohl innerhalb der einzelnen Proben, als auch zwischen den Proben unterhalb 2%. Allgemein war der acetylgehalt im Probeninneren etwas ho Èher, als in den a Èuûeren Bereichen. Die Mikrowellenbestrahlung erlaubte zudem eine effektive Entfernung des u Èberschu Èssigen Acetanhydrids und anderer Nebenprodukte durch Vakuumverdampfung. Unter Vakuum konnten ca. 70% der Chemikalien innerhalb von 30 min. entfernt werden. Keifern-und Fichtenholz enthielt nach 2-stu Èndiger Acetylierung bei 130°C und 2-stu Èndiger Vakuumbehandlung bei 120°C einen Acetylgehalt von 17%. Der Gehalt an restlichen Chemikalien betrug 3%, bezogen auf trockenes, acetyliertes Holz. Die Temperatur in den Holzproben konnte bei 130°C gehalten werden, ohne Ausbildung von heiûen Zonen, auch wenn nur geringe U È berschu Èsse von Reaktionsmitteln verwendet wurden.

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