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Resistance of Thermally Modified Ash (Fraxinus Excelsior Resistance of thermally modified ash (Fraxinus excelsior L.) wood under steam pressure against rot fungi, soil-inhabiting micro-organisms and termites Kévin Candelier, Simon Hannouz, Marie-France Thévenon, Daniel Guibal, Philippe Gerardin, Mathieu Pétrissans, Robert Collet To cite this version: Kévin Candelier, Simon Hannouz, Marie-France Thévenon, Daniel Guibal, Philippe Gerardin, et al.. Resistance of thermally modified ash (Fraxinus excelsior L.) wood under steam pressure against rot fungi, soil-inhabiting micro-organisms and termites. European Journal of Wood and Wood Products, Springer Verlag, 2017, 75 (2), pp.249-262. 10.1007/s00107-016-1126-y. hal-02179527 HAL Id: hal-02179527 https://hal.archives-ouvertes.fr/hal-02179527 Submitted on 10 Jul 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Resistance of thermally modified ash (Fraxinus excelsior L.) wood under steam pressure against rot fungi, soil-inhabiting micro-organisms and termites 1 2 1 1 Ke´vin Candelier • Simon Hannouz • Marie-France The´venon • Daniel Guibal • 3 3 2 Philippe Ge´rardin • Mathieu Pe´trissans • Robert Collet Abstract Thermal modification processes have been have previously been exposed to soil bed test. Thermal developed to increase the biological durability and modification increased the biological durability of all dimensional stability of wood. The aim of this paper was to samples. However, high thermal modification temperature study the influence of ThermoWoodÒ treatment intensity above 215 °C, represented by a wood mass loss (ML%) on improvement of wood decay resistance against soil-in- due to thermal degradation of 20%, was needed to reach habiting micro-organisms, brown/white rots and termite resistance against decay comparable with the durability exposures. All of the tests were carried out in the labora- classes of ‘‘durable’’ or ‘‘very durable’’ in the soil bed test. tory with two different complementary research materials. The brown-rot and white-rot tests gave slightly better The main research material consisted of ash (Fraxinus durability classes than the soil bed test. Whatever the heat excelsior L.) wood thermally modified at temperatures of treatment conditions are, thermally modified ash wood was 170, 200, 215 and 228 °C. The reference materials were not efficient against termite attack neither before nor after untreated ash and beech wood for decay resistance tests, soft rot degradation. untreated ash wood for soil bed tests and untreated ash, beech and pine wood for termite resistance tests. An agar block test was used to determine the resistance to two 1 Introduction brown-rot and two white-rot fungi according to CEN/TS 15083-1 directives. Durability against soil-inhabiting Heat treatment consists of a wood pyrolysis torrefaction micro-organisms was determined following the CEN/TS performed in a very poor oxygen atmosphere to avoid 15083-2 directives, by measuring the weight loss, modulus wood combustion. The environmental impact of this pro- of elasticity (MOE) and modulus of rupture (MOR) after cess is low, heat is introduced in the treatment system and incubation periods of 24, 32 and 90 weeks. Finally, Reti- smoke from wood thermal degradation can be retrieved, culitermes santonensis species was used for determining condensed and purified (Pe´trissans et al. 2007). At its end the termite attack resistance by non-choice screening tests, of life cycle, heat-treated wood can be recycled without with a size sample adjustment according to EN 117 stan- detrimental impact on the environment, contrary to some dard directives on control samples and on samples which chemically impregnated wood containing biocidal active ingredients (CRIQ 2003). Although several processes (e.g. Plato-Process, Bois Perdure, OHT-Process, ThermoWood & Ke´vin Candelier Process, etc.) exist due to conditions used for heat con- [email protected] duction (Hannouz 2014), the basic concept is common, that 1 CIRAD-Unite´ de Recherches BioWooEB, TA B 114/16, is to modify wood chemical structure at a defined tem- Montpellier, France perature in inert atmosphere (Militz 2002). There are 2 LaBoMaP, Arts et Me´tiers ParisTech, Rue Porte de Paris, plenty of end-uses for thermally modified timber in many 71250 Cluny, France different applications, such as exterior cladding, covered 3 LERMAB, Faculte´ des Sciences et Technologies, 54506 decking, flooring, garden furniture, paneling, kitchen fur- Vandœuvre-le`s-Nancy, France nishing, and bathroom decor. Thermal modification of wood, using soft pyrolysis at wood (Curling et al. 2002; Metsa¨-Kortelainen and Viitanen heating temperature ranging from 180 to 280 °C, is an 2010,Ra˚berg et al. 2012). attractive environmentally acceptable treatment to protect The impact of thermal treatment on wood termite wood material against moisture content (MC) variations resistance has also already been studied. However, it (Hill 2006;Pe´trissans et al. 2003) and Basidiomycetes appears that the termite resistance of heat treated wood was degradation (Tjeerdsma et al. 2000), to improve dimen- impacted in a random way, was indiscriminate and even sional stability (Korkut et al. 2012), and increase the dark reduced in many cases, according to modification process coloration of wood (Chen et al. 2012). Therefore, heat conditions. Momohara et al. (2003) worked on Japanese treatment allows to use low durability timber by making it cedar (Cryptomeria japonica D. Don) drying under satu- resistant against decay for end-use in use class 2 and 3.1 rated steam at different temperatures (from 60 to 150 °C) [use class 3.2 has to be checked by field tests (Welzbacher and with several treatment durations (from 6 to 72 h). They and Rapp 2007), and use class 4 being excluded due to the highlighted that Japanese cedar wood samples treated at occurrence of soft rots and termite degradation] (EN 335, higher temperatures (135–150 °C) showed larger weight 2013b) and with high economic value (Allegretti et al. loss due to termite attack than those treated at lower tem- 2012; Kamdem et al. 2002). These upgraded biological peratures (60 °C). They observed significant differences properties conferred to the wood are the result of chemical between 135 or 60 °C and 150 °C. In the case of Japanese modifications of wood cell wall polymers occurring during larch heartwood, steam treatment was also reported to treatment (Inari et al. 2007). However, the surface hardness increase termite attraction (Doi et al. 1998). For severe of the heat treated wood can be improved for several wood treatment temperature, Salman et al. (2016) found that species thermally modified at treatment temperature lower Scots pine sapwood (Pinus sylvestris L.) treated at 220 °C than 210 °C (Sivrikaya et al. 2015a). Low temperature and for 20 h, submitted to termite attack after or without time cause the increase in the hardness value while high leaching, was equally degraded compared to untreated temperature and time decrease the hardness value of heat- wood, although the termite mortality rate was higher for treated wood (Lekounougou and Kocaefe 2014), due to treated wood samples. On the other side, Nunes et al. higher degradation of hemicellulose and cellulose and (2004) studied the resistance of wood heat-treated by hot evaporation of extractive compounds (Karamanog˘lu and oil bath (OHT) to the termite Reticulitermes grassei and Akyıldız 2013; Esteves and Pereira 2009). These last concluded that despite the slightly higher mortality of improvements have an adverse effect on wood mechanical termites in treated samples and smaller mass loss, the properties such as bending and compression strength, difference was not significant. However, when treated and stiffness and shear strength (Dilik and Hiziroglu 2012; untreated counterpart wood samples were side by side Candelier et al. 2013; Hannouz et al. 2015, Hermoso et al. during exposure, termites preferred untreated wood. These 2015). The improved fungal resistance of thermally mod- last results (Nunes et al. 2004) could be justified by the ified wood has also been reported by Viitanen et al. (1994), addition of oil into the wood during the thermal modifi- Sailer et al. (2000), Hakkou et al. (2006), Welzbacher and cation process. However, in such a treatment, the oil is Rapp (2007), Mburu et al. (2006) and Boonstra et al. sufficient to make the wood treated with it more (2007). Sivonen et al. (2003) studied the chemical prop- hydrophobic, making it more resistant to the attack of fungi erties of thermally modified Scots pine exposed to brown and termite. In another study, more similar to this present and soft-rot fungi and found that, as with the untreated work, Sivrikaya et al. (2015b) studied the impact of wood, brown-rot fungi degraded mainly hemicelluloses, ThermowoodÒ process on Reticulitermes grassei termite while soft-rot fungus attacked cellulose more extensively. resistance of different wood species and showed that such a Weight loss caused by fungal attack was dependent on the heat treatment did not enhance the termite resistance of ash thermal modification temperature and duration. Previous wood; the survival rate of the termite workers gradually studies, mainly achieved at laboratory scale, have proven increased irrespective of the increase in temperature, and high correlations between mass loss issued from wood that to a similar extent to the samples degradations. thermal degradation (ML%), treatment intensity (time and The aim of this study was to measure the impact of Ther- temperature) and weight loss (WL%) of heat-treated wood moWoodÒ process conditions (treatment intensity) on the due to fungal decay (Hakkou et al. 2006; Chaouch et al.
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