Bioresistance of thermally-modified Populus tremuloides (North American Aspen) wood against four decay fungi

A study was carried out to investigate the effect of thermal treatment on biological resistance of Populus tremuloides wood against four decay fungi, including T. versicolor, P. placenta, G. trabeum and C. puteana. The weight loss data showed that degradation of untreated wood by the white rot fungus T. versicolor resulted in higher weight loss (57·1%) compared to those by brown rot fungi G. trabeum (21·9%), P. placenta (36·7%) and C. puteana (7·1%). When this species was heat treated at 220°C, the weight loss was reduced to <10%. Increasing temperature and the holding time appeared to affect the resistance against T. versicolor, P. placenta and G. trabeum attacks, but the effect on the resistance against C. puteana was not significant. The humidity during thermal modification affected the degradation of wood against T. versicolor attack, but it did not have a significant effect on the other fungi

Durability of thermally modified Pinus banksiana (Jack pine) wood against brown and white rot fungi

The resistance of thermally modified Canadian Pinus banksiana against four wood decaying fungi was evaluated. Wood samples were treated at different temperatures (190, 200 and 210°C) and exposed to three brown rot fungi as well as to a white rot fungus. Results showed that the untreated wood samples lost more weight when exposed to P. placenta, T. versicolor and G. trabeum compared to the weight loss observed in case of C. puteana. Thermal modification at 210°C improved the resistance of Pinus banksiana against G. trabeum and T. versicolor fungi as evident from the fact that reduction in weight loss of wood was found to be 98·3 and 96·3% respectively

Comparative study on the durability of heat-treated White Birch (Betula papyrifera) subjected to the attack of brown and white rot fungi

The effect of heat treatment on decay resistance of white birch was evaluated for different incubation periods ranging from 2 to 12 weeks using three species of brown rot and one species of white rot fungus. The results of weight loss tests showed that the white rot fungus, Trametes versicolor, effectively degraded the untreated wood (73.5%). While the degradation of untreated wood by brown rot fungi species, Gloephyllum trabeum (11.6%) and Conifora puteana (6.2%), was considerably less compared to T. versicolor, the third brown rot fungi studied, Poria placenta, caused an appreciable degradation of the same species (52.4%). The results clearly showed that the heat treatment reduced the effect of fungi attack on white birch. Increasing the heat treatment temperature from 195 to 215°C resulted in reduction of weight loss, consequently, reduction in fungal attack. As an example, the weight loss reductions due to T. versicolor, P. placenta, G. trabeum and C. puteana attack was 62.2%, 71.3%, 89.6% and 100%, respectively, compared to the weight loss of untreated wood when it is heat treated at 215°C. Thus, these results confirmed that the heat treatment increased the biological resistance of white birch

Effect of thermal modification on mechanical properties of Canadian White Birch (Betula papyrifera)

Wood is a renewable material widely used in the construction industry. However, it is susceptible to fungal degradation. Several chemical products have been developed to improve its durability, but the toxicity of some of these products limits their use. One alternative to chemical treatment is thermal modification of wood. This method improves the dimensional stability of wood and reduces its susceptibility to decay. The impact of different parameters (maximum temperature, heating rate, holding time and gas moisture content) of thermal modification on the mechanical properties of Betula papyrifera was studied in a prototype furnace. The results show a marked decrease in the modulus of rupture with increasing temperature while the modulus of elasticity does not seem to be affected. The hardness increases with maximum modification temperature, and in the absence of moisture in gas, and there is an improvement in the dimensional stability after thermal modification

Resistance of thermally modified ash (Fraxinus excelsior L.) wood under steam pressure against rot fungi, soil-inhabiting micro-organisms and termites

Thermal modification processes have been developed to increase the biological durability and dimensional stability of wood. The aim of this paper was to study the influence of ThermoWood® treatment intensity on improvement of wood decay resistance against soil-inhabiting micro-organisms, brown/white rots and termite exposures. All of the tests were carried out in the laboratory with two different complementary research materials. The main research material consisted of ash (Fraxinus excelsior L.) wood thermally modified at temperatures of 170, 200, 215 and 228 °C. The reference materials were untreated ash and beech wood for decay resistance tests, 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 brown-rot and two white-rot fungi according to CEN/TS 15083-1 directives. Durability against soil-inhabiting micro-organisms was determined following the CEN/TS 15083-2 directives, by measuring the weight loss, modulus of elasticity (MOE) and modulus of rupture (MOR) after incubation periods of 24, 32 and 90 weeks. Finally, Reticulitermes santonensis species was used for determining the termite attack resistance by non-choice screening tests, with a size sample adjustment according to EN 117 standard directives on control samples and on samples which have previously been exposed to soil bed test. Thermal modification increased the biological durability of all samples. However, high thermal modification temperature above 215 °C, represented by a wood mass loss (ML%) due to thermal degradation of 20%, was needed to reach resistance against decay comparable with the durability classes of ‘‘durable’’ or ‘‘very durable’’ in the soil bed test. The brown-rot and white-rot tests gave slightly better durability classes than the soil bed test. Whatever the heat treatment conditions are, thermally modified ash wood was not efficient against termite attack neither before nor after soft rot degradation

Effects of propiconazole on extra-cellular enzymes involved in nutrient mobilization during Trametes versicolor wood colonization

International audienceThe effects of propiconazole on extra-cellular enzyme levels in Trametes versicolor have been investigated during wood colonization and degradation. The working hypothesis was that the biocide could alter metabolic pathways, which could lead to an alteration of extra-cellular enzyme production. In the presence of a propiconazole sub-lethal concentration, the wood degradation rate decrease concomitantly with the lag phase of fungal development observed during wood colonisation. The pattern of production of enzymes involved in polysaccharide degradation (b-glucosidases, glucuronidases, cellobiohydrolases), nitrogen (leucine aminopeptidase) and phosphorus (acid phosphatase) mobilization was only slightly altered in the presence of the biocide. In experiments performed in the presence of propiconazole, there was a strong induction of chitinases at the beginning of the colonization process. Addition of caffeine, a pleiotropic drug, which is also a chitinase inhibitor, together with propiconazole resulted in synergistic inhibition of the fungal growth. The implication of these results in the development of a new wood preservation strategy is discussed

Mathematical Modeling of the High Temperature Treatment of Birch in a Prototype Furnace

In recent years, various wood modification technologies have been commercialized as alternatives to the traditional chemical treatments for wood preservation. The high temperature heat treatment of wood is one of these commercially viable and environmentally friendly alternative wood modification technologies. During this treatment, wood is heated to temperatures above 200°C by contacting it with hot gas. The chemical structure of wood changes leading to increased dimensional stability and resistance to microorganisms. Wood darkens making it aesthetically more attractive. However, it loses some of its elasticity. Therefore, the high temperature heat treatment has to be optimized for each species and each technology. The mathematical modeling is an important tool for optimization. It can also be used as a powerful tool for furnace modification and design. A reliable and predictive model was developed to simulate numerically the heat treatment process. Heat treatment experiments were carried out in the prototype furnace of the University of Quebec at Chicoutimi. The model was validated by comparing the predictions with the experimental data. In this paper, the results of the model applied to birch heat treatment are presented. The model predictions are in good agreement with the data

Initial stages of Fagus sylvatica wood colonization by the white-rot basidiomycete Trametes versicolor: Enzymatic characterization

International audienceThe initial stages of wood colonization and degradation by the white-rot Trametes versicolor have been investigated. T. versicolor was grown on Fagus sylvatica wood chips under solid-state fermentation in the presence of malt agar. The beginning of the colonization process was not associated with peroxidases production or hydrolytic activity. In contrast, a sharp induction of laccase expression was observed during the first colonization days. This induction is not due solely to fungal growth on wood chips since similar data were obtained in the presence of biocide (propiconazole)-treated wood, suggesting that enzyme production is due at least in part to the mycelium surrounding wood chips using nutrients from malt agar medium. Laccase production correlated with wood acetone extractives degradation, in particular with the oxidation of catechin, a major compound of beech extracts. In complementary experiments, woodextracted laccases were shown to be active with wood acetone extracts and pure catechin. Furthermore, wood extractives induced laccase expression. Taken together, these data suggest that the initial stages of wood colonization on malt agar by T. versicolor correlate with wood extractives degradation requiring laccase activity, whereas the other wood-degrading systems (peroxidases and polysaccharides hydrolases) are still repressed