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Influence of clonal variability on the impregnability of poplar hybrids. (+ correction document of 23 April 1990)
1990 - IRG/WP 3614
The new Western European poplar clones (Populus nigra x deltoides and Populus trichocarpa x deltoides) were compared with the reference clone 'Robusta' and some old hybrids. Samples (5x5x50 cm³) with pure tangential/radial surfaces were sawn, including the transition zone between heartwood and sapwood. Treatment by a standard vacuum-pressure impregnation cycle with CCA showed a range of retentions from 2 to 10 kg/m³ for the 23 poplar clones studied. Only minor differences in impregnability were observed between samples of different trees belonging to the same hybrid. Although the new poplar clones in general show no substantial differences in uptake compared to the reference clone "Robusta" and the older poplar hybrids, the penetration of Cu and As was lower. No relation between wood density and impregnability was found. The radial and tangential penetrations were identical. Cu penetration in sapwood was significantly better than in heartwood. Samples of 1 m length revealed a poor longitudinal penetration.
J Van Acker Van, M Stevens, C De Haas

Preliminary study of the fungicidal and structural variability in copper naphthenates and naphthenic acids
1996 - IRG/WP 96-30114
Copper naphthenates, an oil-borne wood preservative listed by the American Wood-Preservers' Association (AWPA), is manufactured by complexing copper(II) with naphthenic acids. Prior to AWPA listing as a wood preservative, field experiments showed that copper naphthenates generally had good stability and were active against wood-destroying organisms. Recently, however, there have been reports of some copper naphthenate-treated poles rapidly failing. One possible explanation for the varying effectiveness could be that the structure, and resulting biological activity, of the naphthenic acids used to make copper naphthenate may vary. To test this hypothesis several naphthenic acids and copper naphenates were obtained and their fungicidal activity against three wood-destroying fungi measured. In addition, the chemical structure of the naphthenic acids were examined by proton- and carbon- NMR. Different activities were observed, especially against a copper-tolerant fungus. Some apparent correlations were seen between the fungicidal activity and chemical structures for the few samples studied.
T Schultz, D D Nicholas, L L Ingram Jr, T H Fisher

Interspecific variability of European oak durability against white rot fungi (Coriolus versicolor): Comparison between sessile oak and peduncle oak (Quercus petraea and Quercus robur)
2001 - IRG/WP 01-10393
The knowledge of wood natural durability against biologic predators enable its external use. The resistance of European oak wood was reported like durable according to the EN 350-2. However, some individuals may contain high durable wood. Our research was focused to understand this variability in oak population that represent the first french species (4.1 millions of ha). Natural durability of European oak heartwood (Quercus petraea and Quercus robur) against white rot fungi (Coriolus versicolor) was tested according to european standard EN 113. The experimental material consists in 23 oaks robur and 26 petraea oaks sampled from 9 French regions. For each tree, 3 twin samples were taken off from heartwood situated at 1.30 m from the bottom of the tree. Different effects were tested by hierarchic variance analysis: "species", "forest within species" and "tree within forest". The tree effect is very significant for biologic natural resistance. Variability between species was also demonstrated. Although the species effect is significant, it's relatively weak compared with tree differences (it was declared significant 5%). Durability classification was determined according European standard EN 350-1. 69.2% of petraea oak trees are classified as high durable, 19.2% durable, 7.7% moderately durable and 3.8% slightly durable. In the case of robur oak 91.3% of trees are classified as high durable and 8.7% durable.
N Ayadi, B Charrier, M Irmouli, J P Charpentier, C J Allemand, F Feuillat, R Keller

Implications for comparability of laboratory experiments revealed in studies on the variability in survival and wood consumption between colonies of Coptotermes acinaciformis (Froggatt) (Isoptera: Rhinotermitidae
1983 - IRG/WP 1196
(Summary of paper 1193) Groups of Coptotermes acinaciformis, originating from six colonies, three taken from each of two localities, 1500 km apart, in northern Australia (Townsville, Darwin) were kept at population densities of 0.005, 0.01 and 0.02 g termites/mL. Survival and wood consumption of the groups after 8 weeks followed a similar pattern in the colonies from both collection areas. Groups were least vigorous at the lowest population density; their performance reached a maximum at a population density of 0.01 g/mL. The subsequent decline in vigour was less marked as the highest population density was approached. However, the actual values for survival and wood consumption varied widely between colonies, irrespective of their origin. It is recommended that in all laboratory experiments which use survival and wood consumption as indicators of termite vigour, controls of a favourable as well as an unfavourable food type are included which would serve to monitor the vigour of the termites. Results from termite sources whose vigour falls below a certain threshold value would have to be treated with caution and could not be used in definative data, as e.g. in defining critical retentions of wood preservatives.
M Lenz

The variability of preservative distribution in test blocks
1973 - IRG/WP 220
The techniques for the assessment of likely effectiveness of preservative systems have long been the subject of much discussion. The whole field has recently been reviewed by Hilditch and Hamblyn (1971) who described in detail many of the laboratory test procedures used, but who also indicated the deficiencies in many of these techniques. It has long been the view of many associated with the wood preservation industry that laboratory tests can only serve as a preliminary method of screening and that final approval by both the company marketing the development and independent authorities, on whom the burden of approval rests, can only be given after detailed testing in the field. The aim of the simple piece of work described in this paper, is to lok at the variability which one might expect in the distribution of preservative in test blocks destined for laboratory fungal evaluation.
F W Brooks, M R Gayles, R W Watson

A study of decay type variability in variously treated Fagus sylvatica and Pinus radiata field test stakes exposed at a vineyard for 30 - 45 months
1998 - IRG/WP 98-10271
Pinus radiata test stakes were treated with 10 kg/m3 of CCA plus 4 lower retentions in a geometric series of 1.5. Fagus sylvatica was treated with 15 kg/m3 and 2 lower retentions. Both timber species were also treated with equivalent retentions of various new generation preservatives (P. radiata was also treated with creosote). Whilst these stakes were exposed at 11 sites in New Zealand (NZ) and 2 in Queensland Australia, this paper reports only data from a single NZ site where preservative and timber species effects on decay type were particularly pronounced. Of particular interest was the finding that copper-azole and copper-quat. treated pine was less susceptible to soft rot attack but more susceptible to attack from tunnelling bacteria, compared to CCA treated wood. Beech was not attacked by tunnelling bacteria but was attacked by an unusual type of fungal cavitation/erosion. These, and other preservative and timber species effects on decay type are discussed.
R N Wakeling, A P Singh

Intraspecific variability in feeding capacity of Coptotermes acinaciformis (Froggatt) (Isoptera: Rhinotermitidae)
1983 - IRG/WP 1175
This paper describes laboratory studies to evaluate the comparative feeding capacity within and between five mound colonies of Coptotermes acinaciformis (Froggatt). Matched specimens of mountain ash, pine and coachwood were exposed to five replicate 10 g groups of termites from each colony source. After an initial 8-week exposure period, all groups were assessed for vitality and continued feeding capacity on pine specimens for a further eight weeks. The investigation showed within-colony variations to be small, but wide variations between colonies were revealed.
C D Howick, J W Creffield

Implications for comparibility of laboratory experiments revealed in studies on the variability in survival and wood consumption between colonies of Coptotermes acinaciformis (Froggatt) (Isoptera: Rhinotermitidae
1983 - IRG/WP 1193
Groups of Coptotermes acinaciformis originating from six colonies, three taken from each of two localities 1500 km apart in northern Australia (Townsville, Darwin), were kept at population densities of 0.005, 0.011 and 0.02 g termites/mL. Survival and wood consumption of the groups after 8 weeks followed a similar pattern in the colonies from both collection areas. Groups were least vigorous at the lowest population density; their performance reached a maximum at a population density of 0.011 g/mL. The subsequent decline in vigour as the highest population density was approached was less marked than at the lowest density. However, the actual values for survival and wood consumption varied widely betwesn colonies, irrespective of their origin. It is recommended that in al1 laboratory experiments which use survival and wood consumption as indicators of termite vigour, controls of a favourable as well as an unfavourable food type are included to monitor the vigour of the termites. Results from termite sources whose vigour falls below a certain threshold value would have to be treated with caution and could not be used in definitive data, as for example the defining of critical retentions of wood preservatives.
M Lenz

Intraspecific variability of durability of Wapa courbaril (Eperua grandiflora) against Antrodia sp. and Coriolus versicolor: effect of radial and height position in the stem
2004 - IRG/WP 04-10531
The variation of a lesser-used species, Eperua grandiflora attacked by brown and white rot has been examined. Trees of this specie showed differences in their behaviour against the type of rot used and also showed evidence of intra and inter tree variation. The “tree” effect is very significant concerning natural resistance. In the same way, there is variation of durability observed according to radial and vertical position in the stem. Although the vertical effect is less significant from practises point of view.
N Amusant, J Beauchêne, M Fournier

Principles behind the laboratory assessment of materials with subterranean termites - Recent perspectives and shifts in emphasis
1986 - IRG/WP 1291
Laboratory assessments of materials against termites aim to give an indication of the likely performance of materials in the field. To meet this objective, test procedures have to provide the conditions that promote the most vigorous activity of the insects. Implications of recent findings on inter- and intracolony variability in vigour, the need to monitor termite activity with differing types of controls, defining more closely the optimal physical environment for each species of termite, and the severity of laboratory trials are discussed. It is further noted that the potential of new test methods needs to be explored and closer attention needs to be given to features of the biology of termites during the design of bioassays, especially in situations of limited termite supplies.
M Lenz

Variation in field test performance of untreated and CCA-treated lesser-known Surinamese wood species
2000 - IRG/WP 00-20213
In Suriname three different field test sites have been used to verify the biological durability of CCA-treated wood and a range of wood species including lesser-known and lesser-used wood species. In total 37 tropical wood species were tested untreated and for 17 of the less durable species CCA-treatments were included as well. Although the three sites are located in the tropical region they differ with regard to soil and micro-climatic conditions. This is reflected by the results gathered from the durability tests. The observed variability shows that relevant conclusions on natural durability and efficacy of a preservative treatment can only be gained if different test sites are used.
J Van Acker, M Stevens, L Comvalius

Biological variability in the oxalate/oxalate decarboxylase system among five isolates of the wood-degrading fungus Meruliporia incrassate
2006 - IRG/WP 06-10573
The “dry-rot” wood decay fungus Meruliporia incrassata has recently attracted attention, primarily in the western coastal United States, as a particularly destructive pest of building material. Recently, the US Environmental Protection Agency (EPA) has accepted a voluntary withdrawal of the historically effective chromated-copper arsenate (CCA) as a preservative for wood used in residential settings. As the new generation of copper-based preservatives appear to be less effective against this fungus, it is becoming increasingly important to new countermeasures against M. incrassata. Oxalic acid and the oxalate-catabolizing enzyme, oxalate decarboxylase, are produced by all wood-decaying basidiomycetous fungi and have often been implicated in many aspects of the decay process. The purpose of this study was to gain a better understanding of the variability among different isolates of M. incrassata through the characterization of the oxalate/oxalate decarboxylase system. Four field isolates of M. incrassata obtained from wood in California were tested, as well as one ATCC isolate from Virginia, and one isolate of the similar European fungus Serpula lacrymans for comparison. All fungal isolates displayed a remarkably uniform production of both oxalate and oxalate decarboxylase, as well as a very rapid wood decay rate in standardized tests. The uniformity of this particular system may make it an effective target for non-specific preservatives; fungicides developed against this system have a greater chance of being more broadly effective across species and genera.
C Howell, J Jellison

Evaluation of variables that influence dynamic MOE in wood decay studies
2009 - IRG/WP 09-20409
The effect of wood moisture content (MC) and outdoor exposure of southern pine lap-joint components on dynamic MOE values was investigated. The use of dynamic MOE as a method of measuring progressive biodeterioration of above ground test samples shows promise, but the accuracy of this method for evaluating test samples subjected to fluctuating environmental conditions has not been reported. The results of this study show that fully water saturated samples had consistently lower MOE values than those obtained at lower MC levels. After the MC was reduced from saturation by about 30%, variation in MOE with changes in MC down to the fiber saturation point were minimal. Outdoor exposure of the test samples also influenced the MOE. After an initial period of outdoor exposure, slightly lower MOE values were obtained for all of the test samples. However, subsequent MOE measurements after additional outdoor exposure were fairly consistent and did not show a trend towards either lower or higher values. For some test samples it was not possible to obtain reliable frequency measurements, resulting in their exclusion from the study.
D Nicholas, J Shi, T Schultz

Onset of mould growth – the effect of climate variability and different geographic locations
2010 - IRG/WP 10-20446
This paper presents a study on how climate conditions at numerous locations in Sweden affect the risk of onset of mould on wood sheltered outdoors. The results indicate that the risk is clearly higher in the south compared to the north of Sweden. These differences are mainly explained by colder and dryer winter periods in the north which is unfavorable for development of mould. The results also show that the climate effect with respect to risk for mould growth has a significant variation between different years. Thus, the risk for unfavorable effects cannot be solely based on predictions for a so-called normal year without considering years with more extreme climate effects. Based on the results it is argued in favor of developing a quantitative method to assess the risk of mould growth using probabilistic methods and reliability analysis. Such a method should be simple enough for the general engineer to implement and serve as a valuable tool in order to avoid inappropriate design and potential health related problems.
M Häglund, T Isaksson, S Thelandersson

Limited variability in biological durability of thermally modified timber using vacuum based technology
2011 - IRG/WP 11-40567
The SmartHeat® thermal timber treatment is a new technology based on the process parameters being steered very precisely mainly due to the vacuum applied and heating system involved. Timber treated with this technology shows a potential for less variability of biological durability in one batch. Several batch treatments were sampled and assessed on statistical variability of decay resistance against Basidiomycetes and soft rotting micro-fungi according to lab testing as described in the standards CEN/TS 15083 part 1 and 2 respectively (only Basidiomycetes test results are reported in this paper). By means of Weibull distribution assessment it was possible to show that variability in biological durability of each treated beam is well controlled and that this variability is limited compared to natural durability of wood species. Lower treatment variability due to precise parameter control for each beam and limited deviations of process parameters within the treating vessel are considered the main contributing factors. The paper also states that lower control of process parameters of some heat treatment processes might induce higher variability of the obtained biological durability than a customer might expect.
J Van Acker, S Michon, J Van den Bulcke, I De Windt, B Van Swaay, M Stevens

In-ground variability of decay intensity within a test field
2012 - IRG/WP 12-20496
Timber exposed in the ground faces most severe conditions in terms of exposure to wetting and fungal decay in the terrestrial environment, therefore wood durability tests are often conducted in test fields preferably ensuring the occurrence of all relevant decay organisms. One can also expect differences in decay within an individual field-test site due to localized distribution of certain organisms. Therefore, relevant decay parameters were examined on the newly prepared in-ground test-field in Hannover-Herrenhausen: Scots pine sapwood and European beech were exposed to record distribution of decay types, decay intensity, and soil parameters. Soft and white rot were found to be dominating. Significant differences of the intra-site variability of decay intensity were observed between wood species and over time. In contrast, differences in decay intensity by different rot types were small. It was concluded that spatial differences in decay intensity were due to localized established fungal flora.
C Brischke, S Olberding, L Meyer, T Bornemann, C R Welzbacher

Variability in durability of some selected South-American wood species
2014 - IRG/WP 14-10831
Within the scope of sustainable forest management one wants to encourage the proper use of lesser known wood species. Therefore the market has to shift from a demand-driven towards a supply-driven market without loss of wood quality. It is generally known that the durability from pith to bark varies thus, affecting the overall durability of wood species. Consequently, a detailed analysis is necessary to map the durability of wood. This study covers a case study on the resistance against white rot and soft rot of three South-American wood species with local Surinamese names: groenhart, maka-grin and djindja-udu. The variability in resistance against white and soft rot was similar with slightly higher mass losses for soft rot. The effect of radial position was significant at the 90% confidence level. Highest mass losses were recorded for sapwood. Within the heartwood part the highest mass losses were recorded for inner heartwood. Groenhart and maka-grin showed no significant difference in natural durability profiles. The sapwood durability of groenhart and maka-grin was comparable to the durability of djindja-udu heartwood giving the opportunity of a wide range of applications of this sapwood. Between trees of the same wood species differences were noticed and could be examined in more detail.
I De Windt, P ’t Hooft, J Van den Bulcke, J Van Acker

The potential of 2D NIR imaging for wood protection research
2015 - IRG/WP 15-20566
Investigating wood and wood-based materials using infrared spectroscopy has since long been explored. Recently, image-based systems have been developed that are used in food and pharmaceutical industries for rapid screening. Such hyperspectral cameras are able to collect spatial and spectral information simultaneously, resulting in a volume with a spectral profile for each pixel of the image. We present here a flexible 2D NIR scanner, implemented in a generic LabView® and MATLAB® framework respectively for image acquisition and data processing. The scanner can be used to evaluate the surface of any wood-based material, either qualitatively or quantitatively given the existence of a proper model to convert the IR signal in a quantitative measure. Examples will be given for the surface of poplar plywood before and after outdoor exposure and the impregnation of treated wood. As such, this technique allows for assessing the variability of specific characteristics in 2D rather than being limited to a single point or average result as is the case with other techniques. In general, 2D NIR scanning is a highly valuable and complementary tool to other non-destructive techniques such as X-ray tomography (structure).
J Van den Bulcke, N Defoirdt, W Li, J Van Acker

Effect of natural variability of European Oak wood on heat treatment process and potential implication on wood durability
2015 - IRG/WP 15-40693
Environmental pressures appeared in France and in most European countries during the last decade has led to the development of more environmentally acceptable preservation methods. In this context, wood heat treatment has been one of the most investigated alternative method during the last years. Treated at temperatures ranging between 180 and 220°C, wood components undergo more or less important chemical modifications conferring to the material new properties like increased decay resistance or higher dimensional stability. However, even if industrial heat treatment processes are relatively well controlled, the main difficulties remaining today are to obtain final products with constant qualities (durability, dimensional stability, colour). These difficulties may be due to the heat treatment processes themselves or the inter- or intra-specific wood heterogeneity. The aim of this study is to assess the effect of the variability of the initial intrinsic wood quality depending on different silvicultural systems, on the level of thermo-degradation recorded for similar curing conditions and consequently on conferred properties to the final end products. Oak wood (Quercus petraea Liebl) boards with different densities were selected from different positions in the same tree and/or from trees from different forests. Samples density was determined by X-ray computed tomography and micro densitometry before and after heat treatment. X-ray tomography observations did not allowed establishing a clear relationship between initial oak density and its susceptibility to thermo-degradation. However, it was noticed an influence of the position in the board and of the nature of the wood (heartwood versus sapwood) on the levels of thermo-degradation. Thermo-gravimetric analysis (TGA) performed on earlywood and latewood sampled within a same board indicated a strong influence of the intra ring heterogeneity, earlywood tending to be more sensitive to thermo-degradation than latewood. Wood quality, often characterized by its density resulting from forests management, appears therefore as an influencing parameter to consider during wood thermo modification.
J Hamada, A Pétrissans, F Mothe, M Pétrissans, P Gérardin

Global survey on durability variation – on the effect of the reference species
2016 - IRG/WP 16-20573
Climate change due to anthropogenic emissions is the largest environmental challenge of our time. Forest-based value chains play an important role in reducing the accumulation of CO2 in the atmosphere. Maximizing the use of wood to tackle climate change requires improved understanding of the service life of timber products. This information can best be obtained from field testing and while there is an abundance of field performance data from sites all over the world, most of the data are not available in a form that can be utilised for service life models. The IRG Durability Database aims to improve the usability of existing performance data and create added value for durability research and service life prediction. The present paper takes the first steps in comparing global field test performance data from the IRG Durability Database for non-durable reference species. Data were obtained from six species above ground and ground contact field tests from 36 sites around the world. For each dataset, decay rates and service life (where applicable) were calculated. Datasets were then grouped together based on test method and species. Decay rate was faster and more uniform in ground contact than above ground. In ground contact, beech decayed most rapidly, followed by Norway spruce and Scots pine sapwood. All appeared to be suitable for use as reference species, however slow-grown spruce should be avoided. There were no statistically significant correlations between ground contact decay rate and the Scheffer Climate Index (SCI). In above ground tests, differences in decay rate were largely related to differences in moisture dynamics. Species with the greatest absorption and retention of water decayed most rapidly. Test methods that absorbed and retained the most moisture (e.g. painted L-joints) resulted in more rapid decay. Above ground decay rate and SCI were significantly correlated in two data sets that had a wide range of SCI values. Correlations were not significant when only European test sites were included. Estimating decay rate from field testing results in highly variable data. Comparing data from global test sites is made more difficult by the absence of common field testing standards.
R Stirling, G Alfredsen, C Brischke, I De Windt, L P Francis, E Frühwald Hansson, M Humar, J Jermer, M Klamer, M Kutnik, P Laks, I Le Bayon, S Metsä-Kortelainen, L Meyer-Veltrup, P I Morris, J Norton, T Singh, J Van Acker, J Van den Bulcke, T M Venås, H Viitanen, A H H Wong

Modelling the performance of bio-based building materials
2016 - IRG/WP 16-20582
The ‘bio-based economy’ represents a growing area of development globally and covers a wide range of building materials including wood and wood-based products. A ‘bio-based’ material is intentionally made from substances derived from living (or once-living) organisms. In this context it means that the materials and products are made from renewable resources, with the criteria that a renewable resource recovers faster than it is drained, in contrast to many mineral and fossil resources. Their successful use in various applications in the building sector requires sufficient performance and reliable performance data are needed. A key instrument for predicting the performance of building materials on the base of test and survey data are models. Performance modelling is therefore an important issue within IRG-WP – in particular addressed within WP 2.1 ‘Prediction of Service Life’ as well as for COST Action FP 1303 ‘Performance of Bio-Based Building Materials’. On occasion of the 47th Annual Meeting of IRG-WP a special session on ‘Modelling’ will be held jointly with COST FP 1303. Exposure, decay, and resistance models related to wood and other bio-based building materials will be presented. Cross links between disciplines are sought and shall be intensified such as between material science, chemistry, building physics, wood and fiber technology, polymer science, biology, mycology, entomology, civil engineering, and architecture. This paper provides an overview about modelling approaches and applications of performance models for design and performance classification. Major challenges related to performance modelling are highlighted and discussed such as quality and availability of data for modelling, the variability of input and output variables, the decay-type specificity of models, and their verification.
C Brischke

Evaluation of field test data
2016 - IRG/WP 16-20594
The resistance against fungal decay and insect attack of wood can be highly variable, between boards and even within boards. The variability in durability is not always an issue, but for high demanding applications information about its reliability is required. This comprises the variability of outdoor performance. Durability testing in laboratory and outdoor exposures can provide a good basis to predict the overall performance of the wood material in specific applications. However, commonly only a durability class or the mean decay rating is given. Only a small number of publications are available on how to express variability in field test data. Nowadays with the availability of easy to operate powerful statistical software, advanced statistical data analysis can be done without fully understanding both, the data and the evaluation method. This can lead to wrong interpretation of the data and drawing incorrect conclusions. Therefore, it is important to know which mathematical or statistical method to use and how to interpret the results. In this paper a series of statistical methods and graphical interpretations are presented to address and visualise variability of test results. The data is obtained from an AWPA E7 field test in Thailand with Teak (Tectona grandis), Makha (Afzelia xylocarpa), and acetylated Radiata pine (Pinus radiata). 20 stakes from each material have been exposed for 5 years at 5 different test sites. The specimens were assessed every 6 months with respect to decay and termite attack.
F Bongers, C Brischke, J Van den Bulcke, W Gard, I De Windt, H Militz

How intraspecific radial variability of the European Oak’s may influence mild pyrolysis process and durability of the material
2016 - IRG/WP 16-40725
Last decades wood is promoted as building material. Unprotected wood exposed to outdoor conditions undergoes a variety of degradation induced essentially by fungi attacks. Heat treatment of wood by mild pyrolysis (180°C T 240°C under inert atmosphere) is a preservation process with a weak environmental impact, and therefore, is viewed as an interesting alternative to the chemical impregnation methods. It is generally well recognized that final properties of thermally modified wood like decay resistance, dimensional stability, mechanical properties or color depend on wood species but also and heat treatment process and treatment conditions like time and temperature. However, in spite of different studies describing the effect of inter specific variability on wood thermal degradation, no study describes the effect of intraspecific variability of wood on thermo modification processes. As wood physical properties as well as chemical composition can vary between and within species, between stands and even within tree, we tested the effect of radial position of European oak wood (Quercus petraea Liebl.) on its thermal stability. Samples of heartwood, sapwood, juvenile wood, earlywood or latewood taken from the radii of 2 trees were ground to fine sawdust subjected to thermogravimetric analysis (TGA) at 220°C for 2 hours using the same heating program. At the same time, holocellulose, cellulose and extractives as well as extracted heartwood and sapwood were also subjected to TGA using the same procedure. Results indicated that heartwood was more sensitive to heat than sapwood, the inner side of heartwood being more sensitive than the outer side. Differences were also noticed between native and extracted wood, the latter ones being less sensitive to thermal degradation. These results were consistent with the stability of each wood cell wall component indicating that extractives were more susceptible to thermal degradation than holocellulose, holocellulose being more susceptible than cellulose. At the ring level, earlywood was shown to be slightly more sensitive to thermal degradation than latewood. It was therefore concluded that since wood radial position and the earlywood/latewood ratio determine the thermal stability of oak wood, the quality and the homogeneity of initial wood boards should be carefully controlled to avoid heterogeneity in the treatment leading to end products with different properties and quality.
J Hamada, A Pétrissans, F Mothe, M Pétrissans, P Gérardin

Decay resistance variability of European wood species thermally modified by industrial process
2017 - IRG/WP 17-40807
Thermal modification is now considered as a new ecofriendly industrial wood modification process improving mainly the material decay resistance and its dimensional stability. Most industrial thermal treatment processes use convection heat transfer which induces sometimes heterogeneous treatment temperature propagation within the oven and lead to the heterogeneity in treatment efficiency. Thus, it is common that treatment is not completely effective on several stack boards, in a same batch. The aim of this paper was to study the decay resistance variability of various European wood species thermally modified. Thermal modifications were performed around 240°C during 4h, on about 10 m3 of 27 x 152 x 2000 mm3 wood planks placed in an industrial oven having a volume of 20 m3, on the following wood species: spruce, ash, beech and poplar. All of the tests concerning the decay resistance were carried out in the laboratory using untreated beech and pine woods as reference materials. An agar block test was used to determine the resistance of thermally modified woods, leached beforehand according to EN 84 standard or not, to brown-rot and white-rot fungi, according to XP CEN/TS 15083-1. A large selection of treated wood samples was tested in order to estimate the variability of treatment efficiency. Thermal treatment increased the biological durability of all leached and un-leached modified wood samples, compared with native wood species. The treatment temperature of 240°C used in this study is sufficient to reach durability classes ‘‘durable’’ or ‘‘very durable’’ for the four wood species. However, the dispersion of weight loss values, due to the fungal attacks was very important and showed a large variability of the durability of wood which has been treated in a single batch. These results showed that there is a substantial need to develop process control and indicator in order to insure that the quality of treated timber is properly evaluated with a view to putting this modified timber on the market under a chain of custody.
K Candelier, L Pignolet, S Lotte, A Guyot, E Cuny, B Bousseau, M-F Thévenon