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Anatomical, physical and chemical changes of Bamboo (Phyllostachys puberscence ) during weathering processes
2008 - IRG/WP 08-10650
Bamboo (Phyllostachys puberscence) culms with 1, 2, 3 year old were exposed to natural weathering condition in Gwangju, Korea for 12 months. Changes in color, surface topography, strength and chemical properties were investigated using various microscopic and instrumental techniques. After one year’s weathering, the color of bamboo became lighter but strengths of bamboo did not change significantly. Depending upon the age of bamboo culms, the rate of the check development and the surface erosion were different. Numerous checks were developed in the 2 and 3 year old bamboo whereas little checks in the 1 year old bamboo were appeared. Regardless of bamboo age, most of parenchyma cells in the ground tissues were degraded and lignin was rapidly decreased at initial period of weathering, although structural polysaccharides were also degraded by weathering.
Jong Sik Kim, Kwang Ho Lee, Mi Young Cha, Yoon Soo Kim


Surface color and roughness characteristics of medium density fiberboard (MDF) panels treated with fire retardants
2008 - IRG/WP 08-40420
The objective of this study was to determine surface characteristics and color change properties of Medium Density Fiberboard (MDF) treated by fire retardants (FR) with 10% concentration. Experimental panels were made using by melamine ureaformaldehyde (MUF) adhesive having 10%, 15%, 20% of melamine. The surface properties of the samples were determined using a fine stylus technique. Three roughness parameters, namely average roughness (Ra), mean peak-to-valley height (Rz), and maximum roughness (Rmax) were determined from the surface of the samples. Color change properties of MDF samples were evaluated to CIE L*a*b* methods by a spectrophotometer (Minolta CM-2600d). It was found that the surface roughness values of the FR treated MDF panels were higher than those of control panels. The highest surface roughness values obtained from MDF panels treated with MAF+BA+NPB, MAF+BA+BX, the lowest values obtained from MDF panels treated with MAF+AL. Also surface roughness of the MDF panels improved with increasing melamine additive rate in the MUF adhesive. According to CIEL*a*b method, color change properties of the samples showed variation as function of chemicals type. Especially, while the highest color change(?E) were determined for MDF samples treated with MINPB and MAF+BA+NPB, the lowest color change (?E) were obtained from MDF samples treated with MAF+AL, MIN.
D Ustaömer, M Usta, S Hiziroglu


Accelerated weathering of nine tropical wood species from Cameroon
2009 - IRG/WP 09-10705
The natural durability of tropical species for building components has been a subject of recent concern and questioning, mainly the resistance to weathering. Weathering resistance of nine tropical species from Cameroon, namely Azobe, Bilinga, Bubinga, Teak, Dousie, Moabi, Musanga, Sipo and Padauk were evaluated using an accelerated weatherometer for 2016 hours. Measurement of moisture fluctuation, weight loss, color change, and surface texture were taken at regular intervals of time. It was found that the weight loss, surface roughness and color change increased with the exposure time of samples to accelerated weathering conditions as compared to the initial property at the beginning of the test. The amount of weight loss during the testing increases with the amount of moisture fluctuation in samples during the test. Moisture fluctuation in sample during weathering was related to the weight loss of weathered samples indicating that the moisture fluctuation may be an indicator of durability. The lowest weight loss and water absorption were observed with Azobe, Padouk, Teak, Doussie and bilinga whereas highest weight loss were obtained for Moabi and Musinga. For color change, reddish, brownish, yellowish colored species such as padouk, Doussie, bilinga exhibit high values of color change parameter in comparison toMussanga light whitish colored species. .
S Pankras, Jinzhen Cao, D P Kamdem


The assessment by visual grading, change of color and ergosterol content ratings, the resistance to mould fungi of treated with wood preservative Scots pine sapwood
2013 - IRG/WP 13-20514
The filamentous (mould) fungi belonging to Ascomycetes, Deuteromycetes group are an cosmopolitan organisms which attacks wooden elements disfiguring them, dropping their value and causing environmental and health hazard. The fungi in a short time cause mainly disfigurement of wood does not effect on strength properties of wood, but with strong prolongation of duration of conditions favourable for their growth, some of them may cause even soft rot of lignocelluloses materials. The using of fungicides is one of the easiest methods to protect wood and other susceptible wood-based materials against mould fungi attack. So, good recognition of natural or given resistance of wood to mould fungi may be regard as important matter. There are some, mainly descriptive, laboratory methods for susceptibility of wood to mould fungi attack determining, however there are not European standards concerning the method. The aim of the research was an attempt of comparison of standard visual grading of mould fungi growth on wood surface with results of instrumental measuring of changes in wood colour and ergosterol content in wood resulting from the fungi growth. The samples of natural and treated with a model wood preservative Scots pine sapwood were the examples of tested materials. The test and control samples were exposed to the individual fungi: Aspergillus niger, Penicillium funiculosum, Paecilomyces variotti, Trichoderma viride, and Alternaria tenuis, and their Mixture (Set I) or set II: Chaetomium globosum fungus. It was observed that results of determinations of ergosterol concentration, seems to be between used methods more detailed and to show even greater differentiation of wood infestation grades than the evaluation based on the descriptive methods. The evaluation of wood infestation by fungi which was based on the measurements of colour changes of wood surface were also more detailed as visually evaluation, but the differentiation of wood infestation grades was not so distinct. The results of the instrumental measurement of the growth of mould fungi on wood may be considered at the moment as supplement to descriptive evaluations expressed in grades of fungi growth. Ergosterol content determination after further investigations may be an alternative to descriptive evaluations.
A Fojutowski, A Koziróg, A Kropacz


The effect of UV irradiation on some technological properties of different polyurethane varnishes coated plywood panels from veneers dried at different temperatures
2014 - IRG/WP 14-40661
In this study, the effect of UV irradiation on some technological properties of three different polyurethane varnishes coated plywood panels produced from Scots pine (Pinus sylvestris L.) and Maritime pine (Pinus pinaster L.) veneers manuactured and dried at different temperatures was studied. Accordingly, 32°C log peeling temperature and three different veneer drying temperatures (110, 140 and 160°C) were chosen. Five-ply-plywood panels with 10 mm thick were manufactured by using melamine-urea formaldehyde glue resin with 54% solid content. UV irradiation process, bonding strength, color measurement and surface roughness tests were conducted on plywood panels according to ASTM G53, EN 314, ISO 7724-2 and DIN 4768 standards, respectively. Polyurethane varnish (ingredients: 37% polyurethane, 63% water) coated plywood panels manufactured from Maritime pine (Pinus pinaster L.) veneers dried at 160°C showed the lowest color change values. The best protection on bonding strength was obtained from the polyurethane varnish (ingredients: 60% polyurethane, 11% xylene, 9% ethyl benzene, 20% 3-methoxybutyl acetate, 1% toluene-2,4-disocianate ) coated plywood panels manufactured from Scots pine (Pinus sylvestris L.) veneers dried at 110°C against UV irradiation.
Ö Özgenç, C Demirkir, Ü C Yildiz, G Çolakoğlu


Color change of timber exposed outdoors - Influence of season exposure test starts
2019 - IRG/WP 19-40865
For the client the material and color of the exterior wall are important, because they affect the impression of the building [1]. However, discoloration of the exterior wall begins as soon as the building is completed, by various factors such as rainfall. We tried to quantitatively evaluate the changes of the exterior wood, and to organize the influences of climate conditions, in order to use the discoloration as design factor. It seems that the difference in the color changes in an exterior wood surface is remarkably influenced by what season the test begins. In order to confirm the difference in the color changes, the starting test month was shifted by one month for each specimen. Those plates were scanned at some intervals to get image data and the chromaticity was measured with a colorimeter. As a result, the following was clarified. The color change was divided into the following two patterns. A: Red → yellow → white → black, B: Red → yellow → black. Black discoloration occurred due to the plate material reaching severe climatic conditions after the ΔL * value reached the maximum value. Lignin is eluted from wood with rain and decolored with ultraviolet rays to turn white [2]. However, it seems that the plate material becomes black as soon as it reaches high-temperature and humidity (without passing through the white period). We believe that the white period is the period until it is hit by hard climate conditions. When mild conditions continue, the white period is extended. Initial discoloration is slow under mild conditions.
K Usami, H Ishiyama


Effects of acetylation on the dimensional stability and decay resistance of kenaf (Hibiscus cannabinus L.) fiberboard
1996 - IRG/WP 96-40059
The objective of this study was to investigate the influence of the acetylation treated kenaf fiber, Phenol formaldehyde resin content level, and three fungi species on the dimensional stability and decay resistance of high density non wood composition boards. A standard ASTM method was used to evaluate weight loss and thickness change. The linear shrinkage and expansion of each species were also determined. All specimens were exposed to decay chambers for 16 weeks. Test results indicated that most of the main factors significantly influence the thickness, length changes, and decay resistance of the high density kenaf fiberboards.
P Chow, T Harp, R Meimban, J A Youngquist, R M Rowell


Combined effects of the treatment of wood with formaldehyde
1978 - IRG/WP 3117
Treatment of fibrous materials with reagents in a vapor phase is neither new nor unique. Numerous examples exist in literature of vapor phase experiments on cellulose fibers and fabrics, and on wood. For many years the textile research and industry have used vapor phase processes for the treatment of textiles. The chemical modification of cellulose is based on different types of reactions e.g. esterification, alkylation, resin formation or polymerization, monomer grafting and crosslinking. Vapor phase treatment of wood offers certain potential advantages over the conventional liquid phase wood impregnation. The higher mobility of low molecular weight compounds in the gaseous state ensures a rapid, uniform and homogeneous distribution throughout the wood structure. The vapor phase treatment of wood is also a better approach from the standpoint of cell wall penetration. Bulking, which takes place in the cell wall only, means that less chemicals are required and that the final weight of the composite is limited. Furthermore, due to the low viscosity of a gas, the application of a lower pressure differential remains possible. Within the framework of a wood improvement programme carried out at the Laboratory of Wood Biology and Wood Technology (University of Ghent, Belgium) the treatments were based on the impregnation of wood with liquid synthetic monomers and with gaseous formaldehyde. The results of the hygroscopic and dimensional behaviour of the wood-plastic-combinations have been published previously. Other papers deal with the physical and chemical interactions between the synthetic products and the natural polymers of the cell wall. This contribution will be restricted to the treatment of wood with formaldehyde in the gaseous state.
M Stevens, J Schalck


Weather testing of timber - discoloration
2001 - IRG/WP 01-20221
The brightness and color saturation of the timber were reduced over time. The perception of an increasingly dark color in the timber over time is due to the gradual reduction in brightness. The period from May to September was characterized by the greatest discoloration of all three periods of the year. Because this period has the largest number of sunlight hours, and the timber is subjected to a greater amount of sunlight. Furthermore, the period from May to September coincides with the rainy season in Japan, which adds to the discoloration.
T Toyoda, M Azuma, Y Hikita


Biodegradation of acetylated southern pine and aspen composition boards
1994 - IRG/WP 94-40020
This objective of this study was to investigate the influence of the acetylation treated wood fiber, Phenol-formaldehyde resin content level, two wood fiber species, three fungi species on the dimensional stability and decay resistence of high density composition boards. A standard ASTM method was used to evaluate weight loss and thickness change. The linear shrinkage and expansion of each species were also determined. All specimens were exposed to decay chambers for 16 weeks. Test results indicated that most of the main factors significantly influence the thickness and length changes and the decay resistance of the high density composition boards.
P Chow, T Harp, R Meimban, J A Youngquist, R M Powell


Effects of boron treatments on partially decayed oak and pitch pine heartwood
1996 - IRG/WP 96-30106
This paper reports results of borate based preservative treatment and leaching experiments on partially decayed oak and pitch pine heartwood. Previous experiments have shown little damage is caused to sound timber of these types when treated with Polybor and Boracol 20 preservatives. This experiment was carried out to assess the suitability of selected borate based preservatives for use in historical ships' timbers and therefore the physical effects of these preservatives on such timber was investigated. The results indicate that weight losses incurred due to treatment with Polybor or Boracol 20 are no more damaging than those incurred by treatment with water. Weight changes were more apparent in decayed timber than in sound timber with greater uptakes in non-leached samples and greater weight losses in leached samples. However, comparable weight changes were recorded between water treated samples and preservative treated samples. Dimensional changes were minimal in most cases, the greatest found in non-leached Boracol 20 samples as expected. These results indicate that treatment with these preservatives is suitable for partially decayed oak and pitch pine heartwood.
S McCutcheon, G M Smith, J W Palfreyman, P Durrant


Effect of cyclic change of temperature on fungal growth and mass loss
1994 - IRG/WP 94-10065
For estimating the effect of cycling change of temparature on fungal growth, four Japanese species, sugi (Cryptomeria japonica), hinoki (Chamaecyparis obtusa), akamatsu (Pinus densiflora) and buna (Fagus crenata), four fungal species, Tyromyces palustris, Gloeophyllum trabeum, Coriolus versicolor, Pycnoporus coccineus, and five temperature conditions, 10, 20, 27, 35°C and cyclic temperature (20°C 12 hours and 30 or 27°C 12 hours) under constant humidity (75% RH) were examined. The results were summarised that the cyclic condition was rather high fungal growth rate in the case of majority of fungi tested but was not surely increased the mass loss of wood. This tendency is rather clear in the case of brown rot like Tyromyces palustris. The cyclic temperature conditions were not favorable to the groth of Serpula lacrymans.
K Suzuki, K Okada


Steam/hold/APM boron treatment - Treatability trials with green gauged radiata pine
1987 - IRG/WP 3439
Freshly sawn 100 x 50 mm radiata pine was green gauged, steam conditioned and preservative treated with a mixture of borax and boric acid using a modified Alternating Pressure Method (APM) treatment schedule. A 12 hour holding period between steam conditioning and treatment resulted in the necessary moisture loss and moisture re-distribution to facilitate treatment to NZ Timber Preservation Authority preservative retention and distribution requirements.
P Vinden


The impact of global warming on the UK distribution of house longhorn beetle Hylotrupes bajulus (L)
2001 - IRG/WP 01-10414
This paper reviews the effects of global warming on insect populations and distribution. The affects of global warming on the spread of Hylotrupes is predicted through a review of research related to the influence of temperature on its life-cycle and flight. Records of Hylotrupes distribution were obtained from published surveys, entomologists and museum collections and were plotted for the UK. The UKCIP98 model for climate change was then used to present the average maximum daily temperatures over the emergence period at present, and in the future. The model predicts a 3°C rise in annual temperature by the 2080's. This increase may enable mated females to fly on a greater number of days and over a greater area. The discussion highlights gaps in knowledge concerning the UK population that makes rate of spread difficult to predict at present.
P Oevering, A J Pitman


Preliminary investigation on the natural durability of Guayule (Parthenium argentatum)-based wood products
2000 - IRG/WP 00-40154
Conventional preservatives used to protect wood from insect and microbial damages are presently of major concern to human health and the environment. Finding alternative and economical preservatives has not been successful. Previous studies have shown that the resinous material extracted from the guayule plant (Parthenium argentatum, Gray) has both insect- and microbial-resistant properties. Unfortunately, it has not been accepted commercially because of the lack of an adequate supply of the raw material. However, the potential domestication of the guayule plant to produce hypoallergenic rubber latex will result in the production of large amounts of waste wood material. This should provide opportunity to use this natural source of the biologically resistant resinous chemicals. The objective of this preliminary study was to determine the effects of the rubber latex-removed wood residues or bagasse and the resinous extracts on termite- and decay-resistant properties. Two types of test materials were used in the study. One was wood impregnated with organic-solvent extracted resinous material from the plant. The other was composite wood fabricated using the residue or whole plant and plastic binder, which was used to improve the physical properties of the composite. Accelerated laboratory tests were conducted to determine the resistance of the wood products against the Eastern subterranean termite and wood fungi (brown-rot). The wood and stem of the guayule plant, wood treated with the resinous extract, and particle and composite wood made from ground guayule exhibited termite and wood fungal resistance.
F S Nakayama, P Chow, D S Bajwa, J A Youngquist, J H Muehl, A M Krzysik


A New Decay Hazard Map for North America Using the Scheffer Index
2008 - IRG/WP 08-10672
Wood decay experts in the USA and Canada use the Scheffer Index for above-ground wood decay potential to decide among design and treatment options to ensure the durability of wood construction. This paper provides an updated North American decay hazard map and includes data on Central America. Index values calculated from recent climate data are higher than published values due to directional or cyclical climate change. Compared to previously published maps there is considerable expansion of the moderate decay hazard zone in the interior wet belt of British Columbia, across the northern edge of the Prairies and around the Gulf of St. Lawrence. This suggests a greater need for preservative treatment in these parts of Canada.
P I Morris, J Wang


Theory of Aesthetics – Charm in Furniture and an Aesthetic Evaluation of Bleaching of the Natural Color of Wood through the Application of Experimental Bleaching Process
2007 - IRG/WP 07-30424
This paper consists of mainly three sections: In the first section, brief information is given on the theory of aesthetics as a branch of philosophy, historical progress of the aesthetics theory is summarized within the context of the term “beautiful”, and aesthetic values as well as the color and aesthetic effects of color in preparing the designs are explained. In the second section, relation between the wood and color is discussed from the viewpoint of aesthetic value, and information is given on the proposed method for bleaching the natural color of wood to some degree in order to develop the aesthetic value and increase the existing charm performance. In the third section, the bleaching methods applied for Scotch pine, Oriental beech, and Black poplar by using different hydrogen peroxide recipes for each are introduced, and the results obtained are evaluated from an aesthetic point of view.
I Usta


Wood protection, a tool for climate change mitigation?
2008 - IRG/WP 08-50257
In the context of global warming and the search for possible strategies to mitigate climate change, forest and forest products have important advantages. Sustainable management makes forest a carbon sink, wood products have the potential to be a carbon sink as well, and their low carbon intensity is a potential for reducing CO2 emissions by substitution to competing materials. After describing these assets of wood products, this paper analyses how wood protection can reinforce them. This reinforcement effect is probably important, but still needs to be quantified.
G Deroubaix


The Effects of Solar Radiation on the Fungal Colonization and Color of Weathered Wood
2008 - IRG/WP 08-10676
Solar radiation rapidly depolymerizes lignin at wood surfaces exposed outdoors producing a suite of low molecular weight aromatic compounds within weathered wood. Fungi colonizing weathered wood are able to metabolize these aromatic compounds, and many of them also contain high levels of melanin to protect themselves from the harmful effects of UV radiation. Both of these adaptations suggest that solar radiation directly and indirectly influences the colonization of weathered wood by fungi. In this study we test the hypothesis that exposure to solar radiation affects the colonization of wood by fungi and the resulting color of the weathered wood. Lodgepole pine decking samples were exposed outdoors for 40 weeks under filters which blocked selected regions of the solar spectrum while allowing other weathering factors to act on samples. Fungi growing at the surface of wood exposed under the different filters were isolated at the end of the exposure period and identified using molecular techniques. The color of the isolated fungi and the weathered wood were also assessed. Wood exposed under filters that transmitted ultraviolet and/or visible light was more frequently colonized by dark colored fungi such as Aureobasidium pullulans and Hormonema dematioides than samples exposed under filters that blocked these components of the solar spectrum. A. pullulans and H. dematioides were also isolated from wood exposed under filters that blocked UV radiation and visible light, but a greater proportion of lighter fungi such as Epicoccum nigrum and Phoma sp. were found in the weathered wood. The color of weathered wood at the end of the exposure trial partly reflected the pattern of fungal colonization. Wood exposed under filters that blocked UV radiation and visible light was greener and lighter than wood exposed under filters that transmitted these wavelengths. We conclude that solar radiation influences the colonization of wood surfaces by fungi and our findings point to a link between the color of the weathered wood and the fungi that colonize the wood.
V Hernandez, C Breuil, P D Evans


High Temperature Treated Wood
2008 - IRG/WP 08-40429
High temperature can modify internal structure and physic-chemical properties of wood by a controlled pyrolysis process. Such treatment, among other changes in properties, modifies the wood color in a way that resembles exotic species, increasing its market value. The main objective of this work is to determine the changes in wood properties caused by the effect of temperature and time, in order to establish patterns of time for treatments performed at 220 °C through correlations based in heat transfer concepts. The high temperature treatment will be set at 220 °C during 20, 30 e 40 minutes in body tests of Pinus spp, using an electric wood dryer without steam, while the volume and mass of the wet wood, the dry wood (0%) and after the treatment ends will be controlled and measured. The results of alterations in color, hardness and dimensional stability of the wood and the data (with different temperature treatments) will be useful to set standards for high temperature treatments using theoretical concepts of heat transfer applied to the wood material, considering the wood properties variation, including cost effectiveness of wood products.
C C Borges, A L Barbosa, R Faber de Campos, S T Targas


Effectos de la intemperización artificial sobre la madera de mezquite (Prosopis laevigata)
2008 - IRG/WP 08-40430
The effects of artificial weathering on Prosopis laevigata wood were studied on eight replicates (150 x 72 x 15mm (l x t x r)) free of knots, cracks and resin. The samples were exposed tangentially to UV light and to water spray during three cycles (1 cycle corresponded 1 week of artificial weathering). The conditioning time between each cycle was thirty days. The effects were measured according to visual appearance, crack formation, and colour changes; the results were then compared to two other well known timber species, namely teak (Tectona grandis) and beech (Fagus sylvatica). The specimens displayed changes in colour after three cycles of exposure. P. laevigata changed from brown to white. Delta C (Delta colour) increased from 5.6 to 9.6. There was less crack formation than in F. sylvatica but more than in T. grandis. Lightness was reduced from 61 to 37 after the first cycle; the lightness value of 35 was maintained at the end of the second and third cycles. The P. laevigata specimens showed several changes in colour after artificial weathering. The Delta C was higher due to the photodegradation of lignin and phenolic compounds caused the UV light and the leaching caused by water.
A Carrillo-Parra, F Hapla, C Mai


Colour change monitoring of photodegradation in Scots pine (Pinus sylvestris) – a short term focus
2009 - IRG/WP 09-40442
Colour change monitoring of photodegradation is a quick and easy method for monitoring rates of photodegradation in timber. A study was undertaken to compare this technique to other monitoring methods, including microtensile strength changes and weight loss. Colour changes due to accelerated sunlight exposure were monitored using a Datacolor check spectrophotometer and compared with a set of controls. Measurements on both samples and controls were performed hourly for the 1st 24 hours and there after daily until 168 hours’ exposure with extra measurements at 200, 350 and 500 hours. A subset of samples, were extracted prior to exposure to check the effects of any colour change due to the presence of extractives. Data was analysed using the reflectance spectra (400-700nm) as well as the CIE-L*a*b* system and ΔE. The majority of colour changes were found to occur within the 1st 24 hours. This was unaffected by the removal of extractives from the wood and was independent of temperature. When compared to the other monitoring methods, colour monitoring has been shown to be the most sensitive method out of the methods compared for monitoring photodegradation in Scots pine.
V Sharratt, C A S Hill, D P R Kint


Vacuum drying of European oakwood: Color, chemistry and anti-oxidant potency of wood. Improving appearance in forest value added products
2008 - IRG/WP 08-40432
In hardwoods used for decorative and appearance purposes, wood colour is one of the most important factors of wood quality; in addition colour is related with durability and biological decay of wood. Wood discolouration during drying is mainly affected by heat, light, physiological reactions, combinations of reactions, biochemical and chemical reactions, and micro-organisms attack. In freshly felled and stored round wood discolorations are initiated predominantly through physiological reactions of living parenchyma cells. Discolouration during kiln-drying decreases the commercial value of hardwoods, since hardwoods are used in the manufacture of furniture and cabinets. On one hand, heat modifies the cell wall components and induces chemical reactions of nutrients and extractives, by other hand the role of oxygen in kiln dryers is very important due to oxidation reaction of phenolic compounds. The formation of coloured substances from a phenolic compound oxidized with air and the formation of dark materials from hydrolysable extractives are considered causes of discolouration. In order to reduce oxidation reaction, vacuum drying process can be used. In addition, it offers reduced drying times and higher end-product quality in comparison with conventional drying operations. Operating at low pressures reduces the boiling temperature point of water and enables an important overpressure inside the material which is advantageous for drying and especially for species that do not support a high temperature level. In this work, experimental results for the vacuum drying of oakwood with conductive heating are presented for different drying conditions. In particular, surface-wood scans, antioxidant capacity of wood, Fourier Transform Infrared Spectra of dust-wood for different vacuum and convective drying conditions. Sample temperatures and pressure in the dryer are logged during drying. The experimental setup (Figure 1) is a vacuum chamber where pressure is regulated between two values (Pmin, Pmax). The chamber is built in glass; one balance is kept inside the chamber in order to log the mass variation of the sample. A thermometer gives the dryer temperature. The heating source is an electrical resistance which temperature is controlled with the help of a PID controller. Experiments are performed on Oakwood disks (7 cm diameter and 2.5 cm height). The conductive heat source is maintained at different temperatures (46°, 61° and 70°C) and pressure in the chamber is controlled at different intervals (60-100, 150-200, and 250-300 mbar). Temperature inside the wood sample is obtained at two different positions. Conventional drying is carried out for comparison in a tunnel dryer. Antioxidant potential in fresh and dry wood samples is determined by using ABTS+• radical cation method. The top surface of vacuum-dried specimens is imaged with an HP scan. Finally it is shown that oak wood which is prone to discolour is degraded by different mechanisms depending on drying method. Our results suggest that oxidation of extractives and thermal degradation of hemicelluloses are the principal mechanisms of degradation, but its importance depends on drying method. Oakwood can be dried under vacuum conditions with an acceptable diminution of discolorations due to low temperature and reduction of oxygen amount with acceptable drying rates.
S Sandoval, W Jomaa, F Marc, J-R Puiggali


Estimating the heat treatment intensity through various properties of thermally modified timber (TMT)
2009 - IRG/WP 09-40459
The suitability of different measures for prediction of the heat treatment intensity was investigated. Therefore, the resistance to impact milling (RIM), the lightness L*, the equilibrium moisture content (EMC), the anti swelling efficiency (ASE) and the total amount of soluble carbohydrates (TSC) of heat treated specimens were correlated with corresponding fungal resistance achieved by heat treatments. Heat treatment temperatures of 180°C, 200°C, 210°C, 220°C, and 240°C for various heat treatment durations from 0.25 to 72 h were applied. The results show, that the decrease in mass (dm) by heat treatments is a suitable measurand to describe the treatment intensity, which is a product out of treatment temperature and duration, where the impact of temperature is predominating the impact of time. The properties examined showed a strong reciprocally proportional relationship with the decrease in mass. Thus different correlations were found for the various treatment temperatures: The higher the temperature applied, the lower was the decrease in mass required for an equivalent improvement of certain wood properties, e.g. biological durability, EMC, and dimensional stability. However, mass loss by Poria placenta correlated well with the resistance to impact milling (RIM), lightness L*, EMC, ASE and TSC of the different heat treated specimens, depending on the heat treatment temperature. Consequently, a reliable estimation of improved fungal resistance of TMT, as well as the quality control of TMT in general, strongly requires certain process information.
C R Welzbacher, C Brischke, A O Rapp


Termite taxonomy and distribution with particular reference to climate change in Africa
2010 - IRG/WP 10-10738
Termites constitute an integral component of various ecosystems in Africa. Termites are also amongst the most difficult of the insects to study because of their cryptic behaviour. There are around 2600 species of termites (Isoptera) in 280 genera which have been described worldwide and about 39% of the total termite species are found in Africa. Some termite species are well known pests of agricultural crops, forest trees, wood products and timber-in-service. Thus, they are responsible for considerable damage in building structures in Africa. Termite identification is crucial to understanding termite distribution and to develop an integrated termite pest management (IPM) system. Published literature on the taxonomy and distribution of termites in Africa with particular reference to climate change is scanty. Little is known about the effect of climate change on the potential distribution of pestiferous termite fauna of Africa, especially the wood destroying exotic species. This African termite review attempts to collate information on termite taxonomy, distribution and climate change and highlight the gaps in knowledge and challenges in Africa, which is the centre of origin of the Macrotermitinae. African economic important termite species will receive sufficient attention for identification and distribution compared to other termite species. The use of traditional identification methods coupled with molecular techniques promises to resolve some of the challenges in termite taxonomy and distribution with particular reference to climate change in Africa, will be discussed.
P O Y Nkunika, B M Ahmed Shiday, G W Sileshi, J R J French, P Nyeko, S Jain


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