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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

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

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

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

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

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

TMT–Interlab–Test to establish suitable quality control techniques - Structure and first results
2010 - IRG/WP 10-40503
As a result of growing quality demands from manufacturers and end-consumers of thermally modified timber (TMT) recent scientific research activities are increasingly focussed on modification mechanisms and by this on the development of suitable quality control methods. To deepen the knowledge in modification mechanisms and to obtain a larger variety of scientific data for TMT depending on the treatment intensity, a worldwide interlaboratory test series with TMT was started with nine research institutions involved, each contributing with their own most appropriate techniques and experiences. Therefore European beech and Norway spruce were thermally modified with different treatment intensities at Leibniz University Hannover and allocated to the involved partners. Basic treatment and material characteristics of the TMT used in the tests are presented in this paper and show that the decrease in mass by thermal modification (dm) is a suitable measure to describe the treatment intensity both for beech and spruce. Furthermore, color values and static mechanical strength properties proved to be highly correlated with dm. Consequently a strength prediction of TMT by color values appears applicable. Furthermore, correlations of dm with other target properties and further indicator measures are promising.
C R Welzbacher

Improvement of the biological performance and dimensional stability of two tropical woods by thermal modification
2012 - IRG/WP 12-40605
Pink cedar wood and rubberwood were thermally modified at 230°C in air for 4 h or for 8 h, and then subjected to bending, compression and hardness tests to evaluate the effect of the treatment on these mechanical properties. The biological performance of the modified wood was also determined, according to EN113, and the dimensional stability measured by means of the anti-swelling efficiency. The thermal modification afforded increased decay resistance and improved the dimensional stability of these tropical woods, at the expense of significant reductions in the Modulus of Rupture and the Work at Maximum Load in the bending test. The reduction in bending strength and in resilience was not significant at the limit of proportionality though; the modified material is hence deemed as suitable for non-structural applications where the occurrence of sudden loads shall not lead ultimately to human harm. Color changes resulted in aesthetic enhancements on these two wood species, particularly so in pink cedar wood. These color changes were readily exploited for the multivariate prediction of all properties studied in this work, including the decay resistance of thermally-modified wood.
M M González-Peña

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

Effectiveness of Copper Indicators in Treated Wood Exposed to Copper Tolerant Fungi
2014 - IRG/WP 14-20554
Wood treated with a copper based wood preservative will typically turn a green color. While the depth of copper penetration can be readily discerned from the green color of the copper it is standard practice in research and commercial treating plants to make use of a color reagent such as Chrome Azurol S, Rubeanic acid or PAN indicator to reveal the penetration more clearly. When copper treated wood is exposed to copper tolerant fungi discoloration of the original green color can occur. Reactivity of the treated wood with the color reagents can also be impaired. In this paper, the effectiveness of copper color indicators in detecting copper in wood attacked by copper tolerant brown rot fungi at early and late stages of decay was evaluated. Neither Chrome Azurol S nor PAN indicator could detect copper in the area where incipient and severe decay took place, even when chemical analysis showed significant levels of copper in these areas. Rubeanic acid was the only indicator which provided positive identification of copper in these samples. An FTIR study demonstrated that the loss of green color in copper treated wood by copper tolerant fungal attack is closely related to the formation of copper oxalate. The finding supports the theory that copper oxalate detoxifies copper and acts as a precursor for decay since a significant amount of copper oxalate was found in the area with discoloration but no visual decay, as well as in the area with severe decay. The results from this study suggest that the ineffectiveness of Chrome Azurol S and PAN indicators may be due to their inability to replace oxalate ion to form the colored complex with copper.
L Jin, K Brown, A Zahora, K Archer

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

Evaluation of color and gloss in decorative applied to cases of Pinus radiata wood impregnated (D. Don) copper type C azole micronized
2015 - IRG/WP 15-20571
Six treatments (one control and five decoration coatings) were applied to radiata pine wood treated with micronized copper azole (uCA-C), for outdoor use (R3) at a rate of 3.08 kg/m3 retention (T2). One decoration coating was applied before impregnation treatment: Prestain P (T3), and two, were applied in mixture with the uCA-C preservative Black Cylinder (T5) and Red Cylinder (T4). Two varnish were tested: a water-based varnish (T6) and solvent based varnish (T7). Additionally, untreated radiata pine specimens were tested as a reference (T1). The changes in gloss and color of these five decorative coatings were evaluated after they were subjected to natural aging tests (EN) for three months, and accelerated aging trials (EA) during an exposure to UV radiation of 340nm for 500 hours. In EA treatments changes in gloss and changes in color showed the lowest variation in T3 and T5, and highest variation in treatment trial T4. In EN trials, changes in gloss and color showed their lowest variation in T3 and T5.The costs of each decoration coating were assessed in terms of performance by timber volume to be coated. The lower cost of the three decoration treatments was T3, with a value of US$ 16 m3, followed by T5 with a value of US$.24/m3. Compared to alternative siding products available on the market, such as fiber cement and vinyl siding, coloured treated wood with prestain P is competitive with vinyl siding and 58% lower cost than fiber cement.
R Garay, M Inostroza

Characterization of biofilm formation on wood treated with vegetable oils by color-based image interpretation method
2015 - IRG/WP 15-40697
The protection of wood in order to extend its service life is an important issue nowadays. As an alternative to traditional wood coatings biofilms can be used. It is a living protective coating for the wood surface against UV and bio-degradation that has the ability to recover from local damage, such as cracks. This paper presents preliminary results of biofilm formation from an 8-month’s field test experiment containing yellow pine (Pinus) and beech (Fagus) impregnated with an olive and linseed oil. Oil treated samples together with non-oil treated as a reference were exposed to natural outdoor conditions on the roof of Eindhoven University of Technology in the Netherlands. Biofilm formation was monitored periodically by imaging wood surface of samples with a digital camera. A method to analyze biofilm appearance on different wood types and oils was proposed. The analysis is based on quantification of the darkening of the wood surface. Current results show that olive oil and beech is the best combination for biofilm formation. The reason for that might be the difference in wood structure and the fact that olive oil cross-link slower compare to linseed oil. Further studies on the role and state of oil, substrate and weather conditions are needed.
K Filippovych, H Huinink, L van der Ven, O C G Adan

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

Optimized composition of alkyd emulsion with nanoparticles of iron oxide for enhancing protection of thermally modified wood
2022 - IRG/WP 22-40940
Thermal treatment is acknowledged as an environmentally friendly method to improve durability of wood and some of its properties, such as biological resistance, dimensional stability, reduced hygroscopy. Despite these improvements, when used outdoors, also thermally treated wood is subjected to the action of environmental factors, like solar radiation, moisture, precipitations, temperature, etc., giving place to a series of chemical and structural transformations, defined as “weathering”, which negatively affect its service life. In this research an alkyd emulsion containing red transparent iron oxide pigments was obtained, whose composition is optimized to protect the decorative properties of thermally treated wood during outdoor exposure. In particular, attention was dedicated to the selection of surfactants for the emulsification of resins and to the investigation of oxidative properties of alternative metal primary driers, which could replace the cobalt. Initially the surface wetting properties of thermally treated wood were investigated and considered for the optimization of the alkyd emulsion formulation. The determination of the surface energy of wood, by means of contact angle, before and after thermal treatment shows that the polar component of the surface energy decreases with increasing temperature of thermal treatment. This explains the more hydrophobic character of thermally treated wood, which must be considered for the formulation of suitable paints and the selection of appropriate additives. In the second part of the research, artificial weathering test was carried out to determine the suitable concentration of red transparent iron oxide pigments, which can give better protection against photodegradation and minimize the color changes of wood surface. The obtained results show that a concentration of 8 % for red transparent iron oxide pigments in alkyd emulsion is necessary to ensure protection of the thermally treated wood surface. Another important conclusion from the obtained results is that the replacement of organic solvent with water is possible and paint with comparable or even better efficiency can be obtained.
E Sansonetti, D Cīrule, I Andersone, B Andersons, E Kuka