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Thermal treatment of wood: European Processes and their background
2002 - IRG/WP 02-40241
Recent efforts on thermal treatment of wood lead to the development of several processes introduced to the European market during the last few years. The total production capacity of heat treated wood in 2001 is estimated as approx. 165.000 m3. In the paper the different heat processes are presented. The general technology as well as scientific data on the chemical transformation of the cell wall polymers, on the biological performance, on the physical and mechanical properties of the treated wood are presented and discussed
H Militz


Durability of pine modified by 9 different methods
2004 - IRG/WP 04-40288
The decay resistance was studied for pine modified by nine methods of wood modification: 1) Acetylation, 2) Treatment with methylated melamine resin (MMF), 3) Acetylation followed by post-treatment with MMF-resin, 4) Thermal modification, 5) Furfurylation, 6) Maleoylation (using water solution of MG or ethanol solution of maleic anhydride), 7) Succinylation, 8) NMA-modification and 9) modification with reactive linseed oil derivative (UZA), Wood blocks of Scots pine (Pinus sylvestris L.) sapwood were modified in pilot plants. Methods 1-5 were performed by the authors at Chalmers University of Technology or at BFH in Hamburg. Methods 5-9 were part of a European research project (the Chemowood project, FAIR-CT97-3187) and therefore each of these modifications was performed by the project participant responsible for the method. For laboratory testing in TMCs (modified European standard ENV 807) and pure basidiomycete culture bioassays, smaller test specimens were cut from the modified wood blocks. Most of the modification methods were applied on test specimens for marine field testing (EN 275) and some methods to produce mini-stakes for field tests in five Swedish fields. Some modification methods result in modified wood with poor durability, whereas other methods (acetylation, furfurylation and MMF-treatment) seem to provide excellent resistance to microbial decay.
M Westin, A O Rapp, T Nilsson


Corrosion of fasteners in heat-treated wood – progress report after two years’ exposure outdoors
2005 - IRG/WP 05-40296
The corrosion of common fastener materials now in use - mild steel, zinc-coated steel, aluminium and Sanbond Z-coated steel – has been evaluated after two years’ exposure outdoors in untreated and heat-treated spruce (Picea abies) respectively. Spruce from South-western Sweden was used. The heat-treatment was carried out in Finland according to the ThermoWood process at a maximum temperature of 220 °C for five hours. The results so far show that the corrosion of fasteners in heat-treated wood according to the particular specification is more severe than in untreated wood. Mild steel and zinc-coated steel has been most susceptible. Stainless steel is hardly attacked at all.
J Jermer, B-L Andersson


Improved resistance of Scots pine and Spruce by application of an oil-heat treatment
2000 - IRG/WP 00-40162
Spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.) were subject to a heat treatment which was carried out in an oil-bath. The aim was to improve the dimensional stability of the treated wood and its resistance against fungi. The bath of vegetable oil provides a uniform heat transfer at temperatures of 180°C, 200°C and 220°C and protects the submersed wood from oxygen. Heat treatment in air atmosphere was also carried out at the same temperatures for comparison. Wood treated in hot oil was more equal in its appearance than wood heated in hot air. The treatment of spruce and pine in the oil-bath resulted in a better resistance against Coniophora puteana in a lab test according to EN 113 compared to the treatment in air atmosphere. In order to achieve the wanted upgrading effect, certain changes of mechanical properties and colour must be accepted. However, the strength loss caused by the heat-treatment in oil was less severe than in air atmosphere. Since all materials and the energy used in the process originate from renewable resources, the oil-heat-treatment appears to be environmentally friendly. All in all, the heat treatment in oil might be a promising approach to upgrade wood for outdoor use.
M Sailer, A O Rapp, H Leithoff


The effects of heat treament on the specific gravity of beech and spruce wood
2003 - IRG/WP 03-40254
The effects of heat treatment on specific gravity of beech (Fagus orientalis) and spruce wood (Picea orientalis) naturally grown and intensively used in forest products industry in Turkey were studied. The wood samples were cut into 2 x 2 x 3 cm. Heat treatment was than applied to the wood samples at four different temperatures (130 °C, 150 °C, 180 °C and 200 °C) and three different durations (2 h, 6 h and 10 h) under air atmospheres. The results indicated that the specific gravity values treated by heating generally exhibited a decrease with increasing the exposure durations and temperatures compared to the untreated wood samples.
S Yildiz, Ü C Yildiz, G Colakoglu, E D Gezer, A Temiz


The effects of heat treatment on the toughness of beech wood
2004 - IRG/WP 04-40283
The effects of heat treatment on toughness of beech (Fagus orientalis) wood naturally grown and intensively used in forest products industry in Turkey were studied. The wood samples were cut into 5 x 5 x 5 cm. Heat treatment was than applied to the wood samples at three different temperatures (130 °C, 150 °C and 180 °C) and three different durations (2 h, 6 h and 10 h) under air atmospheres. The results indicated that the toughness values treated by heating generally exhibited a decrease with increasing the exposure durations and temperatures compared to the untreated wood samples.
S Yildiz, Ü C Yildiz, E D Gezer, Ali Temiz, E Dizman


The effects of heat treatment on anatomical changes of beech wood
2004 - IRG/WP 04-40284
The effects of heat treatment on anatomical changes of beech wood (Fagus orientalis) naturally grown and intensively used in forest products industry in Turkey were studied. The wood samples were cut into 2x2x3 cm and than conditioned at 25 °C and 65 % relative humidity for 3 weeks. Heat treatment was than applied to the wood samples at four different temperatures (130 °C, 150 °C, 180 °C and 200 °C) and three different durations (2 h and 10 h) under air atmospheres. The anatomical changes were determined for each heat treatment variation.
Ü C Yildiz, Z Gerçek, B Serdar, S Yildiz, E D Gezer, E Dizman, A Temiz


Heat treatment of wood strands for OSB production: Effect on the mechanical properties, water absorption and dimensional stability
2002 - IRG/WP 02-40238
The effect of heat treatment on the mechanical and physical properties of commercial OSB strands was evaluated. Heat treatment was applied under inert atmospheric conditions to wood strands. The aim of this study was to examine the heat treatment parameters to achieve significant reduction of thickness swelling (upon exposure to moisture in service) without causing excessive reductions in strength. Heat treatments of 200, 210, 220, 230, 240, 250, and 260°C for 20 minutes were applied and swelling tests were performed. Subsequently the modulus of rupture and modulus of elasticity were measured in wood strands. High temperature treatments resulted in significant reductions in thickness swelling of wood strands but resulted in 20% reductions of modulus of rupture and modulus of elasticity.
G J Goroyias, M D C Hale


Investigation of some technical properties of heat-treated wood
2003 - IRG/WP 03-40266
The objective of this study was to investigate some technical properties of heat-treated wood. Wood heat-treated according to a process intended for wood in above-ground end-uses (European hazard class 3) was subject to the following: · A delamination test according to EN 391 with glulam beams made of heat-treated pine (Pinus sylvestris) and spruce (Picea abies) laminations, assembled with PRF and PVAc adhesive respectively. · Determination of the withdrawal load for screws and nails. · Determination of the emission factor for VOC and the identification of major compounds. Results: · PRF adhesive performed very well whereas PVAc adhesive showed an unacceptable percentage of delamination and thus seems to be unsuitable for gluing heat-treated wood. · There is an indication that the withdrawal load for heat-treated wood is generally lower than for untreated wood. However, the number of tests carried out was quite small and definitive conclusions are difficult to draw. · The emission factor for the heat-treated wood, expressed as TVOC, was less than 10 µg/(m2 x h) and this was less than for untreated reference.
C Bengtsson, J Jermer, A Clang, B Ek-Olausson


The Effect of Heat on the Retention of Ammoniacal Copper Quat (ACQ-AB) onto Scots Pine (Pinus Sylvestris L.) Wood
2008 - IRG/WP 08-40390
In this study, the sapwood of Scots pine (Pinus sylvestris L.) were treated with ammonical copper quat type (ACQ-AB), which is one of the environmentally friendly wood preservatives, by using soaking method as a functions of various temperatures and time. The results indicated that the retention behaviour of ACQ onto the wood was considerably affected by temperature of ACQ solution and treatment time.
M Hakki Alma, A Mukremin Kara


Novel wood modification processes for window and cladding products
2004 - IRG/WP 04-40285
Because of the low natural durability and low dimensional stability of European wood species, the usage of wood for window frames has decreased dramatically during the last decade. In a joint project of several German research institutes and the window industry, following wood modification systems were compared. heat treatment (3 different materials from 2 companies) acetylation (pine sapwood and beech wood acetylated with acetic anhydride) polymerisation (melamine resin treated pine sapwood, Interlace treatment, furfurylation) wax treatment (pine sapwood, which was impregnated with natural resin and waxes) Investigated was the moisture content, dimensional stability, capillary water uptake and the durability. The dimensional stability show a high increase for following materials: heat treated wood, acetylated pine, interlace treated wood and furfurylated wood. The melamine resin treated wood and the wax treated wood show no significant increase in the dimensional stability. The biological durability against different basidiomycetes was tested according to the EN 113. As test fungi, Coniophora puteana, Poria placenta and Coriolus versicolor were used. The results show a very high increase in the durability for most of the treated wood. The wax treated wood shows no significant increase in durability. A novel window frame consists of several functional layers. Different wood properties are demanded for the single layers to achieve optimal window properties. Every modified wood shows a special potential for the use in a functional layer.
A Krause, C Hof, H Militz


Radio frequency heating times for sterilization radiata pine solid piles
2017 - IRG/WP 17-40815
In this work was sterilized wood packaging material of radiata pine, stacked as solid piles without stickers, for determining the heating times using radiofrequency treatment. The experiments were performed in a radio frequency semi-industrial equipment. The results showed that the radio frequency heating times increases with wood volume and that radio frequency treatments were faster than conventional vapour heat treatment.
H Esquivel, V Sepúlveda, J Torres, L Salvo, R A Ananías


Effects of artificial UV weathering and soft rot decay on heat treated wood
2005 - IRG/WP 05-40302
Oil and inert gas oven heat treated pine wood strips 100 µm thick were mildly heat treated (200°C, 30 mins linseed oil, 120 mins oven). Following treatment, specimens were exposed to UV weathering (300 hours) and decay by the soft rot fungus, Chaetomium globosum. The effects of each treatment were assessed by zero span tensile testing, microscopy and by FTIR. Tensile testing of heat treated strips showed greater strength losses in the oil treated samples (73%) than in the oven treated samples (26% loss). Heat treatment darkened the wood strips but this was photo-bleached on exposure to UV artificial weathering. The UV exposure caused some loss in tensile strength (35%) but the additional effects of UV on the tensile strength were less in heat treated wood (oil 15%, oven 18%). The combined effects of UV and fungi on the tensile strengths were less severe for treated wood than in untreated wood, (oil 4%, oven 18%) thus some protection was afforded by the heat tretaments. Exposure of untreated wood strips to the soft rot fungus caused some loss in tensile strength (32%), but heat treated wood showed small but not statistically significant gains in tensile strength after fungal exposure (oil, gain 30%, oven, gain 3%). Microscopic examination confirmed that a soft rot was minimal in heat treated samples, i.e. it was mainly confined to wood cell wall penetration. The combined effects of UV and fungi caused further losses of tensile strength in both oven and oil heat treated samples, but this loss was less severe than that which occurred in untreated controls. However, due to the severity of the initial losses caused by the oil heat treatment, the highest losses overall were in those oil heat treated samples exposed to UV (82%) and UV and decay (78%). Microscopic examination revealed that decay was more advanced in UV exposed samples. The FTIR spectra of oven heat treated samples did not show any change, while the oil heat treated samples increased absorbance at 1737cm-1 and 1450cm-1 relating to the presence of oil. Following fungal decay, no changes were observed, this corresponds with the cavity attack by soft rot fungi, which leave adjacent portions of cell wall material untouched. The ultra violet exposure affected the spectra of all specimens, increasing the absorbance at 1737cm-1. This relates to photo-degradation of the hemicelluloses, forming new carbonyl groups. In the UV exposed untreated wood there were also increases in absorbance at 1510 and 1160cm-1 relating to alterations in lignin structure.
M D C Hale, S C Ghosh, M J Spear


Effects of heat treatment on water repellence and anti-swelling efficiency of beech wood
2002 - IRG/WP 02-40223
The heating of solid wood to higher temperatures is the simplest and the cheapest means for stabilizing its dimensions. For the investigation of the effect of thermal treatment on water repellency effectiveness and anti-swelling efficiency of beech wood (Fagus orientalis Lipsky), air-seasoned samples of beech wood were heated in presence of air at temperatures of 130 C, 150 C, 180 C and 200 C for different periods (2, 6, 10 h). Subsequently, the heated samples and their controls were immersed in water at 20 C, 65 % relative humidity for various periods. Percent of the tangential swelling and rate of the water absorption values of the test and control samples were determined for 2, 4, 8, 24, 48, 72 h on basis of oven-dried measurements. The heat treatment brought about a considerable reduction in water absorption and tangential swelling of the beech wood.
S Yildiz


Study of the degradation of retified wood through ultrasonic and gravimetric techniques
1994 - IRG/WP 94-40030
One of the non-polluting processes that increase the natural durability of wood is a thermal treatment in an atmosphere poor in oxygen, producing what is normally denominated "retified wood". In this study the validity of a non-destructive technique (ultrasound) in order to determine the biodegradation suffered by wood across time has been studied. For this reason, the behavior of a wood species (poplar), submitted to thermal treatments of 220 to 260°C for differing time lenghts (5 to 20 hours), and placed in contact with the fungus Serpula lacrymans during five months of incubation, was analyzed. The results obtained effectively show that these treatments increase the natural life of the wood, which supposes an alternative and non-polluting method, that can be used in the wood preservation field.
D T De Troya, A M Navarrete


Properties of hot oil treated wood and the possible chemical reactions between wood and soybean oil during heat treatment
2005 - IRG/WP 05-40304
Thermal treatment with hot oil as the heating media based on the original idea from oil-heat treatment in Germany was investigated. The treatment was mainly carried out at 200ºC and 220ºC for 2 hours and 4 hours, and the wood species were mainly spruce and fir. This paper focuses on the difference between soybean oil and palm oil and the possible chemical reactions between wood and soybean oil. Generally palm oil was slightly better than soybean oil in improving the moisture resistance properties of heat-treated wood. But soybean oil treated wood appeared to have better decay and mould resistance. The mass loss of wood treated in soybean oil at 220ºC for 4 hours was below 20 % after exposure to Gloeophyllum trabeum in a soil block test, so the treated wood can be classified as “Resistant” according to ASTM D 2017 standards. Natural weathering exposure also shows that soybean oil treated wood is more mould resistant than palm oil treated wood. In order to investigate the effects of absorbed oil on the properties of treated wood and the possible reactions between wood and oils, extraction of different vegetable oil treated wood with chloroform and other solvents was carried out. The results suggest that part of the soybean oil could undergo chemical reactions with wood that renders it of low extractability.
Jieying Wang, P A Cooper


Thermal modification of non-durable wood species 1. The PLATO technology: thermal modification of wood
1998 - IRG/WP 98-40123
The PLATO technology is an innovative upgrading technology with low environmental impact, which can be applied to fast grown and non-durable wood species. This technology is based on a thermal modification of solid wood without the addition of chemicals (e.g. preservatives), consisting of a hydrothermal treatment, followed by drying and curing. The PLATO technology results in a substantial improvement of the natural durability and dimensional stability of wood with only a slight reduction in mechanical properties. Applications of thermally modified wood will include areas where a good durability and/or dimensional stability is required, e.g. garden wood and furniture, wooden sheds, canal lining, joinery, window frames, doors, claddings. In 1998/99 the PLATO technology will be commercialised in the Netherlands. In this paper features of the PLATO technology will be discussed, including selection of wood species, the PLATO process and product development, product properties and applications.
M J Boonstra, B F Tjeerdsma, H A C Groeneveld


Lethal temperature for some wood-destroying fungi with respect to eradication by heat treatment
1984 - IRG/WP 1229
The lethal heat dosis as a function of temperature and time of exposure has been tested for mycelium and for wood infested by three strains of Serpula lacrymans and by Coniophora puteana, Poria monticola, Paxillus panuoides, Gloeophyllum trabeum and Gloeophyllum sepiarium. Even for Serpula lacrymans, which is well known for its sensivity to heat treatment, 30 min at 55°C were necessary to kill the most resistant strain. The lethal dosis of heat was slightly lesser for infested timber than for mycelial cultures in Petri dishes.
M Miric, H Willeitner


Durability of heat-treated wood
1999 - IRG/WP 99-40145
Heat-treated wood from the French process were laboratory tested against decay using agar block test and a modified soil block test. Water absorption, bending strength, lignin content and acid number were also determined to evaluate the effect of heat treatment. Heat treated samples exhibit a higher lignin content and a lower acid number compared to untreated control indicating the degradation of some hemicellulose and extractives compounds. The significant amount of water absorbed during water soaking or exposure to different relative humidity suggest that the heat treatment help in releasing the stress in wood after the removal of hemicellulose and degradation of lignin rather than the reported significant cross link reaction of organic acid and the benzene ring of lignin. Cubes extracted with water or acetone or chloroform and challenged with pure culture of fungus show an appreciable weight loss which confirm the absence of any extractable compounds toxic to decay fungi during the heat treatment. After 12 weeks exposure for laboratory soil block or 6 to 8 weeks for agar block test, significant weight loss was observed. For soil block test, weight loss of 11% was obtained for heat-treated samples exposed to G. trabeum and 46% for P. placenta. About 56% and 54% weight losses were obtained for southern pine control exposed to G. trabeum and P. placenta, respectively. The weight loss of water and acetone extracted heat-treated sample exposed to P. placenta was 49.7% and 53.9%, respectively. Only about 11% and 14.8% weight loss was obtained for water and acetone samples challenged with G. trabeum. The moisture content of tested sample was about 70 ±10% for the un-heated control and 50 ± 10% for heat-treated samples. This treatment may modified the durability from non resistant to moderate/resistant species depending on fungus species as defined in the ASTM 2017 standard. The data from the bending test indicate that such treatment may create a 10 to 50% reduction in MOR and deflection which will limits the use of such wood for structural purposes.
D P Kamdem, A Pizzi, R Guyonnet, A Jermannaud


Durability aspects of (hydro)thermal treated wood
2000 - IRG/WP 00-40160
Samples of several wood species were treated in a two steps process, subsequently hydrothermal and dry heat-treated, by the so-called PLATO-process and analysed for their resistance against fungal attack. Both PLATO-treated and dry heat-treated specimen were prepared and analysed, in order to study the influence of moisture during hydrothermal treatment of wood. The resistance against all of the studied types of fungi was improved considerably after the PLATO-treatment. Especially the resistance against brown rot fungi was increased by the treatment. Also the resistance against white rot and soft rot was improved. The increase of the decay resistance was found dependent on the applied process conditions. The PLATO-treatment was found to be more efficient compared to a one step dry heat-treatment, with respect to improving the resistance against fungal attack. The effectiveness of the treatment is improved by applying a hydrothermal step before the dry heat-treatment step. The process conditions in the curing step appeared to have the largest effect on the resistance against soft rot and brown rot decay. White rot decay was less dependent on the curing conditions and found more affected by the hydrothermolysis, suggesting the decomposition of hemicellulose in the hydrothermolysis.
B F Tjeerdsma, M Stevens, H Militz


Thermal modification of non-durable wood species 2. Improved wood properties of thermal treated wood
1998 - IRG/WP 98-40124
Properties of wood treated in a new heat-treatment process called the PLATO-process have been studied. Several wood species have been treated using this new thermal modification process using a range of process conditions (mainly time and temperature). In this study the characteristics of the treated wood were determined using samples from whole planks treated on pilot plant scale. The modified chemical structure of the wood after treatment results in a product with improved properties. The most important properties of wood, strength, dimensional stability and durability, were determined before and after the heat-treatment. The examined wood species showed a minor loss of strength after treatment. The correlation between the hygroscopicity of the treated wood in moist conditions and the dimensional stability has been studied. Depending on the applied process conditions the hygroscopicity of the treated wood decreased. The hygroscopicity was reduced by 40% and the dimensional stability appeared to have an improvement, ranging to 50%. The durability after heat-treatment was substantially improved.
B F Tjeerdsma, M J Boonstra, H Militz


Effects of heat treatment on modulus of elasticity of beech wood
2002 - IRG/WP 02-40222
Heat treatment is the oldest, simplest and cheapest method for reducing hygroscopicity of wood. The heat treatment protects wood against to biological organisms as well as giving wood dimensional stabilization without damaging environment. The effects of heat treatment on modulus of elasticity (MOE) of beech wood (Fagus orientalis Lipsky) naturally grown and intensively used in forest products industry in Turkey were determined. The wood samples were cut into 2 x 2 x 30 cm and then conditioned at 25 C and 65 % relative humidity for 3 weeks. Heat treatment was than applied to the wood samples at four different temperatures (130C, 150 C, 180C, 200 C ) and three different durations (2, 6, 10 h) under atmospheric pressure. MOE for control and the heat treated samples were recorded at Universal Test Machine. The results showed that MOE of the wood depended to a considerable extent on the heat treatment conditions, decreasing with increasing temperature and duration of the heating.
S Yildiz, G Çolakoglu, Ü C Yildiz, E D Gezer, A Temiz


Heat inactivation of mould fungi on wood
1993 - IRG/WP 93-40012
Heat treatments have been successfully used for eradication of dry rot. The effect of heat treatments at 40, 50 and 60°C for various time intervals on the inactivation of Penicillium brevicompactum was determined. The effect of heat on ungerminated spores and spores "pregerminated" for 24 hours was evaluated by plating on malt-extract agar. Although most ungerminated spores were inactivated after 5 h at 50°C, complete inactivation of ungerminated spores required 60°C for 30 h. Treatment at 60°C for 18 h inactivated the fungal mycelia on wood, as determined with ATP measurements.
J Bjurman


Biological resistance of steam-compressed wood pretreated with boric compounds
1999 - IRG/WP 99-30190
Wood compression under heating is aimed to enhance dimensional stability and surface hardness. Preservative treatment with an appropriate chemical is additionally required for the protection of wood against biological agents under hazardous service conditions. Boron pretreatment of compressed wood was targeted to a mutual benefit of increasing biological resistance of compressed wood as boron was converted to a more stable form through hydration and dehydration reactions under steaming at elevated temperatures in a closed system. Accordingly, boric acid (BA) (at 0.25, 1.00 and 4.70% aqueous concentration)- or phenylboronic acid (PBA) (at 0.34, 0.50, 1.00 and 2.00% aqueous concentration)-impregnated Japanese cedar (Cryptomeria japonica D. Don) specimens were compressed at their radial direction to 50% dry set at 171, 180 and 200°C. The compressed specimens were subjected to decay and termite tests following exposure to a severe ten-cycle wet/dry processes according to Japanese Industrial Standard JIS K 1571 (1998). BA pretreated-compressed wood exhibited remarkable resistance against a white-rot fungus, Trametes versicolor, but not so effective against a brown-rot test fungus, Fomitopsis palustris even at high boron loads which resulted in a high termite resistance. PBA pretreatment appeared to be very effective against both decay fungi and Formosan subterranean termite when wood specimens were compressed at high temperatures and steam pressure.
M K Yalinkilic, W Dwianto, Y Imamura, K Tsunoda, M Takahashi


Comparison of thermally modified wood originating from four industrial scale processes – durability
2002 - IRG/WP 02-40229
This study examined the differences in biological wood properties of heat treated wood originating from four different European industrial heat treatment plants. The manufacturers of heat treated material were: PLATO Hout B.V./Netherlands, Thermo Wood/Finland, New Option Wood/France and Menz Holz/Germany where Oil-Heat treated Wood (OHT) is produced. The results of miniblock tests with basidiomycetes on malt agar showed a substantially reduced mass loss on heat treated material caused by fungal attack compared to untreated controls and heartwood of Douglas fir and oak. Only slight differences in mass loss were found between the four thermally modified materials. Analogous to the classification of natural durability (EN 350-1), PLATO wood and Oil-Heat treated wood were classified as “durable”, Premium wood and Retified wood were classified as “moderately durable“.
C R Welzbacher, A O Rapp


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