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The Effects of Industrial-Scale Heat Treatment and Impregnation with Boron Compounds on Water Uptake and Tangential Swelling of Some Wood Species
2012 - IRG/WP 12-40599
This study evaluated the effects of boron impregnation and heat treatment on water uptake and tangential swelling of spruce (Picea orientalis), pine (Pinus nigra), beech (Fagus orientalis) and poplar (Populus deltoides) wood species. The samples (10 x 5 x 40 - tangential x radial x longitudinal cm) were impregnated with 4 % boric acid and 4 % borax according to the ASTM D-1413 standard method. After the impregnation, heat treatment was applied on the impregnated test samples in an industrial plant, at four different temperatures and two different durations under steam atmosphere. Soft wood and hard wood samples were subjected to the heat treatment at 212 °C - 220 °C, and at 180 °C - 190 °C, respectively, for 90 and 120 min. Heat treated and impregnated test samples were reduced smaller sizes (3 x 3 x 1.5 cm - tangential x radial x longitudinal) for water uptake and tangential swelling tests. The tests were carried out based on TS 2472. Results indicated that the highest retension was 26.9 kg/m3 in pine wood samples impregnated with BA (26.93 kg/m3). Hardwood retention was lower than soft wood retention. In generally, water uptake and tangential swelling ratios of only heated samples was found lower than non-treated control samples.The combination of heat treatment and BX impregnation was negatively affected water uptake especially in spruce and poplar wood. Borax was more hygroscopic than boric acid. The tangential swelling rates of four wood species impregnated with boric acid and borax were found lower than the non-treated control samples. The tangential swelling rates of spruce and pine wood samples impregnated with boric acid decreased compared to the only heated samples. Heat treatment process significantly affected the remaining boron compounds in wood. Although the steam atmosphere in the oven during the heat treatment, the amount of boron leached from wood was low especially in BX treatment.
A Can, S Yildiz, Ü C Yildiz


Effect of boron compounds-furfuryl alcohol treatment of wood on dimensional stability, termite resistance and boron leachability
2001 - IRG/WP 01-40195
Sapwood blocks of Japanese cedar (Cryptomeria japonica) and Caribbean pitch pine (Pinus caribaea) measuring 20 (tangential) x 20 (radial) x 10 (longitudinal) mm were impregnated with furfuryl alcohol (FFA) by a vacuum-diffusion process followed by curing under heating. Boron compounds (boric acid, ammonium borate and ammonium biborate) were mixed in the impregnation solution of FFA. Anti- swelling efficiency, water holding capacity and moisture exclusion efficiency were measured. Boron leachability was determined by ion chromatography with ten leaching cycles according to JIS 9201 (1992). The specimens were exposed to termite attack testing, before and after the cyclic leaching process. The results indicated that FFA imparted to wood greater dimensional stability when mixed with boron compounds. Boron when mixed with FFA behaved differently to boron alone treatment, although it was still leachable. The wood specimens treated with FFA-boron compounds were quite resistant to termites even after severe leaching.
S K Ozaki, M K Yalinkilic, Y Imamura, M F Souza


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


Bibliography on the use of boron compounds for the preservation of wood
1973 - IRG/WP 315
This bibliography is based on an earlier literature survey prepared by J. Thornton and Wm. E. Bruce (O.E.C.D. Document No. 27/DAS/CSI/M/91) which was enlarged and revised for a meeting in Paris in October 1968 (Document 27/DAS/CSI/M554) by Professor W. Bavendamm of Reinbek. The latter (1968) document with its 166 references has now been extended and brought up to date. Acknowledgments are due to Borax Consolidated Ltd. and to the New Zealand Forest Research Institute who have both helped by providing us with further compilations of their own. Boron compounds have been in use in the past and are still found useful in medicine in the form of boric acid solutions and boracic ointment. They have also been used for the conservation of foodstuffs. In the treatment of wood they were first mostly used as fire retardants. Since the Second World War they have become increasingly important in the field of wood preservation.
R Cockcroft, J F Levy


The effect of treatments in boron steaming medium on boron leaching and strength properties of wood
2008 - IRG/WP 08-40409
The combined effect of boric acid impregnation together with boron steaming and steaming heat treatments were evaluated in this study. Boric acid pre-treated wood samples and untreated ones subjected to steaming heat and direct steaming treatment in a close reactor at 13 bar pressure and 180 ºC for 30 minutes. Compression strength parallel to grain of wood samples, leaching test and pH measurements were performed. Quantity of boron in leached and unleached wood samples was determined with ICP (Inductively Coupled Plasma). Retention values obtained in treatments were enough to protect wood against many wood degradation organisms. Approximately 32 kg/m3 and 2.52 to 14.1 kg/m3 retention was obtained in pre-treated samples with vacuum impregnation and treatments in boron steaming medium respectively. After the treatments, all of the samples got dark color and became more brittle due to thermal degradation of wood components. A significant decrease on the compression strength parallel to grain of wood samples was monitored especially subjected to direct steaming boron treatment. Depending on pre-treatment and applied second treatment, strength values were decreased with a range of 6 to 27% compared with controls. Since strong acidic conditions tend to catalyze hydrolysis, dehydration and oxidation reactions in wood that adversely effect the strength of wood, treatments at high temperature caused strength losses. Heat treatment had less degradation potential than steaming in the study. Treatments in boron steaming medium have no/little effect on boron release and almost all boron was leached from the wood samples. Only boron steamed samples decreased boron leaching with a 20% rate. Biological resistance tests are needed to evaluate the performance of the treatments in both leached and unleached samples.
E D Tomak, Ü C Yildiz, S Yildiz, E Pesman


Improvement of wood decay and termite durability resulting from combined treatments based on borax/phenol-formaldehyde impregnation followed by thermal modification
2019 - IRG/WP 19-40871
This study determined the factors influencing the boron content after leaching of pine blocks impregnated with aqueous solution of phenol-formaldehyde (PF) resin with or without borax and subjected to heat treatment by response surface methodology. An experimental design permits to analyze the effects of heat treatment temperature (150, 185 and 220°C), curing time (5, 12, 5 and 20 hours), resin concentration (5, 12.5, and 20%) and boron concentration BAE (0, 2, and 4 %) on the mass gain, boron content as well as degradability. After leaching, the treated samples with 20% PF, and 220°C had high boron content, and the heating time had no significant influence on the boron content. Decay and termite resistance were also studied for treatments involving impregnation of samples with 10% of PF alone or in the presence of borax, followed by curing at 220°C for 5 h. The results of this study indicated that the decay and termite resistance of all samples pretreated and leached is sufficient to envisage use in outdoor exposure.
S Salman, M-F Thevenon, A Petrissans, S Dumarcay, P Gerardin


Proposal for further work on accelerated ageing
1988 - IRG/WP 2314
M-L Edlund


Strength loss associated with steam conditioning and boron treatment of radiata pine framing
1987 - IRG/WP 3438
The combined effect of included defects and wood moisture content on the strength loss of second rotation radiata pine framing following conventional steam conditioning is investigated. The green Modulus of Elasticity (MOE) is reduced by approximately 13% after steaming. When dried after steaming, however, neither the MOE nor MOR is significantly different from unsteamed dried controls.
M J Collins, P Vinden


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


Water-based wood preservatives for curative treatement of insect-infested spruce constructions
1998 - IRG/WP 98-30171
On laying down sanitation measures for wooden constructions infested by wood boring insects, we must take into account static risks for the construction - and, thus, for the security of the user - as well as risks for humans and environment due to the chemical preservative compounds of the treated wood. Analyses on many roof constructions made with spruce (Picea abies L.) have revealed that Hylotrupes bajulus L. and Anobium punctatum De Geer have not the significance given to them for decennies. That often allows to replace solvant-based with water-based wood preservatives in old buildings, for the protection of humans and environment. Therefore, a method has been developed in Switzerland for testing wood preservatives with delayed curative efficacy against the house longhorn beetle. Like the European Anobium Standard EN 370 this method intends to prevent the emergence of Hylotrupes beetles. Laboratory tests with diverse water-based wood preservatives available on the market in Switzerland have shown that particularly boron and benzoylphenylurea derivatives containing products get a sufficient penetration in the wood and prevent the emergence of the beetles.
E Graf, P Manser, B Lanz


Options for accelerated boron treatment: A practical review of alternatives
1985 - IRG/WP 3329
Boron wood preservatives are almost exclusively applied by momentary immersion and block diffusion storage. Alternative techniques are described which can be used to accelerate boron treatment. Diffusion coefficients have been derived to define the acceleration of diffusion with increasing temperature. Schedules are described for pressure impregnation of green timber, involving steam conditioning, evacuation and alternating pressure method treatment. Timber Preservation Authority penetration and retention requirements can be met in approximately 4-5 h. The optimum schedule, however, included a 12 hour holding period between steaming and preservative treatment. A method of applying boron preservatives as a vapour is described, Trimethyl borate vapour reacts with wood moisture to form boric acid. The kinetics of this reaction, however, are very fast. This limits treatment to timber dried to very low wood moisture contents.
P Vinden, T Fenton, K Nasheri


Boron treatments for the preservation of wood - A review of efficacy data for fungi and termites
1994 - IRG/WP 94-30037
Boron treatments have been used for many decades for protection of timber from biological attack and also as a fire retardant treatment. In recent years there has been an increased interest in boron treatments as an option for protection of structural timbers' e.g. timber framing used in termite risk areas. This paper reviews efficacy data for both fungi and termites relevant to this end-use.
J A Drysdale


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


Finite element analysis of boron diffusion in wooden poles
2003 - IRG/WP 03-40263
The problem of describing the migration of dissolved boron in wood is treated with special reference to the commonly used remedial treatment of wooden poles. The governing equations are derived and discussed together with some of the material parameters required. The equations are solved by the finite element method and finally, results showing the effect of different treatment strategies are presented.
K Krabbenhøft, P Hoffmeyer, C G Bechgaard, L Damkilde


Movement of boron from fused boron rods implanted in Southern pine, Douglas fir, red oak, and white oak timbers
1995 - IRG/WP 95-30061
This paper reports the distribution of boron from fused boron rods installed into six-inch (15.2 cm) square timbers of Douglas-fir, Southern Pine, red oak and white oak exposed aboveground. The composition and size of rods was: sodium borate and sodium borate-copper oxide (8.5 x 100 mm²); sodium borate-copper, sodium borate and boric oxide-copper oxide (12 x 76 mm²). The boric acid equivalent was roughly monitored by the curcumin/salicylic acid color test and the presence of copper was detected by the chrome azurol-S reagent. One year after installation of rods, movement of boron was determined by application of curcumin dye to increment cores removed at various distances from the site of boron rod installation. A portion of a sodium borate treated Southern Pine timber was also analyzed by spraying curcumin dye on sawed longitudinal and transverse sections. At 2 years, one foot sections were removed from all timber species, sawed as above, and boron and copper detection reagent sprayed on the sawed surfaces. Movement of copper from rods in all timbers was virtually nil. Both transverse and longitudinal movement of boron from rods was greatest in Southern pine which also had the highest moisture content. Movement of boron was next best in red oak. There was little movement of boron away from the rods in white oak and Douglas-fir.
T L Highley, L Ferge


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


Heat treatment of bamboo
2001 - IRG/WP 01-40216
Bamboo is a fast growing material with remarkable mechanical properties. In many tropical and subtropical countries bamboo is available in suitable dimensions for a reasonable price. Therefore it is used for many purposes which range from the basket production up to the industrial production of parquet or paper. However, bamboo is known as susceptible to fungal or insect attack and it is difficult to treat with preservatives. Therefore BFH investigated the possibility to protect bamboo by other methods and tested the application of a heat treatment. European grown bamboo (Phyllostachys viridiglaucescens) and Asian grown bamboo (Phyllostachys pubescens) were heat treated and were subsequently inoculated with the basidiomycetes Coniophora puteana, Coriolus versicolor and Schizophyllum commune in an agar block test. Further the durability of treated specimens against soft rot fungi was tested. The changes of the mechanical properties (MOE and shock resistance) caused by the heat treatment were determined too. The application of temperatures above 200°C caused a clearly enhanced durability against a basidiomycete as well as against a soft rot attack but the shock resistance was intensely reduced. Further investigations are still ongoing. The study has been carried out with financial support from the Commission of the European Communities, specific INCO programme INCO-DC 961344.
H Leithoff, R-D Peek


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


A new approach to the maintenance of wooden railway sleepers. (Second report)
1988 - IRG/WP 3492
The microenvironment and micro-ecology of wooden railway sleepers was investigated to assess their condition to determine the necessary treatment, repair and replacement criteria. In this report the efficacy of the secondary preservative treatment with solid boron rods is discussed and the development of an in-situ, nondestructive test method based on the creation and assessment of structural dynamic vibrations is described.
W Beauford, P I Morris, A M Brown, D J Dickinson


Durability of different heat treated materials from industrial processes in ground contact
2005 - IRG/WP 05-40312
In this study the durability of heat treated wood originating from four different European industrial heat treatment processes in ground contact was examined. 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. All heat treated materials showed significantly increased durability against decay in ground contact compared to untreated Scots pine (Pinus sylvestris L.), independent from the different heat treatment processes. After four years of field testing, heat treated material appears to be not suitable for in ground contact application, since long service life is required. In analogy to the classification of natural durability (EN 350-1, 1994), durability classes in the range from 2 (durable) to 4 (slightly durable) were achieved by the different heat treated materials. This stands in contrast to statements of suppliers, who promote their material as suitable for in ground applications.
C R Welzbacher, A O Rapp


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 benefits to New Zealand of boron salt treatment of Pinus radiata
1992 - IRG/WP 92-3692
The historical reasons for New Zealand adopting boric salt diffusion of Pinus radiata are summarised, and present day processes and their associated costs are given. The biological hazards of using Pinus radiata untreated are then argued, using endemic fungal and insect species as examples, as well as a discussion of the risks from species that may yet be accidentally introduced into the country.
D J Cross


The rate of redistribution and loss of leachable preservatives under service conditions
1993 - IRG/WP 93-30026
This paper describes experiments carried out to determine patterns of preservative redistribution and any associated losses which occur when wood containing unfixed water-soluble wood preservatives is exposed to service conditions where leaching is possible. Scots pine sapwood treated with disodium octaborate was used as a model system. Results are recorded and discussed for trials representing painted joinery out of ground contact and unpainted stakes half buried in the ground. The results indicate that in the painted samples out of ground contact the water-soluble compound was redistributed longitudinally and away from the joint zone during the first months of exposure, although little redistribution occurred laterally. No difference in redistribution patterns could be associated with paint type. Ground contact stakes showed a loss in the water-soluble compound of about 40% in the first six months exposure. Most of this appeared to occur from the surface zones of the stake exposed to the weather, particularly from the extreme top. In addition, the compound appeared to migrate upwards from the below-ground portion of the stake to the above-ground portion. These results provide new information on the extent of movement of water-soluble preservatives in painted, jointed timber out of ground contact and in unpainted timber in ground contact. It is concluded that the long-term significance of the observed redistribution effects for painted joinery should be evaluated to confirm that there is no likelihood of shortcomings in performance in practice. For the ground contact situation, results confirm that rates of redistribution and loss are high enough to indicate inappropriateness of such materials for practical use without associated technologies to reduce mobilities.
R J Orsler, G E Holland


HCB - a new preservative combination for wood pole maintenance
1996 - IRG/WP 96-30122
New combination of heavy creosoted boron (HCB) applied on hardwood and softwood logs at different moisture content revealed successful diffusion of boron in all sapwoods within 7 days and in all sapwoods plus hardwoods within 15 days. The new cost effective paste sterilizes wood through diffusion and suitable for pole maintenance at groundline and above groundline e.g. cut ends, drilled holes, woodpecker's holes etc.
A K Lahiry


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