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Solvent drying and preservation of timber
1977 - IRG/WP 381
Processes which combine drying and preservation are first reviewed. Some preliminary experiments are then described in which blocks of green Sitka spruce sapwood were immersed, in a solution of tributyltin oxide (TBTO) in methanol at 60°C. Satisfactory penetration of the preservative and exchange of methanol and water occurred in a few hours. The methanol was removed rapidly from the wood by evaporation. Satisfactory penetration of TBTO into initially methanol-saturated samples occurred in a similar period. The factors influencing. such treatments are discussed. High initial moisture content of the wood and a high operating temperature are particularly desirable. Some aspects of the possible commercial operation of the process are discussed.
J A Petty


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


Natural durability transfer from sawmill residues of white cypress (Callitris glaucophylla). - Part 3: Full penetration of the refractory sapwood of white cypress
2000 - IRG/WP 00-40167
The heartwood of white cypress, Callitris glaucophylla, is renowned for its termite resistance and durability against decay. The sapwood, which can represent up to 30% of log volume, is non-durable and refractory to conventional preservative treatment. Previous work ascribes the lack of permeability to oily deposits within tracheids and ray cells. Environmental scanning electron microscopy was used to investigate ultrastructural aspects of sapwood permeability. Several pre-treatment processes to improve permeability were tested with limited success. Solvent drying allowed preservative penetration but damaged the structure of the timber. Neither, long term water soaking nor an oscillating pressure/vacuum cycle had any effect on porosity to water-borne treatments. Through extensive modifications to a standard VPI process we can now repeatedly achieve full penetration with organic solvent-based wood preservative solutions into white cypress sapwood. Effects of this process on the strength of the timber are being evaluated. Work is continuing as to the most effective and efficient treatment schedule and the latest results will be presented at IRG 31.
M J Kennedy, L M Stephens, M A Powell


Borate thermal treatments
1992 - IRG/WP 92-3715
Green, partially seasoned (air-dried, steam conditioned), or kiln-dried southern pine timbers were treated thermally using 15% disodiumoctaborate tetrahydrate solution. After treatment, sections were stored under non-drying conditions to allow for diffusion. Results showed that effective treatment meeting the AWPA minimum retention (0.17 B203 pcf [2.72 kg/m³] in the outer inch) and penetration (2.5-in [64-mm] or 85% of the sapwood) could be obtained only with certain combinations of seasoning, treatment, and diffusion storage. The best results in terms of both retention and penetration were obtained with material steamed and stored prior to treatment using a 10-min hot bath time. Kiln-dried timbers could not be treated effectively. The results suggest that non-conforming treatment of green or partially seasoned timbers will require higher solution concentrations, higher hot bath temperatures, and/or longer diffusion periods to meet required standards. Results also indicated that treatment of smaller stock in dimension sizes (up to 2-in [50-mm]) should be feasible.
H M Barnes, R W Landers, L H Williams


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


Steam conditioning of partially dried radiata and Corsican pine roundwood
1988 - IRG/WP 3499
The effect of partial air drying prior to steam conditioning and its effect on subsequent preservative treatment by the Bethell treatment process was investigated. A high standard of preservative treatment was obtained in both radiata and Corsican pine, irrespective of whether a period of partial drying was imposed before or after steam conditioning.
P Vinden, D R Page, K Nasheri


Survey of conditioning treatment practices in India
1978 - IRG/WP 3127
India has 75.3 million hectares (ie about 24% of total land area) under forests out of which the area of productive forests, from which industrial wood is available, is about 60 million ha. The Task Force on Forest Resources Survey has tentatively estimated that the total growing stock in Indian Forests is 24,000 million cubic metres (m³). The total recorded production of wood in the country is roughly estimated as 25 million m³ annually of which approximately 10 million m³ is demanded by various industries and the remaining is used as fuel. India, with developing economy needs very large resources of timbers for diverse purposes. There is already shortage of timber in the country for various wood based industries and it is expected this will progressively increase with the rapid pace of industrialisation. However, suitable measures are being taken to bridge the gap between demand and supply. The entire 10 m³ of industrial wood requires some sort of protection against wood-destroying agencies. Timber awaiting conversion during storage needs prophylactic treatment while for use as poles, fence posts, sleepers, building material, in cooling towers, boats, ships, in mines, in sea-water, etc., timber should be adequately treated with suitable wood preservatives to obtain satisfactory service life. Both heart and sapwood of non-durable species and only sapwood of durable species need protection against wood-destroying agencies. Wood Preservation on scientific and modern lines was introduced in India by Sir Ralph Pearson of the Indian Forest Service in the year 1908. In India, the first wood preservation plant was established at Bally in Howrah in 1854. Of the total timber extracted in India, only a very small proportion, estimated at about 5% is treated. This amounts to 0.45-0.50 million m³ of wood per annum. The total annual capacity of 140 preservation units, existing in the country at present, is estimated at 0.43 million m³ on single shift basis. IS: 401-1967 (Indian Standard - Code of Practice for Preservation of Timber) covers types of preservatives, their brief descriptions, methods of treatment, and the type and choice of treatment for different species of timber for a number of uses. This standard includes only such preservatives and methods of treatment which have given satisfactory results under Indian condition of service. According to this standard, whatever process of treatment is adopted, timber for treatment should be sound and should be dried to an appropriate moisture content (generally not more than 15% for open tank and 25% for pressure processes). All the wood working etc should be done prior to treatment. In case of timbers, specially some conifers having non-durable heartwood which is refractory to treatment, when treating thick members like railway sleepers, beams, piles, etc, incision of all the surfaces, other than the ends, to a depth of 12-20 mm is necessary.
M C Tewari


The effect of steam conditioning on Southern yellow pine treated with copper naphthenate
1997 - IRG/WP 97-40086
The current study was undertaken to investigate the influence of steam conditioning on Southern yellow pine treated with copper naphthenate (Cu-N). Pre-steamed and /or kiln-dried Southern yellow pine were pressure treated with Cu-N. After treatment, one group of samples were post-steamed. It was found that samples changed color from green to dark-brown after post-steaming. To elucidate the effect of steaming on treated wood, several techniques, namely, environmental scanning electron microscopy equipped with energy dispersive X-rays analysis (ESEM-EDXA), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS) were employed. After post-steaming, ESEM showed clearly crystal deposit on the Cu-N treated samples, and EDXA data suggested that the crystal was copper and oxygen contained compound identified as Cuprous Oxide (Cu2O) by XRD. The amount of Cu2O in wood samples was semi-quantitatively determined with XRD. XPS C1s spectra showed that post-steaming decreased C1 contribution and increased O/C ratio attributed to the loss of oil rich in hydrocarbons. The removal of water solubles extractives rich in carbon explains the decrease of O/C ratio. The resistance of copper to water leaching was improved by pre-steaming contrary to the post steaming which resulted in high copper loss.
Jun Zhang, D P Kamdem, M H Freeman, R D Arsenault


Microwave conditioning of Pinus radiata D. Don for preservative treatment
2000 - IRG/WP 00-40182
This paper reviews the effect of pressure steam conditioning on the permeability and treatability of green radiata pine heartwood and the potential for substituting microwave conditioning for steaming. The penetration of liquids into radiata pine occurs mainly in the radial tissue. The permeability of green radiata pine improves following steam conditioning by blowing out the soft radial tissue. The moisture content of the wood is also reduced following steam conditioning thus increasing the air void volume available for liquid penetration. Intensive microwave irradiation is found to improve the permeability of radiata pine and reduce wood moisture content concurrently thus facilitating immediate impregnation with wood preservatives.
P Vinden, G Torgovnikov, J Romero


Durability of plywood made from soft- and hardwoods assessed according to ENV 12038 after artificial and natural ageing
2000 - IRG/WP 00-20191
Plywood was prepared from Norway Spruce and pure heartwood of Douglas Fir, Scots Pine, European Oak, False Acacia and Macoré using a phenol-formaldehyde glue. The panels of 38 mm in thickness were pre-conditioned according to the following procedures: a) 12 weeks storage at 20°C/65% rh, b) 2 weeks artificial weathering (with rain and UV-radiation at changing temperatures), and c) a natural weathering according to ENV 12037 for 3 month, 6 month and for 9 month whereby the ENV 12038 specimens were cut from the lap-joints. In general for softwood panels the decay was lowest after a 12 weeks` storage and the artificial weathering increased the decay rate more than the natural weathering applied. For False Acacia the durability was gained as predicted by EN 350-2 but not for the other species. Especially for European Oak and Macoré the durability was much lower than expected. Further, it has to be mentioned that the specimens usually showed a more intensive attack close to the nutrient media than at the top of the specimens. This indicates that the laboratory results might be influenced by the thickness of the panel tested because thinner material would be more equally degraded and thus would show a lower grade of durability.
H Leithoff, R-D Peek


Influence of pre-swelling conditioning on swellometer results for CCA and water repellent additive treated wood
1997 - IRG/WP 97-20125
The pre-test moisture content and conditioning history of wafers cut from wood treated with CCA and an emulsion water repellent additive can dramatically influence swelling curves generated using a standard swellometer apparatus. The rate of water uptake and swelling increased significantly as wafers were dried to lower moisture contents prior to immersion swelling. The pre-swelling conditioning history can also influence swellometer curves and confuse the interpretation of relative water repellent efficacy of emulsion water repellent systems. Results support that careful pre-conditioning of wafers is critical for meaningful comparisons of the relative efficacy of water repellent emulsion systems.
A R Zahora


Copper naphthenate-treated Southern Pine pole stubs in field exposure: - Part 1: Gradient & biodeterioration analysis 12 years after treatment
2000 - IRG/WP 00-30242
Naphthenates have been used for the preservation of timber and cellulose since their original identification in Russia in the early 1880's as part of a series of petroleum characterizations. Later work in the development of copper naphthenate as a heavy-duty preservative for poles led to the development of various treating cycles similar to other oil-borne systems. Recent work concerning the post treatment steam conditioning of copper naphthenate treated southern pine has determined that some amorphous copper naphthenate is converted to a crystalline cuprous oxide. In small laboratory tests, this was later determined to be less efficacious than copper naphthenate. This paper reviews the performance of actual pole-diameter stubs placed in a high hazard location containing both termites and potential for early decay attack. Various treating cycles were used to treat the pole stubs in this test including various post-treatment conditioning methods.
H M Barnes, M H Freeman


The effect of alternative pre-conditioning procedures on the durability of wood based board materials to decay fungi
1997 - IRG/WP 97-20105
In the biological testing of wood based board materials it has been shown that exposure of boards in a closed vessel system may lead to inaccurate results due to the build up of volatile substances that inhibit the test fungi. It is thought that this is a transitory effect of freshly manufactured boards. In the European standard for testing fungal durability of board materials which is currently under development (DD-ENV 12038:1996), a leaching pre-conditioning method is used to remove this effect. A variety of alternative ageing procedures have been studied, including natural weathering, leaching and evaporative procedures, to determine the most appropriate pre-conditioning protocol for the decay test. Our results show that there are procedures which are more efficient, and possibly more meaningful in terms of effectiveness or appropriateness of regime for use on board specimens.
S F Curling, R J Murphy, J K Carey


Effect of species, retention and conditioning temperature on copper stabilization and leaching for ACQ-D
2004 - IRG/WP 04-30342
The time to stabilization or equalization of the copper component of ACQ-D was highly dependent on treating solution concentration (preservative retention) and post treatment temperature. Stabilization was rapid for low preservative retentions but extended times were needed for wood treated with higher concentration solutions. The extent of stabilization was also concentration dependent with a higher percentage of copper fixed with lower retention treatments. Increasing the temperature of the treated wood from 22°C to 50°C reduced the stabilization time by up to ten times depending on the ACQ retention and the wood species. There was little species effect for low extractive content red pine (Pinus resinosa), jack pine (Pinus banksiana), white spruce (Picea glauca), balsam fir (Abies balsamea) and trembling aspen (Populus tremuloides). Neither was there a significant difference in the stabilization rates of jack pine sapwood and heartwood. However, Douglas-fir (Pseudotsuga menziesii) stabilized at a greater rate and to a higher degree than the other species with heartwood reacting faster and more completely than sapwood. This is likely attributed to the high reactivity of copper at high pH with phenolic extractives in Douglas-fir.
Y T Ung, P A Cooper


Co-operative tests concerning influence of solvent and drying method on the toxic limit of wood preservatives against Basidiomycetes. Preliminary report
1971 - IRG/WP 204
In the Working Group II of the Organization for Economic Co-operation and Development working group on wood preservation (now International Research Group on wood preservation) it was agreed that more knowledge was necessary concerning the influence of the solvent on the toxic limit of organic solvent types of wood preservatives against Basidiomycetes. A test program was drawn up and after discussion in the mentioned working group the final program was accepted by the co-operating institutes in 1969. In the test program two fungicides, a pentachlorophenol concentrate and tributyltinoxide, solved in four different solvents were enclosed. Considering that an influence of the kind of solvent could coincide with the rate of evaporation thereof from the test blocks, also different drying methods for some solvents were included.
T Hof


Survey of conditioning treatment practices in the Philippines
1975 - IRG/WP 349
The wood preservation industry in the Philippines is at present beset by many problems. An association of the industry similar to those existing in other countries has only been initiated last year by FORPRIDECOM. It is hoped that the formal organisation of this association will bring into focus the importance of this particular industry in the economic and industrial development of the country. Likewise, for the past years, treatment specifications suitable for Philippine conditions, wood species, and wood products are non-existent. Treatment specifications are usually patterned after those of other countries but in most cases, specifications of the American Wood Preservers' Association (AWPA) are generally followed regardless of whether they may or may not apply to our existing climatic conditions and to local wood species. It was only last year, however, that a series of discussions and formulations of acceptable treatment specifications had been started for which substantial progress is being made in co-operation with the private sectors.
R F Casin


Preliminary pole treatment trials with chlorothalonil in hydrocarbon solvent
1994 - IRG/WP 94-40027
A series of 460-mm long, end-sealed southern pine pole stubs were treated with chlorothalonil in hydrocarbon solvent. Over sixty sections were treated using various combinations of initial seasoning (kiln-drying, steam-conditioning), treating temperature (ambient, 200°F), initial air pressure, and final conditioning (steam flash + vacuum, expansion bath + vacuum, steam distillation + vacuum). Disks removed from the treated sections were analyzed for preservative gradient. Results are discussed in terms of treatability and the impact of treating variables on preservative retention, penetration, and gradient shape.
H M Barnes


Survey of North American practice in conditioning forest products before preservative treatment
1972 - IRG/WP 308
Seasoning requirements for the wide range of forest products which are treated with preservatives and fire retardants must be capable of dealing with a very complex set of conditions which are summarized under a number of variables including type and hazard of end use, the most effective distribution of preservative, a wide range of cross sectional dimensions, the possibility of seasoning by a range of special methods which are in part dependent upon available treating facilities and a wide range of physical properties of the wood including, for example, its permeability to fluids. In addition, the wide range of species utilized in end uses requiring preservation means that large inventories are associated with certain seasoning processes such as air drying to the cost of the treater and consumer. There have been trends to use rapid seasoning methods wherever possible, such as boultonizing, and there are now trends to extend the use of other drying methods to some of the products of a larger cross section which are given preservative treatment. These products include railway cross ties and utility poles, and the methods include, for example, vapour drying and special techniques of kiln drying.
J Rak, T S McKnight


Survey of practical methods for conditioning of forest products before preservative treatment
1971 - IRG/WP 39
The seasoning of forest products is undertaken for a wide range of end uses and is becoming increasingly required for applications and building construction and secondary manufacturing industries. A wide range of applications of new technology and specifically required seasoning schedules is being actively developed for such requirements, but less attention has been given to the means by which wood can be prepared for successful preservation treatments by seasoning or more general conditioning treatments. Much of the knowledge of the practical means of achieving good treatments through prior seasoning and conditioning resides in the skill and experience of larger treating companies. Although many of the pertinent means of achieving proper pretreatment seasoning are mentioned in important sets of standards, such as those of the American Wood Preservers Association (AWPA) and the Canadian Standards Association (CSA), it is often necessary for the consumer of treated forest products to develop the appropriate means of seasoning for his special case through reliance on the knowledge of the treater. In the case of a large consumer, such as the major utilities, there is often his own body of experience gained through the activities of a research and development group.
J Rak, T S McKnight


Cost effective extension of service life of bridge tie (sleepers) - Effectively applying borate during Boulton conditioning and treatment with copper naphthenate
2014 - IRG/WP 14-30637
Current longevity of creosote treated wooden bridge ties in the South Eastern US is about 15 to 25 years, which is well below of the average service life of 33-50 years of railroad ties. Such short service life increases costs associated with maintenance of railroads including bridge down time for tie replacement as well as the cost for the new ties themselves. Because of this, many railroads are seeking non-wood alternative ties, even at vastly elevated initial cost. The objective of the study was to see if it is possible to apply borate as part of a dual treatment with copper naphthenate, in order to increase the service life of wooden bridge timbers at minimal additional cost. Green hardwood ties were ported, borate treated, and then Boulton treated with copper naphthenate at a commercial tie treatment plant in Pennsylvania. Diffusion of borate within the wood appeared to be significantly enhanced by the elevated temperature and steam generated during the Boulton cycle and subsequent pressure treatment with copper naphthenate. The achieved retention and penetration of borate and copper naphthenate met AWPA standard retentions and AREMA guidelines. The longevity of ties should be significantly increased by protecting the heartwood with disodium octaborate tetrahydrate (DOT) and the sapwood with copper naphthenate. The results suggested that hardwood ties can be successfully treated with borate during a Boulton cycle and should allow the continued effective use of sustainable wooden bridge timbers.
J D Lloyd, T Chambers, J-W Kim


Steam Pre-conditioning Treatment Prior to Acetylation: Impact on Dimensional Stability, Moisture Response Behaviour, and White-Rot Fungal Resistance of Hevea brasiliensis and Mitragyna ciliata Wood
2022 - IRG/WP 22-40930
The effect of steam pre-conditioning treatment on the dimensional stability, moisture response behaviour, and durability against white-rot fungus P. chrysosporium of acetylated Hevea brasiliensis and Mitragyna ciliata wood species were assessed. Defect-free specimens of both species from the top, middle, and base positions were selected, prepared according to ASTM D143-09 & ASTM D-2017 standards and acetylated following a catalyst-free method. The primary source of variation in this study is the steam-conditioning treatment of specimens at holding periods of 30 minutes (H1), 60 minutes (H2), and 90 minutes (H3) before acetylation modification. Acetylated unsteamed specimens were used as treatment controls (T-CONTROL), while neither steam-conditioned nor acetylated (N-CONTROL) specimens were maintained for comparison. The experiment was a 2×3×5 factorial experiment in Randomised Complete Block Design (RCBD). Results revealed that steam pre-conditioning treatment resulted in a significant weight loss for the H. brasiliensis and M. ciliata, respectively. Effect of steam pre-conditioning treatment measured on the anti-swelling efficiency, volumetric swelling and reduced anti-shrinkage efficiency (ASE) values after repeated cycles of water-soaking revealed significant (P < 0.05) improvements on the dimensional stability and moisture response behaviour of both species, respectively as a function of their weight percent gain (WPG). The decay resistance of the acetylated (steamed and unsteamed) H. brasiliensis and M. ciliata wood was significantly improved and are classified as “highly resistant” to decay caused by P. chrysosporium white-rot fungus with weight loss values >10 %. The results prove that steam pre-conditioning treatment improved reagent accessibility and the acetyl weight gain of acetylated H. brasiliensis and M. ciliata wood. Consequently, their durability, dimensional stability, and moisture response behaviour also improve.
E Uchechukwu Opara, J Mayowa Owoyemi, J Adeola Fuwape