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Accessibility of hydroxyl groups in anhydride modified wood as measured by deuterium exchange
2017 - IRG/WP 17-40784
Acetylated wood shows improved properties largely due to the reduced amount of water in the acetylated cell wall. However, the exact mechanism by which water is excluded in acetylated wood remains unclear. Acetylation reduces hydroxyl content by substitution of hydroxyl groups in wood polymers but may also hinder access to unmodified hydroxyls by physical bulking. This work assesses hydroxyl accessibility in Radiata pine (Pinus radiata) samples that were acetylated and propionylated to different levels by means of deuterium exchange. The deuterium exchange experiments were performed in a novel way using an instrument designed for thermogravimetric analysis. Both acetylated and propionylated samples tend to reduce hydroxyl accessibility, but the relationship between accessibility and weight percentage gain for both modifications deviates from the expected theoretical relationship. The acetylated results suggest that, in addition to hydroxyl substitution, blocking of unmodified hydroxyl groups may play a role in hydroxyl accessibility reduction. The propionylated samples seemed to be damaged by the propionylation reaction, showing higher than expected accessibility. This may be a result of molecular restructuring within the cell wall which exposes new hydroxyl groups after propionylation.
G Beck, S Strohbusch, E Larnøy, H Militz, C Hill

Recent findings clarifying the mechanism of brown-rot decay protection in acetylated wood
2018 - IRG/WP 18-40827
This paper summarizes the findings obtained during my PhD research over the past three years. The results provide insights which help to understand the enhanced brown-rot decay resistance of acetylated wood with particular emphasis on the role of water. The protection acetylation provides is derived from moisture exclusion within the acetylated cell wall, but the exact mechanism by which water is excluded remained unclear. The first two studies conducted elucidate the moisture exclusion mechanism. It was demonstrated that hydroxyl (OH) accessibility is reduced in acetylated wood both by direct substitution of OH groups with acetyl groups and by hindering access of unmodified OH groups, due to steric hindrance. Characterisation of water in the various void structures of the wood anatomy by means of low-field nuclear magnetic resonance (LFNMR) relaxometry revealed that acetylation causes greater water mobility due to weaken interactions between water molecules and the acetylated pore walls. Both these initial studies also compared the moisture properties of the acetylated samples to samples modified with propionic anhydride. The idea was to demonstrate the importance of steric hindrance relative to direct OH substitution by modifying the wood with a larger anhydride molecule. However, the results indicated the propionylated cell walls were damaged in some way. The last two studies investigate acetylated wood decayed by the brown-rot fungus, Rhondonia placenta. Moisture development and chemical changes were assessed by means of LFNMR, OH accessibility and acetyl content throughout brown-rot degradation and revealed a markedly different degradation pattern for acetylated wood compared to unmodified samples, suggesting de-acetylation occurs within the cell wall prior to decomposition. Lastly, brown-rot decay in acetylated wood was investigated from the fungal perspective by determining how acetylation affects expression of fungal enzymes involved in oxidative chemistry and polysaccharide hydrolysis. Clear trends were difficult to observe for the oxidative genes selected, but genes involved in polysaccharide degradation showed a delayed response for acetylated samples and the most highly acetylated samples had the lowest overall expression levels.
G Beck

Hydroxyl accessibility - A brief review of deuterium exchange studies on modified wood
2019 - IRG/WP 19-20656
Wood modification imparts dimensional stability and decay resistance. The mechanism(s) by which this occurs are thought to be related to the bulking of the wood cell wall and subsequent moisture exclusion. Hence, quantification of accessible hydroxyl (OH) groups is of great interest when evaluating and increasing the understanding of the performance of modified wood. The aim of this study was to briefly review previous studies on the use of deuterium exchange as a method to measure OH group accessibility in modified wood with particular focus on preliminary data from a study on furfurylated wood. The experiment included furfurylated wood at three different weigh present gains (WPGs) and at different levels of mass loss caused by exposure to the brown-rot fungus Rhodonia placenta. The main findings were that: 1) OH accessibility in furfurylated samples did not change with increasing WPGs in sound samples, 2) OH accessibility in furfurylated samples increased significantly after initiation of R. placenta decay at commercial treatment level (mean WPG 32%). The increase in OH accessibility in R. placenta decaying wood was attributed to opening of cell wall microfibrils and formation of new OH groups in the brown rot modified lignin and the furfuryl alcohol polymer.
G Beck, C Hill, G Alfredsen

Rates of emission from CCA-treated wood in the marine environment: measurement, modelling and requirements for further research
2001 - IRG/WP 01-50166-12
Accurate estimates of rates of emission of leachate from preservative treated wood are crucial for realistic predictions of the environmental impact of its use in maritime construction. Estimates are available for some commonly used preservatives, but these vary widely. Though variable, these measurements suggest that emission generally decreases exponentially with time. Part of the variation is due to differences in methodology employed. Physical and chemical characteristics of the seawater used (e.g. temperature, salinity, pH and oxygen content) affect emission rate. So too do the specifics of the treatment process especially the preservative formulation used, and pre- and post-treatment handling of the wood. The nature of the treated wood samples is also important, with misleadingly high estimates being obtained from samples with unrepresentatively high proportions of cross-cut surfaces. A suggested strategy for developing an informative and standardised methodology is discussed. To form useful models of impacts of leaching, emission rates need to be considered in conjunction with site-specific information regarding a) water exchange rates between the area where leaching occurs and the sea, and b) the extent of partitioning of leachate between the water column, biota and sediment. The risk of environmental impact may be reduced by modification to treatment procedures and by careful planning of installation.
S M Cragg, C J Brown, R A Albuquerque, R A Eaton

The course of fixation of Cu-Cr-As wood preservatives
1972 - IRG/WP 307
Copper-chrome-arsenic (CCA) preservatives in contact with wood result in an instant extensive increase of pH, because of ion-exchange and adsorption reactions with the wood. During precipitation of the active elements the pH continuously increases but reaches a maximum, when all chrome is consumed. Some of the early reaction products are unstable and slowly convert via dissolution into stable compounds. The conversion proceeds by proton liberating as well as proton consuming reactions. The pH therefore alternatively decreases and increases until the reactions cease after several months. The final equilibrium fixation products are: ion-exchange fixation of Cu to the wood CrAsO4, Cu(OH)CuAsO4 and Cr(OH)3. The chrome fixation is 2nd order with respect to hexavalent chrome in the liquid phase, four regions with distinct chrome fixation rate constants were found. A hypothesis is given for the mechanism of fixation.
S-E Dahlgren

Leaching tests - A paper for discussion
1973 - IRG/WP 221
J W W Morgan

Oxalate production and calcium oxalate accumulation by Gloeophyllum trabeum in buffered cultures
1994 - IRG/WP 94-10075
Most basidiomycetous fungi produce oxalic acid as a result of their metabolic activities and nutrient procurement. There is currently a renewed interest in the role that oxalic acid may play in the decomposition of wood by basidiomycete fungi. It has been observed that although most wood degrading fungi have the capacity to produce oxalic acid, not all of these organisms express this capacity equally in the wood environment. In addition, not all of the fungi which produce oxalic acid will accumulate this metabolite. Very often the production of oxalic acid is coincident with the precipitation of oxalate salts such as calcium oxalate. At this time it is unclear as to what controls the differential production and accumulation of oxalate by wood degrading fungi. An investigative series of experiments was established using the brown rot fungus Gloeophyllum trabeum to examine the conditions which favor oxalate production and accumulation as manifested through the production of metastable calcium oxalate dihydrate crystals. Batch cultures which were buffered by base cation exchange sites of mineral amendments stimulated the production of calcium oxalate crystals. The results of these buffering experiments indicate that at pH values below approximately 6.0 there is a diminution of oxalate accumulation, and that a pH environment of approximately 3.0 is consistently attained in weakly buffered cultures inoculated with this fungus. These pH values correspond to the pH optima for oxaloacetase (EC and oxalate decarboxylase (EC respectively, and thereby suggest a mechanism for both pH control and oxalate production and accumulation.
J H Connolly, J Jellison

Soil chemistry and wood decay
1978 - IRG/WP 2109
Soil is a most complex biological, chemical and physical material; its study is effectively a separate branch of science but almost entirely in relation to ist ability to grow plants - this paper is intendet just to note some known facets that might have relevance to the decay of wood and the performance of wood preservatives.
E A Hilditch

An investigation into the influence of soil cation exchange capacity on preservative component depletion
1994 - IRG/WP 94-20050
The mobility of preservative components from treated wood into the soil environment is regarded as an important determinant of preservative performance. Standard procedures for the investigation of this phenomenon have not been developed to any great extent. Soil bed studies conducted in this laboratory using natural soil and modified soil media have provided interesting comparative data on the influence of cation exchange capacity on preservative depletion. Some of these data are discussed with reference to the development of a standard soil contact depletion procedure.
K J Archer, L Jin

The foreign exchange situation and fate of wood preservation in Nigeria
1989 - IRG/WP 3558
Up to about 15 years ago, wood utilization industry in Nigeria gave no serious thoughts to wood preservation. After this period however, as a result of escalated local demand for sawn timber, logs with wider sapwood and mainly of secondary tree species requiring protection of the sawn timber became dominant in the local timber scene. Preservatives both for protection in and out of ground contacts were available in the past in the market and at affordable prices. However, the value of local currency which has depreciated by about 86% within 48 months has made importation of preservatives a very expensive business. The paper suggests both short-term and long-term solutions for tackling the assult on the forest conservation programme which lack of wood preservation strategy has occasioned in Nigeria.
M A Odeyinde, S C Ifebueme

Selective chromate elimination from the storage-drainage-water of a wood impregnation plant
1980 - IRG/WP 3153
With the Enviro-Chrom-Ex process it is possible to eliminate ecologically and economically hexavalent chromium (chromate) from water selectively. The process which is based on the principle of selective ion exchange works with different chromate concentrations and under the presence of other ions, irrespective of the water hardness. The values of water-offtake reach 0.1 mg CrVI at maximum, causing neither pH alteration nor concentration of the salt-content of the water. The plant which has been installed in the Holzimprägnierwerk AG, Waldkirch, Switzerland, for treating chromium-containing drainage-water permits the chromium-containing regenerates to be recycled into the impregnation process. Using this chromate-recycling-process the harmful substance can be eliminated optimally.
O Wälchli, R Ott, R Hugener, E Graf, B Lieberherr

Studies on the permeability of Norway spruce (Picea abies)
1987 - IRG/WP 2295
It is well known that the bordered pits play a dominating role for liquid transport in softwoods. The mechanism behind pit aspiration during drying or heartwood formation seems to be well understood. The reason why the fixation of the membrane (torus) to the pit opening remains almost irreversible is, however, still unclear. A technique has been developed combining so-called "solvent exchange drying" with scanning electron microscopy. In this way the pit system can be "frozen" and the number of pits in aspiration can be determined. The technique has been used to widen the understanding of pit aspiration. It has also been used to follow pit aspiration during air drying and in connection with efforts to pit aspirated pits by different physical and chemical methods.
I Johansson, K Nordman-Edberg

Some practical implications from recent research on the fixation of CCA preservatives
1975 - IRG/WP 358
The mechanism of fixation of CCA preservatives is briefly described. If the temperature is increased during the primary fixation period, the formation of intermediate fixation compounds is less extensive. The length of the primary fixation period is of practical interest. It is determined by preservative composition and concentration, temperature and wood species. Diagrams are given for Pinus sylvestris. Light exposure and drying during the primary fixation period cause variability in colour intensity of CCA treated wood. Disproportionation of preservative elements with penetration depth is explained by the fixation mechanism. Conversion of intermediate fixation compounds into stable ones occurs even below the fibre saturation point, as long as the moisture ratio is sufficiently high to allow ion transport. Conversion reactions are very slow. A correlation was found between the final pH of treated timber and leachability in fresh water of copper and arsenic. The final pH depends on preservative composition and concentration, wood species and to some degree of drying and storage conditions. An electrolyte such as sodium sulfate does not affect the leachability. In saline waters leachability is increased by complex formation of Cu(II) and Cr(III) with chloride and hydroxide and the salt effect on activity coefficients. The leaching of arsenic is delayed.
S-E Dahlgren

Diffusion and interaction of components of water-borne preservatives in the wood cell wall
1988 - IRG/WP 3474
This study investigates the rates of diffusion and ultimate distributions of copper and arsenate components of wood preservatives in wood cell walls following vacuum treatment. Adsorption studies of copper on red pine (Pinus resinosa) and trembling aspen (Populus tremuloides) wood confirm the importance of cation exchange reactions on the ultimate distribution of copper in the wood substance and its strong dependence on pH of the treating solution. Formulations containing both copper and zinc preferentially adsorb or exchange copper relative to zinc. Under high pH conditions, the arsenate anion is significantly adsorbed into the cell wall. The combined adsorption and fixation of low pH CCA solutions is much slower than adsorption of high pH ACA and CZA formulations, but the reaction with wood is more complete. Diffusion coefficients were estimated for the movement of copper and arsenate components of ACA in cell wall material of both aspen and pine sapwood using a simple membrane model for non-steady state diffusion. The longer diffusion paths inherent in the diffuse porous hardwood (aspen) resulted in much slower equalization of the solute in the cell wall matrix than in red pine. However, in both species, equalization was achieved in a relative short time compared to accepted fixation times for conventional waterborne wood preservatives.
P A Cooper

Assessing health risks to occupants following remedial insecticidal treatment of timber in dwellings
1998 - IRG/WP 98-50101-27
Experiments have been carried out to assess (i) the aerial concentrations of volatile wood preservative constituents, and (ii) the potential for contamination from treated surfaces, following in situ insecticidal treatment of timbers in dwellings. Using white spirit as a model for volatile constituents in the treatment of free-standing, wood-lined chambers indicated that temperature and air exchange rate significantly affect the rate of decrease of aerial concentration, but that the rate of diffusion through the treated wood surface may be the ultimate rate-determining step. A simple mathematical model has been proposed to assist in calculating minimum re-entry times after treatment associated with different wood preservative constituents. Using lindane as a model compound in different solvent formulations, comparison between measurements of the concentration at the surface of the treated wood and pick-up by direct contact has demonstrated the need for an agreed methodology for assessing risk through contamination from treated surfaces. Both methods demonstrated that the amount of lindane close to or at the surface of the treated wood decreased with time, thus reducing potential for pick-up.
R J Orsler, E D Suttie, V Rijckaert

Adsorption of ACQ components in wood
2010 - IRG/WP 10-30522
To investigate the chemical adsorption capacity of copper-monoethanolamine (Cu-Mea) components on wood, the Na+ cation exchange capacity (CEC) of red pine (Pinus resinosa Ait.) was determined and compared to the adsorption capacity of free Mea and Cu-Mea complexes. The CEC increased with increasing pH. Free Mea adsorption as a function of pH followed the sodium adsorption curve except at pH over 9, when it exceeded the CEC. Cu-Mea adsorbed up to the CEC at pH 9.0-9.5 apparently as Cu(Mea)+, whereas the complex in solution is predominantly of the form Cu(Mea)2+. For the quaternary ammonium compound, alkyl dimethyl benzyl ammonium chloride (ADBAC) adsorption isotherm showed two different adsorption mechanisms into wood: ion exchange reaction at low concentration and hydrophobic interaction at high concentration. ADBAC adsorbed at solution concentrations below a critical concentration (hemi-micelle concentration) had high leaching resistance while ADBAC adsorbed into wood at above the critical micelle concentration (CMC) had low leaching resistance. The CMC decreased with addition of Mea and Cu-Mea. The anion, Cl- of ADBAC was only adsorbed at solution concentrations above the CMC and was easily leached out. The adsorption capacity of ADBAC into wood by cation exchange reaction did not achieve the cation exchange capacity (CEC) of wood. However, the total adsorption of ADBAC and Cu achieve the CEC of wood in the presence of copper amine, and ADBAC competes with copper to occupy the same sites in wood.
Myung Jae Lee, P Cooper

Knowledge exchange and transfer from academia to industry in the field of wood protection research – Activities of the IRG-WP Communications Committee
2019 - IRG/WP 19-50354
The International Research Group on Wood Protection (IRG) was founded in 1969 as a structured group of like-minded scientists and technologists focused on generating knowledge of the science of wood deterioration, and novel solutions to provide sustainably and environmentally responsible products for the protection of wood-based materials. The primary function of the IRG is to provide opportunities for the exchange of ideas and information in an informal atmosphere, unencumbered by refereeing of papers or other pre-conditions. While the primary vehicle is the annual meeting usually held in the second quarter of each year with global locations chosen as providing optimal opportunities for interactions between attendees and in settings that are both interesting and economically viable for our diverse attendance from around the world, the changing nature of the inputs into wood protection research over the past five decades, as well as the ever shifting environmental, global and economic influences have led to a desire to provide additional communications vehicles for the IRG members and sponsors, as well as to provide relevant information to the global audience with an interest in wood products protection and the associated research and technologies. This paper addresses the various ways that the IRG Communications Committee has been developing to provide diverse and on-going communications throughout each year.
F Latorre, B Abbott, C Brischke, M Humar, D Jones, E Larnoy, L Nunes, A Preston, T Singh