Your search resulted in 54 documents. Displaying 25 entries per page.
The iron reduction by chemical components of wood blocks decayed by wood rotting fungi
2021 - IRG/WP 21-10979
Brown-rot fungi, a group of wood rotting fungi, is well known to be one of major microorganisms that cause the deterioration of wooden buildings in Japan and have been considered to use chelator-mediated Fenton (CMF) reaction in concert with hydrolytic and redox enzymes for degradation of wood cell wall. CMF can be described as a non-enzymatic degradation system that utilizes hydroxyl radicals produced by the reaction of hydrogen peroxide with ferrous iron in the presence of chelator, and therefore, the reduction process of ferric iron present in wood cell walls is one of the key reactions in this process. To date, various candidates such as low-molecular weight aromatic metabolites produced by fungi, proteins, and lignolytic products have been proposed as iron-reducing compounds. In addition, lignin polymer has been also reported to have the ability of iron reduction although detailed mechanism is not still unknown. In the present study, the authors investigated the iron reduction with wood flour, which was expected to contain both a part of soluble compounds and cell wall polymers, using ferrozine assay in order to obtain the knowledge of iron reduction mechanism. We show that iron reduction capacity by decayed wood samples was higher than that by the samples of sound wood.
R R Kondo, Y Horikawa, K Ando, B Goodell, M Yoshida
The effect of a chelator mediated fenton system on activation of TMP fibres and decolorization of synthesized dyes
2004 - IRG/WP 04-50223
The purpose of this work is to improve our current knowledge of the non-enzymatic mechanisms involved in the brown rot degradation of wood, but also to study the potential applications of a chelator-mediated Fenton system in activation of wood fibers and decolorization of synthesized dyes. In this work, Electron Spin Resonance (ESR) spin-trapping techniques were used to study the generation of hydroxyl radicals in a mediated Fenton system. The activation of Thermal Mechanical Pulp (TMP) fibers was also evaluated by ESR measurement of free phenoxy radical generation on solid fibers. The results indicate that low molecular weight chelators can improve Fenton reactions, thus in turn stimulating the free radical activation of TMP fibers. However, the data also show that excessive and prolonged free radical treatment may cause the destruction of fiber phenoxy radicals. A mediated Fenton system was evaluated for decolorization of several types of synthesized dyes as well. The results show that, compared to a neat Fenton process, the mediated Fenton process increased the production of .OH species to increase the decolorization efficiency. The color of a dilute liquid dyes (Carta Yellow RW, Carta Yellow G, or Cartasol Red 2GF) was effectively reduced to a colorless level after 90 minutes of treatment at room temperature by a mediated Fenton process. In conclusion, this study demonstrates the potential for application, but also the complexity of free radical chemistry in biological materials, especially with regard to the chelation of transition metals and the interaction between free radicals. The complexity of the dyes is similar to that of some organic wood preservatives and may provide a means for remediation of preservative contaminants in soils.
Yuhui Qian, B Goodell, J Jellison
Chelator-Mediated Fenton Chemistry in Wood Degraded by Fungi
2007 - IRG/WP 07-10618
Wood specimens were colonized by individual isolates of brown rot, white rot, soft rot and blue (sap) stain fungi. Ethyl acetate extracts of the ground wood were analyzed for their iron-reducing capabilities using a ferrozine-based assay. Extracts from wood colonized by brown rot fungi showed a significantly greater iron-reducing capability than extracts from wood colonized by white rot fungi or non-decay fungi. The ability of brown rot fungi to produce compounds, and/or modify the wood components, that reduce iron is of relevance to the “chelator-mediated Fenton mechanism” that has been advanced as a theory in the non-enzymatic degradation of wood by the brown rot fungi.
B Goodell, G Daniel, J Jellison, Yuhui Qian
Chemical mediated depolymerization of cotton cellulose for the understanding of non-enzymatic fungal decay
2010 - IRG/WP 10-10731
Small, low molecular weight non-enzymatic compounds have been linked to the early stages of brown rot decay as the enzymes involved with holocellulose degradation are found to be too large to penetrate the S3 layer of intact wood cells. The most pronounced of these which were analyzed in this study are hydrogen peroxide, iron, and oxalic. The compounds related to the Fenton reaction: the combination of hydrogen peroxide and iron caused marked lowering of the degree of polymerization in the cotton cellulose after treatment. This was the case for both iron ions; Fe3+ and Fe2+. A 10mM solution of oxalic acid also showed significant depolymerizing effect on cotton cellulose, whereas diluting the oxalic acid with sodium oxalate to obtain a pH gradient, showed that this decreased the effect reducing of oxalic acid. In addition an organic iron chelator, EDTA, was tested but was found to inhibit depolymerization when in solution with chemicals related to Fenton chemistry. Manganese was tested to see if other metals than iron could generate an significant impact on the degree of polymerization of cotton cellulose and the metal showed good depolymerizing properties as a substitute for iron. We conclude that low molecular weight metabolites are capable of effectively depolymerizing cellulose during incipient decay by brown-rot fungi.
A C Steenkjær Hastrup, B Jensen, F Green III
The Chelator Mediated Fenton System in the Brown Rot Fungi: Details of the Mechanism, and Reasons Why it has Been Ineffective as a Biomimetic Treatment in some Biomass Applications – a Review
2014 - IRG/WP 14-10828
The chelator-mediated Fenton (CMF) reaction requires the action of two types of chelating compounds. The first chelator, oxalate, solubilizes and then sequesters iron, and the second chelator reduces iron. Iron reduction must be controlled near the fungal hyphae to prevent damaging Fenton chemistry from occurring in that location. Similarly, iron reduction must be promoted within the wood/plant cell wall to promote Fenton chemistry in the proximity of the target lignocellulose. The mechanism for that control is reviewed in this paper. Both neat Fenton and the CMF have been examined by researchers seeking to exploit this relatively simple mechanism for biomass conversion and lignocellulose pretreatment systems. This paper reviews why some of that research has not produced useful depolymerization reactions and why excess amounts of reagents have been required. The application of Fenton treatments requires that the reactive oxygen species produced in the reaction be generated within a nanometer of the target substrate (lignocellulose), and for this to occur in biomass treatments using Fenton or CMF systems, iron must first be allowed to bind to the substrate to allow the reactions to proceed within nanoscale proximity to lignocellulose. Further, excess iron in solution and in interstitial space must be removed as this “free” iron will react preferentially with chelators and peroxide preventing appropriate targeted action on lignocellulose.
B S Goodell, M Nakamura, J Jellison
Possible targets of wood modification in brown rot degradation
2014 - IRG/WP 14-40676
Wood modification protects wood from fungal degradation in a non-toxic manner. However, the mechanisms behind the decay resistance in modified wood are currently unknown. The aim of this study was to discuss the i) colonisation, ii) nutrient recognition, iii) transcription, iv) depolymerisation and v) hydrolysis steps in the brown rot degradation progress and explore whether they are inhibited by wood modification, based on new and previously published data from our group. In previous studies, it has been shown that fungi were able to colonise modified wood, to recognise it as a source of nutrients and express genes associated with cellulose degradation while growing on modified wood. In this study, Fenton derived hydroxyl radicals (∙OH) and brown rot cellulases were able to degrade modified wood. We conclude that the five degradation steps discussed in this paper are unlikely targets for wood modification and that wood modification rather inhibits a step that in a schematic overview of the brown rot degradation process is downstream from transcription but upstream of depolymerisation and hydrolysis.
R Ringman, A Pilgård, G Alfredsen, B Goodell, K Richter
Controlling the sapstain fungus Ceratocystis coerulescens by metabolites obtained from Bjerkandera adusta and Talaromyces flavus
1993 - IRG/WP 93-10024
Sapstain causes severe damage to wood and wood products, posing a major economic problem for the wood industry. The purpose of this study was to determine if metabolites from Bjerkandera adusta and Talaromyces flavus would (1) decolorize stain in wood caused by Ceratocystis coerulescens and (2) prevent sapstain by Ceratocystis coerulescens. We studied the interaction of the sapstain fungus Ceratocystis coerulescens against the test fungi Bjerkandera adusta and Talaromyces flavus in dual cultures on agar medium. The metabolites obtained from test fungi were examined on pine veener disks stained by Ceratocystis coerulescens. Our results indicate that the test fungi were antagonistic to the sapstain fungus Ceratocystis coerulescens. The combination of metabolites from the antagonists decolorize the sapstained pine veener disks and killed the existing growth of Ceratocystis coerulescens.
S C Croan, T L Highley
Oxalic acid quantification, oxaloacetase assay and ESI localization of P, C, and Fe from the brown rot fungus Postia placenta
1994 - IRG/WP 94-10063
The mechanism by which brown-rot fungi initiate depolymerization of holocellulose in wood remains unknown. Recently, oxalic acid (OA) has received considerable attention in cellulose breakdown by brown-rot fungi. The OA could serve as a proton donor for hydrolytic or an electron donor for oxidative (Fenton's reaction-H2O2/Fe2+) cleavages of cellulose. The acid may originate via oxaloacetase's action upon oxaloacetate. We report electron microscopic imaging (ESI) to localize Fe and HPLC/oxalic kit colorimetry to purify/quantify OA from hyphae upon agar, southern pine wood blocks (WBs) or in liquid culture. Comparative ESI at 25, 59, 110, 222, and 710 ev of hyphae grown upon agar or WBs demonstrated hyphal Fe (710 ev). Although Fe was not visualized in cell walls of uninoculated WBs, it was in certain wood cell walls of inoculated WBs. The Fe distribution differed from C and P. Oxaloacetase activity was not observed in either Amicon YM10 filter-retained intra-or extracellular fractions of liquid cultured hyphae or in homogenates from decayed WBs. In contrast, HPLC detected OA in both Postia placenta liquid cultures and decayed WBs. The less sensitive oxalic kit (mg vs. ug) did not detect OA in liquid cultures. These results constitute additional evidence for an OA Fe2+/H2O2-Fenton's mechanism for brown rot-induced cellulose degradation. However, OA's origin was not established.
C R Jordan, W V Dashek, T L Highley
The long road to understanding brown-rot decay. A view from the ditch
1995 - IRG/WP 95-10101
Interest in understanding how brown-rot fungi decay wood has received increasing interest in recent years because of a need to identify novel targets that can be inhibited for the next generation of antifungal wood preservatives. Brown-rot fungi are unique in that they can degrade holocellulose (cellulose and hemicellulose) in wood without first removing the lignin. Furthermore, they degrade holocellulose in an unusual manner, causing a rapid decrease in degree of polymerization at low weight loss. Despite the increased research effort, the mechanism of brown-rot decay remains unclear and, furthermore, this research has not provided biochemical targets for inhibition and development of new wood preservatives. In viewing the brown-rot literature, it became apparent that many of the beliefs about brown-rot decomposition of wood are based more on tradition or conjecture than on facts. These myths tend to cloud our understanding of brown-rot decay and as a result may contribute to a misdirection of research efforts. The purpose of this paper is to attempt to identify and clarify some of these misconceptions about brown-rot decay that have become dogma.
F Green III, T L Highley
Targeted inhibition of wood decay (Using everything but the kitchen sink)
1997 - IRG/WP 97-10203
Low molecular weight oxidative decay agents have been implicated in the degradation of wood by brown-rot decay as evidenced by chemical analysis of brown-rotted wood and detection of oxalic acid and hydroxy radicals. Fenton chemistry (H2O2 / Fe++) is often proposed as the mechanism for generating hydroxy radicals. Previous authors have shown iron to enhance the brown-rot hydrolysis of wood, while others have shown suppression of brown-rot by organic and inorganic metal chelators. We have attempted to inhibit brown-rot and white-rot decay of southern pine and maple wood blocks in a series of soil block decay tests using a variety of chemicals targeted specifically at key components of proposed brown-rot mechanisms. Included in these tests were inorganic and organic chelators, calcium coordinating compounds, wood binding dyes, microbial siderophores and common antioxidants -- some previously tested. All chemicals were screened at 1% aqueous (w/v). Only 2 of 28 compounds were effective in significantly reducing wood weight loss by all fungi tested in 12 weeks: napthaloylhydroxylamine (NHA) -- a calcium precipitating agent; and ruthenium red (RR) -- a pectin stain. Both compounds bind preferentially to pit tori and ray parenchyma cells as observed by light microscopy. Targetting the woody substrate for inhibition of decay looks more promising than targetting fungal physiology
F Green III, T A Kuster, T L Highley
The role of oxidation in wood degradation by brown-rot fung
1992 - IRG/WP 92-1562
Brown-rot fungi are suggested to degrade cellulose by oxidation with hydrogen radicalsformed eg. in the conversion of hydrogen peroxide in the Fenton type reactions. The stuctural changes in the holocellulose in wood induced by Fenton's reaction on wood components are very similar to those caused by brown-rot fungi. In this work the effect of the Fenton reaction on wood components was studied. The brown-rot fungi produce extracellular hydrogen peroxide while growing on sawdust medium and on crystalline cellulose. Hydrogen peroxide is apparently formed by the action of an oxidase enzyme. In this work the role of enzymatic oxidation in cellulose degradation by the brown-rot fungus, Poria placenta was studied.
A-C Ritschkoff, J Pere, J Buchert, L Viikari
Evaluation of tropolone as a wood preservative : activity and mode of action
2002 - IRG/WP 02-30282
The fungicidal activity of 2-hydroxy cyclohepta-2,4,6-trienone (tropolone) analogue of b-thujaplicin a natural product responsible for the durability of heart wood of several cupressaceous trees was investigated in vitro on growth of white and brown rot fungi. Results obtained show that tropolone, easily prepared from commercially available products, possesses strong fungicidal activity similar to that of fungicides currently used for wood preservation. In addition, laboratory malt-agar block tests indicate that tropolone, like b-thujaplicin, is able to protect wood blocks against brown rot fungi like Poria placenta but not against white rot fungi like Coriolus versicolor. These differences were investigated on the basis of the mechanism of action of tropolone. Fungal growth inhibition on malt-agar could be prevented by adding iron salts in the medium, which indicates that chelating properties of tropolone are important on its mode of action. Determination of the stoechiometry of the reaction between tropolone and ferric ion shows the formation of a strongly insoluble precipitate involving 3 equivalents of tropolone for 1 equivalent of Fe3+ with a solubility product (Ks) of approximately 10-28 which creates metal limitation conditions inhibiting fungal growth. Moreover, tropolone possesses weak antioxidative properties and is able to inhibit ferric iron reduction by catecholates lowering the redox potential of the iron couple. All these data are consistent with the hypothesis that tropolone inhibits wood degradation by Poria placenta by chelating iron present in wood thus avoiding initiation of Fenton reaction, while Coriolus versicolor which produces several lignolitic enzymes like laccases and peroxidases able to degrade rapidely tropolone is unaffected by tropolone.
P Gérardin, M Baya, N Delbarre, P N Diouf, D Perrin, P Soulounganga, E Gelhaye, J P Jacquot, C Rapin
Degradation of wood veneers by Fenton’s reagents: effects of low molecular weight phenolic compounds on hydrogen peroxide decay and tensile strength loss
2009 - IRG/WP 09-20400
Pine wood (Pinus sylvestris) veneers strips were incubated in acetate buffer containing hydrogen peroxide and iron to mimic mechanisms of brown rot decay and assess the degradation of cellulose through analysis of the tensile properties of the decayed wood. The tensile properties of thin wood strips treated with Fenton system reagents or precursors were determined and correlated to weight loss as reaction conditions were varied. The effect of 2,3‑DHBA concentration on the decay rate of H2O2 in the reaction mixture and the mechanisms of H2O2 decomposition will be discussed. The concentration and ratio of the low molecular weight, phenolic compound 2,3-dihydroxybenzoic acid (2,3‑DHBA) were also studied with regard to the generation of hydroxyl radicals from H2O2 and the resulting weight and strength loss. The pathway and rate of H2O2 decay depended on the pH and the medium (water, buffer) of the reaction mixture. As the concentrations of 2,3-DHBA above an optimal ration with iron, strength loss of the wood strips was reduced. This is likely to have occurred because concentrations of catechols that exceed a 1:1 ratio sequester iron via hexadentate and quadradentate ligand formation as has been previously reported Wood constituents were also shown to reduce Fe(III) to Fe(II) and to drive the Fenton reaction.
Yanjun Xie, R Well, Zefang Xiao, B Goodell, J Jellison, H Militz, C Mai
The Use of Micro-Tensile Testing to Assess Weathering Decay and Oxidative Degradation of Wooden Items
2010 - IRG/WP 10-20433
This paper presents a method to study the weathering performance of wooden items and to assess the oxidative degradation of wood via the Fenton reaction. Weathering resistance and photo-stability of wood was tested using pine wood (Pinus sylvestris) veneer strips measuring approximately 60 µm in thickness. The veneer strips were treated using a reactive chemical to impart surface protection. The artificially weathered veneers were characterised regarding tensile strength loss as well as by means of infrared spectroscopy. The chemical treatment reduced the tensile strength of the veneer strips. During artificial weathering, however, the strength loss of the treated veneers was clearly lower than that of the controls. The shape of the veneers was preserved due to the treatment. In a second approach veneers strips were used to study wood degradation by the Fenton’s reagent in order to minic the long-term deterioration of archaeological wood from marine environments. Veneer strips were incubated in acetate buffer (pH 4) containing hydrogen peroxide and Fe ions (Fenton’s reagent) and tensile properties (measured in a zero-span mode) were determined. Varying the type of iron (ferrous or ferric sulphate) with H2O2 did not yield significant differences in the rates of H2O2 and tensile strength reduction. However, increasing the amount of wood material (the number of wood strips) in the reaction mixture increased Fe(III) reduction in solution indicating that wood constituents participated in this reaction. Increasing concentrations of Fe(III) in the reaction mixture resulted in a decrease in H2O2 in solution. Despite an increase in iron concentration and H2O2 decomposition under these conditions, a uniform and consistent strength loss of 30% was observed at all Fe(III) concentrations tested. At fixed Fe(III) concentrations, increasing the H2O2 concentration linearly increased the strength loss of the veneers.
C Mai, Yanjun Xie, Zefang Xiao, P D Evans, H Militz
Antifouling wood matrix with natural water transfer and micro reaction channels for water treatment
2019 - IRG/WP 19-40853
Wood with abundant nutrition transport channels could be considered as a kind of natural water purifier due to quick and effective passages for separation. Nevertheless, microporosity as main porous structure of initial wood are not enough to effectively separate small molecular, such as organic dye pollutants. Meanwhile, like most filters the fouling resulting in blocking and poor water flux will also restrict their large scale. Here, we incorporate Fenton-like catalysis based on Mn3O4 loading for degradation of methyleneblue with water transfer and separation channel of fir wood (the interfacial area was estimated up to 6×104 m2/m3) to solve the low separating efficiency and fouling problem. The results show that wood matrix treated by hydrothermal carbonization loading with Mn3O4 nanoparticles (Mn3O4/TiO2/wood) exhibited remarkable catalytic efficiency on methylene blue (MB) moles degradation and the fouling problem could be significantly alleviated during Fenton-like catalysis. The turnover frequency of the wood matrix is 6.072×10-3 molMB·molMn3O4−1·min−1 which is much higher than the values reported in the literature. The flux maintained approached 2045 L·m-2·h-1 with a high rejection rate of more than 95%. Wood with natural interconnected micropores as main fluid transfer and micro reaction channels is a promising material for construction parallel-series microreactors, applying to some vital chemical process besides sewage purification and desalination.
G Liu, D Xu, S Chang, J Hu, Xianjun Li5, Y Liu
Effect of acetylation on decay resistance of wood against brown-rot, white-rot and soft-rot fungi
1989 - IRG/WP 3540
Effect of acetylation on decay resistance of wood was investigated using wood blocks of Cryptomeria japonica, Pinus densiflora, Albizia falcata and Fagus crenata. Blocks were treated with uncatalyzed acetic anhydride for different lengths of time and exposed to Tyromyces palustris, Serpula lacrymans, Coriolus versicolor and unsterilized soil. The action of OH-radical on acetylated wood was also examined using Fenton's reagent. The enhancement of decay resistance by acetylation was revealed clearly for all cases of exposures but varying with fungal and wood species used. For a brown-rot fungus Tyromyces palustris, the weight loss reached almost nil in all woods at 20 WPG (weight percent gain) of acetylation, after the striking decrease from 10 to 15 WPG. For a white-rot fungus Coriolus versicolor, it was counted until 12-15 WPG in the perishable hardwoods used, but not in a softwood Cryptomeria japonica, even at 6 WPG. In cases of another brown-rotter Serpula lacrymans and soil burial, effect of acetylation was intermediate between Tyromyces palustris and Coriolus versicolor. Anti-degradation mechanism by acetylation was discussed, from these weight loss - weight gain relationships, and the IR-and 13C-NMR spectral analyses of fungus-exposed wood.
M Takahashi, Y Imamura, M Tanahashi
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
A discussion of current theories concerning CCA fixation
1983 - IRG/WP 3238
The understanding of the fixation mechanism of CCA and related preservatives in wood has been greatly improved by a significant series of recent scientific papers. In view of recent concerns in New Zealand regarding the long-term efficacy of CCA in high decay-hazard situations, it was considered appropriate to review this recent work and to contrast it with theories presented by previous workers.
D V Plackett
Synergistic effects between 2-HPNO, Irganox 1076 and EDTA on the inhibition of wood degradation by Coriolus versicolor
2004 - IRG/WP 04-30331
The efficiency of 2-hydroxypyridine-N-oxide (2-HPNO) as wood preservative has been investigated. As shown using classical experiments as well as using response surface methodology, the efficiency of 2-HPNO as wood preservative is strongly improved in presence a chelator like EDTA and/or of Irganox 1076 an industrial antioxidant. In these conditions, wood preservative efficiency of the mixture the three previous compounds is quite similar to that of tebuconazole used alone. 2-HPNO exhibits an hydroxamic acid function and is a susbtrate of fungal peroxidase. These properties could explain the observed synergy. The implications of these data for the design of new wood preservation strategies are also discussed.
A Mabicka, S Dumarçay, N Rouhier, M Linder, J P Jacquot, P Gérardin, E Gelhaye
Environmental issues: Messages for the wood preservation industry
1985 - IRG/WP 3353
A review of the origins and structure of environmental legislation throughout those territories of the world where wood preservation is a major industry is given. The implications of media, industry and legislation interaction is discussed and suggestions made as to the key issues the wood preservation industry should concentrate its attentions on in the immediate future.
D G Anderson, P Waldie
1983 - IRG/WP 3268
Copper binding capacity of modified wood flour
1992 - IRG/WP 92-3709
Wood flour was modified by reaction with oxidising agents and CCA preservative. The copper chromium and arsenic were removed from the CCA treated wood flour by an acid leaching procedure. The modified wood flours were allowed to react with copper acetate solution and the level of copper fixation achieved was determined. The modified wood flours had greater affinity for copper ions present in solution than unmodified wood flour.
N C Milowych, W B Banks, J A Cornfield
Non-enzymatic Gloeophyllum trabeum decay mechanisms: Further study
2001 - IRG/WP 01-10395
Information will be presented on the mechanisms involved in, and potential application of, non-enzymatic wood decay by brown rot decay fungi. Specifically, the hypothesized role of low molecular weight phenolate derivatives will be discussed in relation to non-enzymatic degradation of wood. The mechanism of binding of iron by cellulose, and binding and reduction of iron by fungal derivatives and model compounds is examined. Positive and negative aspects of potential application of these compounds in the generation of free radicals will be discussed.
B Goodell, J Jellison
A fixation model, based on the temperature dependence of CCA-C fixation
2000 - IRG/WP 00-40163
A model was prepared for the fixation of 1% CCA-C in red pine that allows the prediction of extent of fixation based on the temperature history of the treated wood following pressure treatment. The reaction kinetics of the rapid initial reaction and the slower main reaction were characterized using the Van t'Hoff equation. The initial reaction could be represented by a 10th order chemical reaction and the main reaction by a first order chemical reaction. The main reaction zone in red pine starts once approximately 47% of the total Cr VI in the impregnated CCA-C solution is fixed on wood matrix and is much slower so it controls the fixation rate. The rate constants for the two zones were estimated at a range of fixation temperatures and the temperature dependence defined by the Arrhenius equation. The rate equation and the temperature dependence were combined in a single model for each fixation zone providing an equation that related extent of fixation to the time/temperature history following fixation. The model accurately predicted fixation rate of pine poles exposed to variable temperature conditions following treatment in most cases, although slight changes in the reaction and Arrhenius constants due to natural variability in wood density and other properties could result in relatively large errors in some cases.
P A Cooper, K M F Kazi, Jianbin Chen, Y T Ung
Testing a diffusion and reaction model for the leaching of CCA components from unfixed CCA-treated wood
2002 - IRG/WP 02-50193
A previously described physical model applicable to the leaching of any substance undergoing a first-order fixation reaction with wood is applied to the leaching of CCA components from unfixed wood. Using this model and laboratory leaching experiments with small wood samples immersed in water, the diffusion coefficients and reaction rate constant of Cr6+, total Cr, Cu and As in unfixed CCA-treated red pine (Pinus resinosa Ait) are measured. Modelled reaction rate constants are in general agreement with pure fixation experiments except when determined from experiments involving small samples severely depleted by longitudinal leaching, but this effect is seen to decrease for larger sample sizes. The operation of the model for predicting intermittent Cr6+ leaching is explained through a visual demonstration. The model is shown to have good predictive ability when compared to a leaching experiment involving intermittent immersion and changing temperatures.
L Waldron, P A Cooper