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Lignin degradation by wood-degrading fungi
1986 - IRG/WP 1310
The wood-degrading white-rot fungus Phanerochaete chrysosporium, has been the subject of intensive research in recent years and, based upon isolation of the extracelluar enzyme ligninase, major advances have now been made toward elucidating the mechanism by which this fungus degrades lignin. From these developments, a model emerges which could explain the process by which wood-degrading fungi in general, attack lignin.
P J Harvey, H E Schoemaker, J M Palmer

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

Effect of some resin treatments on fungal degradation reactions
1999 - IRG/WP 99-10318
The effect of impregnation of wood with vegetable oil, tall oil and two water soluble on fungal degradation reactions was assessed by hydrolysis and enzyme activity measurements. The experiments were carried out by using isolated enzyme preparations and a living brown-rot fungus Poria placenta. The results indicate that the inhibitory effect of treatments was clearly directec towards the enzymatic hydrolyzability of the hemicellulosic and cellulosic components of wood cell wall. The water soluble resins and tall oil treatments significantly decreased the ability of isolated enzyme preparation to hydrolyse treated wood substrate. The inhibitory effect of these treatments was focused on the degardation of arabinoxylan and cellulose components of the wood cell wall. The vegetable oil treatment did not significantly prevent the enzymatic hydrolysis of wood substrate. The resin and tall oil treatments seemed also to interfere the production and/or mode of action of hydrolytic degradation pathway of living brown-rot fungus P. placenta.
A-C Ritschkoff, M Rättö, A J Nurmi, H Kokko, A O Rapp, H Militz

Mechanistic aspects of the reactions of copper complexes with lignin in the presence of hydrogen peroxide and lipid hydroperoxide model compounds as proposed for white rot fungi
2001 - IRG/WP 01-10399
The structural principles and the oxidative reactions of the catalytic system consisting of copper, hydroperoxides, and copper coordination compounds that contain aromatic nitrogen atoms are similar to those of catalytic centers of oxidative enzymes involved in delignification reactions of white rot fungi. The system is capable of selectively degrading lignin and its low molecular weight would allow to react oxidatively also at sites of the wood cell wall, where enzymes cannot penetrate. Understanding the mechanisms of white rot would offer perspectives to develop targeted wood preservatives to inhibit these enzymatic and non-enzymatic reactions of wood decay. Studies on the mechanism of the copper/pyridine and 4-aminopyridine resp./hydrogen peroxide system that were carried out with 14C-labeled lignin and cellulose model compounds demonstrated the selectivity of the copper system for lignin structures and the ability of the system to oxidise even non-phenolic lignin. Product profiles of the reactions supported by ESR measurements suggested a non-radical reaction pathway involved in that case. However, when a lipid hydroperoxide model (cumene hydroperoxide, CHP) was used as peroxide source, a variety of free radicals derived from this peroxide could be detected in ESR. Selective staining of treated wood sections with safranin and astra blue showed degradation of softwood and hardwood lignin in the middle lamella and secondary cell wall. Besides its importance for developing targeted wood preservatives, the coordinated copper system has great potential for application for selective lignin degradation in the pulp and paper industry and could therefore replace environmentally problematic chlorine and chlorine dioxide based pulp bleaching stages.
K Fackler, P Lamaipis, E Srebotnik, M Humar, C Tavzes, F Pohleven, M Sentjurc, T Watanabe, K Messner

The kinetics of anhydride modification reactions of wood. Experimental results and theoretical modelling
1998 - IRG/WP 98-40125
Although the chemical modification of wood remains a fertile area for research, there has been little work performed on the kinetics of the modification process. The reaction kinetics of a series of linear chain and cyclic anhydrides has been studied and activation energies of the reaction determined. The reaction kinetic profiles are determined by the relative rates of reaction of the reagent with the cell wall polymeric hydroxyl groups, and the rate of diffusion of the reagent within the bulk of the substrate. Thus initially, the rate of reaction is determined by the reaction of reagent with surface sites, but as reaction proceeds, diffusion processes begin to dominate. The relative contributions of the two processes depend upon a number of variables, which include size of reagent, reaction temperature, and ultrastructure of the substrate. This process has been modelled using percolation theory, which has previously had extensive application in describing the flow of liquids through complex porous media, yet has not been applied to wood. The modelling shows that the reaction profiles are determined by the relative rates of reaction and diffusion.
C A S Hill, J G Hillier

The role of oxygen and oxygen radicals in one-electron oxidation reactions mediated by low-molecular weight chelators isolated from Gloeophyllum trabeum.markup
1994 - IRG/WP 94-10086
The KTBA assay for determination of one-electron oxidation activity was used to assay reactions of low-molecular weight chelators isolated from the brown rot fungus Gloeophyllum trabeum. The assay, performed either under air or nitrogen showed that molecular oxygen was an important factor in chelator-mediated oxidation reactions. A reduction in oxidative activity was observed when superoxide dismutase was introduced to the reaction, indicating that superoxide radicals also involved in the reaction and were scavenged by SOD. The KTBA assay showed, similarly to other assays in our laboratory, that the chelators could reduce Fe(III) to Fe(II). However, once chelators were 'oxidized' in this process they appeared to be redox inactive. Preliminary results indicate that chelator redox activity can only be regenerated in the presence of a reductant such as NADH or oxalate.
Jun Lu, B Goodell, Jiang Liu, A Enoki, J Jellison, H Tanaka, F Fekete

Modification of solid wood: research and practical potential
1997 - IRG/WP 97-40098
The polymeric structure of the wooden cellwall mainly consists cellulose, hemicellulose and lignin. The most reactive sites on these components are the hydroxyl groups. The cellwall polymers (and its reactive hydroxyl groups) are responsible for most physical and chemical properties of wood. By changing the basic chemistry of the cellwall polymers, it is possible to change different undesirable attitudes of wood considerably, so as durability, dimensional stability, hardness and stability against UV-degradation. In this overview paper, the principles of wood modification, reaction types, process parameters and material properties gained by different modification treatments are discussed. Furthermore, the challenges on the way from laboratory scale to commercial application are highlighted.
H Militz, E P J Beckers, W J Homan

Kinetics and mechanism of fixation of Cu-Cr-As wood preservatives. Part 4: Conversion reactions during storage
1974 - IRG/WP 332
Precipitates simulating those produced in wood by preservative fixation reactions were prepared by the reduction of Boliden K 33 and Celcure AP solutions with hydrogen peroxide and hydrazine. The pH changes on aging at 20 and 50°C were studied and related to the chemistry of fixation previously described. Hydrolysis of copper arsenates may render arsenic acid temporarily water soluble pending precipitation by trivalent chrome liberated by the slow hydrolysis and reduction by wood of chromic chromates. As the reduction of chrome is the primary driving force for the fixation of Cu-Cr-As preservatives, pH changes were observed in sawdust treated with dilute CrO3 solutions under different temperature cycles. The pH is essentially independent of temperature during the first three days when chromic chromates are being formed, but the subsequent pH is highly temperature-sensitive. Part of this effect is due to hydrolysis and reduction and part to generation of acidic reaction products in the wood at higher temperatures.
S-E Dahlgren

Chemical reactions involved in furfurylation of solid wood - An investigation by ATR-IR spectroscopy
2006 - IRG/WP 06-40347
Wood modification with furfuryl alcohol (FA) has gained renewed interest during the last five to ten years because of advances in process technology and because of increased focus on the environmental hazards of traditional wood impregnation. The reaction mechanisms involved in the furfurylation process are not yet understood in detail. In the work presented here, the chemical reactions and their end products in the wood cell wall were studied using Attenuated Total Reflection InfraRed spectroscopy (ATR-IR) and knowledge from molecular modelling. Evidence of a polymeric structure of FA in the cell wall was found, but bonding between wood constituents and FA or a FA-polymer could not be verified. Because of many overlapping absorbance peaks in the IR region, wood and FA absorbance bands are difficult to assign without support from extensive molecular modelling. Further modelling is needed to fully understand the possible reactions between wood and FA.
T Mark Venås, L Garbrecht Thygesen, S Barsberg