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The biological effectiveness of wood modified with heptadecenylsuccinic anhydride against two brown rot fungi: Coniophora puteana and Gloeophyllum trabeum
1992 - IRG/WP 92-3705
A modified soil block test was carried out using wood samples reacted with heptadecenylsuccinic anhydride (ASA). This modification gave good resistance to decay brought about by the brown rot fungi Coniophora puteana and Gloeophyllum trabeum during the twelve week exposure period. Results indicated that there was a good correlation between increased loading of modifying reagent and an increase in effectiveness paralleled by a marked reduction in wood moisture content. The effective resistance threshold level was calculated to be about 30% weight gain of ASA. Further discussions regarding the mode of action are included.
C Codd, W B Banks, J A Cornfield, G R Williams


The decay resistance of chemically modified aspen composites to the white rot fungus Coriolus versicolor (L.) Quelet
1998 - IRG/WP 98-40122
Chemical modification of Aspen wood (Populus tremula L.) in the form of solid wood, veneers and sawdust was undertaken by a two step procedure consisting of esterification with maleic anhydride (MA) and subsequent oligoesterification with MA and glycidyl methacrylate (GMA) or allyl glycidyl ether (AGE). Modified wood was thermoplastic and was thermally formed by hot-pressing to produce veneer or solid wood samples with smooth glossy surfaces, while plastic-like wafers were obtained by hotpressing modified sawdust. Chemical modification alone was shown to enhance the biological resistance of Aspen to decay by Coriolus versicolor. In addition, hot-pressing enhanced decay resistance of both unmodified wood and esterified wood veneer samples, although no improvement was found by hot pressing oligoesterified wood. The most effective treatment for the improvement of decay resistance was chemical modification of the sawdust in conjunction with hot-pressing. A microscopic examination of chemically modified and control samples following exposure to the fungus showed more extensive colonisation and decay in untreated, unpressed samples.
M C Timar, A J Pitman, M D Mihai


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


Efficacy of anhydrides as wood protection chemicals - II. Performance against soft rot fungi
1998 - IRG/WP 98-30174
Pine sapwood modified with various anhydrides and with butyl isocyanate was tested for its resistance to soft rot decay. Small stakes were exposed for 20 months in unsterile soil in a fungal cellar test. Wood modified with butyl isocyanate performed better than any of the anhydrides tested, with a threshold level of protection (less than 3% weight loss) at 12% weight percent gain (WPG). Stakes acetylated to 15% WPG did not give complete protection against soft rot. Stakes modified with alkenyl succinic anhydride showed increasing resistance to soft rot with WPG up to about 10% WPG, above which no further improvements were evident. Succinic anhydride and phthalic anhydride treated stakes showed little or no noticeable protection.
S C Forster, M D C Hale, G R Williams


The distribution of introduced acetyl groups and a linseed oil model substance in wood examined by microautoradiography and ESEM
2000 - IRG/WP 00-40169
Microautoradiography, a photographic method that shows the localization of substances labelled with radioactive isotope, and Environmental Scanning Electron Microscopy (ESEM) were combined to enhance sensitivity, resolution and reliability for examination of the distribution of introduced substances in wood. The preparation of microautoradiographs is less complicated when investigated with ESEM and the preparation of ESEM-samples is quick and easy compared to a conventional SEM. When investigating microautoradiographs with ESEM, the wood structure is observed underneath the almost transparent photographic film. Silver grains, indicating the location of studied substances, are clearly distinguish from the wood material. The technique was used in two case studies for examination of cell wall penetration and distribution in pine sapwood. The distribution of acetyl groups, introduced by acetylation with acetic anhydride, and the distribution of a linseed oil model substance, triglycerol trioleate, were examined. Examinations of introduced acetyl groups showed an even distribution of acetyl groups in the wood cell wall at acetylation level of about 5, 15 and 20% (weight gain). Examination of the linseed oil model substance, glycerol trioleate, showed the presence of the model substance on applied surfaces, in rays and in lumen of some latewood cells. No cell wall penetration was observed.
M Rosenqvist


Improvements of stability and durability of beechwood (Fagus sylvatica) by means of treatment with acetic anhydride
1991 - IRG/WP 3645
In the present investigations, beechwood (Fagus sylvatica) was treated with non-catalysed acetic anhydrid at 120°C and some physical- and biological parameters of the treated wood were compared with those of non-treated wood. The radial and tangential shrinkage and swelling, respectively, and the absorption capacity of the acetylated wood against moisture is considerably lower. The durability against fungi improves. The results are discussed.
H Militz


Dimensional stability and decay resistance of wood upon modification with some new type chemical reactants
1994 - IRG/WP 94-40028
Solid wood of home grown species can be upgraded by chemical modification with environmentally acceptable chemicals. The best kwown example of modification reaction is acetylation with acetic anhydride. A continued search for reactive chemicals other than acetic anhydride is ongoing, aiming at the improvement of technical properties of wood. This contribution deals with the results of a screening experiment of different potential chemicals for modification reactions. The following reactive chemicals were selected for the treatment of small wood blocks: glutaric anhydride wether or not in combination with epichlorohydrin; cyclohexylisocyanate; glycidylmethacrylate; propyltrimethoxysilane and sodiumperiodate. The dimensional behaviour (ASE-values; water vapour sorption) and chemical stability (hydrolysis) of modified samples at different weight add-on levels were examined. Decay resistance was tested for all modified samples against Coniophora puteana (pine) and Coriolus versicolor (beech). Esterified wood at a WPG of 25% affords the highest level of improvement to both pine and beech, with ASE-values of 50 up to 70% and low weight losses on fungal exposure, particulary for treated pine.
P Goethals, M Stevens


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


Decay resistance of propionylated Iranian beech against the white rot fungus Tramets versicolor
2008 - IRG/WP 08-30449
In this study, the decay resistance of propionylated beech was investigated against the white rot fungus Trametes versicolor. Iranian beech (Fagus orientalis) was modified with propionic anhydride at different temperatures, concentrations and times without using any catalyst. Different weight percentage gains (WPGs) were obtained under different conditions. The decay resistance of the esterifed wood was studied according to ASTM D 1413 standard against the white rot fungus Tramets versicolor. WL due to decay by the fungus was reduced when WPG increased. A WPG of 17 % was found to be the protection threshold of the propionylated wood.
M R M Farahani, S M Hosseini


Wood preservation by a mixed anhydride treatment: Using simple models of polymeric wood compounds
2008 - IRG/WP 08-30457
Treatment of wood by a mixed aceto/oleic (or other fatty acid residue) anhydride promoted as a safe and environment friendly wood preservation system has been examined quantitatively by liquid phase 13C NMR and solid phase MAS-DEC (proton decoupling) 13C NMR through all its different stages to determine which reactions occur with simple model compounds of the polymeric constituents of wood. The preparation of the mixed aceto/oleic anhydride under different conditions has been followed too. The anhydride forms but its percentage yield was found to be of the order of only 30%. The mix composed of unreacted acetic anhydride, the mixed aceto/oleic anhydride, and great proportions of free acetic acid and free oleic acid which is used for wood preservation yields acetylation of the lignin model compound (i) by reaction of the acetic anhydride with it and (ii) by reaction of the acetic part of the mixed anhydride. In this reaction the whole mixed anhydride is consumed and nothing of it is left. The oleic part of the mixed anhydride apparently is not able to form esters on lignin being far less reactive than the acetic part. Carbohydrates appears much less readily esterified, being polar enough to be repellent to the oleic residue, some acetylation occurring and some traces, and no more than traces, of carbohydrates oleic acid ester occurring too under some conditions. This system of treatment through a mixed anhydride boils down to being just an acetylation with acetic anhydride, mixed with some oleic acid as water repellent, both already known processes.
F Lyon, M-F Thevenon, A Pizzi, G Tondi, A Despres, J Gril, S Rigolet


A survey of factors affecting decay resistance of wood modified with acetic anhydride
2012 - IRG/WP 12-40594
From the range of information published, acetylation appears well suited to provide adequate protection against biological attack for materials derived from typically non-durable wood species. Acetylated wood is now commercially available both in Europe and in the USA. But still there are a lot of unanswered questions related to fungal decay mechanisms in acetylated wood. The paper summarize existing knowledge and highlight future research opportunities related to fungal deterioration of acetic anhydride modified wood. In addition statistical analyses based on previously published data were performed to quantify what factors contribute most to the performance (calculated as test sample/control). The results showed that WPG can explain approximately 50 % of the performance, measured as test sample/control (T/C), for acetic anhydride treated wood. Other of the applied variables, like wood species or type of fungus can reduce the variance in T/C by additional 15 %.
G Alfredsen, P O Flæte, H Militz


Copolymers of tannin extracts as wood protection agents
2017 - IRG/WP 17-30709
Wouldn´t be a dream to preserve wood with the substances which the nature already synthesizes for protecting itself? The idea we would like to pursue is simple: Increase the concentration of these substances, the tannins, trying to fix them properly in wood. It appears easy but it is not. Sensibility against leaching, fungal decay and weathering were observed. In this paper new flavonoid co-polymers were studied for their leaching resistance and their biocidal activity once fixed in wood. These formulations added of low amount of biocides have demonstrated to be: i) hardening- (time & temperature) dependent in terms of water resistance and ii) requiring small amount of biocide (Boron and/or copper) for resisting the attack of white-rot Coriolus versicolor fungi. Interesting perspectives for natural preservatives are opened again.
G Tondi, L Sommerauer, A Oberle, A Petutschnigg, M-F Thevenon


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


Development of beech wood thermo-chemical modification treatments based on different vinylic derivatives of glycerol and polyglycerol
2019 - IRG/WP 19-40855
In this study, a combination between chemical and thermal wood modification has been investigated. Seven types of a low concentration of 10% aqueous additive solution of vinylicglycerol [glycerol-maleic anhydride (Gly-MA), glycidyl methacrylate (GM), and Glycerol methacrylate-maleic anhydride (GM/MA(2eq))], vinylicpolyglycerol [polyglycerol-maleic anhydride (PG-MA), polyglycerol methacrylate (PGM), and polyglycerol methacrylate-maleic anhydride (PGM/MA(3eq))], and maleic anhydride (MA) were impregnated into European beech wood (Fagus sylvatica), known for its low dimensional stability and poor natural durability. Varied with different curing temperatures at 103, 150, 200, and 220oC under inert condition, the modified wood and control were then characterized for their physical, mechanical, decay, and termite resistance properties. We found that, at the same initial weight percent gain (WPG) value (8 – 11%), mass changes (∆m) after thermal treatment, bulking (B), weight loss due to leaching (WLL), swelling (S), wettability, modulus of elasticity (MOE), and modulus of rupture (MOR) values of the additive-treated wood decreased as the curing temperature increased. In contrast, anti-swelling efficiency (ASE), decay resistance against Coriolus versicolor, and termite resistance against Reticulitermes flavipes values of additive-treated wood increased considerably for some treatments as the curing temperature increased, with better results at 200 and 220oC. In other words, the study has disclosed that the addition of some selected additives combined with thermal treatment can improve wood decay resistance and termite resistance better than untreated wood or wood with only thermally modified treatment.
M Mubarok, S Dumarcay, H Militz, K Candelier, M-F Thevenon, P Gerardin


Investigations into the use of Maleic Anhydride/Sodium Hypophosphite as a Wood Modification Process
2020 - IRG/WP 20-40891
The formation of crosslinked bonds between wood constituents is believed to be an effective way to stabilize wood against wet conditions. The possibility to use maleic anhydride (MA) combined with sodium hypophosphite (SHP) as crosslinking agents was studied, using Scots pine sapwood and a model compound. The modified wood showed weight gain and bulking effect after treatment and subsequent Soxhlet extractions, which indicated penetration into the wood cell wall and reaction of the chemicals with the wood constituents. The FTIR spectra confirmed the formation of an ester bond between the wood and MA. Furthermore, a decrease of intensity of band at 1635 cm-1 indicated a reduction of the double bond between carbons in MA after further treatment with SHP, especially at 170 ̊C. Such reactions were studied using monomethyl maleate (MMM) and SHP. The 13C NMR spectra of the reaction product confirmed a reduction of the double bond between carbons. This paper outlines studies undertaken to date, along with outlining aims of ongoing and future work.
I Kim, D Jones, O Karlsson, D Sandberg, O N Antzutkin, F Ullah Shah


Elucidation of reactive sites of wood modified with acetic anhydride: Insights from density functional theory calculations
2020 - IRG/WP 20-40892
Density functional theory (DFT) was employed to investigate the interaction of cellulose and lignin with acetic anhydride for explaining the wood modification process. Atoms in molecules (AIM) and reduced density gradient (RDG) along with non-covalent interaction (NCI) plots were used to analyse the intermolecular bonding characteristics. Cellulose was modelled with a cellobiose unit (dimer of glucose) and dibenzodioxocin was used to represent lignin model. This typical lignin model has three predominant linkages such as β-O-4, α-O-4 and 5-5’. All DFT calculations were performed at dispersion-corrected wB97X-D/6-311g(d,p) level of theory. The obtained results revealed that interaction energy of cellobiose-acetic anhydride was higher (about 20 kJ mol-1) than lignin-acetic anhydride. Structural analysis demonstrated that acetic anhydride undergoes a conformational change in lignin-acetic anhydride conformer to avoid steric repulsion from lignin aromatic moieties. Hydrogen bonds are studied to provide detailed information about strength of the interaction between cellobiose/lignin and acetic anhydride using AIM, RDG and NCI. The results showed that H-bond between cellobiose-acetic anhydride is stronger than lignin-acetic anhydride, and those H-bonds have a non-covalent character. It is observed from AIM analysis that electron density and its Laplacian for cellobiose-acetic anhydride is two-fold higher than lignin-acetic anhydride. A similar result was found in RDG analysis, and the calculated eigen value from electron density is more negative for cellulose-acetic anhydride case. This work suggested that acetic anhydride strongly bound to cellobiose during acetylation of wood rather than lignin model, and the detailed investigated data provides the interaction mechanism of acetic anhydride treatment of wood to some extent.
V Ponnuchamy, A Sandak, J Sandak, R Herrera Diaz


Mechanical and biological durability properties against soft-rot and subterranean termite in the field (grave-yard test) of beech wood impregnated with different derivatives of glycerol or polyglycerol and maleic anhydride followed by thermal modification in an opened or in a closed system
2021 - IRG/WP 21-40917
This paper presents mechanical and biological durability properties in soil beg test (soft-rot test) and field test (grave-yard test) against subterranean termite of the wood modified with an aqueous vinylic derivative of glycerol/polyglycerol or maleic anhydride cured in an opened or in a closed system. Wood modification was performed through impregnation of European beech (Fagus sylvatica) with aqueous solution of polyglycerol maleate, glycerol maleate, or maleic anhydride at 10 or 20% w/w concentration, followed with curing under oven heating (OHT) at 120°C, 150°C, or 220°C in opened system or under heat pressurised steam (HPS) at 150°C in closed system. The modified woods were then characterized for their weight percent gain and mass losses after curing process, mechanical properties [modulus of elasticity (MOE), modulus of rupture (MOR), work to maximum load in bending (WMLB)], and biological durability properties against soft-rotting micro fungi in soil beg test and against subterranean termite (grave-yard test) in a tropical country. Results have revealed that almost all modified wood presented higher MOE values than untreated wood, however, MOR and WMLB decreased up to 27% and 87%, respectively. Biological durability in the soil beg test against soft-rot indicated that almost all modified wood were specified as durable to very durable wood. However, among the treatments, the wood modified with polyglycerol maleate/glycerol maleate/maleic anhydride at 20% under OHT 150°C or the wood modified at lower additive concentration (10%) under OHT 220°C presented significantly better durability against subterranean termite within a period of 328 days in the field.
M Mubarok, H Militz, S Dumarcay, I W Darmawan, Y S Hadi, P Gerardin