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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

Effects of acetylation on the dimensional stability and decay resistance of kenaf (Hibiscus cannabinus L.) fiberboard
1996 - IRG/WP 96-40059
The objective of this study was to investigate the influence of the acetylation treated kenaf fiber, Phenol formaldehyde resin content level, and three fungi species on the dimensional stability and decay resistance of high density non wood composition boards. A standard ASTM method was used to evaluate weight loss and thickness change. The linear shrinkage and expansion of each species were also determined. All specimens were exposed to decay chambers for 16 weeks. Test results indicated that most of the main factors significantly influence the thickness, length changes, and decay resistance of the high density kenaf fiberboards.
P Chow, T Harp, R Meimban, J A Youngquist, R M Rowell

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

Novel wood modification processes for window and cladding products
2004 - IRG/WP 04-40285
Because of the low natural durability and low dimensional stability of European wood species, the usage of wood for window frames has decreased dramatically during the last decade. In a joint project of several German research institutes and the window industry, following wood modification systems were compared. heat treatment (3 different materials from 2 companies) acetylation (pine sapwood and beech wood acetylated with acetic anhydride) polymerisation (melamine resin treated pine sapwood, Interlace treatment, furfurylation) wax treatment (pine sapwood, which was impregnated with natural resin and waxes) Investigated was the moisture content, dimensional stability, capillary water uptake and the durability. The dimensional stability show a high increase for following materials: heat treated wood, acetylated pine, interlace treated wood and furfurylated wood. The melamine resin treated wood and the wax treated wood show no significant increase in the dimensional stability. The biological durability against different basidiomycetes was tested according to the EN 113. As test fungi, Coniophora puteana, Poria placenta and Coriolus versicolor were used. The results show a very high increase in the durability for most of the treated wood. The wax treated wood shows no significant increase in durability. A novel window frame consists of several functional layers. Different wood properties are demanded for the single layers to achieve optimal window properties. Every modified wood shows a special potential for the use in a functional layer.
A Krause, C Hof, H Militz

Durable fibre for durable MDF – testing Tricoya®
2015 - IRG/WP 15-40704
The chemical modification of wood has been a commercial reality for a decade on release of technologies for the modification of solid wood including Accoya®. A challenge and an opportunity for the modification technologies which typically impart dimensional stability, water stability and enhanced biological durability was the adaptation of the technology to wood based panels. This paper presents a summary of the development of Tricoya®, its testing and performance and examples of applications.
E Suttie, J Alexander, M Maes

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

Acetylation of lignocellulosic materials
1989 - IRG/WP 3516
A simplified procedure for the acetylation of lignocellulosic materials has been developed. The acetylation is done with a limited amount of liquid acetic anhydride without the addition of a catalyst or an organic co-solvent. Dimensional stability and biological resistance are both much improved by the acetylation. Equilibrium moisture content in acetylated material is considerably lower than in unmodified material. No reduction of bending strength was found for acetylated solid wood samples. The process can be employed for both fibers, wood particles and solid wood. The process is applicable to hardwoods and softwoods, including solid spruce wood, and to non-wood fibers such as jute.
P Larsson, A-M Tillman

Worldwide in-ground stake test of acetylated composite boards
1997 - IRG/WP 97-40088
Acetylated wood composite stakes are being tested in ground contact (graveyard test) in seven fields around the world. Three types of acetylated wood composites were prepared: spruce fiberboard in Sweden, aspen fiberboard in Madison and rubber wood particle board in Indonesia. Two levels of acetylation were used, a high level of ~20% acetyl content and a low level of 10% acetyl content. Control boards of unmodified wood fiber/particle were also included. Stakes for the in-ground testing were taken from the boards and the size of each stake was 5x30x1.25 cm3. The stakes were put out in four continents: one test field in USA, one in New Zealand, two in Indonesia and three in Sweden. After three years of testing, results show that acetylation of wood provides excellent protection against fungal attack and minimizes swelling.
R M Rowell, B S Dawson, Y S Hadi, D D Nicholas, T Nilsson, D V Plackett, R Simonson, M Westin

Improving the weather resistance of glue-laminated jarrah and karri
1994 - IRG/WP 94-40017
Surface modification and dimensional stabilisation significantly increased the dry and wet shear strength of karri and jarrah lap-shear specimens (laminates) bonded with resorcinol formaldehyde. The combination of surface modification (sanding/sodium hydroxide treatment), and furfurylation produced the highest dry and wet shear strengths. Acetylated laminates had the lowest dry bond strength, but the lowest loss of strength on wetting. In most cases karri laminates showed higher dry, but lower wet shear strength than jarrah. Untreated laminates rapidly delaminated during artificial accelerated weathering, but surface modification and dimensional stabilisation significantly increased the resistance of specimens to delamination. Only a small proportion (5-10%) of acetylated specimens delaminated during accelerated weathering and surface modified acetylated laminates showed no delamination during the weathering test. Laminates treated with a combination of surface modification and furfurylation showed less delamination than specimens treated by surface modification alone. Treatments that increase both glue bond strength and dimensional stability appear to offer an effective means of improving the weathering resistance of glue-laminated karri and jarrah.
J Balfas, P D Evans

Acetylated solid wood. Laboratory durability test (part 2) and field trials
1995 - IRG/WP 95-40048
Degradation of acetylated beech, pine and poplar by soft rot fungi was related to strength loss in a laboratory test. No strength loss was noticed for poplar acetylated to a weight percent gain (WPG) of more than 11.2% and beech with a WPG of 12.8%. Several field trials were set up to determine the durability of acetylated products in practice. They included a field test to determine the durability of acetylated wood, a field test for acetylated claddings with various paints, a field test for acetylated garden wood, an outdoor exposure of acetylated wood to salt water and of acetylated wood to soil and fresh water contact. In these trials the way of design and shape of end products was considered too. This is of industrial use to minimise waste of (expensive) acetylated wood. Results are discussed.
E P J Beckers, H Militz, M Stevens

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

Soft rot decay in acetylated wood. Chemical and anatomical changes in decayed wood
2002 - IRG/WP 02-40231
Acetylated Beech (Fagus sylvatica) and Scots Pine (Pinus sylvestris) wood were studied in soil beds under laboratory conditions for longer periods. High mass losses and dynamic MOE losses were measured in non-acetylated wood and at lower weight percent gains (WPG). Rapid losses of lignin, holocellulose and ?-cellulose occurred in non-acetylated beech wood and no losses were detected at the highest WPG. Changes in chemical composition of acetylated beech wood at lower WPGs was measured. Slight changes in chemical composition of non-acetylated Scots pine wood were also observed and minor changes in acetylated wood at all WPGs; except in holocellulose. An intensive anatomical study was performed by light microscopy and SEM microscopy. The results are presented and discussed. Results showed a significant prevention of acetylation against fungal growth above 8 % and 10 % WPGs in beech and pine respectively.
B Mohebby, H Militz

Termite and fungal resistance of in situ polymerized tributyltin acrylate and acetylated Indonesian and USA wood
2000 - IRG/WP 00-30219
Wood [Indonesian pine (IP), Indonesian Jabon (IJ) and USA southern yellow pine (USP)] was either in situ polymerized with tributyltin acrylate (TBTA) or acetylated and then exposed to termite and fungal degradation both in laboratory tests and field exposure. The TBTA woods had an average weight percent gain (WPG) of 11% for IP, 12% for IJ, and 10% for USP. The acetylated woods had a WPG of 15-27% for IP, 16% for IJ, and 12-21% for USP. All levels of TBTA and acetylation treatments were effective against the brown-rot fungus Tyromyces palustris and the white-rot fungus Coriolus versicolor in laboratory testing. Resistance to subterranean termites [Coptotermes gestroi (Wasmann)] and dry wood termites [Cryptotermes cynocephalus (Light)] was shown in laboratory tests with all treatments. After one year of field testing in Indonesia (AWPA Standard E7-93), TBTA treated specimens gave a grade number of 8 for all 3 woods compared to 0 for the untreated controls (based on a 10 - point scale.) The acetylated specimens gave a grade number of 4 for IP, 8 for IJ, and 6 for USP. Scanning electron microscopy (SEM) showed polymer located in the lumen of the earlywood and latewood of selected TBTA treated specimens, but at low overall polymer weight gain the lumens were not evenly filled. Termite field testing continues on all treated wood specimens.
R E Ibach, Y S Hadi, D Nandika, S Yusuf, Y Indrayani

Resistance of acetylated wood to basidiomycetes, soft rot and blue stain
1994 - IRG/WP 94-40021
Poplar (Populus spp.), beech (Fagus sylvatica) and pine sapwood (Pinus sylvestris) samples were acetylated in a semi-industrial acetylation plant and tested for durability according to European standards. Resistance to Gloeophyllum trabeum, Coniophora puteana and Coriolus versicolor could be reached at a weight percent gain (WPG) of 12%. Susceptibility of acetylated pine to Poria placenta was higher and a WPG of 20% could deminish attack but not prevent degradation by this funguns. Soft rot resistance of wood could already be reached when acetylated to 10% weight gain. An outdoor exposure with acetylated poplar, pine and spruce showed no resistance to blue stain. A residual amount of acetic acid, formed during the reaction, could retard the discolouring by stain but not prevent it.
E P J Beckers, H Militz, M Stevens

Resistance of acetylated wood to biological degradation. Evaluation of field test
1997 - IRG/WP 97-30139
Acetylated wood samples were tested in ground contact (stake test) at two test fields, one in Simlångsdalen, Sweden, and one in Viikki, Finland, according to European standard EN 252. The test samples were inspected annually and their condition was compared with that of untreated controls and of samples treated with two reference CCA preservatives. The use of untreated controls and preservative treated wood also gave an indication of the aggressiveness of decay at individual test fields. Results showed that acetylation has a major impact on fungal resistance of wood. The resistance of acetylated wood with an acetyl content of about 20% is in the same range as that of wood of the higher retentions of the reference preservatives. At acetylation levels above 20%, none of the samples was rated higher than rating 1 (slight decay), either in Simlångsdalen or in Viikki after 5 years of ground contact.
P Larsson Brelid, R Simonson, Ö Bergman

Chitosan for wood protection - state of the art
2005 - IRG/WP 05-30378
The aim of this paper was to give a state of the art description of chitosan as a wood protecting agent. Chitosan is a metal free natural compound derived from crustacean shells and is under evaluation as an environmentally benign wood protecting agent. Information from journals states that chitosan may act both fungistatically and at higher concentrations, as fungitoxic, but the mode of action is not yet fully understood. The hypothesis with most support in the literature is that chitosan interacts with the cell membrane and causes alterations in permeability. It is not proven that chitosan is more effective against a particular class of fungi, but morphological changes and reduction in growth rate is reported from a range of fungi. Results from agar plate growth rate tests are not conclusive with respect to whether high or low molecular weights are most effective against micro-organisms. Other factors than the molecular weights may influence microbial activity of the species studied, i.e. FA, pH, and internal distribution of the monomers, concentration and additives. In results available in the literature it is obvious that there is a dose-response relationship between chitosan and antimicrobial activity. In agar plates a lethal/totally inhibiting concentration is usually between 0.1 and 1 %. Chitosans in solution are more effective against antimicrobial growth than chitosans in suspension (i.e. solid chitosan particles). This is further reflected in that higher concentrations of chitosan are needed in wood than in agar amended plates. If the treated wood is subjected to leaching, around 5 % (w/v) chitosan solutions seems to be needed for good efficacy against fungal decay. Some tests where chitosan fails in decay tests are probably because of the use of to low concentrations, or to low penetration of chitosan solution due to high molecular weight.
M Eikenes, G Alfredsen, E Larnøy, H Militz, B Kreber, C Chittenden

The susceptibility of acetylated Pinus radiata to mould and stain fungi
1992 - IRG/WP 92-1548
The aim of this investigation was to determine the effect of 5, 10, 15 and 20 percent acetylation weight gains on the susceptibility of Pinus radiata sapwood to mould and stain fungi, and to establish if an acrylic paint, an oil-based stain and a water repellant gave superior protection from fungal growth on wood treated to 20% acetylation weight gain, compared to untreated wood. One treatment set was tested using a modified anti-sapstain screening trial method, designed to give optimal conditions of relative humidity (>95%) and temperature (25°C) for mould growth. A second treatment set was exposed to the weather and assessed at 10, 21 and 40 weeks. The results showed that over the three week laboratory trial period, the rate of colonisation by mould fungi of Pinus radiata sapwood treated to 20% acetylation weight gain was significantly (P < 0.001) slower than on untreated wood. This was attributed to the lower availability of readily assimilated nutrients such as sugars and starch in acetylated wood. The rate of colonisation by mould fungi of acrylic-finished sapwood treated to 20% acetylation weight gain was significantly slower than on acrylic-finished untreated wood. Acetylation up to 20% weight gain conferred no protection from mould growth for test samples exposed to the weather. None of the finishes perfomed better on acetylated wood than non-acetylated wood when exposed to the weather.
R N Wakeling, D V Plackett, D R Cronshaw

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

Biological degradation resistance of wood acetylated with thioacetic acid
1983 - IRG/WP 3223
Chemically, modification of wood is being considered as an alternative to conventional preservation by toxic chemicals. Acetylated wood has been reported to be quite resistant to most biodegrading organisms at weight percent gains (WPG) around 15-19. The conventional acetylation techniques with acethic anhyrdride result in generation of acetic acid. However, acetylation with thioacetic acid overcomes this problem. Since different reagents may be reacting with hydroxyls located on different wood components, preliminary investigations on the resistance of wood acetylated with thioacetic acid were carried out. Tests against a brown rot fungus (Poria monticola) were carried out using soil block method with chir, a softwood. The wood exhibited good resistance to this fungus at WPG around 18. Resistance tests against a substerranean termite species Microcerotermes beesoni using forced feading method showed fairly good resistance at WPG around 13. Tests against softrot attack in a running cooling tower, however, did not show any resiastance upto a WPG of 14.
S Kumar, S C Agarwal

Durability of some alternatives to preservative treated wood
2004 - IRG/WP 04-30353
The environmental discussion in Sweden has lead to an increasing use of naturally durable domestic wood species and wood treated according to alternative methods for use above ground. A number of these alternatives have been tested according to field- and laboratory tests and compared to wood treated with preservatives for above ground use. Seven untreated wood species, four alternative wood treatments labelled as environmentally friendly and four wood preservatives are included in the study and as references CCA-treated and untreated pine sapwood were used. The best results against wood decaying organisms were obtained with acetylated wood and heat treated wood. Among the tested naturally durable wood species pine heartwood from Gotland (a pine very rich in wood extractives) and oak were the best, but none of these were as good as acetylated wood or preservative treated wood. After 14 months testing against mould and blue stain, preservative treated wood was less attacked than any other tested material. Among the untreated wood species oak and pine heartwood from Gotland were the best and among the alternative treatments heat treated spruce was the best.
M-L Edlund

Effect of fungal degradation on the chemical composition of acetylated beech wood
2003 - IRG/WP 03-40267
This study investigated the impact of fungal attack on the chemical composition of acetylated wood. Beech wood acetylated to different degrees was exposed to decay by the white-rot fungus Trametes versicolor under solid-state fermentation conditions. Laboratory soil-bed assays were also conducted to study the degradation of acetylated wood by soft rot fungi and other soil-inhabiting microorganisms. Changes in the chemical composition of untreated wood and acetylated wood following exposure to fungal attack were examined by wet chemical analysis, as well as FT-IR and CP/MAS 13C-NMR spectral methods.
H Militz, Dong-won Son, L Gómez-Hernández, R Sierra-Alvarez

Wood plastic composites from modified wood; Part 1 - Conceptual idea, mechanical and physical properties
2006 - IRG/WP 06-40338
Wood plastic composites, WPCs, are rapidly taking shares from preservative treated wood on the decking market. However, the long term performance of the WPC products in this application is uncertain. Therefore, in an attempt to increase the long term performance and durability, the substitution of the unmodified wood component with modified wood has been studied in the work presented in this paper. WPCs, with 70% wood content, from modified wood were successfully produced in semi-industrial scale. The wood component originated from acetylated and heat treated wood. WPCs from unmodified wood were also produced and used as references. Both acetylated wood and heat treated wood exhibits high durability and dimensional stability. Using modified wood in the WPC would not only increase the long time durability, but also enable a higher wood content, in high quality WPC products for exterior applications. The moisture sorption was significantly reduced for WPC with acetylated wood compared with WPC with unmodified wood. Also, for the WPC samples from heat treated wood, a reduced moisture sorption was observed. Microscope analysis clearly demonstrated the formation of cracks in the interface between unmodified wood and polymer matrix after water soaking and drying. No cracks were formed in the acetylated WPC samples. Improvements were also observed for the WPC samples from heat treated wood.
P Larsson Brelid, B K Segerholm, M Westin, M E P Wålinder

Further discussion of biological durability assessments of acetylated wood from several European institutes
2006 - IRG/WP 06-40340
In the last decade, interest in the development of wood modification systems has increased in Europe. Alongside several industrial initiatives for heat treatments, there have also been scaling up and pilot plant projects for chemical wood modification. Between 2000-03, the European Commission funded the "Thematic Network on Wood Modification". This paper features a re-evaluation of work undertaken within that project, assessing the performance of acetylated radiate pine. This re-evaluation comes at a time when acetylated radiate pine is due to be commercially launched. This corresponded with one of the key decisions of the Network, in that modified wood should be regarded as a new wood species, and tested accordingly, with particular emphasis on biological durability and dimensional stability.
D Jones, W Homan, F Bongers

Influence of Acetylation on Fire Resistance of Beech Plywood
2006 - IRG/WP 06-40326
Influence of acetylation on fire resistance was studied in beech plywood. Beech layers were acetylated in a reactor with acetic anhydride at 120ºC for varying durations. Plywoods were made from the acetylated layers and directly exposed to burning flame from their edges for 60s according to ISO 11925-3. Ignition and glowing time were measured in samples. Results were analyzed statistically based on a complete randomized design to determine effect of the acetylation on fire resistance. Results indicated that the acetylation affects ignition and glowing in plywood. Ignition time was increased due to raised weight percent gains and glowing was decreased instead. The acetylated plywood was burning with short blue flames; while flame was long and yellowish in non-acetylated one. This study revealed that the acetylation retards slightly fire in plywood; however it does not resist wood against fire.
B Mohebby, A Talaii, A Karimi , S Kazemi Najafi

Wood plastic composites from modified wood. Part 2 - Durability in laboratory decay tests
2006 - IRG/WP 06-40353
The decay resistance of wood plastic composites, WPCs, was tested according to modified versions of AWPA E10 (soil-block test) and ENV 807 (tests in three un-sterile soils, terrestrial microcosms, TMCs). The WPC materials were conically extruded profiles with 30% polypropylene content. The 70% wood content was untreated Scots pine sapwood, acetylated pine and heat treated Norway spruce, respectively. In the first set of soil-block test control WPC with 70% untreated pine performed poorer than the pine sapwood controls. The fungal preference for the WPC material could be seen in the soil-jars where the WPC blocks were covered with more mycelium than the solid pine blocks. However, the WPCs with 70% acetylated wood were highly resistant to decay. In the TMC tests, the WPC materials with unmodified wood performed better than in the soil-block test but poorer than the two types of WPCs from heat treated spruce and acetylated pine particles. Again, the WPC with 70% acetylated pine particles was practically unattacked.
M Westin, P Larsson Brelid, M L Edlund, G Alfredsen

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