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Bioresistance of Poplar Wood Compressed by Combined-Hydro-Thermo-Mechanical Wood Modification (CHTM) Process
2010 - IRG/WP 10-40532
Bioresistance of treated Poplar wood by CHTM process (Combined-Hydro-Thermo-Mechanical Wood Modification) was studied in the current research work. Resistance against brown rot fungus Gloeophyllum trabeum as well as the soft rot decay was the main concern of this work. Poplar wood blocks were hydrothermally treated at temperatures of 120,150 and 180°C for holding time of 0, 30 and 90 min. afterwards, the blocks were compressed at temperatures of 160 and 180°C for 20 min. The treated blocks were oven dried for 24 hours at 103±2°C. Small specimens were cut from the blocks and exposed to the brown rot fungus according to EN 113. Also, mini-stakes were prepared and exposed to soil according to ENV 807. Results revealed that the bioresistance of the CHTM treated poplar wood increased due to the hydrothermal modification. Increase of the holding time as well as the press temperature reduced the fungal activity in the CHTM treated wood. According to the results of previous and the current works, the treated wood at temperature of 150°C for a holding time of 30min and compressed at press temperature of 180°C was selected as the best treatment.
L Khademi-Bami, B Mohebby


Combined effects of thermal modification and ACQ-D impregnation on properties of southern yellow pine wood
2013 - IRG/WP 13-40637
In this study, samples of southern yellow pine sapwood were first thermally modified and then treated by the alkaline copper quat-type D (ACQ-D) wood preservative. Two heating temperature (180℃ and 220℃) and two concentrations of ACQ-D solution (0.9% and 1.35%) were used in the experiments. The combined effects of thermal modification and ACQ-D on leaching performance, mechanical properties and mold resistance of the treated wood were then investigated. The results of the experiments indicated that thermal modification increased the percentage of copper leaching and decreased the MOR and MOE of wood, and also it affected the compression strength parallel to grain. After the ACQ-D impregnation, the bending properties of thermally modified wood got lowered to some extent. The anti-mold experiment indicated that the ACQ-D impregnation could improve the mold resistance of thermally modified wood.
Wang Wang, Yuan Zhu, Jinzhen Cao


Modifying wood with paraffin wax emulsion impregnation and thermal modification: hydrophobization effect and mechanism of the combined treatment
2016 - IRG/WP 16-40726
The aim of this study was to enhance the water repellency of wood by a combined treatment of paraffin wax emulsion (PWE) impregnation and thermal modification. Two different treating procedures were used to modify the southern pine (pinus spp.). One is first PWE impregnation and then thermal modification, another is first thermal modification and then PWE impregnation. The treated samples were immersed in distilled water, and the water absorption property was tested by gravimetric method and time-domain nuclear magnetic resonance (TD-NMR). The results indicated that the combined treatment showed much better performance than the single treatment, especially the process of first PWE impregnation and then thermal modification. Moreover, the synergism between two procedures were also observed by TD-NMR and scanning electron microscope (SEM). It could be concluded that the PWE impregnation and thermal modification increase the hydrophobicity of wood through decreasing free water absorption and bound water absorption respectively. And the synergistic effect of the combined treatment was mainly due to the redistribution of the paraffin wax during the thermal modification.
Wang Wang, Jinzhen Cao, Cong Chen


Effect of insitu polymerization on practical properties of heat treated wood
2016 - IRG/WP 16-40763
This research was conducted to investigate the effect of combined modification; heat treatment and impregnation with styrene monomer on physical and mechanical properties of poplar wood (Populus deltoides). Test samples were grouped in six levels of control, wood polymer made from styrene, heat treatment at 170 ºC and 200ºC and combined modification; first hat treated at 170 ºC and 200ºC and then impregnated with styrene. The highest weight percent gain and polymer absorption were obtained at combined modified samples that heat treated at 200 ºC. According to results heat treated wood in higher temperature with lower polarity showed more polymer conversion rate and retention. Heat treatment with water absorption reduction was led to dimensional stability improvement. The presence of the polymer by blocking the pores of the wood, resulted in the more dimensional stability. Combined modification improved mechanical properties, especially the compression strength that was more obvious at the temperature 200ºC.
M Ghorbani, M Mohseni Shaktaei


Multiscale modification on water resistance and dimensional stability of Populus cathayana by alkali lignin combined with heat treatment
2018 - IRG/WP 18-40826
The aim of this study was to enhance the water resistance and dimensional stability of fast growing wood by alkali lignin combined with heat treatment. Poplar (Populus cathayana) samples were first impregnated with alkali lignin solution and then subjected to heat treatment at 140, 160, and 180°C respectively for 2h. Properties of leachability, moisture adsorption and water absorption, contact angle, tangential and volumetric swelling for the control and modified samples were investigated. Moreover, the morphological and chemical alterations were analyzed by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and Fourier transform infrared (FTIR) spectroscopy. The results indicated that all of the alkali lignin treated wood showed a great leaching resistance. What’s more, alkali lignin treatment was capable of improving surface hydrophobicity and decreasing moisture and water uptake and thus the dimensional instability of modified wood. These changes were more obvious as the heat-treating temperature increased. The results of SEM, CLSM and FTIR suggested that the alkali lignin existed in cell lumen as well as cell wall of wood fibers and vessels, and small alkali lignin molecules may react with wood matrix. Results from this study could not only enrich the approach as well as reduce the cost of wood modification, but also achieve the aim of higher value application for industrial lignin.
H Zhou, J Li, E Ma


The use of bicine and tricine as possible Maillard reagents in a combined thermal/chemical modification of beech
2019 - IRG/WP 19-40852
The effects of thermal modification have been well established, particularly in terms of reductions in mechanical performance. In recent years, there has been an increase in studies related to the Maillard reaction. More commonly associated with food chemistry, it involves the reaction of amines and reducing sugars during cooking procedures. This paper has attempted to combine the use of amines and thermal modification, with subsequent properties investigated for the treatment of beech (Fagus sylvatica). In this initial study, the combined effects of chemical treatments by tricine and bicine were investigated with thermal modification. Along with some preliminary data on mechanical properties, the modifications which appeared in the wood structure were evaluated by infrared spectroscopy. After the treatment about 6-7 % of WPG was identified in treated samples, but further thermal treatment decreased the WPG to about 5%. The modifications appearing in the spectra were mostly related to increase of the intensities of the bands assigned to C=O groups but also to N-H and C-N groups, with shifting of some bands to higher wavenumber values
D Jones, C-M Popescu, D Krzisnik, M Hocevar, M Humar, M-C Popescu


Improvement of wood decay and termite durability resulting from combined treatments based on borax/phenol-formaldehyde impregnation followed by thermal modification
2019 - IRG/WP 19-40871
This study determined the factors influencing the boron content after leaching of pine blocks impregnated with aqueous solution of phenol-formaldehyde (PF) resin with or without borax and subjected to heat treatment by response surface methodology. An experimental design permits to analyze the effects of heat treatment temperature (150, 185 and 220°C), curing time (5, 12, 5 and 20 hours), resin concentration (5, 12.5, and 20%) and boron concentration BAE (0, 2, and 4 %) on the mass gain, boron content as well as degradability. After leaching, the treated samples with 20% PF, and 220°C had high boron content, and the heating time had no significant influence on the boron content. Decay and termite resistance were also studied for treatments involving impregnation of samples with 10% of PF alone or in the presence of borax, followed by curing at 220°C for 5 h. The results of this study indicated that the decay and termite resistance of all samples pretreated and leached is sufficient to envisage use in outdoor exposure.
S Salman, M-F Thevenon, A Petrissans, S Dumarcay, P Gerardin


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


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


Decay patterns observed in butylene oxide modified ponderosa pine attacked by Fomitopsis pinicola
1983 - IRG/WP 1183
Small blocks of ponderosa pine chemically modified by butylene oxide to three different weight percent gains (WPG) were decayed for 2 months with the brown rot fungus Fomitopsis pinicola. Wood substance loss and the type of decay pattern recognised were fairly similar both for control and blocks treated to 8 and 15 WPG. No difference in attack was observed between radial or tangential walls in latewood tracheids. Microscopical examination of undecayed wood blocks treated to 23.7 WPG revealed numerous cracks in both the middle lamella regions of radial walls and in cell corners of latewood tracheids. The fungus had gained entry to the cracks, possibly via bordered pits and rays. Attack started from the cracks and progressed along the middle lamella and towards the cell lumen.
T Nilsson, R M Rowell


Improved resistance of Scots pine and Spruce by application of an oil-heat treatment
2000 - IRG/WP 00-40162
Spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.) were subject to a heat treatment which was carried out in an oil-bath. The aim was to improve the dimensional stability of the treated wood and its resistance against fungi. The bath of vegetable oil provides a uniform heat transfer at temperatures of 180°C, 200°C and 220°C and protects the submersed wood from oxygen. Heat treatment in air atmosphere was also carried out at the same temperatures for comparison. Wood treated in hot oil was more equal in its appearance than wood heated in hot air. The treatment of spruce and pine in the oil-bath resulted in a better resistance against Coniophora puteana in a lab test according to EN 113 compared to the treatment in air atmosphere. In order to achieve the wanted upgrading effect, certain changes of mechanical properties and colour must be accepted. However, the strength loss caused by the heat-treatment in oil was less severe than in air atmosphere. Since all materials and the energy used in the process originate from renewable resources, the oil-heat-treatment appears to be environmentally friendly. All in all, the heat treatment in oil might be a promising approach to upgrade wood for outdoor use.
M Sailer, A O Rapp, H Leithoff


About the water and biological resistance of some new chemically modified wood composites
1997 - IRG/WP 97-40077
As well known, wood represents a valuable natural composite material with a very large utilisation as solid wood or in wood based composite materials. Its qualities but also its defects as the dimensional instability, the susceptibility to biological attack, the anisotropy, are due to its complex structure. Research has demonstrated that the chemical modification of wood, meaning the involving of its main chemical components through their reactive alcoholic hydroxyl groups in chemical reactions with different chemical reagents, can be a new way to ameliorate the wood or wood composites but also to obtain new wood based materials. The chemical thermoplasticization of wood, studied theoretically and experimentally by the Japanese researchers as Matsuda, Mori, Morita, Nakano, Shiraishi, Ueda seems to be a very interesting possibility. The paper presents the results of our experiments concerning the chemical thermoplasticization of wood through oligoesterification and the obtaining and characterisation of some products based on this type of chemically modified wood. In fact the main goals of this stage of the researches were: - the obtaining and characterisation of the thermoplastic wood; - the study of the thermoformation possibilities for the thermally flowable material obtained as sawdust; - the evaluation of the possibilities to carry out this chemical modification process as a surface treatment for solid wood; - the evaluation of the water and biological resistance for the obtained products.
M C Timar, M D Mihai, G Baciu


Durability of different heat treated materials from industrial processes in ground contact
2005 - IRG/WP 05-40312
In this study the durability of heat treated wood originating from four different European industrial heat treatment processes in ground contact was examined. The manufacturers of heat treated material were: PLATO Hout B.V./Netherlands, Thermo Wood/Finland, New Option Wood/France and Menz Holz/Germany where Oil-Heat treated Wood (OHT) is produced. All heat treated materials showed significantly increased durability against decay in ground contact compared to untreated Scots pine (Pinus sylvestris L.), independent from the different heat treatment processes. After four years of field testing, heat treated material appears to be not suitable for in ground contact application, since long service life is required. In analogy to the classification of natural durability (EN 350-1, 1994), durability classes in the range from 2 (durable) to 4 (slightly durable) were achieved by the different heat treated materials. This stands in contrast to statements of suppliers, who promote their material as suitable for in ground applications.
C R Welzbacher, A O Rapp


Combined effects of the treatment of wood with formaldehyde
1978 - IRG/WP 3117
Treatment of fibrous materials with reagents in a vapor phase is neither new nor unique. Numerous examples exist in literature of vapor phase experiments on cellulose fibers and fabrics, and on wood. For many years the textile research and industry have used vapor phase processes for the treatment of textiles. The chemical modification of cellulose is based on different types of reactions e.g. esterification, alkylation, resin formation or polymerization, monomer grafting and crosslinking. Vapor phase treatment of wood offers certain potential advantages over the conventional liquid phase wood impregnation. The higher mobility of low molecular weight compounds in the gaseous state ensures a rapid, uniform and homogeneous distribution throughout the wood structure. The vapor phase treatment of wood is also a better approach from the standpoint of cell wall penetration. Bulking, which takes place in the cell wall only, means that less chemicals are required and that the final weight of the composite is limited. Furthermore, due to the low viscosity of a gas, the application of a lower pressure differential remains possible. Within the framework of a wood improvement programme carried out at the Laboratory of Wood Biology and Wood Technology (University of Ghent, Belgium) the treatments were based on the impregnation of wood with liquid synthetic monomers and with gaseous formaldehyde. The results of the hygroscopic and dimensional behaviour of the wood-plastic-combinations have been published previously. Other papers deal with the physical and chemical interactions between the synthetic products and the natural polymers of the cell wall. This contribution will be restricted to the treatment of wood with formaldehyde in the gaseous state.
M Stevens, J Schalck


Biological degradation resistance of pine wood treated with dimethylol compounds
1989 - IRG/WP 3528
The study reports the increase of dimensional stability and biological degradation resistance of pine wood (Pinus sylvestris L) after impregnation with dimethyloldibydroxyethyleneurea. Decay resistance was determined according to BS 838:961. Nearly complete protection against Coniophora puteana, (Schum.ex Fr. Karst) weight loss of 2-3% was shown when modification, expressed as weight gain, exceeded 15%. Resistance to biological attack of modified wood is speculated to be due to modification of the wood components and cross linking with dimethyloldihydroxyethyleneurea.
C L Videlov


Decay resistance of high performance biocomposites based on chemically modified fibres
1998 - IRG/WP 98-40120
Different partners within the framework of a European research project produced high performance biocomposites aiming at the utilisation of board materials as durable products both in dimensional and biological degrading circumstances. This paper summarises test data, which indicate the potential of board materials produced with modified fibre material. The chemical modifications applied cover a range of technologies, which were selected for scaling up experiments. Acetylation, as well as alternative methods like maleiation, phthalylation, succinylation, oxidation and silylation were investigated. Fibre source, density variation and the use of several types of glues were parameters of the total set-up. Basidiomycete testing was carried out using specific methodology for board materials elaborated in CEN standardisation committees.
V Rijckaert, J Van Acker, M Stevens


Potential toxicants for controlling soft rot in preservative treated hardwoods. Part 4: Evaluation of combined diffusion and toxicity
1979 - IRG/WP 2129
A large number of inorganic and organic preservatives were evaluated as potential soft rot control chemicals, by their degree of inhibition of fungal growth after allowing them to diffuse through a 6 mm thick wood slab. The tests were inoculated with wood powder from soft-rotted CCA treated poles. Pentachlorophenol was unable to diffuse quickly through the wood slab, although formulations with hexylene glycol showed some promise. Hydroxyisoxazole gave good results as did a number of other organic materials including "Busan 30", "Busan 52", "Permapruf T", sodium oxinate, sodium trichlorophenate, "Gloquat C", „Hyamine 1622", butyl icinol, and the commercial bandage materials "Osmoplast" and "Wolman pole bandage". Of the inorganic materials tested, good results were obtained with "Basilit BFB", with other Cu-F-B formulations including "Blue 7", and with fluoroborate and fluorosilicate preparations in general. Arsenates also showed some promise.
E W B Da Costa, O Collett


Decay patterns observed in butylene oxide modified ponderosa pine after exposure in unsterile soil
1982 - IRG/WP 3211
Small blocks of ponderosa pine (Pinus ponderosa Laws) chemically modified with butylene oxide to three different weight gains were exposed for 6 weeks in unsterile soil. Severe surface decay caused by soft rot fungi and tunnelling bacteria was observed in blocks with 8 weight percent gain. The soft rot attack was restricted to the outer parts of the radial walls in the latewood tracheids. Bacterial attack occurred both in the radial and tangential walls. Very few soft rot cavities were found in blocks with 15 weight percent gain. Some attack by tunnelling bacteria was observed in the outermost parts of the radial walls in the latewood tracheids. Wood blocks with 23.7 weight percent gain showed no signs of attack. A solution of crystal violet was used for examining pathways in ponderosa pine wood. The results indicate that the uneven distribution of cavities is due to improper penetration of the modifying agents into the outer parts of the radial walls in the latewood tracheids.
T Nilsson, R M Rowell


Sustainability Through New Technologies for Enhanced Wood Durability. COST Action E37 – A New Action in the Forestry Domain
2004 - IRG/WP 04-40293
The main overall objective of the action is to concentrate on the contribution of wood durability on the sustainability through the development of systems for quality assurance and perfoamance of modified wood and wood products as alternatives to wood treated with traditional preservatives. By this means it seeks to improve and consequently increase the cost-effective use of sustainably produced European timber, wood-based fibre, and recycled raw materials. The action will seek to optimize methods for testing and characterizing durability performance against physical as well as biological factors. This will exploit relevant selected results from specific aspects of the preceding COST Action E22 on “Environmental optimization of wood protection” and in the EU thematic network for wood modification. It will also exploit specific achievements from COST Action E18 “High performance in wood coating”.
R-D Peek


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


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


Effects of a formaldehyde and sulphur dioxide treatment on decay and mechanical properties of aspen waferboard
1983 - IRG/WP 3242
Aspen wafers were sequentially treated under vacuum with formaldehyde and sulfur dioxide gas and pressed into waferboard bonded with powdered phenol formaldehyde resin. Decay resistance and strength properties were determined before and after simulated weathering. The water resistance of the phenol bonding system was lost in board made from the gas-treated wafers. This white rot fungus Coriolus versicolor was unable to decay treated waferboard in a soil block test, but the brown rot fungi Gloeophyllum trabeum and Poria placenta decayed the samples as severely as untreated controls.
E L Schmidt


Photo-discoloration and Degradation of Wood and its Stabilisation by Modification with Benzoyl Chloride
2004 - IRG/WP 04-40274
Photo degradation of Pinus roxburghii (chir pine) and Hevea brasiliensis (rubber wood) was studied under artificial accelerated weathering conditions in a Xenon test chamber. The irradiated samples were analyzed for color changes and chemical changes. Analysis of colour changes in wood surfaces by UV-Vis. irradiation was carried out using a colour measuring (CIELAB) system and chemical changes were monitored using FTIR and fluorescence spectroscopy. Irradiation modified physical and chemical characteristics of wood surfaces and resulted in rapid colour changes, reduction in lignin content and increased concentration of chromophoric groups on the wood surfaces. Colour changes were correlated with formation of carbonyl groups and lignin decay rate determined by FTIR measurements. Fluorescence emission spectra measured from un-weathered wood shows excitation wavelength dependence. Photo irradiation leads to a rapid reduction in the emission intensity, broadening of spectra and a significant red shift in the emission maximum. Photo stability of wood surfaces esterified with benzoyl chloride was also assessed. The modification was characterized and analyzed by fluorescence and FTIR spectroscopy and photo-stability of modified wood was assessed. Esterification of wood by benzoyl chloride suppressed the colour changes (photo-discoloration) and also reduced the lignin degradation and generation of carbonyl groups on irradiated wood surfaces. Results show esterification of wood with benzoyl chloride was effective at inhibiting photo-degradation of wood polymers.
K K Pandey


Microscopical analysis of formaldehyde-acid modified wood
1981 - IRG/WP 3182
Cross-linking of wood with gaseous formaldehyde improves its hygroscopic and dimensional behaviour, and its resistance against micro-organisms. However, formaldehyde cross-linking reactions take place only in the presence of an acid catalyst, which results in losses in mechanical By optimization of a formaldehyde-sulfur dioxide vapour phase process the reaction conditions were established to limit losses in modulus of elasticity and bending strength to a few percent. Under these circumstances, impact strength losses of about 50 to 75% were still noted. The reaction of formaldehyde with cellulose has been studied intensively in textile research. However little is known on the fundamental aspects of the interaction of formaldehyde with lignin and wood. In order to get further insight into the effects of a formaldehyde-acid catalyzed reaction on the technological properties of wood a fundamental analysis of the interactions of both compounds with wood has been carried out.
M Stevens, N Parameswaran


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


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