Resistance of thermally modified ash (<Emphasis Type="Italic">Fraxinus excelsior</Emphasis> L.) wood under steam pressure against rot fungi,soil-inhabiting micro-organisms and termites

Thermal modification processes have been developed to increase the biological durability and dimensional stability of wood. The aim of this paper was to study the influence of ThermoWood^® treatment intensity on improvement of wood decay resistance against soil-inhabiting micro-organisms, brown/white rots and termite exposures. All of the tests were carried out in the laboratory with two different complementary research materials. The main research material consisted of ash (Fraxinus excelsior L.) wood thermally modified at temperatures of 170, 200, 215 and 228 °C. The reference materials were untreated ash and beech wood for decay resistance tests, untreated ash wood for soil bed tests and untreated ash, beech and pine wood for termite resistance tests. An agar block test was used to determine the resistance to two brown-rot and two white-rot fungi according to CEN/TS 15083-1 directives. Durability against soil-inhabiting micro-organisms was determined following the CEN/TS 15083-2 directives, by measuring the weight loss, modulus of elasticity (MOE) and modulus of rupture (MOR) after incubation periods of 24, 32 and 90 weeks. Finally, Reticulitermes santonensis species was used for determining the termite attack resistance by non-choice screening tests, with a size sample adjustment according to EN 117 standard directives on control samples and on samples which have previously been exposed to soil bed test. Thermal modification increased the biological durability of all samples. However, high thermal modification temperature above 215 °C, represented by a wood mass loss (ML%) due to thermal degradation of 20%, was needed to reach resistance against decay comparable with the durability classes of ‘‘durable’’ or ‘‘very durable’’ in the soil bed test. The brown-rot and white-rot tests gave slightly better durability classes than the soil bed test. Whatever the heat treatment conditions are, thermally modified ash wood was not efficient against termite attack neither before nor after soft rot degradation.     

Laboratory evaluation of boron-containing quaternary ammonia compound, didecyl dimethyl ammonium tetrafluoroborate (DBF) for control of decay and termite attack and fungal staining of wood

This study evaluates the decay and termite resistance of wood treated with didecyl dimethyl ammonium tetrafluoroborate (DBF), a recently developed quaternary ammonia compound containing boron. Laboratory decay resistance tests were performed using brown-rot fungus, Fomitopsis palustris and white-rot fungus, Trametes versicolor. Treated wood specimens were also subjected a 3-week-termite resistance test using subterranean termites, Coptotermes formosanus. Decay resistance tests showed that wood specimens treated with 0.5 and 1.0% DBF solutions were well protected against both fungi even after a 10-day severe leaching process, suggesting the adequate fixation of DBF in wood. DBF treatment at 0.1% concentration was efficient against subterranean termites, Coptotermes formosanus Shiraki based on mass losses in both leached and unleached wood specimens. The ability of DBF to inhibit discolorations by selected mold and stain fungi was also screened in laboratory conditions. DBF at the highest concentration level (1%) provided limited protection against mold and staining fungi tested, however, it was effective for only short-term protection (1 or 2 weeks) at lower concentrations. These results suggest that DBF is promising to protect wood to be used outdoors against both fungal decay and termite attack however field tests are needed to observe the performance of DBF-treated wood in ground contact.     

Orientierende Untersuchungen zur Dauerhaftigkeit von?Prosopis?kuntzei Harms

The heartwood of Prosopis kuntzei showed excellent resistance against the basidiomycete Trametes versicolor and the subterranean termite species Reticulitermes banyulensis. The wood was classified as moderately durable in soil contact. The low mass losses are presumptively caused by leaching effects in addition to soft rot decay.     

Effect of essential oil compounds and plant extracts on decay and termite resistance of wood

Essential oils and their derivatives have a long history of safe usage as antimicrobial agents in food industry. In this study various essential oils and extracts from plants were screened for their ability to inhibit wood decay and termite attack in laboratory decay and termite resistance tests using treated wood specimens. In the laboratory decay resistance tests, wood specimens treated with essential oil compounds were subjected to brown-rot fungus, Tyromyces palustris, and white-rot fungus, Trametes versicolor for three months. The specimens were also subjected to termite attack by subterranean termites, Coptotermes formosanus for three weeks in laboratory conditions. The formulation with cinnamaldehyde (DF3) was found to be effective against both the brown-rot and white-rot fungi used in the study. However, the formulation with cinnamic acid (DF8) was able to protect wood specimens against only the white rot fungus and about 50% mass loss occurred in the specimens subjected to the brown-rot fungus. The mass losses in the wood specimens treated with cassia oil containing formulation (DF4) showed that cassia oil was effective against both fungi. The wood tar oil and dodecanal compounds also inhibited fungal decay in the specimens. The wood specimens treated with the formulations used in termite resistance tests were more resistant against the termites when compared to specimens treated with the formulations in decay resistance tests. Even after severe weathering process, treated wood specimens showed resistance against the subterranean termites. Results suggest that essential oils and plant extracts might be important to develop new wood preservatives that are less harmful to the environment and humans than recently available ones.     

Fungal and termite resistance of wood treated with 4-methoxytrityl tetrafluoroborate

This study evaluates the decay and termite resistance of Scots pine (Pinus sylvestris L.) treated with 4-methoxytrityl tetrafluoroborate (MTFB). Decay resistance tests of unleached samples showed that 2%, 1.5% and 1% concentrations of MTFB (15.4 kg/m³, 11.1 kg/m³, and 7.4 kg/m³, retention levels, respectively) gave less than 2% decay of Postia placenta and concentrations of 2% and 1.5% less than 2% decay of Coniophora puteana. Wood specimens treated with 4-methoxytrityl tetrafluoroborate solutions were not protected against the brown rot fungi after a 14-day severe leaching process, suggesting excessive leaching of the chemical from wood. Treatment with 2% concentration protected against subterranean termites, Coptotermes formosanus Shiraki based on mass losses in both leached and unleached wood specimens in comparison with lower concentration levels. These results suggest that 4-methoxytrityl tetrafluoroborate might be promising to protect wood being used outdoors against termite attack. However, 4-methoxytrityl tetrafluoroborate did not protect wood against fungal decay. Field tests are needed to observe the performance of 4-methoxytrityl tetrafluoroborate treated wood in ground contact.     

Gloss of thermally densified alder (Alnus glutinosa Goertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.) wood veneers

Thermo-mechanical densification of wood is performed to improve physical and mechanical properties of wood. During this treatment aesthetic properties of wood, including gloss, also change. Therefore, the purpose of this study was to determine the effect of short-term thermo-mechanical (STTM) densification in different wood species (alder (Alnus glutinosa Goertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.)) on their gloss changes. Commercial wood veneers were densified in a hot plate press for 4 min at temperatures of 100, 150 and 200 °C, pressures of 4, 8 and 12 MPa. Gloss was evaluated at 20°, 60° and 85° angles of incident light using PICO GLOSS 503. Gloss measurements showed an enhancement of aesthetic properties of densified wood. Findings of this study indicated that both densification temperature and pressure have a significant effect on wood gloss. Gloss values of densified wood increased with increasing densification temperature and pressure for all investigated species. Compared to non-densified wood, gloss (85°) values (across/along the grain) for alder, beech, birch and pine increased after treatment to 2109.1/2376.9, 1728.6/2311.1, 2787.5/3000, and 2591.7/1216.7 %, respectively. The greatest gloss values were recorded at 200 °C and pressure of 12 MPa for all tested angles of incident light and for all densified wood samples. Gloss changes for birch were the highest, but the glossiest surface was observed for pine among all investigated species after wood densification.     

Structural bonding of ash (Fraxinus excelsior L.): resistance to delamination and performance in shearing tests

The utilization of ash (Fraxinus excelsior L.) allows for a significant enhancement of the load-bearing capacity in structural laminated products. However, such applications fundamentally require high-strength and durable bonds between lamellas and in finger joints. Therefore, the aim of the present survey was to evaluate ash bondings in terms of resistance to delamination (EN 302-2) and shear performance (EN 392). Investigations were performed with five adhesives: phenol-resorcinol-formaldehyde (PRF), melamine-urea-formaldehyde (MUF-1, MUF-2), polyurethane (PUR), emulsion polymer isocyanate (EPI) and varying closed assembly times as key bonding parameter. For all tested adhesives and closed assembly times, the shear test showed high wood failure percentages and bond strength values that compare to solid ash. In contrast, for resistance to delamination, significant differences were found between the adhesives as well as between closed assembly times, with improving resistance to delamination for increasing closed assembly times. The best performance was determined for the PRF-adhesive and long closed assembly times. However, standard requirements for resistance to delamination could not be met by any of the adhesives. The resistance to delamination showed no correlation with the shear performance for any of the adhesives. Microscopic examination of the bonded joints revealed that both the penetration behavior of the adhesives and glueline thicknesses clearly correlated with the closed assembly time.     

Physical,mechanical and biological properties of thermo-mechanically densified and thermally modified timber using the Vacu<Superscript>3</Superscript>-process

Densification and thermal modification change wood properties in different ways depending on the treatment conditions and the wood species. In the presented investigations, densification and thermal modification were applied consecutively. The primary objective of this treatment combination was the compensation of reduced mechanical properties due to the thermal modification by densification. The combined processes were applied to five European wood species: poplar (Populus nigra L.), beech (Fagus sylvatica L.), Norway spruce (Picea abies Karst.), English oak (Quercus robur L.) and European ash (Fraxinus excelsior L.). Depending on the mean density of the species, a thermo-mechanical densification of 43 or 50% was imposed to improve mechanical strength parallel to the grain. Subsequently, the densified material was thermally modified in the so-called Vacu³-process at 230 °C and 20 or 80% vacuum and at 240 °C and 20% vacuum. The thermal modification resulted in changing wood colour, mechanical strength, hardness, dimensional stability and durability. All the wood modification processes were carried out at industrial scale after pre-tests at laboratory scale. The modified material was characterized regarding flexural properties, static and dynamic hardness, structural integrity, abrasion resistance, moisture dynamics, dimensional stability, and durability against white, brown and soft rot fungi. In summary, the test results showed that the consecutive application of thermo-mechanical densification and thermal modification leads to significantly improved durability whilst mechanical properties at least for beech, ash and poplar remained and the material is dimensionally stable.     

Comparative studies on the in-ground and above-ground durability of European oak heartwood (Quercus petraea Liebl. and Quercus robur L.)

The durability of European oak (Quercus petraea Liebl. and Quercus robur L.) is controversially discussed since a long time. While it is classified as a “durable” timber species (durability class 2, according to EN 350-2), results from different studies indicated a lower durability. Therefore comparative studies with sessile oak and English oak were carried out including laboratory resistance tests against different basidiomycetes, soil box tests against soft rot and other soil-inhabiting micro-organisms, as well as in-ground and above-ground field trials at different test sites. Both oak species were rated “non-durable” (durability class 5, DC 5) in soil box tests and in-ground field trials and “slightly durable” (DC 4) in above-ground field trials. Solely results from laboratory tests with pure basidiomycete cultures led to partly better estimates (“very durable” to “moderately durable” DC 1-3), but did not represent the organisms responsible for decay in the field. For oak, EN 350-2 reflects only laboratory results but not the performance of the material in real field situations.     

Crack formation in unfinished siding of aspen (Populus tremula L.) and Norway spruce (Picea abies (L.) Karst.) during accelerated weathering

Crack formation is a serious defect that may reduce the lifetime of unfinished wood in service. An accelerated weathering test was carried out to study crack formation of solid wood board specimens of aspen (Populus tremula L.) and Norway spruce (Picea abies (L.) Karst.). The influence of the boards' distance from the pith was also studied. The aspen specimens developed a higher number of cracks than the spruce specimens. However, these cracks were shorter and less injurious than those propagating in spruce wood. It is concluded that a solid wood siding of aspen will show at least as good a performance as spruce regarding crack injuries. For both aspen and spruce, boards taken from near the pith had a lower proportion of long cracks than boards taken further out. This supports the rule that boards with a high proportion of annual rings perpendicular to the surface (the boards near to the pith) have a higher resistance to crack formation than boards with a high proportion of horizontal annual rings.     

Verklebung von Buchenholz für tragende Holzbauteile

The load bearing capacity of glulam could be enhanced by using lamella of European beech (Fagus sylvatica??L.). Essential requirements for the production of those beams are adhesives which allow for a durable und reliable bonding of lamella. The paper shows to what extent commercially available MUF and PU adhesives and adapted bonding parameters ensure gluing of European beech timber for load-bearing timber structures. Both beech wood containing heartwood and beech wood without heartwood were included in the study. With regard to technical approval, the chosen test methods were resistance to delamination according to EN??302-2 (2002) and shear test of glue line according to EN??392 (1995). From the two tested MUF systems it was evident, that delamination decreased by increasing the closed assembly time. The requirements of EN??301 (2006) were fulfilled for adhesive type??I and??II. Without any limitations beech wood containing heartwood could be glued using MUF-1. On the other hand, the results of the PU adhesive were insufficient. Light-optical micrograph examinations show that long assembly times secure the formation of a glue line. It was assumed that the curing process is retarded by beech wood. No relationship was found between the results of the shear strength test and the delamination test. For quality control of glulam the delamination test is recommended. Based on the positive results an application for technical approval of glulam consisting of beech was made. For this reason beech-glulam can be generally utilized in service class??1.     

Evaluation of particulate zinc and copper as wood preservatives for termite control

Subterranean termites are a major factor in the biodegradation of wood construction products. In this study the efficacy of wood treated with micronized copper, zinc oxide and their mixture was compared to that of wood treated with soluble amine copper oxide against subterranean termites in a laboratory test. All of the formulations tested were effective in controlling wood degradation by the termites, with copper being slightly more effective than zinc and micronized copper being slightly more effective than amine copper.     

Surface treatment for preventing decay and termite attack in wood using didecyl dimethyl ammonium tetrafluoroborate (DBF) incorporated with acryl-silicon type resin

Surface treatment of wood was carried out using acryl-silicon type resin including didecyl dimethyl ammonium tetrafluoroborate (DBF), boron-containing quaternary ammonia compound. Surface-treated wood specimens were exposed laboratory decay resistance tests after completing a 10-cyle severe weathering process. In laboratory decay resistance tests, one brown-rot decay fungus, Fomitopsis palustris and one white-rot decay fungus, Trametes versicolor were used. The specimens were also subjected to laboratory termite resistance tests using subterranean termites, Coptotermes formosanus. Wood specimens treated with 2% DBF and resin containing preservative solution showed improved decay and termite resistance suggesting that the preservative solution at 2% DBF concentration provides lasting protection against wood degradation owing to the amount of DBF remaining in the wood after severe weathering process. However field tests are needed to determine the performance of surface-treated wood with DBF and the acryl-silicon type resin in more realistic conditions.     

The biological effectiveness of wood modified with linear chain carboxylic acid anhydrides against the subterranean termites Reticulitermes flavipes

The work described in this paper has demonstrated that chemically modified Corsican pine sapwood with a homologous series of linear chain carboxylic acid anhydrides provided bioprotection against the subterranean termites Reticulitermes flavipes. By varying the reaction time, various levels of modifications were obtained. There was no significant reduction in feeding above 16% WPG (weight percent gain due to modification), suggesting that modification to WPGs greater than this did not offer additional protection. The type of anhydride employed has little influence on resistance against termites.     

A non-contact method for the determination of fibre direction of European beech wood (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.)

This paper introduces a non-contact method for the identification, quantification, and documentation of fibre direction of European beech wood (Fagus sylvatica L.). The developed approach is based on an automated visual analysis of the spindle pattern formed by the medullary rays, also termed wood rays. Each spindle is identified by means of image analysis technique, its position and orientation is determined, and the fibre direction of discretised elements is calculated. The individual process steps necessary to obtain an estimate of the fibre direction of a board are explained using the examples of five different failure types. In all examples, the estimated fields of fibre direction are congruent with the actual fibre direction determined by means of (1) the orientation of all present shrinkage cracks, which are established indicators for the fibre direction in wood, and (2) the fracture pattern after tensile testing. Employing the presented approach could open up new possibilities for the characterisation of European beech and other hardwood species with multi-row medullary rays in several fields of application, in particular regarding stress grading.     

Density profile and microstructural analysis of densified beech wood (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) plasticized by microwave treatment

This study was carried out in order to determine the efficacy of microwave (MW) plasticization for wood densification purposes. The plasticization process was carried out using a continuous feed laboratory MW at a frequency of 2.45 GHz. European beech (Fagus sylvatica L.) specimens measuring 50 mm?×?40 mm?×?8 mm were MW treated (plasticized) with an output of 3.5 kW at a conveyor speed of 0.4 m/min. Afterwards, MW plasticized specimens were densified with a ratio of 50%. Microscopic structure changes of densified wood were detected using a scanning electron microscope (SEM) and density profiles were measured using the X-ray densitography. An average density of 677 kg m^?3 and 771 kg m^?3 increased significantly to 951 kg m^?3 for radially densified and to 1194 kg m^?3 for tangentially densified specimens. X-ray densitography results show uniformity of density profiles through specimen thickness, which confirmed the evenly plasticized volume of wood. Microscopic structure observation revealed that the MW plasticization was not accompanied by any fractures, and deformations present in the densified wood were due to viscoelastic buckling of cell walls without crack propagation. Therefore, MW treatment can be considered as an effective method for wood plasticization.     

Evaluation of white rot decay in phenol-formaldehyde resin treated European beech (Fagus sylvatica L.) LVL by drilling resistance measurements

Improving the properties of laminated veneer lumber (LVL) through wood modification expands its usage as building material, especially for outdoor applications. The outdoor performance of LVL products needs to be tested against different biotic agents, and methods are needed for testing and evaluating their effect on the structural integrity of LVL. In this study, drilling resistance (DR) measurements were used to quantify the effect of fungal decay in phenol-formaldehyde (PF) resin treated European beech (Fagus sylvatica L.) LVL caused by white rot fungi. Material specific peculiarities and their effect on the evaluation method were studied such as the effect of drill bit blunting, moisture content (MC), drilling direction and PF resin content on the DR of PF-modified LVL. The drilling direction in relation to veneer and glue layers had a significant effect on DR and feeding resistance (FR). The PF resin treatment increased the DR. Feeding resistance was found more sensitive to the blunting of the drill bit than DR. The effect of MC on DR and FR was found to be insignificant. The effect of PF resin content on the prediction of mass loss (ML) by DR became prominent only for ML by white rot decay below 10 %. Correlations between DR, ML due to fungal decay and weight percent gain were established and described with a two-factor regression model. The drill bit feed rate of 0.5 m min^?1 and the rotational frequency of 3500 min^?1 as well as the transversal drilling in relation to the veneer (glue) layers were recommended for the assessment of beech LVL treated with PF resin. The DR measurements showed high potential as a fast standard evaluation method for decay and strength loss of LVL products.

     

Manurial Effect of Wood Ash and Refuse Tea on Nutrient Status and Yield of Tea (Camellia Sinensis L.)

A field experiment was carried out to determine the effects of wood ash and refuse tea with urea on yield and nutrient status of tea. Experimental plots were located in the St Coombs Estate, Tea Research Institute, Talawakelle, Sri Lanka. Six treatments (1 ton wood ash plus 20 ton refuse tea ha^-1 year^-1{T₁}, 2 ton wood ash plus 20 ton refuse tea ha^-1 year^-1{T₂}, 1 ton wood ash plus 20 ton refuse tea plus 587 kg urea ha^-1 year^-1{T₃}, 2 ton wood ash plus 20 ton refuse tea plus 587 kg urea ha^-1 year^-1{T₃}, present TRI fertilizer mixture{T₃}, and control{T₃}, without any fertilization) were arranged according to Randomized Complete Block Design with three replicates. Macro and micro nutrient contents in soil and leaf were analyzed5 months after applying treatments and yield was recorded in weekly intervals.T₂ applied plots indicated significant positive effect (p<0.05) on the yield and significantly (p<0.05) higher Potassium and Calcium content in the soil. Significant effect (p<0.05) of Nitrogen and Carbon content in the soil was given by T₁. Electrical conductivity and pH changes in soil were not any significantly different among all the treatments whilst higher macro and micro-nutrient concentration was observed in the soil, treated with T₁,T₂,T₃and T₄. It is evident from results that wood ash, refuse tea with urea can be successfully used to promote sustainable tea cultivation in the Mattakelle soil series (Rhodudults/Tropudults;USDA classification) which having high buffering capacity.     

A comparative study on brown-rot fungus decay and subterranean termite resistance of thermally-modified and ACQ-C-treated wood

The resistance of thermally-modified and Alkaline Copper Quaternary type C (ACQ-C) treated aspen (Populus tremuloides Michx), jack pine (Pinus banksiana Lamb.), yellow-poplar (Liriodendron tulipifera L.), and Scots pine (Pinus sylvestris L.) against the brown-rot fungus (Gloeophyllum trabeum) and Eastern U.S. subterranean termite (Reticulitermes flavipes) was studied. Wood materials were thermally-modified at a temperature of 210 °C for 15 min. ACQ-C was impregnated into yellow-poplar and jack pine wood at three different retention levels and at each level both leaching and non-leaching procedures were conducted. Results indicate that ACQ-C-treated yellow-poplar and jack pine became significantly more resistant to the brown-rot fungus compared to the thermally-modified wood and the untreated control. Thermally-modified yellow-poplar and jack pine were more resistant to this fungus than untreated wood. For aspen and Scots pine, the resistance to G. trabeum was improved after the thermal modification, but it remained susceptible to this brown-rot fungus decay. Termite susceptibility of thermally-modified aspen, jack pine, and yellow-poplar was comparable to that of untreated controls. Significantly greater termite attack occurred on thermally-modified Scots pine wood than it did on untreated wood. This likely is attributed to some compounds contained in Scots pine wood that inhibited termite attack.     

Bending performance of 3-layer beech (Fagus sylvativa L.) and Norway spruce (Picea abies (L.) Karst.) VTC composites bonded with phenol–formaldehyde adhesive and liquefied wood

Low quality beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) were densified with viscoelastic thermal compression (VTC) process to two different degrees of densification, and lamellas were used to manufacture different types of 3-layer VTC composites. Bending properties of 3-layer VTC composites bonded with phenol formaldehyde (PF) adhesive and liquefied wood (LW) were determined and compared to 3-layer composites produced with undensified beech or spruce wood lamellas. Morphology of VTC spruce wood of higher density was analysed with fluorescent microscopic technique. All composites produced with densified beech lamellas and bonded with PF adhesive had significantly higher values of modulus of rupture (MOR) and modulus of elasticity (MOE) than composites produced with undensified lamellas. Densified spruce lamellas contributed to better bending performance of 3-layer VTC composites bonded with PF adhesive to some extent. Furthermore, composites bonded with LW had significantly lower MOR and MOE values compared to composites bonded with PF adhesive. Study of VTC spruce wood microstructure showed that densification caused non-uniform deformation of cell wall structure, in which cell wall fractures were observed.