Soil Bed Tests Research Articles

Mechanical properties and biological durability in soil contact of chemically modified wood treated in an open or in a closed system using glycerol/maleic anhydride systems

ABSTRACT This paper presents mechanical properties and biological durability properties against soft-rot (soil bed test) and subterranean termites (grave-yard test) of the wood modified with a vinylic derivative of glycerol or polyglycerol and maleic anhydride at different curing conditions. Wood modification was performed through impregnation of European beech (Fagus sylvatica) with an aqueous solution of polyglycerol maleate, glycerol maleate, or maleic anhydride at 10 or 20% w/w concentration, followed with curing under oven heating (OHT) in an open system (120°C, 150°C, or 220°C) or under heat pressurised steam (HPS) at 150°C in a closed system. Results revealed that almost all modified wood presented higher modulus of elasticity (MOE) values than untreated wood, however, modulus of rupture (MOR) and work to maximum load in bending (WMLB) decreased considerably. Biological durability in the soil bed test against soft-rot indicated that almost all modified wood was specified as “durable” to “very durable”. 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 excellent durability against subterranean termites within a period of 328 days in the field.

Weathering Stability and Durability of Birch Plywood Modified with Different Molecular Weight Phenol-Formaldehyde Oligomers.

This study investigated the effect of phenol-formaldehyde (PF) resin treatment on the weathering stability and biological durability of birch plywood. Silver birch (Betula pendula) veneers were vacuum-pressure impregnated with four different PF resins with average molecular weights (Mw) of 292 (resin A), 528 (resin B), 703 (resin C), and 884 g/mol (resin D). The aging properties of PF resin modified birch plywood were analyzed using artificial weathering with ultraviolet (UV) light, UV and water spray, and weathering under outdoor conditions. The same combinations of PF-treated plywood specimens were then tested in soil-bed tests to determine their resistance against soft-rot wood decay. It was not possible to compare weathering processes under artificial conditions to processes under outdoor conditions. However, the weathering stability of birch plywood treated with PF resins A, B, and C, scored better than plywood treated with commercial resin D (regardless of solid content concentration [%]). Results from unsterile soil bed tests showed improvements in resistance to soft-rot wood decay compared to untreated plywood and solid wood. Mass loss [%] was lowest for birch plywood specimens treated with resin of highest solid content concentration (resin D, 20%). Provisional durability ratings delivered durability class (DC) ratings of 2–3, considerably improved over untreated solid wood and untreated birch plywood (DC 5).

A reverse chemical ecology approach to explore wood natural durability.

SummaryThe natural durability of wood species, defined as their inherent resistance to wood‐destroying agents, is a complex phenomenon depending on many biotic and abiotic factors. Besides the presence of recalcitrant polymers, the presence of compounds with antimicrobial properties is known to be important to explain wood durability. Based on the advancement in our understanding of fungal detoxification systems, a reverse chemical ecology approach was proposed to explore wood natural durability using fungal glutathione transferases. A set of six glutathione transferases from the white‐rot Trametes versicolor were used as targets to test wood extracts from seventeen French Guiana neotropical species. Fluorescent thermal shift assays quantified interactions between fungal glutathione transferases and these extracts. From these data, a model combining this approach and wood density significantly predicts the wood natural durability of the species tested previously using long‐term soil bed tests. Overall, our findings confirm that detoxification systems could be used to explore the chemical environment encountered by wood‐decaying fungi and also wood natural durability.

Fungal deterioration of a novel scrimber composite made from industrially heat treated African highland bamboo

A novel engineered scrimber was manufactured from heat treated African highland bamboo Yushania alpina (K. Schum.) W.C. Lin on an industrial scale. Scrimber are a group of engineered wood products that consist of long, slender particles resulting from a non-cutting defibration technique. Those are heat treated, impregnated with phenolic resin, highly densified and the product is believed to be resistant to biodegradation by wooddestroying fungi. The highland bamboo scrimber was tested for resistance against basidiomycete monocultures and soft rot in a soil bed test. The soft rot soil bed test caused nearly 20 % mass loss and 61 % stiffness loss for the scrimber made from untreated bamboo. Heat treatment reduced the ML to 5% for the 200 °C variant, whereas stiffness loss was only slightly reduced for heat treated variants. All treatment temperatures led to 50 % fungal stiffness loss. The notably high abiotic mass loss in sterile samples reduced with treatment temperature. The heat treatment did not affect the durability class resulting from the test against basidiomycete monocultures. Although the variability in heat treated samples was slightly lower, all variants achieved durability class 1. The soil bed test against soft rot resulted in durability classes 1, 2, 3 and 4. When based upon stiffness as parameter, the durability class was 4, whereas mass loss led to DC 1 for treatment at 200 °C, DC 2 for 180 and 160 °C and DC 3 for the untreated control, respectively. The development of substrate moisture content over time indicated that fungal growth can possibly be delayed via heat treatment, but not stopped. The minimum target treatment temperature to achieve a notable improvement in mass loss was 180 °C.

Durability of Eucalypts wood in soil bed and field decay tests

This evaluated the natural resistance of wood from seven Eucalyptus trees in field decay and soil bed tests. Two 12-year-old trees were randomly sampled per species, with 2,2 m logs being obtained from the basal section of each tree. The samples were taken in two positions in the radial direction of the stem (middle heartwood and transition zone; containing heartwood and sapwood). The field decay tests were installed in three municipalities in the southern state of Espirito Santo, and the soil utilized soil from the three field decay test areas. The field decay tests were evaluated after six, 12 and 18 months after installation and the soil bed tests after six months. The Scott-Knott test (p ≤ 0,05) was used in the analysis and evaluation of the tests. The sapwood-heartwood (transition region) exhibited the greatest mass losses for the field decay and soil bed tests. On average, for the soil bed test the lowest mass losses were observed for the soil of Vargem Alta (5,00 %), with greater mass losses observed for Sao Jose do Calcado (7,05 %) and Jeronimo Monteiro (9,90 %). In the field decay test the organisms present in the soil of Sao Jose do Calcado and related to the organic matter content Eucalyptus grandis and Eucalyptus saligna more intensely

Assessing the natural durability of different tropical timbers in soil-bed tests

Ground contact speeds up timber decay because of the large number of microorganisms in soil. This study, we assessed the natural durability of seven tropical species using the European standard EN 807 (2001). We embedded samples of Dalbergia granadillo, Cordia elaeagnoides, Swietenia humillis, Tabebuia donell-smithii, Hura polyandra, Enterolobium cyclocarpum and Tabebuia rosea and temperate species Fagus sylvatica (as a control) in sandy, clay-sandy-loam and clay-loam for 8, 16, 24 and 32 weeks. We evaluated durability of the samples by determining the mass loss and modulus of elasticity (MOE) loss. The results varied significantly (p < 0.001) depending on timber species and soil type considered. The D. granadillo and C. elaeagnoides were the most durable, with mass losses of 4.5%, 6.5% and MOE losses of 4.5%, 20.5%, respectively. F. sylvatica, T. rosea and E. cyclocarpum samples were the least durable, with mass losses of 22.3-25% and MOE losses of 35.8-59.8%, respectively. Decay was most aggressive in sandy-clay-loam soil followed by the clay-loam soil and finally the sandy soil.

Performance of waterborne copper/organic wood preservatives in an AWPA E14 soft-rot laboratory soil bed test using modified soil

Abstract Soil chemistry is known to have a major effect on the degradation of treated wood by basidiomycete fungi in laboratory and exterior ground-contact exposures. However, this topic received little attention from a soft-rot (SR) decay perspective. In the present paper, laboratory SR tests were performed with two different types of forest soils, which were also modified. Test samples, made of Pinus glabra (Walt.) (pine) were treated with four commercial copper/organic waterborne preservatives. In addition, soluble or particulate copper and the organic co-biocides quarternary ammonia compound or tebuconazole, were individually examined. After 19 months of soil bed exposure, moderate to severe degradation was observed in all treated samples in both soils. Surprisingly, microscopic examination showed minimal SR decay. Samples in the neutral soil had extensive tunneling bacterial deterioration and the best performance was observed with both copper/quaternary commercial formulations. Samples in the acidic soil appeared to have some white-rot and bacterial deterioration and all four commercial copper/organic formulations showed good statistically equivalent efficacy. For samples treated with only copper, the particulate copper samples performed statistically equivalent or slightly better than amine copper, while samples treated with only the organic quarternary or tebuconazole performed poorly in both soils.

Resistance of thermally modified ash (Fraxinus excelsior 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.

Wood dimensional stability and extractives as reasons for termite and fungal resistance of the lesser known Albizia malacophylla Kenyan wood species

Studies were carried out on termite and fungal resistance of the lesser known Albizia malacophylla Kenyan wood species. In addition wood dimensional stability, amount and chemical nature of heartwood extractives was also evaluated. Wood resistance against white rot tropical fungi was based on a laboratory soil bed test and subterranean termite resistance in the field according to American Wood Protection Association: E7-93 (1993) standard. Wood extractives were subjected to infra-red analysis using standard laboratory procedures. Albizia malacophylla heartwood is dimensionally stable (5.5 %) with a less dimensionally stable sapwood (9.6 %). Heartwood extractive content is high (9.7 %) in comparison to sapwood (4.6 %). Albizia malacophylla heartwood is resistant to fungi (8.1 %) mass loss and very resistant to termites (4.8 %) mass loss reported after 6 months exposure. Removal of extractives significantly lowered heartwood dimensional stability, termite and fungus resistance. Heartwood extractives were able to inhibit the growth of fungi under laboratory sterile conditions. Infra-red analysis of crude heartwood extractives indicated presence of aldehydes, ketones carbonyl compounds, esters, aromatic, carboxylic acids and aliphatic carbonyl compounds. Put together, the nature, amount of heartwood extractives and wood dimensional stability are at the origin of the found termite and fungus resistance of A. malacophylla wood.

The wood preservative potential of long-lasting Amazonian wood extracts

Investigations were carried out on the efficacy of extracts from seven Amazonian woods (Bagassa guianensis, Manilkara huberi, Sextonia rubra, Vouacapoua americana, Andira surinamensis, Handroanthus serratifolius, and Qualea rosea) with varying natural durability to reduce soft-rot degradation in a 6-wk soil-bed test. Six of the wood extracts had shown efficacy against soft-rot fungi. In particular, the preservation efficacies of B. guianensis, H. serratifolius, and S. rubra extracts were highly significant up to retention levels of 23, 25, and 12 kg m−3, respectively. Three extracts (A. surinamensis, H. serratifolius, and Q. rosea) were then tested against Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot), in an agar-block test. H. serratifolius wood extract was very efficient at protecting P. sylvestris samples at 5.1 kg m−3 against the brown rot. This extract could be used as a basis for new wood protectant formulations.

Efficacy of Bagassa guianensis Aubl. extract against wood decay and human pathogenic fungi

Extractives that provide natural resistance to Bagassa guianensis Aubl. heartwood were examined. Soil-bed tests showed that the B. guianensis heartwood resistance was significantly reduced after ethyl acetate extraction, whereas methanol and especially water extractions improved the resistance. The ethyl acetate extract was submitted to a bioguided fractionation, and fractions were tested against one wood-destroying fungal strain (Pycnoporus sanguineus) and two human pathogenic fungal strains (Candida glabrata (yeast) and Trichophyton rubrum (filamentous dermatophyte)). Fraction F7, which exhibited the strongest antifungal activity, was subsequently fractionated by high performance liquid chromatography (HPLC). Six previously described compounds were isolated. Although the two moracins, 6-O-methyl-moracin N (3) and moracin N (4) were the most active against fungal strains with MIC values between 4 and 16 μg ml−1, the isolated compounds showed less or equivalent antifungal activity than the initial fraction. Possible synergism between compounds 3 and 4 and other secondary metabolites have been hypothesized. Our study demonstrated that this extract as a whole might be used as a wood preservation or antimycotic product.

Biological effectiveness of didecyl dimethyl ammonium tetrafluoroborate (DBF) against basidiomycetes following preconditioning in soil bed tests

Evaluation of wood preservatives in soil-contact tests is becoming an important issue since detoxification of wood-protecting compounds by fungi and bacteria found in soil may decrease the resistance of treated wood. In this study, the decay resistance of wood treated with didecyl dimethyl ammonium tetrafluoroborate (DBF), a recently developed quaternary ammonia compound, was evaluated in both soil bed and laboratory decay resistance tests. Small specimens (5×10×100 mm3) of DBF-treated and untreated sugi sapwood were subjected to decay in laboratory soil bed tests (DIN ENV 807 (2001)) followed by Basidiomycetes tests (DIN EN 113 (1996)). Exposure in field soil and compost soil substrates was used to observe the effects of wood degrading and other soil-inhabiting micro-organisms on the decay resistance of the specimens. Soil bed tests showed that DBF-treated wood specimens at 7.7 kg/m3 retention level (1% DBF solution concentration) showed better performance compared to 0.01 and 0.1% DBF treatments. The 7.7 kg/m3 retention level was also effective to protect the wood specimens against Coniophora puteana and Coriolus versicolor in Basidiomycetes tests. It is concluded that detoxification of wood preservatives in soil contact is an important factor to determine protective properties of treated wood in ground contact applications. Further experiments with larger specimens are needed to observe the performance of DBF-treated wood at higher retention levels in field above ground and ground contact tests.

The use of an acoustic technique to assess wood decay in laboratory soil-bed tests

This study assesses the changes in elastic behaviour (i.e. modulus of elasticity – MOE) and mass loss of different hardwood and softwood species exposed to decay in laboratory soil-bed tests. Elasticity moduli were determined using conventional static methods as well as a dynamic method based on flexural vibration. The results obtained show a high correlation between dynamic and static bending measurements for all the timber species tested at different stages of fungal decay. Furthermore, the non-destructive MOE assessment proved to be a good tool for the early detection of wood decay.