Degradation of Norway spruce (Picea abies) heartwood and sapwood during 5.5 years’ above-ground exposure

Abstract

Differences in durability between heartwood and sapwood of Norway spruce [Picea abies (L.) Karst.] were investigated to determine wood qualities most favourable for use in outdoor constructions above ground. Trees grown on sites with either good or poor access to water were used. Seventy-eight specimens measuring 20 × 50 × 300?mm³ separated into heartwood and sapwood, half untreated, half painted, were exposed horizontally outdoors above ground for 5.5?years with the pith side up and the bark side down. Crack length and crack number were measured. Fungus growth and surface changes were visually estimated. Fungus type was determined by microscopic analysis. The main finding was that spruce heartwood had fewer and shorter cracks and less surface-discolouring fungus growth than sapwood. This was valid for both painted and untreated wood. After 2?years’ exposure, the cracks in sapwood (upper surface) were more than three times longer and about five times more numerous than in heartwood for both painted and untreated boards. Microscopic study showed that surface discoloration was due mainly to Aureobasidium pullulans, together with a few other discolouring fungi. After 5.5?years, initial decay was established on the surface and in the end grain of four untreated test objects.     

Response of maple sapwood to injury and infection

In sapwood challenge experiments in Acer rubrum, columns of discolouration initiated by wounding and inoculation with pioneer fungi (Cephalosporium sp., Phialophora sp.) were similar in size to untreated wounds. Inoculation with decay fungi (Pleurotus ostreatus, Trametes versicolor) produced larger columns of wound-initiated discolouration. The removal of bark around a bore wound caused a significantly larger column to form compared to the sum of the columns inititiated by separate wounds. Stage-I discoloured wood, not associated with obviously rotted wood, had concentrations of mobile cations and soluble phenols similar to sapwood. Stage-II discoloured wood, spatially associated with rotted wood, was frequently bounded by a chemically distinct boundary layer and the discoloured wood contained significantly greater concentrations of mobile cations and soluble phenols than stage-I discoloured wood.     

End grain water absorption and redistribution in slow-grown and fast-grown Norway spruce (Picea abies (L.) Karst.) heartwood and sapwood

Abstract

Wood is susceptible to decay by rot fungi if it is exposed to high-moisture contents during long periods of time and it is therefore important to limit the duration of such periods. Critical points in outdoor wood structures are, for example, end grain surfaces in joints where water can get trapped after a rain. It is therefore of interest to study both absorption and redistribution of moisture in wood. This paper presents moisture content profiles during end grain water absorption and redistribution in Norway spruce (Picea abies (L.) Karst.) measured by computed tomography with the specimens in individual climate boxes. Heartwood and sapwood of two provenances (slow-grown and fast-grown wood) were included. No major differences were seen between the water uptake of the slow-grown and the fast-grown wood since the densities were similar despite of the large difference in growth ring width. However, for the sapwood specimens, the moisture content was higher further into the specimens than for the heartwood specimens in agreement with previous studies. For the slow-grown wood, the redistribution was also generally more rapid for the sapwood specimens than for the heartwood specimens.     

Gaseous treatment with allyl isothiocyanate to control established microbial infestation on wood

Applicability of gaseous treatment with allyl isothiocyanate (AIT) was evaluated for controlling the established microbial infestation of wood in the laboratory. Small sapwood specimens from five wood species measuring 20 mm (T)×20 mm (R)×10 mm (L) were first preincubated on 2% malt-agar medium with placing them on a fully grown monoculture of seven test fungi. After 7 weeks of preincubation they were transferred to fresh medium and exposed to AIT fumigant at concentrations of 2360 and 23600ppm AIT in the air of a petri dish to determine threshold values of exposure periods for each test fungus. The 2360 ppm concentration was not effective forPenicillium funiculosum, Gliocladium virens, orRhizopus stolonifer for any of the wood species-exposure period combinations. Those test fungi could grow even at 23600ppm after 48h exposure whenCryptomeria japonica andFagus crenata were used as wood substrate. Growth of other test fungi was inhibited at 2360ppm with a few exceptions in the case ofAspergillus niger. The required periods of exposure to suppress microbial regrowth were different with wood species-test fungi combinations. As two wood-decaying basidiomycetes,Trametes versicolor andFomitopsis palustris, were easily controlled at 2360ppm after 24h exposure regardless of wood species, AIT treatment proved applicable to the control of internal decay of utility poles and other relevant products in service.     

Weathering durability of CCB-impregnated wood for clear varnish coatings

Outdoor performances of a polyurethane varnish and an alkyd-based synthetic varnish coated over chromium-copper-boron (CCB)-impregnated Scots pine (Pinus sylvestris L.) and chestnut (Castanea sativa Mill.) [10 (R) × 100 (T) × 150 (L) mm] were investigated. These varnishes were also applied to the wood surface as sole coatings or impregnated into wood as water-repellent (WR) solutions. Outdoor exposure was performed in the Black Sea region of northern Turkey (41°N, 39.43°E) where humid weather predominates throughout the year and accelerates decomposition of coated wood surfaces. The wood panels were exposed at 45° south on their tangential surfaces. After 9 months of exposure to summer, autumn, and the following winter season, the color and glossiness changes of the exposed surface, adhesion of the coating layer to the wood surface, water absorption through the coating layers, mass loss, and the hardness of the board surface were studied. CCB impregnation greatly stabilized the surface color of varnish-coated panels of both wood species. Gradual decreases of adhesion between varnished layers and preimpregnated surfaces were attributed to probable weakening of interactions at the interface of the treated wood and the film layer. A superficial cleaning process of treated wood is suggested to improve glossiness and adhesion. The coated wood surface became harder with time on outdoor exposure until a maximum hardness occurred followed by softening, whereas the uncoated surface softened steadily. Polyurethane varnish yielded a harder surface than synthetic varnish. Mass losses of wood panels after 9 months of exposure were negligible for all treatments compared with the untreated controls, which were totally discolored and eroded on the surface. It is concluded that long-term exterior wood protection has been achieved by a successful combination of an appropriate preservative treatment followed by a compatible surface-coating process.     

A feasibility study of using two-component polyurethane adhesive in constructing wooden structures

This investigation was conducted to determine the feasibility of using a two-component polyurethane （PUR） adhesive, with special waterproof properties, in constructing wooden structures. We designed and conducted tests to compare the shear strength and adhesion performance of PUR with polyvinyl acetate （PVAc） adhesive on block-shear specimens constructed of oriental beech （Fagus orientalis L.）, fir （Abies alba Mill.）, poplar （Populus deltoides Bartr.）, white oak （Quercus alba L.）, sycamore （Platanus orientalis L.） and white walnut （Juglans cinerea L.）. The values of the percentage of wood failure were also determined in specimens constructed with each adhesive. The highest shear strength values of both adhesives were obtained in specimens constructed of beech, while the lowest shear strength values were obtained in fir and poplar specimens. Average shear strength of the PUR adhesive was 16.5% higher than that of the PVAc adhesive. Specimens constructed of fir, poplar and sycamore were characterised by the highest percentages of wood failure, whereas the lowest average percentages of wood failure were obtained in beech and oak specimens. With the exception of oak specimens, there was no statistically significant difference between percentage of wood failure among the PUR and PVAc adhesives. Generally, the PUR adhesive showed an acceptable adhesion performance on wood materials used in our study.     

Response of colour and hygroscopic properties of Scots pine wood to thermal treatment

The effect of heat treatment on the surface colour and hygroscopic properties of pine wood were investigated in this study. Boards of Scots pine wood (Pinus sylvestris L.) were subjected to thermal treatment at 200°C, for 4, 6, and 8 h. The change of equilibrium moisture content and density values of the specimens in order to facilitate the understanding of the treated material behavior. The colour parameters L*, a* and b*, used to depict the total colour change (Δ E) of wood surface, were shown to change proportionally to the treatment intensity. Moreover, swelling in the tangential and radial directions and absorption of the specimens appeared to be enhanced in great extent by the thermal treatment process. The mean value of swelling percentage in the tangential direction decreased 10.26%, 17.22%, and 19.60% for specimens treated for 4, 6, and 8 h, respectively, referring to the final measurement after 72 h of immersion. In radial direction, mean value of swelling percentage decreased 19.56%, 32.75%, and 34.65% for treated for 4, 6 and 8 h, respectively, after 72 h immersion, which attests the decrease in swelling and improvement in the hygroscopic behavior of Scots pine wood.     

Variation in the decay resistance of larch to fungi

? Decay resistance of larch (Larix sp.) to fungi was evaluated on heartwood samples belonging to 3 species (L. decidua, L. kaempferi and their hybrid), 3 races of European larch (polonica, sudetica and alpine), 13 wood lots (populations) and 313 trees.

? Larch wood appeared, on average, as moderately durable although a high variability was observed. At the sample level as well as at the mean individual tree level, durability ranged from class 1 to 5 according to EN 350-1 standard. At the population level, larch wood varied from ‘durable’ to ‘slightly durable’. Genetics played a major role in decay resistance at the species, provenance and tree levels. Environmental factors such as the position of heartwood samples and the age of trees were also identified as a source of variability.

? The most durable wood was not necessarily from old native alpine stands of European larch: some young larches from faster growing lowland origins also produced durable wood.

? Genetic improvement of larch wood durability appeared therefore likely by the selection of the best populations for decay resistance as well as from the selection of individuals.

     

Laboratory and environmental decay of wood–plastic composite boards: flexural properties

The flexural properties of wood–plastic composite (WPC) deck boards exposed to 9.5 years of environmental decay in Hilo, Hawaii, were compared to samples exposed to moisture and decay fungi for 12 weeks in the laboratory, to establish a correlation between sample flexural properties and calculated void volume. Specimens were tested for flexural strength and modulus, both wet and dry, at 23°C and 52°C. Some specimens degenerated to only 15% of original flexural strength. UV radiation had no impact on flexural properties of field-exposed boards; loss occurred mainly on the side opposite to the sun-exposed surface. The mechanism of the aging process on colonization of WPC by fungi was examined and is consistent with development of slow crack growth in the polyethylene matrix combined with wood decay by fungi. Wood particle decay, moisture, and elevated temperature were the major factors causing composite degradation, indicated by accumulation of voids and a severe decrease in flexural properties. To simulate long-term field impact (including decay) on WPC flexural properties in the laboratory, conditioning of specimens in hot water for an extended period of time is required. Exposure to water (70°C/5 days) was adequate for simulating long-term composite exposure in Hawaii of 4?×?15?×?86 mm³ specimens.     

Screening of properties of modified chitosan-treated wood

Abstract

Chitosan is a biopolymer derived from chitin in crustacean shells. Over the past decade it has been studied as an environmentally benign wood-protecting agent. It is assumed to act as a fungi-stat against a wide range of fungi and even as a fungicide at higher concentrations. This study investigated the properties of wood treated with modified chitosan of different molecular weights. Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.) samples were impregnated with two chitosan solutions differing in their average molecular weights. The chitosan solutions were depolymerized by nitrous acid to one solution of high molecular weight and one solution of low molecular weight with a concentration of 5% (w/v). The results show changes in sorption properties, antifungal properties, fire-retardant properties and mechanical properties of modified chitosan-treated wood. Heat-modified, chitosan-treated wood showed similar properties to chitosan-treated wood, except for brownish coloration, enhanced hydrophobation, and slightly reduced antifungal and fire-retardant properties. The modulus of rupture and hardness showed little or no change. The modulus of elasticity of the heat-modified, chitosan-treated wood increased by 27% compared with untreated wood.     

Factors affecting the fungal colonization of pine lumber

This study investigated whether the physiological condition of wood influenced patterns of colonization by mould and sapstain fungi. The extent of fungal defacement on sawn pine lumber Pinus nigra var. maritima that had been killed by gamma‐irradiation was compared with the defacement on untreated, still living timber that had been aged for up to 16 weeks prior to being sawn. All the sawn lumber was exposed to the natural inoculum of sapstain and mould fungi in a working sawmill environment over a 4‐week period. The results indicated that the pattern of fungal defacement differed markedly in dead or aged wood compared with untreated wood. Mould fungi were most prevalent on the dead irradiated wood, whereas sapstain fungi dominated the freshly sawn lumber which was still living. The differences appear to be independent of wood moisture content and may be related to the production of inhibitory compounds by living cells in wood as it becomes senescent and dies.     

Detection of early stages of wood decay by acoustic emission technique

Acoustic emissions of pine wood samples (Pinus sylvestris L.) previously infected with the soft-rot fungi (Chaetomium globosum Kunze) and brown-rot fungi (Coniophora puteana (Schum. ex Fr.) Karst.) were measured in the perpendicular to grain compression test, in the radial direction. It was found that even a minimum mass loss (below 1%) caused by enzymatic deterioration of the wood substance resulted in an increase in acoustic emission level in the compression test measured perpendicular to grain in the radial direction. A particularly sensitive indicator of wood enzymatic destruction were cumulative counts of acoustic emission related to the value of the applied compression load. Received 4 March 1997     

Efficacy of radio frequency treatment and its potential for control of sapstain and wood decay fungi on red oak,poplar, and southern yellow pine wood species

The effectiveness of radio frequency (RF) treatment in the control of wood decay fungi (Gloeophyllum trabeum, Ganoderma lucidum, and Irpex lacteus) and sapstain fungus (Ceratocystis fimbriata) in red oak (Quercus spp.), poplar (Populus alba), and southern yellow pine (Pinus spp.) was evaluated in the laboratory as an alternative to methyl bromide (MB) treatment. Wood samples (15.5 x 10 x 10 cm) were inoculated with fungi from a 7-day culture by dipping them to a depth of one face deep (2 cm) into inoculum and incubating them at 25°C for 14 days. Identical wood samples were left uninoculated as controls. Subsequent to incubation, the wood blocks were exposed to RF radiation in an industrial 40-kW dielectric oven at temperatures between 60° and 70°C for 2 min. The test fungi were recovered and reisolated from all of the control wood blocks but not from RF-treated wood blocks. RF treatment resulted in complete inhibition of the fungus in 98%-100% of the wood samples. Moisture content loss (≥1%) was noted after wood had been exposed to RF treatment. Moisture content may be an important factor to consider with RF treatments. RF treatment can, therefore, potentially provide an effective and rapid quarantine treatment as an alternative to MB fumigation for certain pathogen-wood combinations. This article reports the results of research only. Mention of a product does not constitute an endorsement or recommendation by USDA for its use.     

Heterotrophic components of biofilms on wood artefacts

Heterotrophic components of biofilms on wood artefacts were studied at the Conservation Laboratory for Wood Artefacts of the University Suor Orsola Benincasa of Naples, Italy. The aim of the study was to add new information on the micro-habitats represented by biofilms formed by wood-dwelling organisms. Light and electron microscopy of histological features of woods used to make the artefacts showed that the woods belonged to species of lime (Tilia sp.), poplar (Populus sp.) and pear (Pyrus sp.). A Denaturing Gradient Gel Electrophoresis analysis performed on heterotrophic microorganisms colonizing the artefacts led to identify four species of bacteria, namely Bacillus cereus, B. mycoides, B. subtilis and Microbacterium oleivorans, and seven species of fungi, namely Alternaria alternata, Aspergillus fumigans, A. versicolor, Cladosporium cladosporioides, C. oxysporum, Fusarium oxysporum and Penicillium chrysogenum. Based on its morphological features, an insect found on some artefacts was identified as the xylophagous beetle Nicobium castaneum (Anobiidae). The influence of wood type and environmental conditions on the diversity of microorganisms was discussed.     

Impregnated wooden claddings and the influence of nanoparticles on the weathering performance

Abstract

This work was an investigation of the effect of nanoparticles on the durability of wood specimens exposed to artificial weathering. TiO₂ and clay nanoparticles were mixed with preservative (Wolmanit CX-8) for improving the durability of Norway spruce (Picea abies). Impregnated and untreated specimens were subjected to Atlas Solar Simulator accelerated ageing test chamber for solar radiation and water spray exposure. The effectiveness of the treatment against colour and chemical changes was investigated using CIEL*a*b* colour measurements system and Fourier transform infrared analysis. The present study showed that the wood specimens that had been treated with preservatives containing nanoparticles were slightly more stable against artificial ageing than both untreated specimens and specimens treated with preservative alone.     

Methodology to assess both the efficacy and ecotoxicology of preservative-treated and modified wood

? Wood used in outdoor conditions out of ground contact is susceptible to weathering, inducing both fungal decay and leaching of components to the environment.

? This paper presents a methodology to determine these two parameters for untreated, preservative-treated and modified wood. Therefore, the wood was first leached and subsequently exposed to fungal decay of the most prominent wood-rotting fungi. The crustacean Daphnia magna was exposed to the leachates to provide information on their impact on the environment.

? Combining both parameters reveals that preservative-treated wood and modified wood are capable of protecting the wood adequately for application under use class 3 conditions without posing a threat to the environment.

? This proves the suitability of the concept of combining efficacy and ecotoxicology for the evaluation of new types of wood treatments.

     

Mycorrhizal status of some fungi fruiting beneath indigenous trees in Burkina Faso

During the rainy season, putative ectomycorrhizal fungi were observed under three species of Caesalpinioideae Afzelia africana Sm., Isoberlinia doka Craib. and Stapf. and Isoberlinia dalziellii Craib. and Stapf., one species of Dipterocarpaceae Monotes kerstingii Gilg. and two species of Euphorbiaceae Uapaca guineensis Müll. Arg. and Uapaca somon Aub. and Lean. The fungi belong to the orders of Agaricales, Aphyllophorales, Boletales, Cantharellales, Gautieriales, Hymenogastrales, Russulales and Sclerodermatales. Some of these fungal species e.g. Lactarius gymnocarpus Heim., Cantharellus pseudofriesii Heinem., Scleroderma dictyosporum Pat., Scleroderma verrucosum Pers., Scleroderma sp2 and Russula sp1, are common to the tropical tree families known to form ectomycorrhizas. A few species of these fungi e.g. Amanita hemibapha (Berk. and Br.) Sacc., Inocybe sp1, Boletellus sp3, Lactarius sp2 and Xerocomus subspinulosus Heinem., are observed only under mycorrhizal trees belonging to the group of Caesalpinioideae legumes. However, seven fungal species Coltricia cinnamomea (Pers.) Murr., Boletellus sp5, Austrogautiera sp. (hypogeous), Lactarius sp1, Russula annulata Heim., Russula sp2 and Scleroderma sp1 seem more specific to the Uapaca species. In all, twenty-seven putative ectomycorrhizal fungi were recovered and only five fungal species were isolated from sporocarps and maintained in pure culture. Four Scleroderma species were confirmed as mycorrhizal fungi on A. africana, Isoberlinia spp. and two East African trees, Brachystegia speciformis Benth. and Afzelia quanzensis Welw. The two Uapaca species, B. speciformis and M. kerstingii possess both arbuscular mycorrhizas and ectomycorrhizas.     

Evaluation of thermally modified beech and spruce wood and their properties by FT-NIR spectroscopy

Quality assessment of thermally modified spruce (Picea abies (L.) Karst) and beech (Fagus sylvatica L.) wood and of the corresponding reference samples was carried out by means of non-destructive FT-NIR spectroscopic measurements and PLS regression. Oven-dry and basic density as well as MOE and MOR determined by 3-point bending tests were evaluated. The focus was put on specimens produced from material that had been thermally modified in an industrial scale kiln. Modelling results range from poor to very good. The results of the spectra taken from the spruce samples resulted in better prediction results than the spectra of the beech samples. This could be due to different proveniences or variation in the industrial modification process. The results indicate that FT-NIR surface measurements of sound thermally modified wood samples could be applied to evaluate several characteristics before and after the modification process. The method could be used for screening during pre-sorting of thermally modified wood.     

Biological performance,water absorption,and swelling of wood treated with nano-particles combined with the application of Paraloid B72<Superscript>®</Superscript>

We evaluated fungal decay and mold resistance, leaching, and water absorption of nano-compounds and Paraloid B72^® (PB72) in treated wood specimens to develop new methods of consolidation by combining nano-particles and consolidants. Scots pine wood specimens were treated with dispersions of nano-CuO, nano-ZnO, nano-B₂O₃, nano-TiO₂, and nano-CeO₂. PB72 treatments of nano-particle-treated wood specimens were then carried out by either vacuum or immersion for 24 h. Previously, decayed wood specimens were also consolidated with the nano-compounds and PB72. PB72 treatments reduced element release from treated wood specimens. Nearly all nano-compounds + PB72 treatments increased the biological performance of treated wood specimens against decay fungi tested. PB72-only treated wood specimens had the highest weight losses in decay tests. No improvements were obtained in mold resistance tests when the nano-compounds and PB72 were combined. In nano-compound-only treatments, unleached specimens showed slightly lower water absorption values compared to untreated control specimens. Incorporation of PB72 into nano-compound-treated wood specimens resulted in considerably lower water absorption and volumetric swell. In previously decayed specimens treated with the nano-compounds and PB72 solution, water absorption after 2-h immersion declined compared to control specimens.     

Influence of the thermo-hydro-mechanical treatments of wood on the performance against wood-degrading fungi

Hybrid poplar (Populus deltoides × Populus trichocarpa) and Douglas-fir (Pseudotsuga menziesii) wood specimens were densified with three variations of thermo-hydro-mechanical (THM) treatment. The THM treatments differed in the steam environment, including transient steam (TS), saturated steam (SS), and saturated steam with 1-min post–heat treatment at 200 °C (SS+PHT). The bending properties, FTIR spectra, and colour of the THM wood specimens were studied before and after exposure to two different wood decay fungi, brown rot Gloeophyllum trabeum, and white rot Trametes versicolor. The results showed that the performance of densified hybrid poplar wood was considerably poorer than the performance of Douglas-fir heartwood. The FTIR spectra measurements did not show changes in the densified hybrid poplar wood, while some changes were evident in densified Douglas-fir specimens. After fungal degradation, the most prominent changes were observed on the SS+PHT specimens. Colour is one of the most important parameter predominantly influenced by the wood species and the intensity of the densification process for both wood species, while after fungal exposure, the colour of all densified Douglas-fir specimens obtained more or less the same appearance, and densified hybrid poplar specimens resulted in lighter colour tones, indicating that the pattern of degradation of the densified and non-densified specimens are similar. The 3-point bending test results determined that the THM treatment significantly increased the modulus of rupture (MOR) and modulus of elasticity (MOE) of the densified wood specimens, while fungal exposure decreased the MOE and MOR in hybrid poplar and Douglas-fir specimens.