Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2011
Abstract
No abstract has been registered
Abstract
Development of surface moulds and staining fungi on painted spruce panels with known origin and wood properties was investigated over a period of 4 years. Materials of Norway spruce (Picea abies) were sampled from two sites with high-productive forest on lowland in South-eastern Norway and two low-productive sites at higher altitudes and somewhat farther north. Claddings were processed from inner centreboards (mainly heartwood) and outer centerboards of both butt logs and second logs. A sub-sample of radially sawn claddings was compared with corresponding tangentially sawn claddings. Heartwood proportion, density, annual ring width, knot diameters and knot area were measured. All panels were coated with the same water-borne alkyd modified acrylic paint system. Most of the tangentially sawn claddings were coated on the side facing pith, but a sub-sample was coated on the opposite side for comparison. The specimens were exposed with 45˚ angle of inclination facing south in a field trial in Oslo from 2007 to 2011, and mould growth was evaluated visually according to EN 927-3. 7.7% of the specimens were rated as 2, 71.4% were rated as 3, 19.4% were rated as 4, and 1.5% were rated as 5. Outer boards were rated significantly higher than inner boards, while differences between origins were not significant. There was a tendency of decreased rating with increasing heartwood proportion, but the relationship was not significant. Nor was there any significant effect of annual ring with, density or knot properties. Neither the difference between radially and tangentially sawn claddings, nor the difference between specimens coated on the side facing pith was significant.
Abstract
Wood used in outside applications is susceptible to weathering and photo degradation, which often leads to surface discoloration, loss of brightness and surface deterioration. Research has shown that acetylated wood is more resistant against brown rot, white rot and soft rot, and more dimensionally stable than untreated wood. However, acetylated wood seems still to be disfigured by surface moulds and staining fungi. Samples of acetylated Southern Yellow pine at three different treatment levels; low, intermediate and high acetyl content were exposed at two test sites, Ås (Norway) and Bogesund (Sweden) against north and south from September 2010 until March/May 2011. Considerably more precipitation was recorded in Ås in the initial potential fungal growth phase than in Bogesund. As expected, untreated wood had higher mould ratings than acetylated wood. At Ås the tendency was that samples with low acetyl content had lower mould ratings than samples with higher acetyl content. This effect was not found in Bogesund. This may be due to considerably less precipitation in Bogesund compared to Ås. At Ås samples exposed against north tended to have higher mould ratings than panels exposed against south which could be due by less direct sun causing longer time of wetness and more ideal conditions for mould growth.
Abstract
Scots pine (Pinus sylvestris L.) is an important softwood species in Northern Europe and is frequently used as material for various wood protection systems. In Europe, EN 113 is the standard basidiomycete laboratory durability test method, using mass loss as evaluation criteria. In this paper quantitative real-time PCR (qPCR) and thermogravimetric analysis (TGA) was used to characterize colonization by basidiomycetes in Scots pine sapwood, but also to learn more about the EN 113 test. Two different wood sample sizes were tested. For Gloeophyllum trabeum the largest sample size gave the highest mass loss, while for the smallest samples Trametes versicolor gave the highest mass loss. As expected, fungal DNA content and mass loss in Scots pine sapwood samples decayed by G. trabeum became higher with increasing incubation time of 16 weeks. More unexpectedly, the T. versicolor DNA content in Scots pine sapwood samples was highest at the start of the incubation period and declined during the incubation period, while mass loss increased during the 28 week incubation period. The fungal colonization in the side and middle of EN 113 samples was tested. Highest DNA contents of G. trabeum were measured in the sides during 16 weeks of incubation. The T. versicolor DNA content was higher or similar in the side compared to the middle of the samples until week 20. For weeks 20 and 22 the DNA content was higher in the middle than in the sides, while for the remaining incubation period (weeks 24, 26 and 28) it was quite similar. TGA was shown to be a useful and fast method for chemical characterization of brown rot decayed wood, but cannot be used for white rot decayed wood. For T. versicolor moisture and fungal DNA explained most of the variation in mass loss, while for G. trabeum moisture explained most of the variation in mass loss.
Abstract
Wood exhibits a highly anisotropic mechanical behavior due to its heterogeneous microscopic structure and composition. Its microstructure is organized in a strictly hierarchical manner from a length scale of some nanometers, where the elementary constituents cellulose, hemicelluloses, lignin, and extractives are found, up to a length scale of some millimeters, where growth rings composed of earlywood and latewood are observed. To resolve the microscale origin of the mechanical response of the macro-homogeneous but micro-heterogeneous material wood, micromechanical modeling techniques were applied. They allow for prediction of clear wood stiffness (Hofstetter et al. 2005,2007, Bader et al. 2010a,b) from microstructural characteristics. Fungal decay causes changes in the wood microstructure, expressed by decomposition or degradation of its components (Côté 1965, Schwarze 2007). Consequently, macroscopic mechanical properties are decreasing (see e.g. Wilcox 1978). Thus, in the same manner as for clear wood, consideration of alterations of wood in a micromechanical model allows predicting changes in the macroscopic mechanical properties. This contribution covers results from an extensive experimental program, where changes in chemophysical properties and corresponding changes in the mechanical behavior were investigated. For this purpose, pine (Pinus sylvestris) sapwood samples were measured in the reference condition, as well as degraded by brown rot (G. loeophyllum trabeum) or white rot (Trametes. versicolor). Stiffness properties of the unaffected and the degraded material were not only measured in uniaxial tension tests in the longitudinal direction, but also in the three principal material directions by means of ultrasonic testing. The experiments revealed transversal stiffness properties to be much more sensitive to degradation than longitudinal stiffness properties. This is due to the degradation of the polymer matrix between the cellulose fibers, which has a strong effect on the transversal stiffness. On the contrary, longitudinal stiffness is mainly governed by cellulose, which is more stable with respect to degradation by fungi. Consequently, transversal stiffness properties or ratios of normal stiffness tensor components may constitute suitable durability indicators. Subsequently, simple micromechanical models, as well as a multiscale micromechanical model for wood stiffness, were applied for verification of hypotheses on degradation mechanisms and model validation.
Abstract
In 2005 an extensive test program including field tests was set up in order to obtain more data on the durability and long term performance of modified wood and semi-durable wood species. One of the main challenges for modified wood is to predict accurate service life time in UC3 (Use use class 3, above ground) and UC4 (use class 4, in soil or fresh water contact). So far, data from in-service conditions are rare, while several studies have evaluated the durability in lab or field test exposure. However, there is still a lack of studies comparing replicate modified wood products in both field and lab exposure. This study evaluates the efficacy of modified wood in AWPA E10, three different types of soil in lab (ENV 807), three test fields in-ground (EN 252) and two close to ground (horizontal double layer test) set-ups at two test sites. The test material includes furfurylated, acetylated and thermally modified wood in addition to reference treated and control samples. In laboratory, both furfurylated, acetylated and thermally modified pine (212ºC) performed well. The modified wood samples performed at the same level, or better, than the reference CC and CCA preservatives in retentions for UC4 applications. In the horizontal double layer test, five years is still too short time to be able to draw firm conclusions. However, in the most accelerated HDL set-up, all controls have failed or are moderately to severely decayed whereas most preservative treated, furfurylated and acetylated wood are sound or only slightly decayed. After 5 years of testing CCA-preserved wood performs better in-ground in field tests than in lab tests, whereas modified wood generally performs slightly poorer. Just like in the lab tests, however, acetylated wood performs equal to CCA-preserved wood in UC4. Furfurylated wood performs equal to or better than UC3 level preservative treated wood. Thermally modified wood actually performs much poorer than all preservative treated wood references. Finally, natural durability classification of the same treatment in different lab and field tests was surprisingly similar.
Authors
Gry AlfredsenAbstract
Modified wood can provide protection against a range of wood deteriorating organisms. Several hypotheses have been put forward for the mode of action against wood decaying fungi, including inhibition of action of specific enzymes, but they still need further testing. This paper summarizes results from a project focusing on molecular studies of fungal colonization in modified wood. The focus has been on furfurylated wood, but also thermally modified and acetylated wood has been studied. Among the main finding was that wood modifications have an effect on the exploitation face of both brown and white rot colonization, but not on the exploration face. As already reported in a range of papers wood modification effects the wood moisture content, and this was confirmed within this project. New information was gathered about the effect on gene expression. Even before any mass loss was detected, differences in gene expression were measured. [...]
Abstract
Brown rot is the most common and destructive type of fungal decay for wood in service. These fungi depolymerize preferentially the structural carbohydrates, cellulose and hemicellulose in the cell wall leaving oxidized lignin behind. Modified wood can provide protection against a variety of wood deteriorating organisms, including decay fungi. However, there is still little known about the mode of function of the different wood modifications concerning the decay resistance. The biochemical mechanisms and gene products induced in brown rot during growth in modified wood are poorly understood. In this paper the data collected from mass loss studies and qPCR and qRT-PCR were used for profiling growth dynamics and gene expression of the brown rot fungus Postia placenta in different wood substrates through different stages of decay. Pinus sylvestris (L.) sapwood was used for the following treatments and modifications: chromated copper arsenate CCA (0.67%), furfurylation (WPG 37), thermal modification (D212) and acetylation (WPG 23). Untreated Pinus sylvestris (L.) sapwood was used as control. Samples were taken at different time intervals from 2 to 26 weeks. The highest mass loss and the highest fungal DNA content were found in the control samples while acetylated wood had the lowest mass loss and fungal DNA content. These results reflect a close relation of mass loss and fungal DNA content, both reflecting the amount of Postia placenta decaying the samples. Generally, expression of the investigated genes was highest in CCA treated wood. In the beginning of the incubation of all treated wood samples, the genes coding for oxidative metabolic activity had higher expression levels than the untreated control. In the end of the incubation most of these genes were less expressed than in the untreated control. The genes used for carbohydrate metabolism and the alcohol oxidase showed a significant decrease after 14 weeks of incubation. At the same time an increase in gene expression of an enzyme putative involved in lignin decomposition was detected.
Abstract
Some of the most common Norwegian wood species were tested in a Double layer test in South East Norway. After eight years of exposure the highest decay rating (≥3) was found in Scots pine sapwood, Norway spruce, alder, birch and aspen. Two wood types had decay rate ≤1: Scots pine heartwood and cedar. Wood moisture was logged and compared with precipitation during a two month period the second year of exposure. Scots pine sapwood had higher wood moisture content than Norway spruce, and a good correlation was found between precipitation and wood moisture content. When comparing similar materials exposed at three different geographical locations in Southern Norway, the samples exposed in Bergen had higher decay rating than samples exposed at Ås and Oslo.
Abstract
Moisture is often recognised as a key factor regarding the long time performance of wooden products, and one of the main challenges for timber products is to predict accurate service life in use class 3 (not covered above ground) and use class 4 (in soil or fresh water contact). A range of durability classification studies have been performed both in field and laboratory. But for several wood species information regarding the durability in use class 3 is lacking. Also, there is still a lack of studies comparing replicate wood products in different field exposure situations. This study evaluates the natural durability of different North European wood species in two different climates and in two different use classes. The wood species were compared with imported species and two preservative treatments. The overall picture shows a higher decay rating for wood species tested in ground contact compared with the results from the above ground “Double layer tests”. Moreover, the woods tested in Western Norway are more decayed than those tested in Eastern Norway. These findings can be explained by higher decay risk in use class 4 than in use class 3, and higher decay risk in a humid climate (Western Norway) than in a dry climate (Eastern Norway). The results indicate similar ranking of the durability of the wood species regardless of the environment they have been exposed to. The results from a linear regression show that MOE-loss of the mini-stakes after three years describes 70 % of the variation in decay rating of the “Double layer” stakes after six years exposure in Western Norway. This result strongly indicates that MOE-loss can be a prospective tool for rapid field testing of natural durability of wood.