Measurements of fungal wood decay on Scots pine and beech by means of X-ray microdensitometry

In this work, we present a fast and promising method to evaluate the natural durability of wood based on X-ray microdensitometry. Tested on beech and Scots pine wood samples, our findings show that this methodology and the traditional EN standards methodology based on mass loss are strongly correlated. X-ray methodology is less time consuming (we can detect the effectiveness of the attack within 5–6 weeks) and less expensive (very cheap plastic Petri dishes instead of the expensive glass Kolle flasks); moreover, the proposed method allows to thoroughly examine the phases and the kinetics of the fungal attack, and to investigate the spatial repartition of the attack within the samples due to the low thickness of the sample.     

Influence of wood moisture content and wood temperature on fungal decay in the field: observations in different micro-climates

In this study, Scots pine sapwood (Pinus sylvestris L.) and Douglas fir heartwood (Pseudotsuga menziesii Franco) specimens were exposed in double layer field trials at four different exposure sites and under different exposure conditions (in total ten test sets). The material climate of wood in terms of wood moisture content (MC) and wood temperature was automatically monitored over a period of 6 years and compared with the progress of decay. The aim of this study was to highlight the interrelationship between microclimate, material climate, and decay as a basis for the establishment of dose-response functions to be used for service life prediction of wood and wood-based products. Differences in resulting decay dynamics between the test sites as well as between the different types of exposure were quantified and discussed with respect to corresponding microclimatic and material climatic conditions. The time between the beginning of exposure and the first occurrence of visible decay varied between the sites and influenced the total decay development. The fundamental importance of direct decay factors, such as MC and wood temperature, were underlined and basic requirements for establishing dose-response-functions to be used in service life prediction models were derived.     

Immunological detection of decay in wood

Summary An enzyme-linked immunosorbent assay (ELISA) was used to detect and quantify Postia placenta (Fr.) M. Lars. et Lomb. in decaying wood. The fungus was detected as early as ten days after inoculation suggesting that ELISA may be effective in detecting early incipient decay. Decay-induced weight loss in P. placenta decayed spruce blocks was correlated with the absorbance values obtained in the ELISA reaction.     

The bacterial factor in wood decay

Summary Bacteria and actinomycetes are probably the most common wood-inhabiting microorganisms, certainly they are the most adaptable in terms of environmental influences. When considering them as factors in wood decay they may be roughly classified into four groups for convenience and ease of comparison. 1. Those bacteria which affect the permeability to liquids of wood but have no significant effect on strength properties.—2. Those types which attack the wood structure.—3. Bacteria which only function as integral members of the total microflora and are associated in the ultimate breakdown of the wood.—4. The passive colonizers which have no effect upon the wood at all but which have a marked influence on the remainder of the population by their antagonistic activities.—As bacteria and actinomycetes cetes have previously been held to be of minor importance in the field of wood degradation, these microorganisms are discussed in terms of the above four groups in an attempt to bring out their true importance.     

Enzymatic degradation of cellulose,cellulose derivatives and hemicelluloses in relation to the fungal decay of wood

Summary Cellulases and hemicellulases (mannanase and xylanase) from culture filtrates of various fungi, including a brown rot fungus, Polyporus schweinitzii and a soft rot fungus, Chaetomium globosum, have been isolated and characterized. Investigations of their molecular weights, pH- and temperature optima and stabilities indicate that hydrolases of the wood destroying fungi are very similar to one another and to hydrolases from various other plant organisms. Substrate specificities and the effect of substituents on the natural substrates have also been investigated. Routine tests for mannanase and xylanase were carried out with model substrates (mannan from Tubera salep, xylan from wheat straw), but preliminary tests with complex hemicelluloses isolated from wood showed that these too could be broken down to monoor oligosaccharides. The results presented are discussed in relation to possible roles of the various enzymes in vivo.Paper presented at the Int. Wood Chemistry Symposium, Seattle, 3. IX. 1969.With support of the Deutsche Forschungsgemeinschaft.     

A rapid method for screening potential biological control agents of wood decay

Sixteen isolates of microfungi, obtained from freshly felled pine, were screened for inhibitory activity on a number of wood-decay basidiomycetes. The screening procedure employed a bi-layer test which involved growing the potential biocontrol isolates on either agar medium or irradiated pine discs. The influence that the two different substrata had on subsequent inhibition of decay fungi may have important implications for the screening of isolates for biocontrol activity. The use of such techniques for screening biocontrol agents is discussed.     

Effects of polyvinyl alcohol on leachability and efficacy of boron wood preservatives against fungal decay and termite attack

In this study, the use of polyvinyl alcohol (PVA) as boron fixative agent was investigated. Two levels of PVA (2.5 and 4%) were evaluated with disodium octaborate tetrahydrate (DOT) at three concentrations (1, 2 and 4% boric acid equivalent (BAE)) using a double vacuum impregnation process on Scots pine sapwood specimens. Leaching was performed according to a laboratory leaching procedure. Boron analysis using atomic absorption spectrometer showed a significant reduction in boron leachability for the samples treated with both concentrations of PVA when compared to the stand-alone boron treatment leading to boron retentions capable of preventing wood biological degradations. Decay resistance of the leached specimens was evaluated using the brown rot fungus Poria placenta. Even if complete protection was not fully achieved, an improvement in decay resistance was observed for the samples treated with DOT in presence of PVA. This leak of efficacy was attributed to a decrease in the biological activity of the complexed boron against fungi. Durability of treated wood against termite attack, evaluated using Reticulitermes santonensis, indicated a significant enhancement for the samples treated in presence of the fixative agent compared to the pure boron treatment.     

Uptake of metal toxicants by fungal hyphae colonising CCA-impregnated wood

Summary Electronmicroscope microanalyser (EMMA-4) analysis of Poria monticola colonising pine wood treated with a copper-chrome-arsenate preservative has shown that the fungus removes copper chromium and arsenic from the wood and stores these elements within the hyphae to the extent of 3–4% on a mycelial dry weight basis. The total uptake of each element varies from spot to spot examined (each 0.2 m dia.) but is on an average correlated with the concentration of the element in the impregnated wood. It appears that the rate of copper uptake is higher than of arsenic uptake.     

木材天然耐腐性室内试验标准方法的研究

采用三种培养基、两种白腐菌、两种褐腐菌对马尾松、毛白杨的天然耐腐性进行了试验。结果表明:砂子锯屑培养基法对采绒革盖菌(Corjolus versicolor)和绵腐卧孔菌(Poiraplacenta)的生长较快,对木材腐朽力,即重量损失较明显。     

Mechanical behaviour of Eucalyptus wood modified by heat

Summary  Eucalyptus wood (Blue gum) shows very high mechanical performances, presents very few knots and gives strong glued joints, reasons that justify its interest for structural uses, carpentry and furniture components or even building construction. The inconveniences of this species are its slow and difficult drying process and its low dimensional stability – with very high swelling and shrinkage coefficients. The drying process has been studied at INETI and the problem revealed to be solved with appropriate drying schedules and the stresses released by a steam treatment. Heat treatment of Eucalyptus wood has been identified as one of the most promising techniques to increase its dimensional stability. Studies in this area still proceed. This paper presents some test results that show the influence of heat treatment in the strength properties of this wood, namely the bending modulus of elasticity and tensile strength perpendicular to grain, in addition to the explanation of dimensional stability evaluation and some results of dimensional stability treatments. Received 15 June 1998     

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     

Evaluation of a modified Iosipescu shear test method for determining the shear properties of clear wood

A modified Iosipescu shear test method is proposed as an alternative for measuring the shear properties of clear wood. The method adopts four-point asymmetric loading procedure in the Iosipescu shear test but with the loading positions shifted to the neutral axis of the specimen. The original V-notched specimen is replaced by a combination of polyvinyl chloride blocks at two ends and a bow-tie-shaped wood specimen in the middle to provide a better stress pattern at failure. The measured shear strength and shear moduli are compared with results from compression test and off-axis tension test. Finite element analysis is also carried out to study the stress distribution in the wood specimen. Results show that the new shear test setup can provide close-to pure shear stress state in the specimen yielding better estimates of the shear properties of wood. The shear strength obtained by the new test setup is slightly lower than that from the off-axis tensile test which is probably due to the relatively thick specimen chosen in this study.     

A non-destructive approach for assessing decay in preservative treated wood

This study investigated the suitability of the non-destructive vibration-impulse excitation technique to assess the attack of preservative-treated wood in contact with the ground. Small stakes (10×5×100 mm³) of treated and untreated Scots pine sapwood were exposed to decay in laboratory-scale terrestrial ecosystems. Different soils were used to prove the influence of different types of wood destroying micro-organisms. Wood decay was monitored periodically for one year by determining mass losses and changes in dynamic modulus of elasticity. The results show a large variability in resistance against attacking fungi, depending on wood preservative and soil type. The non-destructive approach using the dynamic modulus of elasticity proved to be a good and sensitive tool for assessing the attack of stakes in laboratory soil testing.     

Sorption of copper and lead by citric acid modified wood

The sorption characteristics of citric acid modified wood to remove copper and lead ions from aqueous solution under batch conditions have been investigated. Sorption was pH dependent with increasing uptake at higher pH values. The kinetics of sorption for both ions was rapid with 90% sorption taking place within the first 60 min regardless of its initial concentration. Sorption can be explained by a second-order kinetics model from which the rate constant, the equilibrium sorption capacity and the initial rate were calculated. From these parameters, the predictive models for Cu and Pb sorbed (q _t) in time t and at an initial concentration (C _o) are given by q _t=C _o t[0.31C _o–2.29+(0.04C _o+5.19)t] and q _t=C _o t/[0.06C _o–6.59+(0.01C _o+4.48)t] for Cu and Pb, respectively. Using these models the predicted and experimental uptakes of Cu and Pb were compared and discussed. Maximum sorption capacities of modified wood under present experimental conditions were 23.70 and 82.64 mg/g for Cu and Pb, respectively. However, for untreated wood the corresponding values were 2.56 and 7.71 mg/g indicating a tenfold increase in sorption upon citric acid modification. Ethylene diamine tetraacetic acid and nitrilotriacetic acid complexed with both ions render sorption less favorably. However, salicylic acid had little influence. In a binary system, Pb ions were more favorably sorbed than Cu ions which could be due to the larger ionic radius of the former ions.     

Classification of thermally modified wood by FT-NIR spectroscopy and SIMCA

Quality assessment of thermally modified wood has evolved as one of the major fields in the research on thermal modification of wood. This study investigates NIR spectroscopy in combination with the pattern recognition method of soft independent modeling of class analogies (SIMCA). Focus is put on identifying different treatment intensities of thermally modified samples of beech, ash, and Norway spruce. The results indicate that SIMCA classification based on NIR spectroscopy could be used for quality control of thermally modified wood. The method might be applicable for producers (pre-delivery checks) and customers (reception control). However, transfer from laboratory to industrial conditions needs further investigation.     

Molecular identification of decay fungi in the wood of urban trees

Trees are valuable for urban areas, however, are also susceptible to wood rot fungi. For accurate and fast assessment of the severity and evolution of decay in standing trees, a molecular technique was used to identify the causal agents of wood rot. Fruit bodies of wood decay fungi were collected from infected trees in various stands in Germany. Thirty-six species were identified by traditional methods. The DNA of fruit bodies was extracted, ITS-rDNA amplified by PCR, and ITS regions sequenced. Wood samples from infected urban trees were collected, the entire DNA extracted from affected wood parts, and fungal ITS amplified and sequenced. Fungal species were identified by comparing sequence data with the fruit body data. The technique enables an accurate and rapid identification of causal rot fungi in urban trees.     

Production and markets of modified wood in Russia

Understanding the state of market for modified wood as well as the forces that affect its future development will be essential for those seeking to enter the Russian market. Information on modified wood from websites of companies, research and development organisations, woodworking-oriented magazines and forums, and official Russian statistics were explored, and finally verified by personal contacts with experts. A number of modification methods have been either researched, developed or pre-commercialised during the past 15 years, but only few of them have been adopted by users. Mostly, the modification methods have been copied, further developed and commercialised from variations of thermal modification originally introduced in Western Europe. Modified wood products are still considered premium goods among Russian consumers. Political initiatives aim at increasing the share of wood in construction and renovation but also at import minimisation, which reduces the penetration of foreign producers into the markets. There are approximately 20 producers of thermally modified timber (TMT) with an overall annual capacity of 60,000–65,000 m³. The current annual market for TMT is estimated to be approximately €35–40 million. In contrast to the European mainstream end uses of TMT, there is also a market for massive and glued thermally modified logs in Russia.     

Water-repellent efficiency of thermally modified wood as affected by its permeability

This study shows how the air permeability of thermally modified wood contributes to its water-repellent efficiency. For this purpose, freshly cut boards of hornbeam(Carpinus betulus), poplar(Populus nigra), and heartwood of oak(Quercus castanifolia) were modified at a steam temperature of 180 °C for 3 h inside a Thermo Wood kiln.The porous structure, permeability, and water uptake of wood were affected differently by thermal modification,depending on the wood species. The creation of microcracks in the cell walls, due to collapsing of fiber cells,resulted in a noticeable increase in the permeability of hornbeam. Despite checking in the poplar wood structure,its permeability was negatively affected by thermal modification. In contrast to oak and poplar, a negative waterrepellent efficiency was observed for the modified hornbeam, caused by an increase in the permeability.     

Evaluation of decay resistance of wood products made from borax-impregnated wood and bonded with a formaldehyde-free cornstarch and tannin adhesive

? At present, the production of wood composites mainly relies on the petrochemical-based and formaldehyde-based adhesives such as phenol-formaldehyde (PF) resins and urea-formaldehyde (UF) resins, which are non-renewable and therefore ultimately limited in supply.

? This paper concerns the decay resistance of wood products bonded with a new, environment-friendly adhesive derived from abundant and renewable cornstarch and tannin. To improve the total resistance of the composite against both Coriolus versicolor and Coniophora puteana rot fungi, borax (di-sodium tetraborate) was added in proportions of 0.5%, 1% and 2% (w/w) to the cornstarch-tannin adhesives.

? The results show that increasing the concentration of borax in the adhesive decreased the mechanical properties of the composite. The best way to avoid this problem was to use wood impregnated with borax.

? Biodegradation studies were conducted on new composites, first without any treatment, followed by borax at 0.5% aqueous solution treatment. The results show that wood impregnated with borax, in the presence of tannin and sodium hydroxide in the adhesive improves the total resistance of the wood composite against both Coriolus versicolor and Coniophora puteana rot fungi.

     

Elastic constants for wood by an ultrasonic method

Summary Ultrasonic measurements were carried out on cubic specimens of six species (pine, spruce, douglas-fir, oak, beech, tulip-tree). An orthotropic model of wave propagation was used to interpret these measurements and compute estimates of the elastic compliances. In order to calculate the off-diagonal stiffness terms, velocities were computed on samples with faces at an angle to the principal directions. The elastic compliance matrix was calculated by inverting the stiffness matrix.We thank François Thiercelin, Centre National de Recherches Forestières Nancy, for useful suggestions and assistance in processing the data