Verfahren der zerstörungsfreien Holzprüfung—Entwicklungstendenzen in Nordamerika und Folgerungen für die Anwendung in Mitteleuropa

Acoustic-Emission (AE) and Acousto-Ultrasonics (AU) are techniques both used for determing the internal structure of wood and wood based materials. Up to now the important applications are the recognition and localization of internal wood properties and defects including decay; strength tests; monitoring and controlling of drying, glue-line curing, sawing process and sharpness of sawing tools; and the effects of long time load on wooden structural members. The recent development in the field of non-destructive evaluation by acoustic methods in North America will also influence and accelerate the development in this field in Europe.     

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.     

Effect of heat treatment intensity on wood chemical composition and decay durability of Pinus patula

Heat treatment is an effective method to improve biological resistance of low natural durability wood species. The aim of this study was to enhance the decay resistance of Pinus patula, an African low natural durability softwood species, via wood thermal modification technique. Heat treatment was performed on wood specimens under inert conditions at different heat treatment intensities to reach mass losses of 5, 10 and 15%. Heat treated specimens were exposed to fungal decay using the brown rot fungus Poria placenta. The wood chemical and elemental composition was determined as well as extractives toxicity before and after wood thermal modification to understand the reasons of durability improvement. The treated specimens exhibited a significant increase in their durability against wood decay in line with the severity of the treatment. Wood holocellulose was found to be distinctly more sensitive to the heating process than the lignin constituent. In addition, obvious correlations were observed between weight losses recorded after fungal exposure and both holocellulose decrease and lignin ratio increase. The same correlations were observed with the elemental composition changes allowing using the observed differences for predicting of wood durability conferred by heat treatment. Furthermore, no significant differences were observed between the toxicity of Pinus patula wood extractives before and after its thermal modification.     

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.     

Auftreten und Ausbreitung von Hallimasch in Beregnungspoltern

Armillaria mellea s.l. causes peripheral decay in the sapwood of Norway spruce and silver fir timber stored under water sprinkling. Growth and decay patterns are described for a large number of stacks as well as for laboratory experiments. Water sprinkling as a means of economic wood preservation is not questioned. Some decay, however, must be taken into account when storing wood for three years or more.     

Experimental verification of an orthotropic finite element model for numerical simulations of ultrasonic testing of wood poles

Ultrasonic testing is a non-destructive and non-invasive method which has been used for internal condition assessment of wood poles in electric transmission and distribution lines. The reliability of this method of evaluation relies on a good understanding of propagation of ultrasonic waves in wood. However, a full-waveform analysis in ultrasonic testing is rarely performed in practice because of difficulties in establishing realistic values for the elastic parameters, modeling the material damping and characterizing the dynamic response of an ultrasonic transmitter. In this paper, a calibrated orthotropic finite element model for numerical simulations of ultrasonic testing of a sound red pine pole is presented. In the calibrated model, the dynamic modulus of elasticity in the radial and tangential directions, Poisson’s ratio and damping ratios are estimated from ultrasonic testing; whereas the dynamic modulus of elasticity in the longitudinal direction is estimated from transverse-vibration testing. The measured response of an ultrasonic transmitter to a one-cycle sinusoidal pulse of 50 kHz is used as dynamic excitation and introduced in the numerical model as displacement-time history. Results of the first arrival of compression waves and the frequency response magnitude computed at three receiver locations are in good agreement with the obtained ones from ultrasonic testing. The calibrated orthotropic finite element model will be used for a better understanding of propagation of surface and compression waves in ultrasonic testing for the detection of early stages of decay in wood poles.     

Correlation between brown rot decay and Pilodyn measurements

Assessment of brown rot decay is one of the most important issues within remedial treatment of attacked wood constructions. Pilodyn is a well-established tool for the assessment of density of several commercially important plantation species, therefore the authors were interested in its suitability to evaluate rate of decay as well. The Pilodyn measurements performed on Norway spruce wood exposed to several brown rot fungi clearly indicate correlations between needle penetration and mass loss.     

Resistance of European and hybrid aspen wood against two brown-rot fungi

The decay resistance of European (Populus tremula L.) and hybrid (P. tremula x tremuloides) aspen wood against brown-rot fungi was investigated after three different treatments, i.e. conventional drying, press drying and heat treatment. For both aspen species, the mass loss after exposure to Gloeophyllum trabeum was higher than after exposure to Coniophora puteana, regardless of the wood treatment. Conventionally and press dried aspen wood had similar mass losses. However, heat treatment appears to be an effective method to improve the decay resistance of aspen wood, reducing the mass loss by about 30% compared with conventional and press drying. As a function of mass loss, wood exposed to G. trabeum had lower moisture content than wood exposed to C. puteana. This is thought to be due to differences in the degradation pattern between the two brown-rot fungi. On the other hand, European aspen appears to be slightly more resistant to decay than hybrid aspen.     

The protective effect of 23 paint systems on wood against attack by decay fungi

A laboratory method was used to evaluate the protective effect of 23 different paint systems on Norway spruce wood against decay fungi. Weather-o-meter treated and non-treated paint films on wood were tested. Results were compared to those obtained on unprotected spruce wood. Finishes included in the study were primer oils, solvent-borne alkyd paints, water-borne acrylic paints, water-borne mixed alkyd/acrylic paints, alkyd emulsions and stains in different paint system combinations with one to four coats. The growth of the decay fungi of the paint films was estimated by visual inspection. After 5 months of incubation, microbial activity in the wood below the paint films was evaluated. Growth of the fungi in the wood below the paint film was measured by an indirect chemical method for estimation of microbial activity. Paint systems including a solvent-borne alkyd coat usually had a good performance when tested without prior weathering but degenerated most during the weathering process as judged from the altered water absorption and fungal growth rate. Paint systems including a treatment with a primer oil exhibited low moisture uptake also after weathering. A clear effect of fungicide additions was also seen. A water-borne penetrating oil with an acrylic top coat exhibited no visual surface attack before weathering, and low microbial activity in wood for all decay fungi before and after weathering.     

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.     

Mikrobiologische Untersuchungen an frischem und gelagertem Holz von Bäumen aus Waldschadensgebieten und Prüfung der Pilzresistenz des frischen Holzes

Comparative microbiological investigations on the fresh wood of healthy and diseased Norway spruce trees show an increased occurrence of fungi and bacteria in the diseased trees. However, microorganisms in the wood do not seem to be a causal factor for the spruce decline; they are secondary pathogens which add further stresses to the wakened trees. Experiments on the storage of spruce logs with bark for 6 to 7 months yield a nearly equal attack by staining fungi of the wood of diseased trees as compared to the healthy ones. Decay experiments in Kolle flasks with wood samples of spruce and European beech trees do not show a different decay susceptibility towards wood destroying fungi between the wood of healthy and diseased trees.     

Natural decay resistance of LVL made of veneers from durable and non-durable wood species

Laminated veneer lumber (LVL) was laboratory manufactured using veneers from decay and non decay resistant species in order to evaluate changes in the durability as a result of the LVL manufacturing process, and to test if the mixing of decay resistant species and non decay resistant species can improve durability. Laboratory soil block test and field test were conducted. The durability of solid wood was comparable to that of LVL made using the same species. For LVL made using veneer from durable and non-durable wood species, durability was improved when two faces and one core veneers were from decay resistant species.     

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.     

Technische und wirtschaftliche Gesichtspunkte bei der Bereitstellung der forstlichen Biomasse

The arrcars in thinning, the growing demand, for raw wood by the wood working industry and the increase in raw material prices on the international markets are the reasons why work science will have to develop new methods of yield which allow wood mass above the ground to be utilized to a greater degree. In this paper, several methods of processing and the machines applied presently in Central Europe and Scandinavia are described. The suitability of these methods and machines, their efficiency and various economic aspects are dealt with and evaluated in summary.     

Aussichten und Handlungsbedarf des Holzleimbaus im Hinblick auf den EG-Binnenmarkt 1992

This paper contains some statements on the consequences of the establishment of the Common Market concerning the future standards for wood grading up to testing the final products. The actual situation of laminated wood production in Europe is described and a forecast of future developments especially within the Federal Republic of Germany attempted. The efforts, contributions and also the opportunities missed by the German wood working industry as well as related problems are discussed.     

Testing the durability of timber above ground: evaluation of different test methods

A large number of studies on the decay performance of wood in outdoor exposure have been conducted in the past. However, no test methodology for wooden components exposed above ground reflecting the variety of different loads has been established so far. Many test protocols were modified in different ways throughout the years and results were often published only in an encoded or incomplete way. This makes it difficult to obtain comparable results to work on a comprehensive above-ground test methodology. Therefore, a comparative study on moisture performance and the resulting decay response was conducted. Five different wood species were exposed according to 24 different test methods representing a wide range of different exposure situations including in- and on-ground exposure. After three years of exposure the moisture load as well as decay development differed between the test methods and tested materials. Different parameters were identified influencing the moisture performance of wood in the respective test set-ups and finally an attempt was made to set up a test methodology providing sets of test methods for differently severe applications within use class 3.1 and 3.2 as defined in the European standard EN 335 (2013).     

Moisture content (MC) and multinuclear magnetic resonance imaging (MRI) study of water absorption effect on wood treated with aminofunctional silane

The aim of this study was to determine susceptibility of aminoethyl aminopropyl trimethoxysilane (AEAPTMOS)-treated wood to absorption of liquid water. Absorbability was analysed by measuring absolute moisture content of wood and by MRI. These analyses were based on the results of previous studies on resistance against decay fungi in case of wood treated with the same chemical compound. In their previous studies the authors found that AEAPTMOS exhibits enhanced hydrophobic properties and thus increased resistance to the action of specific abiotic and biotic factors. The advantageous fungicidal properties of wood treatment systems indicate that AEAPTMOS may be considered as an environmentally friendly solution, being an alternative to conventional biocidal agents. Results indicate that this method may be used in laboratory analyses assessing the relative amount of water uptake through the wood surface.     

Effects of chemical modification on the mechanical properties of wood

Chemical modification has been recognized as an efficient strategy for dimensionally stabilizing wood and protecting it from environmental damage, such as deterioration due to weathering and fungal decay during the service period. Studies reported in the literature mainly concern the establishment of workable modification techniques, testing methodologies, and assessment of the durability of modified wood. The development of wood modification techniques has recently been reviewed; limited information is however given on the effects of chemical modification on the mechanical properties of wood that are of importance to it as an engineering material. This paper reviews the effects of wood modification, typically by heat treatments and impregnation with low molecular weight resins, reactive monomers, or hot melting paraffins on the mechanical properties of wood. The modifying variables associated with mechanical properties of wood such as wood species, treating temperature and time, catalyst, type of solvent, weight percent gain, and molecular structures of the modifying agent were analysed and the results interpreted. The reasons for changes in the mechanical properties of wood are discussed.     

天然生物矿化木材中硅及其他元素含量

很多种木材细胞中都含有二氧化硅、草酸钙、碳酸钙等无机晶体,这些无机物质在木材中起到了提高木材物理力学强度,克服木材自身缺点（如易腐、易燃、尺寸不稳定等）的作用,在结构上这些无机物质与木材本身构成了一种天然复合材料,即木材-无机质复合材料。生物矿化研究以活立木为对象,为木材生物改性和新材料开发提供了新思路。要实现木材-无机质生物矿化复合材料的人工模拟,关键是研究木材中无机硅等的含量情况以及生物矿化所形成的木材-无机质复合材料的形成机理。本文主要对生物矿化木材中矿物质的含量情况进行探讨,并提出今后的研究方向。