VOLUME 54, ISSUE 3/2013

Robinia (Robinia pseudoacacia L.) is an important wood species for the Hungarian woodworking industry. Beside so called conventional varieties existing since decades new varieties with specific properties (e. g. honey production, fuel wood, and fodder). As a result of the cooperative work of private forest owners and breeder new fast growing Robinia varieties have been selected and planted at different sites. Physical, mechanical and anatomical properties of wood material from 35 site/variety combinations were investigated, with the aim to show possible utilizations. The performed investigations proved, that in spite of the fast growing (annual rings even wider than 30 mm) the basic characteristics of wood did not fall behind the properties of conventional Robinia wood.

Using the high-frequency densitometry, the local differences in density within an annual ring of wood can be analysed. An example of using this method for the analysis of changes in density as a result of thermal modification is presented for oak. A comparison of the initial density before and the density after the thermal treatment, the study was carried out on the same sample. It can be summarized that the measurement of the local change in density in wood is possible, and the density of the early wood is reduced as a result of thermal treatment, significantly more compared to that of the late wood.

The influence of density and panel structure on the modulus of rapture (MOR) and modulus of elasticity (MOE) is presented and discussed. Three-layered as well as single-layered panels of core layer and surface layer material were produced on laboratory scale and tested for MOR, MOE and internal bond (IB). The MOE of single-layered panels made of core layer and surface layer material, respectively, are comparable. A three-layered panel with the same mean density shows a higher MOE due to the specific raw density with surface layers of higher density. The MOR of three-layered cementbonded particleboards is positively influenced by the higher MOR of the core layer material. The goal of lowering the raw density of cement-bonded particleboards with a given recipe, technology and panel-structure is limited. With an investigation of the cement phases and the degree of hydration in correlation to recipe, technology and panel structure, potential may definitely be seen. Preliminary tests show, that only 60-70 % of the used cement hydratises to cement stone. Considering the displayed interrelation, the reduction of the raw density is to be expected with increasing efficiency of the cement.

Bark from spruce (Picea abies Karst.), pine (Pinus sylvestris L.), beech (Fagus sylvatica L.) and oak (Quercus robur L.) were investigated with regard to a material utilization for three-layer particle boards bonded with urea formaldehyde resin. The results show that a proportionate usage of barks, especially from pine, spruce and oak, leads to considerably reduced formaldehyde emissions of the boards. With an amount of up to 30 % (by weight) spruce bark in the core layer, the physical and mechanical properties of the boards can furthermore be maintained.

Electric fields have been evaluated for the protection of wood against attack by wood-destroying fungi. We could show that a lowpulsed electric field (PLEOT) had an inhibiting effect on wood estroying fungi compared with the tested reference power sources alternating and direct current. The study examined the suitability of PLEOT for use in wood preservation and evaluated the use of different wood and fungi species, different wood dimensions, the use in ground contact, as well as the test setup in the laboratory and the installation of the technology in the field. Different wood species could be protected by means of PLEOT against degradation by white and brown rot. Additionally, the degradation of wood could be stopped after four weeks establishment of the fungi. The use of PLEOT in ground contact resulted in lower weight loss of PLEOT-protected samples compared with untreated samples.

The project was carried out in cooperation with the electric power company RWE for a period of four years. Within the project, failures of wooden utility poles were investigated with regard to the intensity of infestation at different locations of utility pole transmission lines. The investigated poles failed before expected minimum service life. The maximum service life of investigated poles was 15 years. Field tests at different locations were carried out to investigate the intensity of infestation caused by fungi and bacteria, which were established within the soil. Furthermore, premature failures of utility poles were investigated. The type of decay was evaluated as well as the copper content. The field tests have shown that the intensity of infestation is dependent on local conditions. In most cases, a higher rate of infestation was limited on specimens, which were close to the utility pole. The major part of investigated pole sections of premature failures was infested by brown rot fungi particularly copper tolerant fungi.

Currently the identification of the most dangerous dry rot fungus Serpula lacrymans can be performed by DNA analysis based on the conventional species-specific PCR. The Mykolabor Dresden has developed and validated a real-time PCR method, which has an improved diagnostic sensitivity, specificity and reliability in comparison to previously established conventional PCR detection of S. lacrymans.

In the course of a research project investigations on the indoor air quality of timber frame constructions have been conducted in Holzforschung Austria in Vienna. The aim of the project is to find ways to monitor VOC levels and to reduce VOC concentrations in indoor air of two full scale test rooms (30 m³ each). This aim should be reached by blocking, storing or ventilating of the VOC. One room was covered with OSB and the second one with OSB and additional gypsum plasterboard. The room covered with OSB showed higher VOC levels than the second room covered with OSB and additional gypsum plasterboard. Within the first two weeks the indoor air had reached average VOC levels. The additional gypsum plasterboard was able to retard VOC emissions from the OSB panels so that peaks in VOC levels showed up later and were lower than in the reference room. During the remaining time of the research project further material combinations are to be investigated in the test rooms.

Rising demand for biofuels leads to a necessary enhancement of raw material base. The intended use of wood alternatives requires a fuel-side adjustment. To test the thermo-chemical properties systematically blended pellets consisting of wood and miscanthus are produced. The mixed pellets are characterized regarding to the ash and volatile components. Ashes, produced in a rotary kiln at 550 °C, are examined with regard to their melting behaviour. Finally combustion tests are carried out in a laboratory fluidized bed reactor. A rising proportion of wood causes an improvement of the ash behaviour. Also a positive influence on the emissions is measured by the addition of wood. Substitution of wood by admixing of Miscanthus is possible.