JAHRGANG 46, AUSGABE 3/2005

Deutscher Text:

Strength properties of Norway Spruce were determined in the RT-plane. The experiments were accomplished with a special micro testing machine. The deformation properties were measured by a contactless optical procedure. For this reason digital images, taken in discrete steps during the test, were analysed for the determination of displacement and strain in the RT-plane of the specimens. The mechanical properties (strength, stiffness) were determined in dependency of the microstructure (latewood, early wood). The interpretation of the results shows a significant correlation of strength and stiffness from the wood structure and specimen dimension. Furthermore the large influence of several cell types and their different effects to the cell tissue were recognised.

The aim of the investigations described in the following was to determine the influences of the storing conditions on the formation of odour causing compounds in the pine wood. Round wood as well as wood chips stored under different conditions were included. The parameters temperature, material moisture and access of light and oxygen were varied. The investigations of the round woods showed very clear differences in the concentration of wood components both in the log cross section and in the log height. Among others the fatty acids of which odour causing organic compounds can originate, above all aldehydes, count to the wood components. Regarding the wood chips storage it was stated that in addition to the storage temperature and the wood chips moisture content above all the access of light and oxygen affects the formation of aldehydes.

TD: ln spite of the well known ecological relevance, clear felling takes place in the autochthonous dry forests of the Paraguayan Chaco to get farmland. Reasons for the inefficient wood utilization and forest management are missing knowledge about the technological wood properties, the workability, the potential uses and markets for the Chaco tree species. This was the reason, why wood anatomy, chemical composition and some physical as well as technological wood properties of the two relatively unknown tree species Prosopis kuntzei and Schinopsis cornuta were investigated. Possible timber utilizations are discussed for both tree species.

Since the properties of thermally treated wood have already been researched sufficiently, a short survey is to gain information about the materials' applicability for practical use. Therefore buildings put up or equipped with thermally modified timber have been evaluated, photographed and evaluated in regard to the material behaviour. The buildings haven't been compared to one another but separately evaluated due to specific structural criteria as well as different kinds of wood and various surface treatments. Thus, the article is seen to be the report of a survey concerning the application of thermally modified wood in Switzerland. Typical properties of thermally treated wood, as decreased hygroscopicity, enhanced durability against fungal decay and reduced mechanical strength, didn't carry weight as after several laboratory tests expected. The high anti-swell-efficiency of thermal treated wood proved clearly. Lowered equilibrium moisture could not be proved because there's no appropriate method for measuring the moisture content of built-in thermally treated wood. Due to the low age of viewed buildings there is no certain information concerning the durability.

During every single edge approach there is a significant contact between edge material and work piece material when peripheral milling of wood and wood based material. Under common rotation numbers this contact takes less than a millisecond and takes place in a thin layer which includes the edge material as well as the work piece material. Due to effecting motions and forces, due to the surface roughness of the involved materials and due to their inhomogeneity of properties inside of this interface mechanical vibrations, high temperatures and material abrading of both components are obtained called wear. The knowledge about the effecting mechanisms is the basement to develop innovative tools and procedures as well as to configure the existing in an optimal way.

By plasma-treatment with a dielectric barrier discharge (DBD) at atmospheric pressure and ambient air prior to a coating process wood and derived timber products can be conditioned in such a way, that coatings (paints, lacquers, glues) will be absorbed quicker and the levels of adhesion will increase. Thus, the fracture strength of laminated wood can be increased significantly and a reduction of the amount of glue required is feasible. Another conceivable application could be the partial abandonment of frequently used primers. Furthermore, the utilisation of new materials and material combinations will be possible. The traditional preservation by means of coating and impregnation can be optimised in durability and in function by the plasma-treatment. With the plasma-treatment the quality of wood and derived timber products is improved, thereby heightening competitiveness relative to other materials.

Electronic Speckle Pattern Interferometry (ESPI), a noncontacting method to measure deformation of mechanically strained specimens, is introduced by means of some wood- technological examples. It is shown that the method is suitable to obtain new detailed insight in a variety of mechanical problems, e.g. in adhesive bonding and in wood machining.

At the Institute of Wood Technology Dresden, a rapid method was developed which records the late defects of delamination and greying of surface materials directly on the unprocessed film. The influences of the chemical formulation components and the characteristic values (solids content, viscosity, density, pH-value, penetration time, molar ratio, molar mass distribution) of different UF impregnating resins, finishing varnishes, laboratory-produced decorative foils and edging materials as well as coated wood-based panels on the processing and usage properties of decorative foil and edging material for broad surface coating and wrapping were investigated. The reason for the delamination of the coating materials can be the penetration of components of the foil lacquer into the impregnation zone. The influence of the climate on the migration of the formulation components is of immense importance. From this it can be concluded that the balanced moisture and temperature balance of coating materials and carrier boards has a great influence on the later adhesion and product quality. The cause of greying of processed films is the reduction in the solubility of certain plasticizers as a result of progressive crosslinking of the reactive binder component.