VOLUME 50, ISSUE 4/2009

Squared timber and glued laminated timber GLT The project will show, that large dimension timber (LDT) from Norway spruce can be transformed into value added products for the market of construction timber, if the full potential of the technical properties of LDT is used to meet the technical requests set by the market. The new and extended requests for squared timber and GLT according to the German and European standards admit a sophisticated classification of those products. In front to this the quality of LDT differentiates from the butt to the top of the stem, over the cross section, by the grading method and by the sawing pattern. On the basis of more than 2900 experiments it was shown, that the whole width of properties of LDT is suitable to produce ambitious products for the market. Especially on edge stressed and laminated timber has been studied. New types of structural beam elements with a higher stiffness and constant density could be fabricated. Beyond this the GLT could be used for visible surfaces.

The South American nation of Paraguay, containing the highest rate of deforestation in Latin America, is threatened with the loss of its remaining natural forests, due to large scale land use changes to agriculture, pasture and settlements. A better knowledge of technological properties and potential applications of these wood species could contribute to a sustainable use and valorisation of remaining forests. Within a diploma thesis [10], anatomical, physical, mechanical and chemical properties as well as natural durability of the wood species Peltophorum dubium (Spreng.) Taub. and Inga uruguensis Hook & Arn. Wood were examined. In result, possible applications as well as recommendations for processing were specified.

By means of sound velocity and eigenfrequency, the dynamic modulus of elasticity (MOE) parallel and perpendicular to the grain was determined on lamellas of Norway spruce. In addition, raw density, knottiness and growth ring angle were determined. The dynamic MOE showed a local minimum for a growth ring angle of 30°. The MOE calculated from sound velocity was higher compared to the eigenfrequency measurements. A multiple linear regression revealed a significant influence of raw density, knottiness and growth ring angle on the sound velocity, but no clear relationship between the explanatory and the dependent variables was found. By means of sound velocity and eigenfrequency, a reliable detection of knots was impossible. Raw density and MOE strongly varied; this indicates the potential of a quality sorting procedure.

Chemical/mineralogical and physical/technical investigations on wood concrete show that wood concrete made with Portland cement sets and hardens very slowly. This is due to water-soluble organic substances in wood which form complexes with calcium ions and thus inhibit the crystallization of portlandite. The problem of the incompatibility of wood particles and cement was solved by using a special binder composition containing dodeca calcium hepta aluminate fluoride (12CaO·7Al2O3·CaF2). Increased ettringite formation during the hydration of the cement in the presence of wood enables rapid setting and hardening of wood concrete. In dependence on the proportion of wood in wood concrete, it was possible to produce concrete of plastic consistency with bulk densities between 600 and 850 kg/m3 and strengths between 2 and 10 MPa.

The improvement of product quality as well as the increase of production efficiency is indispensable in production processes. However, the simultaneous increase of cutting velocity also involves a risk when tools and tool holders are balanced insufficiently. In the scope of a cooperative project funded by the German Society for Wood Research (Deutsche Gesellschaft für Holzforschung - DGfH) and the German Federation of Industrial Research Associations (Arbeitsgemeinschaft industrieller Forschungsvereinigungen – AiF; AiF-No.: 14273 ), the Institute of Machine Tools and Production Technology (IWF) of the TU Braunschweig and the Fraunhofer-Institute for Surface Engineering and Thin Films (IST) have developed – in cooperation with partners from industry – a sensor-integrated hollow shank taper tool holder, which detects unbalances and clamping forces autonomously during the working process. By applying thin film sensors to the planar support of the tool holder, the tool holder in connection with the machine control has the ability to activate an emergency stop signal when unacceptable unbalances or clamping forces occur. Therefore, the operational safety is already heightened significantly during the running up of the spindle.

Evaluate the influence of water activity [aw], temperature and pH on the radial growth and lag phase of Physisporinus vitreus (E-642), a basidiomycete used in the biotechnical process of bioincising. Radial growth was monitored for 20 days on MEA medium. Five levels of aw (0.998, 0.982, 0.955, 0.928, 0.892) were combined with three incubation temperatures (10, 15, 20 °C) and three pH (4, 5, 6). Data analyses showed a highly significant effect of aw and temperature (P<0.0001), and a significant effect of pH (P<0.05). The radial growth rate and lag phase of P. vitreus were very sensitive to aw reduction. Although P. vitreus was able to grow at the selected temperatures and pH values, the lag phase increased with decreasing aw, and growth was already inhibited at aw = 0.955. Optimal conditions for growth of P. vitreus were aw = 0.998, 20°C and pH 5. The response surface model provided reliable estimates of the three kinetic parameters and confirmed the greater dependence on aw than on temperature or pH under in vitro conditions. Low levels of aw can prevent growth of P. vitreus, so wood moisture content should be adjusted accordingly.

There is still a high demand for paints based on alkyd resins and drying oils. In comparison with paints and varnishes just drying by evaporation of a solvent, oxidative drying coatings are superior in performance. Additionally they are based on renewable raw materials. Oxidative drying systems need a metal based drying accelerator, normally Cobalt salts of organic acids. Currently there is concern that the toxicologic cobalt carboxylates might be classified as category 2 carcinogens at some time in the future. As a result of this problem there is a demand for alternative driers. We will discuss the drying results achieved with a cobalt-free drying accelerator.

One of the main problems, the European industry has to solve until 2010, is the implementation of the VOC guideline (guideline 1999/13/EC). The aim of a European project in the program Intereg IIIB/CADSES was to examine the degree of implementation of the VOC guideline in selected European countries. This was done by examining selected firms of different branches and offering support for finding final solutions. It was found that the efforts for wood coating enterprises in Germany and Slovenia are much higher than in the rest of Europe, where the threshold values for need of acting are lower. The completed project is continued in a following topic where small and medium sized enterprises in 2009/2010 still have the possibility to get free advice in drawing up a VOC balance sheet and possible reduction strategies.