VOLUME 51, ISSUE 4/2010

Terms like “high-tech” and “low-tech” accompanying us day by day and the technology leadership in a certain area is an important indicator for the development and the power of the national economy mostly. Our civilization is marked by technology. This is the basis of our standard of living but also creates challenges as the impact of new technologies often is recognized with delay.

The manufacturing of compressed wood is due to several densification treatments probable. Because of the inhomogeneous character of wood the densification enables the improvement of a new material with better properties. The following study showed compression tests which are accompanied by a finite element simulation (FE) with strong simplified two-dimensional meso-mechanical material model.

When evaluating the test results of the short-term properties internal bond (dry and after 2 h boiling, respectively), modulus of rupture, modulus of elasticity, thickness swell and water absorption after immersion in water for 2 h and 24 h, respectively, shear strength and moisture content of OSB and solid wood panels in the present paper, it was observed that the thermal posttreatment of the aforementioned wood-based materials had a positive effect on most mechanical properties tested. European standard requirements could be clearly met in most cases for the conducted test types for the respective wood-based material. Especially the moisture-related properties, i. e. thickness swell, water absorption and moisture content, were positively influenced throughout. The thermally modified materials showed far better values than the respective untreated materials. The studies will be continued with additional adhesive systems.

Most mechanical properties of the produced wood-filled silicone-elastomer composites were reduced in comparison to unfilled silicone-elastomer references. It can be assumed that the interfacial bonding between the silicone-elastomer and wood particles is too weak to reinforce the composite. The external forces do not appear to be transferred from the matrix to the wood particles. By filling the silicone-elastomers with wood particles the density and the hardness (Shore A) increases. The use of wood fibers with a length/diameter ratio around 100:1 increased the teardrop resistance significantly. Significant reduction in tensile strength, elongation at break and restoring force were observed, and a high increase of water uptake was monitored. A major goal of the work was the substitution of pyrogenic silicic acid, as a material with a high specific surface (200 m²/g to 400 m²/g (Hofmann and Gupta, 2001)), reinforces the silicone compound. The results show that the use of wood particles did not increased the mechanical properties of the compound. Wood particles can be used as non reinforcing, inactive filler such as diatomaceous earth and silicic acid.

Up to now WPC have predominantly been used in profile extrusion processes. With its rates of considerable growth, WPC has also captured a share in the market of injection moulding. In the medium field of stressing range, WPC is often used as an alternative for glass fibre reinforced polypropylene or mineral filled polypropylene. At this, several characteristics have to be considered.

The biological durability of wood polymer composites (WPC) is an important condition for exterior applications, e.g. decking or cladding. Investigations on the determination of the biological durability and on approaches for its improvement are shown. Beside implementation of biocides and hydrophobic agents, one idea was to use fillers made from thermally modified pine. After industrial production of samples with different compositions, physical and biological properties of the WPC variants were determined by lab and field tests. In result, a decreased water absorption and a reduced mass loss after fungal attack was found compared to a standard variant with native wood filler. However, the reduction of flexural modulus of elasticity (MOE) indicated an influence of fungi on the cohesion between the polymer matrix and the wood filler. Contrary to the expectations, the biological tests showed no clear influence of the composition on the resistance against mould fungi. In consequence, a need for an appropriate test method for WPC was deduced. Such a test method shall be developed and evaluated within an intended R&D project.

To evaluate the suitability of powder coatings for natural fibre based composites intended for furniture applications, fiber mats from flax, hemp, kenaf, cocos and wood fibres were impregnated with acrylic resin, pressed to boards and powder coated. Surface quality was judged using profilometer measurements. Although all fiber types were in principle well suitable for the powder coating process, distinct differences were found with respect to the quality of the surface. Besides fiber type, surface quality was significantly influenced by resin loading and pre-treatment of the carrier board as well.

Looking for measures to improve the energy performance of their buildings, owners frequently opt for conventional solutions, such as composite thermal insulation systems based on rigid foam polystyrene, due to worries about possible complications, e.g. damp. A central aim of a study, carried out at the Technische Universität München as part of the research cooperation “Holzbau der Zukunft” (Timber Construction for the Future), therefore was the development of a catalogue, promoting refurbishment measures, based on the usage of timber and derived timber products. A series of fact sheets on the recommended measures, that can be copied and added to an energy performance certificate, set out what is involved in each case. They contain a short description of the proposed measure, and illustrations to represent the situation before and after measures are taken. Plus a summary of the advantages and disadvantages, as well as an explanation of the main structural and physical aspects such as thermal insulation, thermal bridges, damp proofing, acoustic insulation and fire protection. To conclude, the main parameters affecting the cost effectiveness of the particular measures are set out in a table.

The article deals with the application of Sub-micrometer Computed Tomography (Sub-µm-CT) for the characterization of wood based panels, specifically from oriented strand board (OSB), particleboard (PB) and medium density fiberboard (MDF). One of the biggest challenges was the sample size and with this the maximum achievable resolution. The different sizes of the structuring elements in the three panel types (strands, chips, fibers) request different representative sample sizes. The reconstructed images from the CT data then enable both, qualitative and quantitative characterization of wood materials and the reconstruction of volume models.