VOLUME 58, ISSUE 3/2017

The formation of cracks in wooden components is the consequence of its anisotropy under changing climatic conditions. Due to swelling and shrinking in the hygroscopic range wood undergoes numerous dimensional changes. Tensions occurring on the surface and the interior of wooden elements can provoke cracking. Cracks are often considered as defects and reason for numerous negative consequences such as compromised aesthetics, risk of harm through splinters, accumulation of moisture, mechanical degradation, or even starting point for fungal decay. If and to what extent cracks affect the use of wooden components is strongly dependent of their size, position, and the respective application. In some cases it is even a moot question if cracks have a negative effect at all. Within this paper the authors summarize the results from three different studies on the susceptibility of different materials to the formation of cracks, the effect of cracks on wood moisture content and potentially risk for fungal infestation as well as optical deficiencies. Based on the experience from different research institutes the problems and challenges related to the assessment of cracks in timber are highlighted and an evaluation protocol is proposed and put up for discussion.

A novel wood-fibre insulation board with a low density (approximately 50 kg/m³) was developed by utilizing a two-component polyurethane binder. In a comparative analysis the developed insulation board showed different product properties than the industrial products bonded with bi-component fibres. Besides the lower product flexibility of the polyurethane-bonded wood-fibre insulation material, a higher compressive stress and lower water absorption can be achieved compared to selected industrial products. Furthermore, the use of polyurethane has technological advantages, since polyurethane-bonded wood-fibre insulation materials can be cured by means of hot steam. Thus, all wood-fibre insulation materials currently produced in the dry process could be produced with the same process.

Fibre-reinforced plastics (FRP) are often used in sports industry, especially for the structure of cycling, racket and sliding sports equipment. Computer-based product development strategies, that are commonly used in the aerospace and automotive industry, are also be deployed in the sports industry during the last years. Hence, the stiffness and strength of new snowboards designs could be simulated by using finite element method (FEM). By using such computer-aided engineering (CAE) tools the influence of different bio-based and renewable materials on the mechanical properties of the sliding sports equipment can be analysed. In this work an ecological snowboard made from bio-based and renewable resources consists of flax-fibre semi-finished products, bio-based thermosetting resin, bio-based sidewalls and a core element of poplar solid wood is developed. By means of the FE-simulation the parameters ply angle and ply thickness of the flax-fibre semi-finished product as well as the core thickness are variated, until the bending stiffness and bending stress is equivalent to a conventional snowboard. The volume-FE and shell-FE model will be verified on manufactured prototypes with a 3-point bending test according to DIN EN ISO 14125 (2011).

Flat-clinching offers the possibility of producing metal-wood-joints without any complementary joining elements. The hygroscopicity of the wood materials leads to moisture adsorption and desorption. Thus, the moisture content influences the flat-clinching process as well as the strength of the metal-wood-joints after the joining process. By conditioning the wood materials, the dependency of the joint strength on the moisture content was proven and optimal process parameters were detected. Furthermore, the structural anisotropy of the wood materials influences the formation of the interlocking as well as the work hardening of the metal component, which was proven by micro hardness measurements.

Generally, passed machine acceptances are a precondition for a successful conclusion of a machine purchase. Although some standards regulate the procedure for the statistical analysis of produced small batches in this context, the specific problem in the wood and furniture industry is hardly taken into consideration. The applicability is often ruled out with reference to the particular properties of wood and wood-based materials and the variety of attributive quality characteristics of the surface impression. This paper focuses on the complexity of problems, explains the basics and discusses the results of exemplary application tests on a moulding machine and a processing centre. Furthermore, it shows how sensory quality tests during machine acceptances can be used in analogy to the methods of process capability studies. The procedure recommended in VDMA 8669 (1999) is identified as a suitable method for the wood and furniture industry.

The qualitative and quantitative determination of mould fungi is a main topic within indoor hygienic and environmental medicine expertise. Molecular DNA-based methods are particularly appropriate for reliable and fast diagnostics with high specificity and sensitivity. To develop a mould DNA analysis tool, four different genome regions of selected fungi were analysed. Therefrom, specific DNA markers were derived and evaluated. Finally, specific detection assays based on real-time PCR were developed using TaqMan hydrolysis probes. As a result of a basic validation, essential test parameters of the individual assays were determined, including the specific detection limits with reference to genomic DNA and spore number. The practical application of diagnostics, in particular the determination of its performance in comparison to other well established microbiological methods, is the subject of further research.

In many technical recycling processes urea-formaldehyde-bonded (UF-bonded) particle- and fibreboards are subjected to thermo-hydrolysis at temperatures much higher than 100 °C. Due to such a treatment hydrolysis of the urea-formaldehyde-resin (UF-resin) in the boards unfolds and liberation of ammonia from the boards sets in. Ammonia reacts with formaldehyde and volatile organic acids, like formic acid and acetic acid, leading to mitigation of formaldehyde release and abatement of liberation of volatile organic acids.