VOLUME 55, ISSUE 6/2014

The density, dynamic and static modulus of elasticity, bending strength, compression strength in grain direction as well as the Brinell hardness were determined. The elastic moduli determined in dynamic measurements are higher than those measured in static experiments. The differences of the static values are lower for eigenfrequency measurements are lower than those determined through sound transmission. Additionally, the differences in sound transmission depend on the test frequency of the measurement device and the dimensions of the tested sample. All properties correlate linearly with the density. The quality of the correlation varies and depends on the variability of the properties of the samples, amongst others. The resulting equations determined in this study may be used for density corrections for bending strength and MOE.

The morphological characteristic of fibre pulp for the manufacture of MDF is an important quality criterion. The characterisation of fibre pulp for process control is not yet fully solved until now. The speed of analysis, the heterogenetic composition of particles (dust, single fibres, fibre bundles), fibre agglomeration, and a differentiated morphologic data analysis are still problematic. In a collaboration of the Gesellschaft zur Förderung angewandter Informatik e. V. (GFaI), the Fraunhofer Institute for Mechanics of Materials (IWM) and the Institut für Holztechnologie Dresden gemeinnützige GmbH (IHD) a prototype system for the morphological characterisation of fibre pulps as well as a suitable particle classification system were developed.

The WKI calculation model published by Mehlhorn (1986) was up-dated for the formaldehyde emission potential of currently produced particleboards. The chamber concentration determined by EN 717-1 (2004) and the gas analysis value determined by EN 717-2 (1994) were introduced as reference values. The calculation model with a linear correlation between relative humidity and chamber concentration is suitable for relative humidity values below 50 %. For the calculation of values in the range above 50 % relative humidity, a calculation model was developed with an exponential term for the influence of relative humidity. First test confirm, that the WKI calculation model developed with particleboards is suitable for medium density fibre boards (MDF) as well.

Precise knowledge about the raw density profile of wood-based composites is crucial for R&D, quality assurance, and process control. The capability of X-ray measuring devices is overestimated so far. A round robin test by means of currently applied systems provides non-identical results in comparison to each other. The results deviate, furthermore, from the assumed real raw density profile determined by gravimetric reference method. Maximum deviations are observed within the surface layer section, which is most relevant for numerous panel properties. The insufficiencies are caused by radiation physical effects occurring during the penetration of polychromatic ionising radiation through inhomogeneous materials, which are not considered by gauge calibration up to now. Accuracy enhancement is achievable through an optimised X-ray measuring device with improved calibration and data evaluation mode.

Four recipes of WPC were compounded with eleven different compounding and compacting technologies. All recipes contained same amounts and types of additives. They were different in wood content from 40 % to 70 % and in melt flow rate (MFR) of matrix polymer polypropylene (PP). The two high filled recipes were extruded the other ones injection moulded. Granulates as well as test samples were analysed by light microscopy. Injection moulded samples were additionally analysed by scanning electron microscopy (SEM) and UV-spectrometry (USMP). From distribution of mixing partners, compaction and twisting of cell structures can be concluded how forces act in the processes. SEM shows if fibre particles are well connected to the surrounding polymer matrix or not. Conspicuous are voids in samples of mostly all process which cannot be correlated to moisture. USMP enables to show how hard lignin in samples is thermally treated in the processes.

Sustainable materials that can be produced, processed and used with little negative impact on the environment have increasingly come into focus of the public, politics and industry. Wood, one of the oldest working materials, fulfills the many of requirements of these “modern” materials. For this reason, wood should be used increasingly. But besides being sustainable, a material must also have all the necessary requirements for todays technical appliances which not only include its mechanical performance, but also a high reliability, processing compatibility and reproducibility. The project HAMMER aims to enable the application of this natural material in high-tech products such as vehicles. Necessary steps on the way to producing wood-based construction parts for vehicles are: the production and characterization of wood-based multi-material systems, the development of a compatible joining strategy, the creation of repair and recycling concepts and the development of concepts which enable the integration of wood-based construction elements into the vehicle production process.