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VOLUME 58, ISSUE 1/2017

Special methods for morphological characterisation of lignocellulosic fibres; Part 3: Influence of fibre morphology on the properties of thereof produced MDF

Language: German
Pages: 5 - 10
Authors: Christoph Wenderdel, Andreas Weber, Martin Hielscher, Detlef Krug
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Properties of medium density fibreboards (e. g. mechanical and surface properties) are in great extend influenced by the fibre morphology. The characterization of fibre morphology for process control is not yet fully solved. The speed of analysis, the heterogenetic composition of particles (dust, single fibres, fibre bundles), fibre agglomeration, and a differentiated chemical and morphologic data analysis are still problematic. In part 1 the theoretical background for the classification of fibres structural units was discussed and in part 2 methodological basics for the morphological characterization (separation of particles, image analysis and identification of specific values) were displayed and used. In part 3 the influence of pulping parameters and pulp properties on the resulting MDF properties are determined with the use of multiple linear regression method.

Defined particle geometries for the central layer of a weight-reduced particleboard

Language: German
Pages: 11 - 15
Authors: Thomas Stehle, Dan Talpeanu, Matthias Schneider

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Wood is increasingly used to generate energy, leading to a shortage of the raw material. To counteract the increasing pressure on the market due to the prices and the procurement of wood material, the wood products industry produces and develops light particleboards with a lower density. A new concept for producing weight-reduced particleboards uses defined, suitable particle geometries in the central layer. These particleboards are made without light fillers, which serve as a substitute for wood particles in the central layer of existing lightweight particleboard products. If there is a suitable particle geometry in the central layer of a three-layer particleboard, the required amount of wood per unit of volume decreases. Different chip geometries will be produced and tested for their technological suitability by adjusting and adapting various cutting tools, tooling and machining parameters.

Compression, relaxation and swelling behaviour of solid wood, wood powder and wood-plastic composites (WPC); Part 2: Relaxation, swelling and swelling forces

Language: German
Pages: 16 - 23
Authors: Hans Korte, Stefan Ofe, Harald Hansmann

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Swelling and shrinking of solid wood and wood composites are deeply investigated for a long period. Swelling and shrinking of a relatively novel type of material, wood-plastic composites (WPC) have not yet been investigated in depth. In contrast to classical wood composites, WPC are compounded and extruded or injection moulded at high temperatures of up to 200 °C and at high pressures of up to 2000 bar. Moisture levels of freshly produced WPC are below 1 %. In this study comparison of compression at uniaxial load, relaxation, swelling and swelling pressure behaviour of solid wood, wood powder and WPC has been done. Part 1 starts with compression at high temperature and high pressure of solid wood, wood powders and WPC. Part 2 will be about relaxation, swelling and swelling pressure. Solid wood cubes build up high swelling force when restrained, and show a high volume swelling if allowed to swell unre-strained. WPC shows a comparable high swelling force under restrained condition, but only one tenth of the volume swelling of solid wood and wood powders.

Artificial weathering of beech veneer treated with three varying phenol-formaldehyde resins

Language: German
Pages: 24 - 30
Authors: Tom Franke, Claudia Lenz, Sven Hertrich, Niklas Kuhnert, Martin Kehr, Nadine Herold, Alexander Pfriem

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Three various phenol-formaldehyde resins with varying molecular weight were investigated in respect to their potential to protect wood surfaces against photooxidative degradation. Thin beech veneers (Fagus sylvatica L.) were impregnated with the phenol-formaldehyde resins under vacuum conditions for 24 h. Subsequently, the phenolic pre-polymers were cured for 1.5 h at 150 °C. The weathering test was performed in an artificial weathering test according to the European standard EN DIN 927-6 (2006). After the test period of 960 h of UV irradiation the specimens were evaluated in respect to their colour changes, their chemical stability and the structural changes on the specimen surfaces. Thus, CIELab colour measurements, infrared spectroscopy and field emission environmental scanning electron microscope investigations were applied. It can be concluded, that phenol-formaldehyde resins with low and medium molecular weight indicating increased resistance against weathering compared to high molecular weight phenol-formaldehyde resin. However, for all investigated wood properties each treatment displayed significant increased performance compared to the untreated control.

Ultrasonic-assisted turning of wood and wood-based materials

Language: German
Pages: 31 - 35
Authors: Thomas Stehle, Stojanka Ivanova, Hadi Ghassemi

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The ultrasonic-assisted machining is a hybrid production process in which the tool is superimposed with vibration at ultrasonic frequency (i. e. frequency of more than 20 kHz). The results of numerous studies regarding the use of ultrasonic-assisted machining of various materials showed that cutting forces can be significantly reduced and cutting quality can be improved. This fact leads to an increased productivity. However, it is still not completely clear which effects produce these improvements due to the oscillating movement of the tool at very high frequencies. This requires a closer examination and more investigations. Very few studies are available, particularly for ultrasonic-assisted machining of anisotropic materials. Hence the influences of various process parameters in the ultrasonic-assisted turning of wood and wood-based materials were investigated by the Institute for Machine Tools (IfW) at the University of Stuttgart within the framework of the DFG project HE 1656/171-1 "Basic research for vibration-superimposed cutting of wood and wood-based materials". In this study, the process parameters included cutting parameters and vibrational parameters. As this paper will explain, the interaction between these parameters and anisotropy of wood significantly influences the required cutting force during machining processes.

Development of an innovative electrostatic scattering procedure for flexible abrasives

Language: German
Pages: 34 - 45
Authors: Detlef Kleber, Rico Emmler, Petra Behnsen, Thorsten Pflüger, Eberhard König, Ralf König, Ekkehard Scobel, Lothar Kretzschmer, Andrea Toth, Stefan Georg, Gunnar Schneider, Steffen Exler, Torsten Balting, Peter Gräbner, Alexander Gerling, Gunter Niemtschke

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Due to variations in the raw material, to plant set-up and plant malfunctions, application errors may occur in the manufacture of flexible abrasives. Changes in the product used are material and cost intensive. For a novel method of electrostatic deposition the influence of dosing, application technique, conveyor belt used, electrode geometry, high voltage type and modified grain on the quality of the abrasive (in particular with regard to grain distribution and grain orientation as well as the absence of residual grain as a technological parameter) has been investigated, and algorithms for process management have been developed. Based on the physical relationship between charging, transport and deposition of the abrasive grain onto the binder layer a pilot plant for the manufacture of high-quality flexible abrasives has been designed. It has been found that the quality of the abrasive belt is related to the manufacturing parameters of electrostatic grain application.

Review: Wood foam – an alternative to petrochemical foam material

Language: German
Pages: 46 - 51
Authors: Frauke Bunzel, Nina Ritter, Julia Scholtyssek

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A wood foam based on lignocellulose was developed at the Fraunhofer Institute for Wood Research WKI. The foam consists of 100 % wood and required no additive like binder or adhesives, because of the strength of the foam caused by the own bonding forces of the wood. Thus, any possible health risks due to emissions from adhesive are excluded. The result of the processing is a lightweight base material with a porous, open-cell structure and low bulk density. Foams can be manufactured in a density range between 50 kg/m³ and 200 kg/m³. Wood foams are interesting from an ecological and economic point of view for a variety of applications.

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