VOLUME 50, ISSUE 5/2009

One- and three-layer particleboards with densities varying from 200 kg/m3 to 650 kg/m3 are produced from hemp shives (Cannabis sativa) and stalks of sunflower (Helianthus annuus), topinambur (Helianthus tuberosus), maize (Zea mays) and miscanthus (Miscanthus sinensis gigantheus). The mechanical and physical properties of these boards are presented. Particleboards made from hemp shives, stalks of sunflower and topinambur and of low densities (400 kg/m3 to 500 kg/m3) were able to fulfill the minimum requirements for internal bond strength according to the EN 312 but could not achieve the adequate values of bending strength. Three-layer particleboards were made of topinambur stalks in the core layer and spruce particles in the surface layer, both bonded with UF-resin (12 % solid resin content). With a thickness of 19 mm and a density of 475 kg/m3 these particleboards have even higher values of internal bond strength as a 22 mm industrial standard particleboard made of wood chips with a density of 500 kg/m3 or as the innovative lightweight boards made with expanded polystyrene in the core layer and a density between 430 kg/m3 to 460 kg/m3. The bending strength of these three-layer boards produced in the laboratory matches those of lightweight standard industrial particleboards. For a comparison between boards produced in the laboratory and in the industry, the different conditions of production have to be considered.

In order to study the effect of spreading quantity as well as the grain angle on internal bond strength three layered specimens bonded with a one component polyurethane (PUR), a melamineurea formaldehyde (MUF) or phenol-resorcinol-formaldehyde (PRF) adhesive were produced from spruce wood. By varying the grain angle of the middle layer from 0° (parallel to grain of the surface layers) to 90° (perpendicular to grain of the surface layers) in incremental steps of 10° the effect of grain direction was investigated. Furthermore, the spreading quantity was varied in a wide range (70 g/m2 to 600 g/m2). At low spreading quantities (lower than 200 g/m2) a significant effect of the grain angle as well as of the spreading quantity on internal bond strength was observed, whereas at higher spreading quantities the effect was reduced.

The fundamental knowledge on the properties of wood concrete has been successfully advanced and its performance shown in exemplary application regions by material specific investigations and the realisation of demonstration projects. The problem of compatibility between cement and wood has been solved by using a specially composed binder. Regarding functional and constructive behaviour, wood concrete was found to be marketable compared with competing products offering atheistic advantages for high quality surfaces. The present results show that wood concrete possesses a promising potential as a material for construction components and elements as well as the facades of buildings and in interior fitting. Since it is possible to vary the constituents of wood concrete, this composite material can be produced with a range of mechanical and building physical properties. Thus the functional performance and artistic appearance of the material can be successfully optimized for a particular application.

Thermally modified timbers can be used to produce three-layer solid wood panels for exterior use. The optimum approach by manufacturers of solid wood panels should be to ship typical base material (of adequate quality) in order to be thermally treated. The build-up of thermally modified lamellae as outer layers and untreated wood as core layer proved to be very advantageous. The gluing of the lamellae can be done with commonly used resin systems and optimised press parameters without any disadvantages. Strength properties were only slightly reduced with the use of thermally modified wood, dimensions and dimensional stability, respectively, were improved. When using outdoors surface coating is recommended. The research will be continued.

With the required replacement of chemical solvents by watersoluble solvents for coatings significant higher drying times and equal or higher energy consumption are necessary using the present technology. In this case the infrared technology will become more and more important. It is known, that infrared will penetrate deeper into coatings and plastic films. For some coatings the heating of the substrate will be supported, if required. The emission spectrum of infrared systems should be adapted to the absorption of the objects during the thermal treatment of coatings. It is also known, that the typical and highest absorption values of water and of many plastics (see water soluble coating) are in the range of 3 µm up to 6 µm. The best correspondence with the absorption spectrum of water and plastics can be achieved with a STIR-emitter (dark radiator) at e.g. 600°C emitter temperature.

The altar-panel in the chapel of the Augustusburg castle was painted on lime wood by Lucas Cranach the Younger in 1571. After having reduced the thickness of the panel with a size of 2,37 m x 3,18 m to a thickness of 11 mm in 1858, climatic fluctuations led to instability and strong cracking. Finally the main crack went 1,80 m into the painting. Cautious treatment was meant to stabilize the panel and control humidity in the wood. For that purpose the roof had to be thermally disconnected because it overheated in the summer season. It was possible to reduce the extreme climatic fluctuations (25 % … 100 % RH) by controlled admissions of cool and moist air. After securing the cracks, the altar-panel was strengthened by a moisture- accumulating rear panel consisting of removable balsa wood elements which were impregnated with Sebosil HB and finally protected by a 16 mm thick laminated panel consisting of poplar/balsa lightwood. The structure rests on stainless steel rolls and in a read cedar wood frame which is stiffened by carbon fibre. Sideways pushing springs are used to minimize the friction force during shrinking. A 5 m high timber structure consisting of read cedar wood boards with a vertical jalousie was erected behind the altar for climatic regulation.

The manufacture of usable windows made from thermally modified timber (TMT) could be demonstrated in the project. The technological feasibility (mechanical processing, gluing, coating) was proved in all cases. However, TMT windows will not be suited for all kinds of use in the same way. Due to the TMT characteristics there are limits with respect to extremely wind load, to impact load, to hailstorm risks, and to burglar resistance. Further studies are necessary in the future to determine stress limits based on defined restrictive conditions also in connection with the shape and the dimensions of the windows as well as increasing glass weights.

This paper presents some solution methods to optimize the vehicle routing planning in round timber transport. They are based on the metaheuristic tabu search. Transport costs are an essential factor in the purchase of round timber and can be reduced drastically by using optimisation techniques. In an introductory example the problem and its characteristics are described. After that, an explanation of the developed solution methods follows. These methods differ mainly by their used neighbourhood structures. Extensive numerical studies compare the single solution methods with each other and also use the computations of Standard-Solversoftware as benchmark. These tests prove the high quality and practical interest of the presented solution methods. It is possible to generate solutions of high quality for even large problems in short computation times.