VOLUME 57, ISSUE 6/2016

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 unrestrained. WPC shows a comparable high swelling force under restrained condition, but only one tenth of the volume swelling of solid wood and wood powders.

It was determined that under the conditions of this study (short-term weathering for 500 hours in a xenon test device), high colour stability of HDPE-based wood polymer composites (WPC) may be obtained by using colour pigments and antioxidant while in the case of PP-based WPC, the additional use of a UV-absorber and light stabilizer increases colour stability. The use of an acid scavenger does not appear to be required to increase colour stability under the conditions of this study. In general, it was confirmed that changes in colour and lightness of PP-based WPC are stronger than of HDPE-based WPC which was attributed to the stability of the matrix polymers. In subsequent investigations it should be determined if HDPE-based WPC benefit from the addition of UV absorbers and light stabilizers also since it may be assumed that HDPE-based WPC will behave similarly to PP-based WPC in the long term. Concerning the flexural properties, it was shown that the stabilizers used cause a deterioration of the flexural strength, especially when PP is used as matrix polymer. This indicates an interaction of these additives with the coupling agent. After 500 hours of weathering in a xenon device, flexural strength was more affected for the formulations which included stabilizers than for the formulations without stabilizers.

Good tribological properties in combination with acceptable mechanical properties allow profiles made of WPC an application as a carrying and sliding element in the conveyor technology. The large variation of quality of WPC profiles, which are currently available on the market, is problematic for a high safety in technical parts as well as their connection. The article presents the material selection of high-filled WPC profiles for technical parts and their bolted connection according to definite criteria and gives a comparison to other wood-based materials.

The innovative LCD array technology for diagnostics of wood-decay fungis in the area of wood and building protection requires contamination-free and automatic DNA extraction systems, which allow both a high sample flow and less time efforts. Currently available automated extraction systems in combination with special kits for plants, yeasts and bacteria are limited regarding an application. This is because of the low quantity and the bad quality of extracted fungal DNA in comparison to a manual extraction. To overcome this problem different protocols for extraction of fungal DNA taken from different practice samples were tested with an automatic DNA extraction system and evaluated using LCD array patterns. In the result, procedures for an automatic DNA extraction system were developed, whose quality and quantity of fungal DNA is comparable to manual ex-traction methods.

In the evaluation of aesthetical properties of wood surfaces the gloss and its variation play an important role. Present work first presents generally valid regularities of the gloss for machined and coated surfaces. The measurement of gloss with different viewing angles was examined in details and the use of the GU85/GU60 ratio has been proposed as an additional powerful characteristics. Measurements result on different wood samples and coated surfaces (furnitures) have been processed and evaluated, and the important role of surface roughness is demonstrated. Finally, the field of possible gloss values was plotted with constant roughness lines. Based on detailed experimental results the following main conclusions may be drawn: The reflection of wood surfaces considerably depends on the angle of illumination and, therefore, the use of a standardized measuring angle is indispensable. The results with different measuring angles which are in use today are not direct comparable. The 60° measuring angle is generally suitable to evaluate the gloss properties of wood surfaces. We recommand the use of the GU85/GU60 ratio to get additional useful informations. The surface roughness has considerable influence on the gloss grade and it is direct relation to the gloss ratio. Removing the reflecting micro-mirrors from the surface, the homogenization of gloss is possible. The use of high gloss coatings suppresses the influence of surface roughness on gloss. The field of expected gloss is given as a function of gloss ratio and surface roughness.

Resilient floor coverings such as PVC or linoleum are newly laid in Germany every year on 70 million m² and counting. For newly laid as well as for the much bigger part of former installed resilient floor coverings a protective layer is recommended to preserve the quality of the flooring (e. g. usability, appearance). UV-curing systems hardened by mobile UV devices directly on the building site are a fast, sustainable, and user friendly approach. As a basis for the coating development typical representatives of resilient floor coverings such as PVC, Linoleum as well as PET of various manufacturers were characterised intensively. Finally, three varnish systems were developed which have promising properties regarding wetting, adhesion, abrasion, sanding, chemical resistance, and elasticity.

Application of wood as reinforcing material in natural fibre-plastic composites is currently limited to the use of wood-fibres or -particles. These wood-fibre reinforced thermoplastics are known as wood-plastic composites (WPC). In production of these composites, wood-fibres are mixed with the polymer with the use of thermoplastic processing methods. However, in this way the use of the material properties of wood is far not sufficient. Wood itself is a natural fibre composite with structural anisotropy that can be used for technical material developments. The article describes ways of processing veneers and thermoplastic films to veneer prepregs. The aim is to efficiently develop the potential of wood in combination with plastic as an alternative to the WPC.