VOLUME 46, ISSUE 2/2005

TD: Fibre materials, particularly MDF, HDF, insulation boards or shaped materials, are variously used in furniture and packaging industry and in the construction industry. In conventionally production processes, the wood fibres are mixed with synthetic resin. In this work successes were obtained by substitution of the resin with special enzymatic incubation of fibres using different xylanases and cellulases. The short incubation of fibres with 3 to 7 % of hydrolases already leads to substantial improvement of strength and hygroscopic properties of glue-free MDF and doorskins in lab- and industrial scale. The board strength properties meet the standard of EN 622-5. Further investigations are necessary to improve the hygroscopic properties and to reduce the enzyme costs.

The drying behaviour of different wood species was investigated during combined application of microwave heating and low vacuum. Drying rates of a few percent per minute are reached. Therefore the drying of single boards within a process chain is possible. The drying rate linearly depends on the specific power used. Moisture and temperature profiles during the process were determined. Because of the characteristic development, temperature can be used for process control. Problems were encountered during drying of wood species with distinct heartwood parts due to the differences in initial moisture content of board cross section.

Thermally modified timber (TMT) has been industrial scale produced in Europe for 10 years. Four basic technologies have been established essentially: the hot air technology developed in Finland, the treatment with steam under increased pressure, the Oil-Heat-Treatment and the technology with nitrogen atmosphere. The treatment temperatures are between 160 and 230 °C. The thermal modification leads to an increased resistance against wood destroying fungi. The dimension stability is improved, the moisture uptake such as shrinking and swelling are reduced. But, the strength properties are reduced in the same way. Therefore a right choice of wood species and treatment conditions, according to the application, is necessary. The colour change is making TMT a possible substitute for tropical wood species, also in interior applications, like furniture and floorings. Actual TMT is not applicable and not recommended for load bearing applications. Thermally modified timber is a relatively new product with a specific property profile and therefore should be considered as an own wood species. Long-term experiences are available only in a small range. This is to consider by woodworking and application thermally modified timber.

Wood Plastic Composites (WPCs) are a new generation of materials with plastics as a matrix material and embedded wood particles and fibres as well as distinctive additives. The material is processed by means of an extrusion process or injection moulding but also other shape building processes are possible. Wood is added for technical (better or specific properties) and economical reasons (cost reduction). An analysis of the productivity in comparison to wood and wood based materials shows that currently WPCs are only competitive if the possibilities of the various shapes for technical solutions and for design purposes are used properly. There is still a great potential in improving the materials as well as the process itself.

Lightweight construction materials are increasingly used because of their good handling and the decrease of the transport costs. The characteristics of these materials with the cutting process exhibit some characteristics. Structure destruction of the honeycomb, fraying of fibre bundles and chipping on corners and edges are to be avoided. New tools were developed and tested for getting qualitatively better cuts of edges of lightweight construction materials. For the formatting of boards with sensitive surfaces and intermediate layers a progress with high alternative top bevel tooth geometry is obtained. The correct tool selection as partners of the various lightweight construction materials decides on the cut quality and service life. Routers with smooth cut and drills with new cutting geometry achieve these goals.

Optimisation of wood cutting procedures is very important from an economic point of view. The main points of interest are quantity, quality, tool wear and energy consumption which influence production costs. Beside that human and environmental factors come more and more in the centre of attention. To realise the optimisation the process behaviour must be known. That means input and output parameters has to be defined and also the connection between both categories of magnitudes expressed by modelling equations. A differentiation between the machining process and the mating process between knife and work piece leads to the knowledge, that parameters describing the mating process are specific and independent of single machining process. It results an increase of the range of validity of the models. That means the models should be developed only with magnitudes of the mating process like cutting velocity, average chip thickness and cutting path instead of feeding velocity, rotation number, cutting depth and feeding path. The conclusion is that the machining process could only be arranged optimally if mating process is in optimal configuration. In the paper important magnitudes and possible modelling approaches are shown. Based on the defined parameters and the models a recursive optimisation sequence is introduced. The main steps are the material selection followed by the geometrical and kinematical selections. In the several steps a variation area is generated of arrangement possibilities for the cutting procedure. Every step finishes with choice of a limited number of accepted selections from the variations. Finally the optimal configuration regarding edge material, edge geometry and kinematic conditions according to the given marginal conditions of the investigated process will be obtained.

The IHD has developed a test methodology for determining the formaldehyde emission from wood-based panels immediately after their production. From the initial formaldehyde concentration a suitable threshold value could be derived, which allows an assessment of the wood-based panels with regard to E1-0uality. The investigations have shown that the analysis method is also very well suited for the determination of the formaldehyde concentration in the test chamber or room air as well as in aqueous absorption solutions.

The influence of wood decaying fungi to mass loss and sound velocity in spruce was observed. Tested fungi were Trametes versicolor, Gloeophyllum trabeum, Lentinus lepideus und Poria placenta. The mean mass loss was about 4 % for white rot and 4-28 % for brown rot (depending on the type of fungus). The decrease of sound velocity is bigger for brown rot than for white rot. It seems that fresh decays with only a small mass loss hardly can be detected because of the natural variation of the measured values.