VOLUME 53, ISSUE 6/2012

In this study a thermal treatment of two important wood species in European wood industry – beech (Fagus sylvatica) and poplar (Populus euramericana cv. Pannónia), in paraffin were analysed. Important properties, like moisture uptake capacity, dimensional stability, equilibrium moisture content and moisture uptake rate were investigated. Heat treatment in paraffin improved the imensional stability of wood significantly. Equilibrium moisture content of heat treated wood was lower compared to natural wood by all humidities. Due to that, moisture uptake rate was lower by heat treated wood during the whole absorption process

Currently available particle boards for furniture industry and interior outfitting with a density of more than 630 kg/m³ are too heavy for different applications. Therefore, the reduction of the density of particle boards by use of various light-weight fillers up to a range of 450 to 500 kg/m³ was investigated. Inorganic as well as organic filler materials were used in the middle layer to manufacture three-layered particle boards with densities in the area of 400 to 600 kg/m³ and thicknesses of 30 mm. The attained panel properties were compared to the requirements, as given in DIN EN 312 (2010), of particle boards of the P2-type – boards for interior fitments, including furniture, for use in dry conditions. Amongst others, positive results could be reached with extruded polystyrene, cork granules and expandable unexpanded polystyrene. The requirements concerning internal bond strength and thickness swell as for the P3-type could be met – with regard to bending properties partly not. Part 1 showed the current situation of lightweight panels as well as material and methods of experimentation. Part 2 shows selected results.

In this study, medium density fibreboard (MDF) was produced from three clones of poplar (Populus e. vernirubensis, Populus e. costanzo, P. e. 561.41 ). The results showed that higher resin content increased mechanical properties of panels. A maximum of these properties was observed at 11 % resin content. Although effect of press time is not significant on bending properties a maximum of these properties was obtained at 5 min. The internal bond was improved by increasing of press time so that a maximum of this property was observed at 5 min press time. Thickness swelling after 2 h and 24 h was decreased by increasing of resin content and the mimimum of swelling was observed at 11 % resin content. Although effect of press time was not significant on thickness swelling a mimimum of swelling was observed at press time of 5 min. Maximum of strength properties of boards was obtained at a press time of 5 min and resin content of 11 %. Also minimum of thickness swelling of boards was obtained at a press time of 5 min and resin content of 11 %.

In the present study the influence of wood fibre morphology and shape factor (aspect ratio) as well as fibre content on the basic mechanical properties of injection mouldable Wood-Polypropylene-Composites was investigated. In order to feed the fibre fractions into the extruder in a technically feasible way, a method was developed to convert the wood fibres into free-flowing fibre agglomerates. The highest reinforcing potential was shown by fractionated fibres from spruce and thermo-mechanical pulp, both having separated individual fibres with a high shape factor. Significant improvements of the properties of composites could be achieved by increasing fibre content and using the coupling agent system MAH-PP (5 wt %) giving a good fibre-matrix-adhesion.

The article summarizes issues associated with the combination of wood with other materials, such as concrete and fiber reinforced plastics (FRP). Particular interest is paid to the combination of wood with glass-fiber-epoxy material. The issues that need to be investigated include fundamental interface properties such as degradation mechanisms, adhesion mechanisms, resistance to environmental factors and failure phenomena. The depth of research needed is demonstrated in the study of crack development in a laminated reinforced arch. A model of the laminated arch radially reinforced with glass-fiber-epoxy rods was instrumented with crack propagation gauges and a high-speed camera was used to monitor crack development. Stress in the reinforcing rods was monitored as a function of external load and crack position. The experiment demonstrated the effectiveness of the reinforcement and revealed some drawbacks in the instrumentation and adhesive interface.

Particleboard mouldings are a special group within wood particle-based materials. Their manufacturing technology differs from the production of extruded and flat pressed particleboards, respectively, especially due to the press process which takes place inside closed mouldings. Currently adhesives with high melamine contents and in comparably high dosages are used for the production of particleboard mouldings for exterior uses in order to achieve the desired permanent weather resistance. This can lead to heightened formaldehyde emissions, which was not seen to be a problem so far due to subsequent coating and the exterior use. In case the requirements with regard to formaldehyde emissions for the area of particleboard mouldings tighten in the future, manufacturers of such products need to face this demand. Objective of this research was the development of alternative adhesive systems, which ensure compliance with formaldehyde emission limits and high moisture resistance of the particleboard mouldings at the same time.

Sweet chestnut is with regard to the global climate change a very interesting tree species for forestry in Germany. A problem for the commercialisation of the wood is a wood defect called ring shake, which is not noticeable from outside the tree. It was investigated if two chosen non-destructive measuring methods (sonic and electrical resistivity tomography) are able to detect ring shake in standing trees. For the investigations, 55 trees were selected in the forestry district Haardt. They are subdivided in three different silvicultural treatments in two age groups. All of them were measured with the sonic and the electrical resistivity tomograph. Also the moisture content was measured over the cross section so altogether three factors of influence (age, silvicultural treatment and moisture content) were investigated.

The determination of treatment quality requires the development of reliable and rapid methods. During recent years, several methods featuring different advantages and disadvantages were developed. At the department of Wood Biology and Wood Products (University of Gottingen) the suitability of electron spin resonance spectroscopy (ESR-spectroscopy) was evaluated. The use of ESR-spectroscopy is based on the formation of stable free radicals during the thermal modification process. These stable free radicals lead to an increase in the ESR signal intensity that correlates well with the treatment intensity and can thus be regarded as a potential marker for various property changes of TMT. Therefore, the ESR-spectroscopy shows great potential for an application in the quality control of TMT

One major factor which influences the producibility of small diameter hardwood is besides the material availability, the cost of the first break-down. In Part 2 of this study three different types of saw mill technologies are analysed. First a band saw head rig, second a gang saw and finally a band saw line were compared. The results showed high variation of the cost depending on sawing technology and the production volume. The data showed that only lowest log price qualities could be paid for the small diameter timber due to high processing cost. The study shows that a cost-effective small diameter hardwood processing is only possible using frame saw and reducer band saw systems for the species sycamore, oak and ash. A profitable processing of small diameter beech is not possible. In order to enhance yield, new technologies or yield limits for the minimal acceptance of board width have to be discussed.