VOLUME 60, ISSUE 5/2019

MDF properties equal the total of the properties of matrix, fibres and the interdependency of both. Little is known about the mechanical properties of the single wood fibres and fibre bundles, especially in relation to different pulping parameters. This work displays a method to apply tensile strength tests to single fibres and fibre bundles. Results are shown regarding the influence of pulping parameters such as cooking time, temperature, grinding plate distance on the tensile strength and stiffness of single fibres and fibre bundles for the manufacture of medium density fibreboards (MDF).

EN 350 (2016) allows formally to determine durability classes (DC) for wood products and wood based materials, which was previously only possible for untreated wood in the form of natural durability. In a first study, the durability classification of chemically modified (modified with 1,3-dimethylol-4,5 dihydroxyethyleneurea, DMDHEU) and preservative-treated specimens of various hardwoods and softwoods were determined. The objectives of the work were the determination of mass losses caused by basidiomycetes (CEN/TS 15083-1, 2005) and soft rot fungi (CEN/TS 15083-2, 2005) and to classify durability according to EN 350 (2016). The results showed that a durability classification of chemically modified and preservative treated wood is possible. The methodology for evaluating the data proposed in EN 350 (2016) needs to be optimized.

This study reports the comparative investigations of the biological durability of identical specimens from individual in-ground field tests and laboratory tests. The investigation consisted of the evaluation of the field trials with soil contact after five years of exposition. The biological durability in soil contact and the degradation behaviour of the specimens were taken into account. Thermally modified European beech and Norway spruce with various treatment intensities were used. Increased biological durability by thermal modification was determined for the lab test in accordance to EN 113 (1996) and for the in-ground test EN 252 (1990, 2015). The decay rates, degradation velocities, and the durability factors were determined to classify the durability (DC) inspired by EN 350 (2016). The modified beech wood treated at 220 °C reached classification DC 2 (durable). Modified spruce achieved DC 4 (slightly durable) at most. By determining the degradation rates, an initialization phase for the higher modified test specimens was determined. A correlation to the L*b* colour values and the degradation rate as well as the durability factor could be established for the modified beech test specimens. However, this was less than the correlation of the mass loss to the L*b* colour value of the laboratory test. With the spruce test specimens a stronger scattering of the L*b* - colour values was determined. The comparative analysis between thermally modified wood from the soil contact test and the laboratory test showed that due to various influencing factors such as diversity of the soil substrate and incubation time of the laboratory test specimens, a final assessment of the durability is only possible by means of validation under real conditions.

In the last decades, an increasing infestation with moulds has been detected in church organs. Although the general causes are largely known, the implementation of preventive measures is difficult in individual cases for technical and financial reasons. In a research project, procedures for mould prevention in organs were evaluated on the basis of theoretical considerations, computer-aided simulations as well as laboratory and practical tests. The climate data, which were recorded in four church organs in the Dresden area and in eastern Saxony over a period of two years, were incorporated into a specially created numerical simulation model. In this way, inaccessible organ components of the wind system could be represented as individual fluidic models, and critical areas were visualized. Positive effects of ventilation and air filtration were proven in laboratory tests and in the objects.

The paper deals with the structural alteration of Norway spruce (Picea abies (L.) Karst.), European beech (Fagus sylvatica L.) and oak (Quercus robur L.) owing to both ammonia treatment and ammonia treatment in combination with mechanical densification. The ammonia treatment was conducted using gaseous or anhydrous ammonia. The structural changes were studied by incident light microscopy. As a result of the ammonia treatment, a dark colour was achieved for spruce (light brown), beech (brown) and oak (black). The ammonia fumigation in combination with a final drying step resulted in both a permanent shrinkage and increase in the raw density of all wood species examined. Microscopically, self-densification of the wood structure as well as changes in pore sizes and geometries could be demonstrated. The additional mechanical densification step resulted in sig-nificant structural homogenization and further increased raw density for all wood species tested. Taking into account the appearance and structural alteration, properties analogous to tropical wood species were established.