VOLUME 54, ISSUE 1/2013

In this study, mechanical properties of Hornbeam wood (Carpinus betulus L.) at four different locations of Caspian forests (North of Iran) are investigated. The locations are including Asalem

(37°56´55. N, 48°52´84. E), Visar (36°11´57. N, 51°06´26. E), Sangdeh (36°05´28. N, 52°25´41. E) and Golestan (36°25´41. N, 51°35´25. E). The test materials were derived from randomly chosen

trees. Mechanical properties such as static bending strength, compression strength parallel to grain, impact strength and shear strength are measured on two moisture levels: green and air-dried (12 % moisture content). The results are obtained for the species at different geographical locations, ages, and mechanical properties.

In literature, numerous studies concerned on the succession of infestation by fungi of wood surfaces have been described. The present study is the first attempt to investigate the succession of blue stain fungi, mould and basidiomycetes by PCR-based techniques. The surfaces of modified and unmodified wood with and without coatings were examined after natural weathering. Within one year of natural weathering, the succession of typical blue stain and mould fungi by using specific primer pairs was observed. It was found that the coated modified panels were more affected by Aureobasidium pullulans than by Cladosporium sp. After nine months, uncoated panels were additionally affected by Alternaria/Ulocladium, DNA from Trichoderma sp. and Aspergillus sp. could not be detected during the investigation period. It was demonstrated that PCR-based methods are very sensitive techniques for the early investigation of the development of blue stain and mould growth, long before the fungal growth is visible by visual assessment.

For insect control by heat, according to German technical rules a minimum temperature of 55 °C is required for at least an hour in the interior parts of infested timber. This investigation evaluates some of the aged literature on which this view is based and again determines the minimum exposure time for controlling house longhorn beetle larvae at temperatures between 55 °C and 90 °C. Thermal transfer in these new experiments was kept as low as possible and occurred almost entirely by air which was not moved. In contrast to common understanding a significantly shorter exposure time proved sufficient to destroy all larvae safely. Moreover it became clear that just slight temperature increases lead to unexpected reductions of required exposure time. With increasing larva size the heat sensitivity of larvae decreased: For safe destruction of middle-sized larvae at 70 °C, four minutes were sufficient, very large larvae required six minutes. At all examined temperatures, death appears not to have been caused by desiccation, but as a consequence of direct heating.

The safety in use of plywood-based scaffold boards arises from its load bearing capacity and its serviceability. At Institut für Holztechnologie Dresden (IHD) there was analysed the damage on structure of the boards resulting from moisture permeated on the edges. The reduction of moisture input and the life-time extension of scaffold boards is achievable by using a permanently elastic surface coating material on edges and on boundary area of the worktop.

The shear strength of PVAc, bone glue, skin glue and fish glue were tested on spruce and oak wood after gluing, at variable relative humidities between 35 % and 65 % and at standard atmospheric conditions. The shear strength of the bone glue reached values that were about the same as those of samples bonded with PVAc. The wood failure percentage of all adhesives and both types of wood was at 90 to 100 %. Due to the high proportion of wood failure, the influence of wood species on the shearing strength was clearly noticeable. As a result of the higher shear strength of oak wood, the bonded oak samples had significantly higher values than the spruce samples.

Sonic and electrical resistivity tomograms of 46 standing chestnut trees in six stands varying in age and silvicultural treatment were compared to stem disks after harvest. The combinations of these methods allowed the detection of ring shake. The proportion of affected trees increased with stand age. Neither wood moisture distribution within the stem cross-section nor silvicultural treatment showed a significant effect on the proportion of trees with ring shake.

The determination of treatment quality requires the development of reliable and rapid methods. At the Department of Wood Biology and Wood Products (University of Gottingen) the suitability of near infrared spectroscopy (NIR-spectroscopy) was evaluated. Keeping in mind a potential online application, the NIR-measurements were conducted with a simplified procedure by using a low resolution and a limited wavelength region in order to accomplish a fast measurement. By means of multivariate regression methods, the predictability of several TMT-properties was tested. The prediction of mass loss during the thermal modification as well as the moisture content after conditioning was done with sufficient accuracy. However, the prediction of mechanical properties was less accurate and might have suffered from inner cracks that could not be detected by NIR-spectroscopy due to the limited penetration of infrared light. Nevertheless, it was concluded that NIR-spectroscopy features a high potential for an online application in the quality control of TMT.

Foil-coated 3-D furniture fronts are especially used in kitchens and bath rooms. These fronts are coated using vacuum press technique. After a longer time of usage, delaminations of the foils from the MDF substrate can occur. The causes of these delaminations are not fully understood. Therefore an offline test to determine the peeling resistance of foil-coated fronts was developed in the framework of a research project. In addition, aging tests with varying duration and climatic conditions to test the long-term stability of 3-D furniture fronts were created and investigated. The results of these tests were compared with established tests of the heat resistance of foil-coated foils.

Experiments were made to examine the physics of the tracheid effect. The radiation is transmitted in lumens of the cells as well in the cell walls. Subsurface damages caused by machining operations affect the tracheid effect, but the tracheid effect cannot be used to evaluate the extent of the damages.