VOLUME 56, ISSUE 6/2015

Welded joints of wood are well known to have a poor resistance to moisture and liquid water. In order to improve this resistance, the influence of natural additives (rosin and lignin) in the interface previous to welding is studied. The shear strength and mode I critical energy release rate of the joints after water soaking and/or acclimatization in various climatic conditions were evaluated. In comparison to welded joints without additives, those welded with additives resist longer time under liquid water. At room conditions, tensile shear strength of welded joints with additives is less than in welded joints without additives. The same findings are observed for the fracture properties. Nevertheless, joints welded with additives show higher tensile shear strength after soaking and re-acclimatization and less sensitivity to high moisture environments. Natural additives in the interface previous to welding have a positive effect regarding the water resistance of the joints to water; however, the welded material is still partially water soluble.

The manufacture of very thin MDF is possible with state of the art MDF plants. With a suitable adjustment of the properties of such very thin MDF they are possibly usable as substitute for paperboards for packaging purposes. The requirements for this are that these novel very thin MDF show paperboard like properties and are recyclable within the common waste paper stream. In this paper it is shown that with a suitable combination of adjustments within raw materials and technology the manufacture of very thin MDF with paperboard-like properties (in the following named as “dry-paperboard”) is possible. Modifications and variations were applied on the raw material (fibre raw material, alternative binders) and on the processes of mat forming and hot-pressing.

The awareness of the population can be rise for sustainable construction and insulation products. Therefore, the development of standardized insulation panels based on natural raw material is necessary. This study deals with the investigation of straw materials for the production of insulation panels with densities below 300 kg/m³. As raw materials for the panels were used hemp, corn and wheat straw as well as miscanthus. The panels were manufactured in a hot press process. In addition to the thermal conductivity of the panels, the bulk density and the particle distribution of the different starting materials were determined. The first results show that the panels from the raw materials of annual and perennial crops can compete with the insulating materials on the natural resources market with regard to thermal conductivity. These findings provide a basis for further efforts in transfer from laboratory to industrial conditions for consumer applications.

The article summarizes results of aging behaviour of WPC same and mixed material welds. The object of investigation was the durability tests against water, long-time heat and global UV weathering on WPC-joints in the case of vibration welding. The results show a limited durability of WPC against long-time heat and global UV weathering in comparison to unfilled matrix material.

A cladding with vertical boards of Norway spruce (Picea abies) comprising different coating systems had been exposed to natural weathering oriented south west in Vienna for five years. Weathering behaviour of the boards was assessed in intervals and wood moisture content was measured over the first 22 months of exposure. The moisture protective properties of the coating systems were assessed using laboratory methods. The results of weathering behaviour indicated higher coating durability with higher dry film thickness and lower transparency of the coating systems. The coating systems provided a certain degree of moisture protection that was influenced by paint colour, water permeability and surface roughness. Panels with low permeable coatings showed a better performance in natural weathering.

The evaluation of the protective potential and lifetime prediction of exterior wood coatings can be conducted using diverse physical and chemical analysis and testing tools. In part 2 of this study methods for the determination of thermal and micromechanical coating properties and their weather-related changes are described: the dynamic scanning calorimetry (DSC) and the instrumented microindentation which were applied to determine the glass transition temperature and the microhardness of unexposed and exposed wood coatings, respectively. Both parameters are very sensitive towards changes in intermolecular interactions of polymer based materials and were found to be very suitable for the detection of weather-related structural changes and resulting damages or functional failing of exterior wood coatings.