VOLUME 50, ISSUE 3/2009

The mechanical and hygric characteristics of particleboards depend on numerous factors; these are inter alia the morphological, physical and chemical properties of the raw materials. Some differences in the properties between wood and residues of agricultural plants like length of the fibers, content of inorganic components and chemical composition are represented here. In particular, some chemical properties of particles made from stalks of sunflower (Helianthus annuus), topinambur (Helianthus tuberosus), maize (Zea mays) and miscanthus (Miscanthus sinensis gigantheus) as well as hemp shives will be specified.

The emission of formic and acetic acid from differently prepared particleboards was determined using the flask method technique. The boards were made from sap- and heartwoods of Douglas fir (Pseudotsuga Menziesii (Mirb.) Franco) using trees of various ages and from two different sites. The boards were bonded with alkaline phenolic resins (PF-resins) and tannin formaldehyde resins (TF-resins) as well as with acid curing melamine urea phenol formaldehyde resins (MUFF-resins) and adhesives based on polymers of diphenylmethandiisocyanates (PMDI). The results reveal that the emission of volatile acids is decisively controlled by the pH-value of the water extractives of the boards as well as by their buffering capacity. At high pH-value the emission of formic acids (pka = 3,7) is much more suppressed due to the strong formation of formate ions than in case of acetic acid (pka = 4,8). Moreover, the results indicate that the emission of acetic acid from PF-bonded and TF-bonded boards is much higher than that from MUPF- and PMDI-bonded boards. This fact has been attributed to the degradation of acetyl groups in wood by alkali and is in conformity with previous published results. The difference in the emission of formic and acetic acids from PF- and TF-boards is more pronounced than in MUPF- and PMDI-boards due to the stronger shift in the equilibrium state by alkali towards the formate ions. The age of the trees seems to have, if any, no significant influence on the release of volatile acids; however sapwood emits generally less formic and acetic acid compared to heartwood. The results are of high significance, as recently environmental issues associated with emission of the volatile organic compounds (VOC) from wood-based panels came under scrutiny.

In this study, the relationship between wet bending strength and wet transverse tensile strength of Oriented Strand Boards (OSB) and particleboards (PB) is investigated. The need for research derives from the problem of stress development in the tensile test specimen possibly occurring during wet pre-treatment according to EN 1087-1 and causing pre-existing defects of the composite prior to the actual strength testing. The wet bending strength presents an alternative test method and offers advantages in test handling as there is no need for gluing on test yokes for load transmission. Insofar as a correlation between the values of wet bending strength and wet transverse tensile strength exists, the wet bending strength test could present a suitable method for the evaluation of the composite after wet storage. The results are separated into board types and are shown and discussed in two parts (OSB part 1 and PB part 2). For the particle boards tested the correlations between the test methods with dry and wet specimens as well as the correlations of transverse tensile strength and bending strength were relatively indistinct compared to the OSB options tested in part 1.

The roof construction of the church at Burkhardswalde is a well known architectonical sight of the landscape part of middle Saxony near by Nossen. The church was a church of pilgrimage in the 13th and 14th century. The roof is a steeply inclined architecture, witch is indicating on a certain age of construction. The church history documentations in the archives are incompletely. Definite information’s about the 15th and 16th century, especially about the edification of the roof are no existing. Dendrochronological investigations provided to precise dates of encase of the beam constructions. Wood anatomical and dendrochronological analyses on 6 cores from beams (fire, Abies alba Mill.) could verify that the roof were built in the late Gothic period.

Wood Plastic Composites (WPC) have been used for several years as complex composite materials in a wide range of applications. The development is based on the availability of new fields and products. Most raw material supplier’s offer optimized products for the production of WPC e.g. special pre processed wood fibers and optimized additives. These optimized raw materials can achieve a higher property level and better characteristics, as well as optimized products for its field of use. The second part deals with wood as a major component of WPC and will describe wood in its anatomical specification and its properties; chemical modification of wood particles as well as the pre-processing technology and the properties of the processed material.

Coating is necessary in many cases even for wood-plasticscomposites (WPC) to obtain an acceptable lifetime and a decorative appearance. Next to coating with thermoplastic foils, the application of liquid or powder coatings is an alternative for surface protection of WPC. For this purpose, coating technologies have to be developed, which provide high-quality surfaces, in particular for use under out-door conditions. The low polarity as well as the low surface tension of the polyolefine matrix materials complicate surface coating considerably. Results of coating trials showed that a good wetting of the surface and a sufficient adhesion of the coating layers can be achieved by a pre-treatment of the WPC surfaces with flame or plasma in connection with the application of suitable primers. A high number of coating experiments were carried out under laboratory conditions to demonstrate the application of liquid and powder coatings. Possibilities of their practical realisation will be shown. Prospects of success and risks including the achievable surface quality have been analysed for coating of WPC with liquid or powder coating systems.

Natural drying oils as binder for paints on art objects became known already in the medieval times. Due to the good experiences with those materials, the oils were used also for wood conservation in the 19th century; with fatal consequences to some extend. The wood softens due to irrevasible decomposition phenomenoms of the oils. A feasable method for final restoration is to be developed. Similar decomposition phenomenoms with oils were discovered with oil coated genuine wood products, which were packed to soon and therefore showed a very unpleasant odour. The oils were permanantly damaged. Therefore a later drying process became imposible. Oxidised oil coats are very strong and are only to be removed from paintings through a special technique. Exemplarily it is possible to use laser cleaning and solvent gels. In preservation of monuments and historic buildings boiling linseed oil has shown great results in removing old paint coats, since not only an impregnation but also an undercoat of the wood has been achieved. After experimenting in the paint industry with synthetic resin systems in the past, a renaissance of natural products can be seen today. Besides the fundamental question for renewable raw materials, a trend can be seen in good and approved product features. In the field of restoration and preservation, oil paint has the advantage of appropriate aging of the surface.

The mineral impurities aggravate the quality of the chipboards regarding the cutting property. Within the framework of a German Federal Ministry of Economy (BMWi) research project a new quick test for chipboards was developed, which allows the chipboard branch to check the chipboards regarding mineral impurities quickly, cost-effectively and practicably.

Since June 2008, at www.silvaportal.info an information portal on forest and forestry of the border close region of Saxony, Czech Republic (Bohemia) and Poland (Lower Silesia) is available. The portal has been established within two INTERREG-IIIA-Projects by the Institut für Holztechnologie Dresden (IHD). Silvaportal contains information on forest authorities, on natural of forests, and forestry and gives an overview on culture and tourism of the border region and names partners from forestry and wood industry.