VOLUME 52, ISSUE 5/2011

The low spreading of automated systems for hardwood grading leads to the conclusion that application limiting deficits exist. Different users of this grading technology point out that these shortcomings are in the range of possible color grading. Wood-sections with red heart, stain or enemas caused by fungi can be problematic to the grading systems. Part 1 of this article defines the different grading problems. Part 2 discusses a possible solution to improve existing deficits in color grading by an innovative sensor concept. To test this newly developed sensor the different color features of beech wood are classified in this preliminary study. This innovative sensor concept should improve existing grading systems and lead them to more precise defect detection. Therefore the different color matters of beech wood are classified during this pre-investigation.

By the development of “BalanceBoard” with a combination of wood and expanded starchy grains with lower bulk densities like cereals, maize, rice, amaranth and quinoa the raw density of the boards can be reduced about 30 %. The mechanical-technological properties, like internal bond strength, surface strength and thickness swelling are comparable to the technical demands of standard chipboards and could also partially be optimized. Pfleiderer Group has succeeded with BalanceBoard in a new generation of wood derived timber product which is produced with high marketability in a patented procedure.

The new development which is introduced under the name Conti-Sound takes all significant disturbing variables during calibration into account by measurement of the sound reflection including the influence of varying properties and conditions of the panel surface. It compensates the developing contamination of the sensors during production by a so called no-load measurement in the gaps of the panels. It simplifies the use of so called sound pictures by self-learning software which supersedes the necessity to set the calibration for each panel grade. This allows not using a costly movable frame for calibration purpose. The informative value about changing panel properties by means of a sound picture will be improved. Further new development beside under the names Ply-Scan and Blow-Scan take specific characteristics of different panel types and different requirements of data evaluation and visualization into account.

Thermal treatment of wood leads to the formation of decomposition products which have an influence on the fibre-to-fibrebonding as well as on the emission of the fibres and MDF made there from. Pulps from pine and beech wood chips were prepared using the thermo-mechanical (TMP process) and chemo-thermo-mechanical process (CTMP process). Part of the pulps was washed by water and urea solution, respectively to remove wood decomposition products. The unwashed fibres contained more soluble lignin components and monomeric sugars compared to the washed fibres. The results reveal that washing of the fibres increased the pH value of their cold water extracts due to the remove of volatile formic and acetic acids. Washing the fibres with urea solution reduced the release of acetic acid more than washing with water. Also, the emission of volatile ketones and alcohols was diminished by washing. In contrast, the emission of volatile aldehydes increased partly. Moreover, formaldehyde release of unwashed and washed CTMP was lower compared to corresponding TMP. The formaldehyde release of the fibres decreased significantly by washing, especially with the urea solution.

The requirements for surface quality of wood based panels are increasing with new products in spite of non existing quantification. The process safety of the manufacturing process requires a technical monitoring of quality. Existing methods and instruments for the quality control of surfaces can not be used on account of the measurement speed and the ambient conditions. A measurement method and a interpretation algorithm was developed, that directly delivers a statement about the roughness and waviness of the surface of MDF and HDF boards in the manufacturing plant on the basis of an image processing system. It creates no standard-compliant values for the characterization of surface, but about the change of surface features can be concluded to the causes of errors and quality.

At the Institut für Holztechnologie Dresden (IHD) first research was carried out on the development of a biotechnological process for the production of spalted timber. Therefore, the fungal species involved in spalting of native wood was analyzed by molecular methods. The interaction of selected fungi was studied on artificial media and on wood specimens. It is shown that different fungi induce zone lines on beech but in a lower intensity than in native spalted timber. The establishment of an economic process for the biotechnological production of spalted wood requires more systematic studies to determine process parameters. The selection of fungi and the process control by substrate humidity and temperature are particularly important.

Wood of Norway spruce (Picea abies (L.) Karst.) is known to have a low permeability which is related mainly to the aspiration of bordered pits during wood drying. The resulting low impregnability complicates treatment of Norway spruce with liquid preservatives or wood modification substances. Short term incubation of Norway spruce wood with the white rot fungus Physisporinus vitreus is a biotechnological approach for improving the permeability of refractory species. The process, called bioincising, is based on the growth of the fungal hyphae through the tracheids and xylem ray parenchyma and in consequence, a preferably selective degradation of pit membranes. The present article provides the most relevant findings from intensive research and optimization on the bioincising-process.

The effect of different physical-chemical pre-treatment methods onto the surface properties of Polyethylene and Polypropylene based WPC was studied. Among them are flame treatment, the Pyrosil technique, plasma treatment with and without silane dotation as well as gas phase fluorination. It was shown that all of the investigated techniques lead to an enhancement of the specific surface energy of the WPC materials whilst the strongest growth was achieved by plasma and fluorination techniques. The increase of the polar fraction of the surface energy indicates the formation of functional groups on the WPC surface.