VOLUME 51, ISSUE 5/2010

After pressing medium density fibreboards (MDF) pick up different amounts of moisture depending on the used raw material and binder as well as the attendant relative air humidity (r. h.). Change in the moisture content induces a change in roughness (Ra), irrespective of the used binder. MDF bonded with alkaline tannin-formaldehyde resins (TF-resins) show higher moisture content than the corresponding MUF-bonded boards at the same relative air humidity, nevertheless the TF-boards show less change in roughness with increasing moisture content. Moreover, boards made from recycling fibres exhibit, in general, less increase in moisture content and less change in average roughness (Ra) on increasing relative humidity. This applies for boards bonded with acid curing MUF-resins as well as for alkaline curing TF-resins. MUF-bonded boards with cork in the surface layer have very smooth surfaces and experience less roughness change over a wide range of moisture content.

The present contribution illustrates the curing characterization of a urea-formaldehyde resin by model-free kinetics. Starting with dynamic differential scanning calorimetry, the degree of conversion of the curing reaction is calculated from the resolved thermograms. Model-free kinetic analysis is performed based on these data, allowing the comprehensive characterization of the curing reaction as a function of exposure time and temperature. The combination of model-free curing kinetics with a suitable design of experiments allows the prediction of end product properties from cure-monitoring measurements.

When evaluating the test results of the long-term properties creep behaviour and dimensional stability of OSB and solid wood panels in the present paper, it was observed that the thermal post-treatment of the aforementioned wood-based materials had varying effects on said properties. Whilst the creep behaviour, when tested according to ENV 1156 and DIN 68874-1, respectively, of heat-treated OSB improved in comparison to untreated control samples, SWP values were slightly lowered, although still on a high level. The dimensional stability, however, is not significantly influenced by the thermal modification. All values of OSB and SWP, respectively, were close to one another.

Chemical wood modification is a relatively novel technology to improve material properties of solid wood such as dimensional stability and resistance against wood decaying fungi and insects. The technology improves wood both with regard to already existing applications and offers the possibility to open up new fields of application by reducing several natural weak points of wood. Thus, wood gains competitiveness towards other materials such as plastics, metals and concrete. Already since the 1930th, various processes to modify wood have been developed worldwide. Several thermal and chemical modification processes of solid wood, however, have only been successfully commercialised in the last decade. This review introduces three of the most advanced processes of chemical wood modification: acetylation with acetic anhydride (Accoya®, Titan Wood,), furfurylation with furfuryl alcohol (Kebony®) and cross-linking with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) (Belmadur®, BASF).

The principle of the drawing cut is a possibility to influence the cutting forces, the work piece surface quality, the noise and dust emissions and the tool wear of wood planing positively. This effect can be achieved by increase of the tool inclination angle λS larger than 0°. In the past only the range of this angle between 0° and 50° – mostly lower – has been investigated on planing tools. Following a new approach by Prof. Dr.-Ing. habil. Dr. h. c. Roland Fischer of adjusting the inclination angle of planing tools in a range between 45° and 85° Institute of Wood and Paper Technology (Technische Universität Dresden) has investigated a promising development. A theoretical analysis of the cutting conditions of planing with inclined edges shows reasons, mechanisms and effects of the cutting process. Therefore a base is a look back to the history of planing and research work in the past.

In a study performed at Institut für Holztechnologie Dresden (IHD), different types of conductive MDF were coated with low-bake-powder and UV powder. Various surface designs were chosen as model samples of real furniture elements. The effect of different pre-processing techniques were studied to obtain coatable surfaces. Pre-processing procedures were sanding, thermo-smoothing and brushing. The model samples were produced in the IHD and the surface-properties of the model samples were tested there. The powder coating was carried out on an industrial equipment. The properties of the MDF were tested before powder coating. After the application the surface properties of the coated model samples, such as roughness, thickness of the layer and adhesion of the layer were measured. Climate tests were carried out to investigate cracks. The results of the industrial powder coating experiments demonstrate the strong influence of the pre-processing technique onto the coating quality. It is showed that thermo-smoothing is the best pre-processing procedure for powder coating of MDF.

In this contribution the potential of powder coating technology for the surface finishing of natural fibre based composite parts was investigated. Fibre mats consisting of flax, hemp, kenaf, coco, and wood fibres as well as mixtures thereof were impregnated with two different resins at two resin loadings each. The impregnates were pressed to boards. Half of the boards were surface grinded before finishing with the powder coating and half were powder coated directly for comparison. It was found that any type of used fibre material could be coated without obvious surface problems like uncoated defect areas, pinhole or crack formation. However not all types of fibre mats achieved the same degree of surface quality. Surface quality was quantified using profilometer measurements. The characteristic roughness parameters were used to study the influences of fibre type, resin type and amount and grinding on surface quality.

This article comprises the assessment of market opportunities of modified solid wood (MMH). In this first part of the two article the research design is introduced. It consists of a description of a research model regarding the market opportunities for a new wood product and the necessary methodical steps. The research model is based on the theory of organisational buying behaviour and on the data of a business-to-business survey. The survey included the topics: used raw materials and their strengths in the specific applications; the requirements regarding product properties in the specific applications; degree of information and interest; willingness to use and to pay for modified solid wood; decision process of raw material choice.

In case of constrained moisture expansion swelling often is the reason for the main mechanical load of timber constructions. This paper shows the results of some tests measuring the swelling pressures over time of small wooden specimens made of untreated spruce or after radial densification of spruce.