VOLUME 53, ISSUE 2/2012

The hydro thermo mechanical densification process depends considerably from the parameters temperature, conditioning time and pressing time. A Master thesis examines their impact to mechanical properties. Due to resource issues, the economic utilization of fast grown and low value wood has currently received a lot of attention. Viscoelastic thermal compression (VTC) is a densification process for veneers that takes advantage of lignin glass transition at elevated temperatures. This patented process takes place in a specially equipped hot press with heating, cooling and steam boiler components. The process consists of a conditioning phase by steaming the hybrid poplar veneers, the compression phase and a cooling phase in order to solidify the lignin. The experimental design of the current study comprised different treatment combinations of conditioning time, compression rate and compression time, and evaluation of the modulus of elasticity in bending (MOE), modulus of rupture (MOR), shear strength parallel to the grain and glueability with different loading rates. The results show that increasing conditioning time elevates MOE, MOR and shear strength. The rate of compression did not show a significant trend and compression time improves MOR and MOE. Shear strength was not influenced in any systematic trend. An optimal phenol formaldehyde solid resin loading rate in the range of 50 g/m2 and 70 g/m2 could be identified.

Bioincising with Physisporinus vitreus is a process that aims at the improvement of the wood preservative uptake in wood species with a low permeability, such as Norway spruce (Picea abies (L.) Karst.). Bioincised and untreated specimens were dipped or vacuum impregnated with wood preservatives and substance uptake was assessed gravimetrically. The penetration 3-iodo-2-propynyl butylcarbamate (IPBC) into the wood was additionally analyzed by high-pressure liquid chromatography (HPLC) and wood resistance was assessed according to the standards EN 152-2 (1988) and EN 113 (1997). In the bioincised wood samples a significantly higher uptake of all the different preservatives was determined and the HPLC-method revealed that IPBC penetrated deeper into bioincised wood than into control samples. The improved uptake of preservatives into bioincised wood resulted in a significantly higher resistance. The results of this study show that the biotechnological process with P. vitreus can be used to improve wood durability by increasing the uptake and penetration of wood preservatives.

The integrated pre-pressing and high frequency pre-heating (IVHF) technology uses an AC field generated by a capacitor. Influenced by the AC field the dipoles within the mat/particle layer are stimulated to oscillate, producing heat. In contradiction to existing technologies, the mat is pre-heated and pre-pressed in the IVHF pre-press. High frequency (HF) pre-heating leads to a faster rise of temperature in the middle of the panel. The critical temperature of 110 °C in the middle of the board was achieved rather in comparison to conventional technology of about 110 s for OSB. In spite of the reduced interior board pressure it was possible to press OSB mats with a moisture content of 10 % in the core layer of the board. For conventional manufacturing the moisture content in the middle of OSB mats is varying between 5 % and 7 %. The main objectives – significant reduction of press duration and significant reduction of binder share – were achieved for OSB manufacturing.

In general, interrelationships between process parameters and properties of heat-treated wood are reasonably well known. However, the already applied processes should be further optimized in terms of the growing requirements of modified products and energy-efficient process management. Odour emissions are, for example, one of the major problems. The present study is dealing with the reduction of emissions of volatile organic compounds (VOCs) of heat-treated wood in autoclaves in two different treatment atmospheres. Additionally, the influence of the process parameters on the mechanical wood properties was investigated. Two test series were conducted under different process conditions in both atmospheres. The results of chemical studies revealed a marked reduction of acid emissions due to process modification, while the release of formaldehyde partly markedly increased. The more the emission values changed, the greater was the modification of the mechanical properties.

The diffusion properties of oil/wax systems on industrially finished wooden floorings were investigated on flooring elements of the wood species steamed beech, beech TMT, oak and European Larch of five producers. Measurements of diffusion properties were carried out with coated wood samples using the drycup-method to determine water vapour diffusion rates and to calculate the diffusion equivalent air layer thickness (sd-value). The tested systems were very open to diffusion and their resistance to water vapour diffusion was either low or could not be measured. In contrast, two film forming parquet coatings (water borne system, UV-curing system) revealed significant resistance to water vapour diffusion. Higher water vapour permeability of wood surfaces treated with oils and waxes may be beneficial to buffer the humidity of interior air.

The service life of polymeric coatings on wood considerably depends on the impacting climatic factors. In order to examine the long-term performance of polymeric wood coatings the ageing properties of three wood coating systems exposed at eight different international sites have been analysed. The dose quantities D for the different exposure sites have been calculated by means of climate indices described in literature. The chemical degradation processes have been investigated by FTIR spectroscopy in the ATR mode on selected bands and evaluated as impact quantity W. According to the models of Pearson and Spearman statistical coherences between D and W could be calculated. On the basis of these correlation results and the main component analysis alternative climate indices with a higher degree of correlation have been derived. Thus, climate-induced degradation processes can also be determined on complex polymeric inorganic mixed systems such as coating materials by means of ATR FTIR spectroscopy. This method is suitable for controlling ageing effects within the polymeric matrix in the wood coating development process.

VOC Regulation (2004/42/EG) and Decopaint Directive (2004/42/EG) enforce the usage of solvent poor coating systems. Beyond their natural origin drying oils exhibit many advantages as excellent optic and haptic, what is increasingly appreciated by the customers. Disadvantages for their further dissemination are the long drying times and partial aggravating odors. In a joint project of the Institut für Holztechnologie Dresden (IHD) with the companies of Hesse GmbH & Co. KG and Venjakob Maschinenbau GmbH cobalt-free oil compositions for furniture and floors were developed which are dry after a two minutes lasting thermal drying by microwave or infrared radiation process. The samples showed no blocking and met the requirements of the Deutsches Institut für Bautechnik (DIBt) according to the sanitary evaluation scheme to estimate the innocuousness of a construction product. Samples with higher chemical resistance were produced by taking the microwave treatment. Because of the high energy consumption and the strong dependence of the surface temperatures after microwave treatment from the wood volume and moisture the optimized infrared technology is recommended.

The options of the utilization of lignin in chemical products are discussed, based on actual literature. Beside the utilization as a polymer, the Lignin can be converted into aromatic monomers and oligomers by various processes: oxidative cleavage, pyrolysis, hydration or enzymatic cleavage. Using these processes, it remains challenging to obtain aromatic monomers in an efficient way in high yield and without the formation of by -products. The processes of hydrolysis, reductive and oxidative cleavage were identified as the most promising techniques for the material use of lignin, while the process of pyrolysis can be used for the production of lignin-based fuels. Combining several cleavage processes can increase the monomer yield. Several approaches exist for the enzymatic cleavage of lignin, but none of them has yet been used for a technical process.