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Pleschberger H.,Wood us Competence Center for Wood Composites and Wood Chemistry | Teischinger A.,Wood us Competence Center for Wood Composites and Wood Chemistry | Teischinger A.,University of Natural Resources and Life Sciences, Vienna | Muller U.,Wood us Competence Center for Wood Composites and Wood Chemistry | And 2 more authors.
Drying Technology | Year: 2013

The influence on the drying behavior as well as the mechanical properties of lumber of small-diameter hardwoods at different low-temperature convection kiln dryings was investigated. Standard test methods in three-point-bending and the modulus of elasticity in three-point-bending, compression tests parallel and perpendicular to the grain, as well as Brinell hardness tests were performed in order to assess the drying quality. Furthermore, non-standard tensile tests perpendicular to the grain and fracture energy tests in radial/longitudinal and also in tangential/longitudinal crack propagation systems were carried out as a most sensitive test method. The results showed significant changes of the specific fracture energy, bending strength, compression strength parallel and perpendicular to the grain, and the Brinell hardness with good drying performance at the same time. © 2013 Copyright Taylor and Francis Group, LLC.


Veigel S.,University of Natural Resources and Life Sciences, Vienna | Follrich J.,Wood us Competence Center for Wood Composites and Wood Chemistry | Gindl-Altmutter W.,University of Natural Resources and Life Sciences, Vienna | Muller U.,Wood us Competence Center for Wood Composites and Wood Chemistry
European Journal of Wood and Wood Products | Year: 2012

In this study, lap shear strength as well as specific fracture energy of bonded specimens from spruce wood were determined in order to verify whether the calculation of adhesive fracture energy is a suitable tool for the mechanical characterization of different adhesive systems, especially in comparison to the commonly used lap joint test method according to the European standard method EN 302-1. Two different test methods were applied for measuring the fracture energy by using a double cantilever beam (DCB). For both methods the DCB is separated along the bond in mode I fracture. While both adhesive systems applied showed similar shear strength values, differences were much more pronounced regarding the specific fracture energy of the bonded joints. Especially the application of the fracture energy concept, i.e., the separation of the DCB in a single load cycle, provided results with higher informative value than the results of standard lap shear tests. © Springer-Verlag 2010.


Riegler M.,Wood us Competence Center for Wood Composites and Wood Chemistry | Andre N.,University of Tennessee at Knoxville | Gronalt M.,University of Natural Resources and Life Sciences, Vienna | Young T.M.,University of Tennessee at Knoxville
International Journal of Production Research | Year: 2015

In regression analyses, correlations between independent variables (e.g. process variables) and dependent variables (e.g. product quality) are of major interest. However, only statistically significant correlations ensure a reliable interpretation of how process variables affect product qualities. In this respect, accurate time alignment of independent variables is crucial to obtain regression models with acceptable validation that are influenced by temporal phenomena (e.g. industrial processes) only. In this study, the commonly used static form of time alignment, where only the distances between consecutive process parameters and the average production speed are considered, is compared to a newly developed dynamic calculation of time lags. The dynamic calculation of time lags was achieved by modelling the continuous bulk material flow. The two different methods of calculation were then applied on an industrial production of particleboards to predict final board strength properties. Results of regression models showed that the use of dynamically calculated time lags improved the predictability of the internal bond strength of boards by 67% compared to statically calculated time lags. Consequently, final product strength properties could be predicted more accurately, which should lead to lower costs of rejects and a higher efficiency of material inputs. © 2015 Taylor & Francis.


Oltean L.,University of Natural Resources and Life Sciences, Vienna | Teischinger A.,University of Natural Resources and Life Sciences, Vienna | Hansmann C.,Wood us Competence Center For Wood Composites and Wood Chemistry
Wood Research | Year: 2010

This paper displays the results of a survey as the second part of a research work concerning the wood surface discolouration of the most traded wood species in Europe due to UV light irradiation. The aim of this study is to visually classify the wood surface discolouration according to the L*, a*, b* and ΔE* values after 120 hours of artificial indoor sunlight exposure. A questionnaire was prepared in order to evaluate the attitude of researchers in the field of wood science, towards the surface discolouration due to UV light irradiation of sixteen wood species. From this survey it emerged that there was a low uniformity of answers, and the observers appreciate colour and colour changes subjectively. A visual classification of the wood surface discolouration of specific wood species and a correspondence to the measured values is given. Recommendations for future research works are also presented.


Frybort S.,Wood us Competence Center for Wood Composites and Wood Chemistry | Mauritz R.,Doka Industrie GmbH | Teischinger A.,BOKU Vienna | Muller U.,Wood us Competence Center for Wood Composites and Wood Chemistry
European Journal of Wood and Wood Products | Year: 2010

Effects of chemical treatment of wood on the bonding strength of Norway spruce strands (Picea abies Karst.) embedded in a-cement matrix were investigated by means of a-pull-out test. Strands of varying thickness were used whereas a-strong influence of thickness on bonding strength could be observed. Using thick strands (800 μm) showed negative effect on bonding strength which is due to the swelling effect. The treatment of thin strands (400 μm) showed that using wet strands (∼ 90% moisture content) leads to the best results compared to untreated dry (12%) strands. By addition of setting accelerators (ammonium chloride) bonding strength of wet strands was even improved. Furthermore, effects of hot water and sodium hydroxide extraction as well as sodium silicate treatment were examined. © 2009 Springer-Verlag Zusammenfassung.


Forsthuber B.,Holzforschung Austria | Muller U.,Wood us Competence Center for Wood Composites and Wood Chemistry | Teischinger A.,University of Natural Resources and Life Sciences, Vienna | Grull G.,Holzforschung Austria
Polymer Degradation and Stability | Year: 2013

In this study, we hypothesized that the use of UV absorber of the hydroxy-benzotriazole class (BTZ) and micronized TiO2 (NTiO 2) as mineral UV screener could stabilize the chemical and mechanical properties of clear wood coatings based on a high Tg/low T g multiphase acrylic binder dispersion. The photooxidation rates were compared using ATR-FTIR techniques and tension tests. For qualitative and quantitative chemical analysis and correlation to the mechanical properties, multiple linear regression (MLR) was used, which was a suitable method to monitor the chemical changes of the polymeric binder and to investigate the influence of these light stabilizing additives on the photooxidation behavior. The analysis of mechanical properties of the acrylic binder during exposure to Xenon arc light showed that both BTZ and NTiO2 stabilized the Young's Modulus and the elongation at break during the whole cycle. BTZ showed better results. However, it led to a strong decrease of the initial Young's Modulus whereas NTiO2 showed no comparable effect. We concluded that BTZ was very efficient in reducing the photooxidation and the accompanied change of the elastic properties of the acrylic binder. NTiO2 only stabilized the high Tg component of the multiphase acrylic binder whereas the photooxidation of the low Tg component was accelerated. This may be explained by a photocatalytical activity of NTiO2. © 2013 Elsevier Ltd. All rights reserved.


Konnerth J.,University of Natural Resources and Life Sciences, Vienna | Eiser M.,Wood us Competence Center for Wood Composites and Wood Chemistry | Jager A.,Vienna University of Technology | Bader T.K.,Vienna University of Technology | And 5 more authors.
Holzforschung | Year: 2010

Red oak wood (Quercus rubra L.) samples were submitted to an enzymatic treatment with a commercial mixture of hemicellulases aiming at the selective depolymerization and removal of the hemicelluloses. Mechanical properties of treated samples were characterized and compared with untreated samples at two hierarchical levels. At the macrolevel, tensile properties revealed to be less sensitive to degradation of the cell wall matrix compared to compression and hardness properties. Results obtained through indentation at the microlevel indicated that hardness and the so-called reduced modulus of treated wood were significantly lowered. Accordingly, hardness and reduced elastic modulus have proven to be most sensitive to modification of the cell wall matrix by reducing the content of hemicelluloses. It is proposed that transversal and shear stresses, which are mainly carried by the cell wall matrix, are additional parameters having strong effects on elastic modulus obtained by nanoindentation. Micromechanical modeling was employed to confirm the observed changes. There is consistency between the measured and the modeled properties, obtained at both the microlevel and the macrolevel of wood. © 2010 by Walter de Gruyter Berlin New York.


Oltean L.,University of Natural Resources and Life Sciences, Vienna | Teischinger A.,University of Natural Resources and Life Sciences, Vienna | Teischinger A.,Wood us Competence Center for Wood Composites and Wood Chemistry | Hansmann C.,Wood us Competence Center for Wood Composites and Wood Chemistry
European Journal of Wood and Wood Products | Year: 2011

The knowledge of the influence of different temperature ranges on mechanical properties of kiln dried timber is very important in structural applications. The current paper deals with an investigation of the influence of low and moderate temperature drying schedules on the selected mechanical properties of Norway spruce wood (Picea abies L.). The drying experiments were performed at four different temperatures (45, 55, 65, and 80°C) and clear wood specimens were prepared for the mechanical tests, three-point bending test, impact bending test, and tensile test perpendicular to the grain, respectively. The results of this systematic investigation were statistically analysed and as a conclusion, it can be stated that the mechanical properties investigated were not influenced by the drying temperatures applied. © 2010 Springer-Verlag.


Follrich J.,Wood us Competence Center for Wood Composites and Wood Chemistry | Teischinger A.,Wood us Competence Center for Wood Composites and Wood Chemistry | Teischinger A.,University of Natural Resources and Life Sciences, Vienna | Muller U.,Wood us Competence Center for Wood Composites and Wood Chemistry
European Journal of Wood and Wood Products | Year: 2011

The effect of ageing processes on internal bond strength of three-part specimens produced from Norway spruce wood (Picea abies Karst.) bonded with one-component polyurethane (PUR), two-component emulsion polymer isocyanate (EPI), melamine-urea-formaldehyde (MUF) or phenol-resorcinol-formaldehyde (PRF) adhesive was studied. By varying the grain angle of the middle part from 0° (parallel to grain of the surface layers) to 90° (perpendicular to grain of the surface layers) in incremental steps of 10° the effect of grain direction was investigated. The specimens were exposed to a three-step ageing cycle lasting for seven days (50°C/95% relative humidity (rH), -20°C/65-70% rH and 75°C/15% rH) which was repeated twelve and twenty-four times, respectively. In general, a decrease in internal bond strength of the exposed specimens was observed. For all tested adhesive systems, influence of ageing processes was more pronounced for flat-to-end grain joints compared to longitudinal joints. For samples bonded with PUR adhesive strength reduction was lower compared to the other adhesives used. © 2010 Springer-Verlag.


Follrich J.,Wood us Competence Center for Wood Composites and Wood Chemistry | Stockel F.,Wood us Competence Center for Wood Composites and Wood Chemistry | Konnerth J.,University of Natural Resources and Life Sciences, Vienna
Holzforschung | Year: 2010

Three-part specimens were produced from Norway spruce wood (Picea abies Karst.) and bonded with the following adhesives: melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF), and a two-component emulsion polymer isocyanate (EPI). The effect of alternating climate conditions on bond strength was studied by tensile tests. The specimens were exposed to a three-step ageing cycle lasting for 7 days [50°C/95% relative humidity (RH), -20°C/65- 70% RH and 75°C/15% RH] which was repeated 24 times. In general, a decrease in internal bond strength of all exposed specimens was observed but it was highest in the case of MUF-bonded joints. Furthermore, a significant decrease of the tensile strength of the wood adherend perpendicular to the grain in the tangential direction was determined after the cyclic climatic changes. The mechanical performance of the different adhesives in the bond line was tested by means of nanoindentation. Reduced values of elastic modulus, hardness, and total indentation were observed after climatic treatment, particularly for the rigid MUF adhesive, whereas the flexible adhesive EPI did not show such changes. © 2010 by Walter de Gruyter Berlin New York.

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