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Ters T.,University of Natural Resources and Life Sciences, Vienna | Follrich J.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Zuckerstatter G.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Hinterstoisser B.,University of Natural Resources and Life Sciences, Vienna
Wood Material Science and Engineering | Year: 2011

During thermal impact on wood the properties and chemistry of the biopolymer composite are changed. The effect of ageing processes at moderate temperatures on tensile strength perpendicular to grain of Norway spruce wood [Picea abies (L.) Karst.] was studied, along with chemical changes. Test 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. A significant decrease in tensile strength in the tangential direction was observed. Chemical changes in the wood matrix resulting from the artificial ageing cycle were assessed by attenuated total reflection Fourier transform infrared spectroscopy, solid-state [13C]cross-polarized magic angle spinning nuclear magnetic resonance spectroscopy, and detection of the volatile and semivolatile organic compounds by headspace solid-phase microextraction gas chromatography coupled to mass spectrometry. The sugar composition of hemicelluloses was analysed by acid methanolysis. During artificial ageing chemical changes influencing the mechanical properties mainly occurred in the polysaccharide matrix, whereas the lignin remained unaltered. © 2011 Taylor & Francis.


Veigel S.,University of Natural Resources and Life Sciences, Vienna | Muller U.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Keckes J.,Austrian Academy of Sciences | Obersriebnig M.,University of Natural Resources and Life Sciences, Vienna | Gindl-Altmutter W.,University of Natural Resources and Life Sciences, Vienna
Cellulose | Year: 2011

Cellulose nanofibrils were prepared by mechanical fibrillation of never-dried beech pulp and bacterial cellulose. To facilitate the separation of individual fibrils, one part of the wood pulp was surface-carboxylated by a catalytic oxidation using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) as a catalyst. After fibrillation by a high pressure homogenizer, the obtained aqueous fibril dispersions were directly mixed with different urea-formaldehyde-(UF)-adhesives. To investigate the effect of added cellulose filler on the fracture mechanical properties of wood adhesive bonds, double cantilever beam specimens were prepared from spruce wood. While the highest fracture energy values were observed for UF-bonds filled with untreated nanofibrils prepared from wood pulp, bonds filled with TEMPO-oxidized fibrils showed less satisfying performance. It is proposed that UF-adhesive bonds can be significantly toughened by the addition of only small amounts of cellulose nanofibrils. Thereby, the optimum filler content is largely depending on the adhesive and type of cellulose filler used. © 2011 Springer Science+Business Media B.V.


Rathke J.,University of Natural Resources and Life science | Stratev D.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Stratev D.,Vienna University of Technology
BioResources | Year: 2013

In Central Europe the main species that are used for the production of sawn wood are spruce, pine, and European beech. After the sawing process, the sawn timber is technically dried to a certain moisture content by means of condensation drying. The water movement in the cellular structure, which is caused by the drying process, draws some of the extractives into solution. In the process of kiln drying, hot air evaporates the water and the dissolved extractives. Some of the water condenses on the floor and the walls of the kiln, while the rest is blown out with the steam. Therefore, condensate was taken from the bottom of the kiln as well as from the energy recovery system. A chemical analysis by means of purge-and-trap showed the presence of volatiles that could be classified as typical for the wood materials from which they originated under the conditions of high temperature and high moisture content.


Rathke J.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Sinn G.,University of Natural Resources and Life Sciences, Vienna | Konnerth J.,University of Natural Resources and Life Sciences, Vienna | Muller U.,Wood K plus Competence Center for Wood Composites and Wood Chemistry
Materials | Year: 2012

Internal bond strength testing is a widely used approach for testing quality traits of wood based panels. Generally, failure of internal bond specimens is due to adhesion and/or wood failure in the specimen. It has been reported that a composite product with a large variation in the vertical density profile fails in the center part of the board which is either the middle of the core layer or the transition zone between core layer and face layer. The density in the failure zone is typically 50% lower than the maximum density in the face layers. The aim of this study was to analyze the strain distribution in a specimen under tension perpendicular to the panel plane. The results showed that a high variety of strain magnitude occurred in the specimen. The strain is either aligned with the tension direction or a tension zone is built in one of the edge zones leading to failure. Vector graphics of the specimen show the problematic test setup of internal bond strength measurement. Strain spots in the edges lead to the assumption of an uneven stress distribution due to the momentum which results from non-perfect alignment or irregularities in the test setup.© 2012 by the authors.


Stratev D.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Stratev D.,Vienna University of Technology | Hansmann C.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Rathke J.,University of Natural Resources and Life Sciences, Vienna
BioResources | Year: 2015

The demand of the global economy for fossil resources needed for the production of fuel and basic chemicals is expected to exceed supply in the coming decades. Because of its heavy reliance on fossil fuels for increased efficiencies over the 20th century, the chemical industry has been particularly motivated to harness alternative raw materials, such as biomass, that are environmentally and economically sustainable. Biorefineries have provided stable, large-scale means of converting biomass into base chemicals, but until recently the main focus has been on the conversion of the mainly cellulosic fraction of edible plants into biofuels. Second- and third-generation biorefineries are striving to be more economically integrated and sustainable by utilizing raw material fractions to a greater extent and by not competing with the agriculture and food sector. The goal of this study was to evaluate the potential of kiln-dry condensate as a source for production of bio-based chemicals. The condensates of three typical European wood species were analyzed. Part 1 evaluated the volatile extractives; Part 2 concentrates on semi- and non-volatile extractives of kiln-dry condensates.


Sinn G.,University of Natural Resources and Life Sciences, Vienna | Muller U.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Konnerth J.,University of Natural Resources and Life Sciences, Vienna | Rathke J.,Wood K plus Competence Center for Wood Composites and Wood Chemistry
Materials | Year: 2012

This is the second part of an article series where the mechanical and fracture mechanical properties of medium density fiberboard (MDF) were studied. While the first part of the series focused on internal bond strength and density profiles, this article discusses the fracture mechanical properties of the core layer. Fracture properties were studied with a wedge splitting setup. The critical stress intensity factors as well as the specific fracture energies were determined. Critical stress intensity factors were calculated from maximum splitting force and two-dimensional isotropic finite elements simulations of the specimen geometry. Size and shape of micro crack zone were measured with electronic laser speckle interferometry. The process zone length was approx. 5 mm. The specific fracture energy was determined to be 45.2 ± 14.4 J/m 2 and the critical stress intensity factor was 0.11 ± 0.02 MPa. © 2012 by the authors; licensee MDPI, Basel, Switzerland.


Hansmann C.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Konnerth J.,University of Natural Resources and Life Sciences, Vienna | Rosner S.,University of Natural Resources and Life Sciences, Vienna
Wood Material Science and Engineering | Year: 2011

Contact-free digital image analysis was performed of the radial shrinkage of fresh, fully saturated small spruce wood beams. An experimental test set-up was developed to ensure constant distance from the charge-coupled device camera to the sample surface as well as constant climate and light conditions during the whole experiment. Dimensional changes were observed immediately after the drying process began. An unexpected distinct effect could be observed which could not be explained by drying surface layers only. After a fast initial radial shrinkage a slowing down of the dimensional changes occurred at high mean moisture contents. A complete interruption of any dimensional changes followed. Finally, a recovery from shrinkage was even observed. It is assumed that strong negative pressure occurred in the fully saturated capillaries owing to dehydration which led to additional dimensional changes. As a consequence, the break of the water column and aeration in these capillaries finally resulted in a recovery period in the shrinkage rate due to the pressure release. After this effect, the dehydration was characterized by a phase of fast and almost linear shrinkage due to drying surface layers. Finally, the shrinkage slowed down to zero when reaching equilibrium moisture content. © 2011 Taylor & Francis.


Hauptmann M.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Pleschberger H.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Mai C.,University of Gottingen | Follrich J.,University of Natural Resources and Life Sciences, Vienna | Hansmann C.,Wood K plus Competence Center for Wood Composites and Wood Chemistry
European Journal of Wood and Wood Products | Year: 2012

This study seeks to assess the potential use of the CIEDE2000 color difference equation in wood science. Therefore, a set of oak wood samples were prepared and assessed by experts. The visual perception of the observers was correlated with the two different color difference equations CIELAB from DIN 6174 and the CIEDE2000 equation. For a practical example two different types of wood were bleached and exposed to UV-light. The results showed that the CIEDE2000 equation outperformed the CIELAB equation. The CIELAB equation showed generally an overestimation of the color change (ΔE) for wood applications, compared to the nontrivial CIEDE2000 equation from 2001. © Springer-Verlag 2011.


PubMed | University of Natural Resources and Life Sciences, Vienna, Wood K plus Competence Center for Wood Composites and Wood Chemistry and Austrian Academy of Sciences
Type: Journal Article | Journal: Cellulose (London, England) | Year: 2015

Cellulose nanofibrils were prepared by mechanical fibrillation of never-dried beech pulp and bacterial cellulose. To facilitate the separation of individual fibrils, one part of the wood pulp was surface-carboxylated by a catalytic oxidation using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) as a catalyst. After fibrillation by a high pressure homogenizer, the obtained aqueous fibril dispersions were directly mixed with different urea-formaldehyde-(UF)-adhesives. To investigate the effect of added cellulose filler on the fracture mechanical properties of wood adhesive bonds, double cantilever beam specimens were prepared from spruce wood. While the highest fracture energy values were observed for UF-bonds filled with untreated nanofibrils prepared from wood pulp, bonds filled with TEMPO-oxidized fibrils showed less satisfying performance. It is proposed that UF-adhesive bonds can be significantly toughened by the addition of only small amounts of cellulose nanofibrils. Thereby, the optimum filler content is largely depending on the adhesive and type of cellulose filler used.


Follrich J.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Vay O.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Veigel S.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Muller U.,Wood K plus Competence Center for Wood Composites and Wood Chemistry | Muller U.,University of Natural Resources and Life Sciences, Vienna
Journal of Wood Science | Year: 2010

The effect of different machining processes on surface roughness and on adhesive tensile strength of end-grain-bonded spruce wood specimens was studied. Surfaces that had been cut with two different circular saws containing 48 and 96 teeth were compared with those that had been further processed by smoothing with a microtome, machine planing, or sanding. Two different adhesives and two different spreading quantities were used to join the test specimens by their end-grain surfaces. Increasing tensile strength of the bonded specimens was observed with increased surface roughness, which was ascribed to an enlarged bonding area in the case of circular-sawn samples with a rough surface. On the other hand, more pronounced starving of the bond line and thus decreased bond strength was observed in the more open cells of the smoothed end-grain surfaces. A positive effect regarding tensile strength was further observed with increased spreading quantity of the adhesives. Machining was found to particularly affect earlywood tracheids, whereas surface roughness of latewood tracheids was comparable for the differently treated end-grain surfaces. © 2010 The Japan Wood Research Society.

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