Thermal and moisture flux in soft fibreboards

The thermal conductivity of several wet and dry processed industrial soft fibreboards was determined at temperatures between10°C and30°C. Additionally, the thermal conductivity was tested relative to the moisture content ranging from an oven-dry sample to a moisture content of 85% relative humidity. Furthermore, the water vapour diffusion was investigated to determine the resistance factor and the diffusion coefficient under ‘dry cup' and ‘wet cup' conditions and the sorptions were tested by means of the sorption isotherms. The thermal conductivity increases with increasing temperature at about 0.45% per Kelvin and with increasing moisture at about 0.17×10−2W/mK per percent volumetric moisture content. Furthermore, the thermal conductivity depends on the manufacture (dry or wet process) and is influenced by density. The water vapour resistance factor increases and the diffusion coefficient decreases with increasing density. Both factors decrease with increasing moisture content and they are dependant on board thickness, composition and manufacturing. The sorption isotherm is similar to solid wood below about 80% relative humidity but strongly increases for soft fibreboards with binding fibres and additives of ammonium phosphate or sodium borate and boric acid when above 80% relative humidit

Untersuchungen zur Bestimmung der Poissonschen Konstanten an Fichtenholz

Zusammenfassung: An Fichtenholz wurden mittels inkrementaler Wegaufnehmer die E-Moduln in den drei Hauptschnittrichtungen (längs, radial, tangential) und die sechs Poissonschen Konstanten nach Klimatisierung im Normalklima bestimmt. Das Verhältnis der E-Moduln ET:ER:EL wurde mit 1:2,43:25,4 ermittelt. Es wurden folgende Poissonsche Konstanten bestimmt: μRL= 0,022, μTL=0,015, μLR=0,376, μLT= 0,420, μTR=0,335, μRT=0,64

Porosity and pore size distribution of different wood types asdetermined by mercury intrusion porosimetry

In this work, densities and porosity parameters are determined on domestic and overseas soft- and hardwoods by application of pycnometric methods and mercury intrusion porosimetry (MIP). Great variability was found in bulk density, porosity and in the specific surface area. According to the pore size distribution, four pore size classes could be distinguished: macropores (radius 58-2μm and 2-0.5μm), mesopores (500-80nm), and micropores (80-1.8nm). The pore size distribution can vary even in the case of comparable pore volumes. The hardwoods, particularly the European diffuse-porous ones, show a higher amount of micropores, which represent the microvoids or cell wall capillaries. Ahigh cumulative pore volume can also be the result of a high content of micropores with poorer accessibility. The value of the total specific surface area from MIP measurements is, generally, below those values obtained by the water vapour adsorption technique. These results can provide information for further investigations on the sorption behaviour and the fluid intake as technological characteristics in industrial processes of impregnation and penetration of coating materials or adhesive

Thermal conductivity and water vapour transmission properties of wood-based materials

For several wood-based materials (plywood, OSB, melamine faced board (MFB), particle board and fibre board), the thermal conductivity was determined as afunction of the temperature (ranging between 10 and 30°C) and also the moisture content (from an oven-dry sample up to amoisture content at 80% RH). Furthermore, the water vapour resistance factor of these materials as well as of the coating (at MFB) and the diffusion coefficient were determined under dry cup (performance at low humidity dominated by vapour diffusion) and wet cup (performance at high humidity with liquid water and vapour transport) conditions. Thermal conductivity increases with rising temperature, moisture content and density. Moreover, aclear decrease of thermal conductivity was found with decreasing particle size at the same density level, from solid wood over plywood and particle board to fibre board. The water vapour resistance factor of the wood-based materials increases with rising density and decreases with increasing moisture content. An influence of the particle and fibre board thickness was also revealed. In contrast to the remaining materials, an increase of the water vapour resistance factor with increasing moisture content was measured for the coating. The diffusion coefficient decreases with rising density and moisture conten

Moisture-dependent, viscoelastic creep of European beech wood in longitudinal direction

In the present study, the pure viscoelastic behaviour of European beech wood is analysed in the longitudinal direction at three different moisture contents. The moisture-dependent creep compliance is identified using a four-point bending test device. The viscoelastic behaviour is ascertained to be linear with moisture content and quantified by means of a Kelvin-Voigt model approac

Moisture-dependent, viscoelastic creep of European beech wood in longitudinal direction

ISSN:0018-3768ISSN:1436-736

Untersuchungen zur Quellung und Wärmedehnung von Faser-, Span- und Sperrholzplatten

Zusammenfassung: Es wurde die Quellung und die Temperaturdehnung in Plattenebene sowie die Dickenquellung von diversen Holzwerkstoffen (Faser-, Span- und Sperrholzplatten) untersucht. Dabei zeigte sich ein stark reduziertes Quellverhalten (differentielle Quellung) in Plattenebene zwischen 80% und 95% relativer Luftfeuchte (rLF) gegenüber dem Quellverhalten zwischen 35% und 80% rLF bei allen untersuchten Plattentypen. Weiter konnte eine Abhängigkeit der Quellung von der Dichte innerhalb einer Holzwerkstoffgruppe (innerhalb der verschiedenen Sperrholzplattentypen sowie innerhalb der verschiedenen Spanplattentypen) festgestellt werden. Die unterschiedliche Quellung der Sperrholzplatten parallel und quer zur Faserlängsrichtung der Deckschicht war stark von der gemessenen Schicht abhängig (⊥ oder ||). Bei der Dickenquellung konnte innerhalb der verschiedenen Spanplattentypen eine Abhängigkeit von der Dichte festgestellt werden. Bei den Sperrholzplatten entsprach die Dickenquellung in etwa der tangentialen Quellung bei Vollholz, trotz der radialen Ausrichtung der einzelnen Furniere. Dies liegt in der behinderten Quellung quer zur Faserrichtung in der Plattenebene begründet. Die Temperaturdehnung ist mit 3.7 bis 5.9×10-6m/(m·K) bei allen Holzwerkstoffen sehr gering. Bei der untersuchten Sperrholzplatte (niedrigster Wert) entspricht sie der Wärmeausdehnung von Vollholz in Längsrichtung. Die Wärmeausdehnung der Span- und Faserwerkstoffe beträgt ungefähr das 1,5-fache des Sperrholze

Der Einfluss der Temperatur auf die Biegefestigkeit und den Elastizitätsmodul bei verschiedenen Holzwerkstoffen

Zusammenfassung: Der Einfluss der Temperatur auf die Biegefestigkeit und den Elastizitätsmodul von acht verschiedenen Holzwerkstoffen (2 MDF, 1 OSB, 2 Spanplatten, 2 Sperrholzplatten (Buche und Fichte), 1 Massivholzplatte) im Bereich zwischen -20°C und +60°C wurde untersucht. Dabei wurde zwischen 20°C und 60°C eine Reduktion der Biegefestigkeit von 12-39% und eine Reduktion des Elastizitätsmoduls von 14-46% gemessen. Das Verhalten der Arbeit bis zur Maximalkraft variierte in diesem Bereich stark. So wurde zwischen 20°C und 60°C je nach Holzwerkstoff eine Zunahme bis zu 48%, aber auch eine Abnahme bis zu 31% gemessen. Zwischen 20°C und -20°C nahm die Biegefestigkeit zwischen 5% und 22% und der Biege-E-Modul zwischen 3% und 27% zu. Nur bei der Massivholzplatte in Längsrichtung nahm der Biege-E-Modul um 6% ab. Bei der Arbeit bis zur Maximalkraft streuten die Werte zwischen einer Abnahme um 19% und einer Zunahme um 10

Thermal behaviour of Norway spruce and European beech in and between the principal anatomical directions

Thermal conductivity (ThCond), thermal diffusivity and heat capacity of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) have been determined for all principal directions - radial (R), tangential (T) and longitudinal (L) - depending on the moisture content (MC) and ThCond was additionally measured in 15° steps between these directions. The ThCond was determined in a guarded hot plate apparatus. For determining thermal diffusivity and heat capacity, the same apparatus was supplemented with thermocouples and the temperature evolution was evaluated numerically by a partial differential equation. The results show expectedly that ThCond increases with increasing MC, whereby the highest increment was observed in T and the lowest in L direction. ThCond is higher for beech than for spruce in all anatomical directions and the conductivity for both species is more than twice as high in L direction than perpendicular to grain. The highest ThCond is found for beech at a grain angle of approximately 15°. The lowest ThCond shows spruce at an angle of approximately 60° between T and R direction. Thermal diffusivity is similar for both species and decreases with increasing MC. Its differences with regard to the anatomical directions correlate with those of the ThCond values. Heat capacity is lower for beech than for spruce and shows a clear increase with increasing M