The effect of fine strands in core layer on physical and mechanical properties of oriented strand boards (OSB) made of beech (Fagus sylvatica) and poplar (Populus tremula)

This paper discusses the influence of three different content levels of fine strands in the core layers on the physical and mechanical properties of European beech and poplar oriented strand boards (OSB). The results show that increasing the fines content in the core layer from 10 to 50 %, based on total board weight has no significant effect on bending strength and modulus of elasticity (MOE). All panels exceeded the minimum requirement for bending strength and MOE set by EN standards. The highest modulus of rupture (MOR) and modulus of elasticity (MOE) was determined for panels solely made of poplar with different level of fines content. Increasing the amount of fines in the core layer raised the internal bond (IB). Panels made with 30 % fines in the core layer showed highest internal bond strength values. As the fines content increased from 10 to 50 %, thickness swelling decreased. Water absorption after 24 h showed the same declining trend as thickness swelling.     

Comparison of mechanical properties of oriented strand board made from trembling aspen and paper birch

This study compared the performance of oriented strand boards (OSB) made from trembling aspen, a low-density hardwood species, and OSB made from paper birch, a medium-density hardwood species. The birch strands were thinner than the aspen strands to ensure a comparable specific surface. Three levels of adhesive content were used: 3.5%, 5.0%, and 7.0%. Internal bond (IB) and modulus of elasticity (MOE) and modulus of rupture (MOR) for flatwise and edgewise bending were determined. Both species performed equally well in IB (3.5% adhesive content: 0.46 MPa, 5.0%: 0.60 MPa, and 7.0%: 0.65 MPa). The values of MOE in flatwise bending were slightly lower for birch than for aspen panels (11.8 GPa for aspen and 10.6 GPa for birch), and the MOR values were not significantly different (combined 68.3 MPa). Edgewise bending properties were not significantly different for the two species with a MOE of 10.5 GPa and a MOR of 43.2 MPa.     

Effects of MDI content on properties of thermally treated oriented strand board (OSB)

The paper discusses the influence of methylene diphenyl diisocyanate (MDI) content on mechanical properties of thermally post-treated single-layered oriented strand boards (OSB). The OSB differed in adhesive content (3, 4 and 5%) and the high temperature (HT) level of the thermal modification (TM) (untreated, 160, 175 °C). To characterise the mechanical behaviour of the OSB, the modulus of rupture (MOR), modulus of elasticity (MOE), and internal bond (IB) of dry and boiled specimens were determined. In addition, the adsorption and desorption isotherms were investigated. The hygroscopic sorption isotherms were calculated according to the Hailwood-Horrobin equation. It was observed that the MOR and the IB of the post-treated OSB are significantly increased with higher MDI content. An increase of the MDI content from 3% up to 5% is not sufficient to compensate the loss of strength caused by TM. However, an increase of MDI-content of about 1% compensates the significant loss of IB of dry and boiled specimens. The MOE is not influenced by TM. With increased adhesive content, thermally treated and untreated specimens show slightly higher values. The thermal post-treatment of OSB alters the wood-water-interaction. The hygroscopicity is reduced. The higher the HT level, the lower is the sorption behaviour. It was also detected that a higher MDI content does not influence the hygroscopicity.     

Influence of hydrothermal modification of fibers on some physical and mechanical properties of medium density fiberboard (MDF)

Any treatment of fibers can influence properties of medium density fibreboard (MDF). In this research, the effects of hydrothermal treatment on physical and mechanical properties of MDF were studied. Industrial fibers were hydrothermally treated in a stainless steel reactor at 120, 150 and 180 °C for 0, 30 and 90 min as holding time. Test boards were made based on 0.7 g/cm³ target density, with 10 mm thickness under a pressure of 30 bar and at a temperature of 170 °C and a press time of 10 min. The boards were tested for internal bonding (IB), moduli of elasticity (MOE) and rupture (MOR), thickness swelling and water absorption. Results showed that the water absorption was not affected by the hydrothermal treatment; while the thickness swelling was improved and the boards became dimensionally stable. The MOE was slightly reduced due to the hydrothermal treatment. The MOR and the IB were significantly decreased by the hydrothermal treatment.     

Tailor made OSB for special application

The purpose of this study was to develop speciality oriented strand board (OSB) with high stiffness for use in products such as engineered wood flooring (EWF). Three-layer oriented strand boards were manufactured from two feedstocks of strands: a mixture of 90% aspen (Populus tremuloides) and 10% of paper birch (Betula papyrifera), and 100% of small diameter ponderosa pine logs (Pinus ponderosa). The OSB panels were manufactured under a factorial design of three resin contents, two density profiles, and three weight ratios for the face and core layers. Tests to determine density, bending modulus of elasticity (MOE), internal bond (IB) and thickness swelling (TS) were performed according to ASTM standard D 1037-06a. The results showed that the higher values of bending MOE for panels made from aspen/birch mixture and ponderosa pine, 8190 and 9050?MPa, respectively, were obtained for the same combination of factors. Such high bending MOE values are very close to Baltic birch (Betula pendula) plywood, a product known for its high stiffness. The effect of resin content on IB is more pronounced for panels made from ponderosa pine than panels made from the aspen/birch mixture. Thickness swelling of panels made from ponderosa pine strands is higher than thickness swelling of panels made from a mixture of aspen and birch strands. The results indicate the potential to tailor an OSB for a specific application such as EWF.     

A study of oriented structural board made from hybrid poplar

Some basic physical and mechanical properties of oriented structural board (OSB) made from fast growing hybrid poplar, such as modulus of rupture, modulus of elasticity, internal bond strength, nail and screw holding power, thickness swelling after water and humidity absorbing, thermal conductivity and sound absorbing coefficient, have been tested and compared with values from random strand board. Effects of board density on these properties were analyzed revealing some general relationships for OSB. The feasibility of hybrid poplar as raw material for OSB production is also discussed.     

Oriented Strandboard (OSB) Panels Made from Kenaf Stalks and Aspen

Abstract

The specific gravity of these panels varied from 0.68 to 0.75. The amount of kenaf, resin content significantly affected the modulus of rupture and the modulus of elasticity values of aspen-kenaf boards. Boards with 25% kenaf and 75% aspen produced MOR and MOE values comparable to commercial oriented strandboard (OSB). Percentage of kenaf and resin levels were significant factors influencing the internal bond (IB) strength when compared to the commercial OSB. The 25% kenaf and 75% aspen boards produced IB values that could meet the required standard. Aspen-kenaf boards obtained lower values for linear expansion. Lower percentage of kenaf flakes and higher resin content controlled thickness swelling. However, boards with 50% kenaf and 50% aspen flakes made with 6% resin resulted in a thickness swelling of less than 10%.     

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

The influence of temperature on the bending strength (MOR) and the modulus of elasticity (MOE) of eight different wooden materials (2 MDF, 1 OSB, 2 particle boards, beech and spruce plywood, solid wood panel) was tested at temperatures between -20 °C and +60 °C. Thereby a reduction of MOR of 12–39% and of MOE of 14–46% was measured in the range of 20 °C and 60 °C. The work to maximal load varied within a large range. Depending on the wooden material there was an increase of up to 48% or a reduction of up to 31% between 20 °C and 60 °C. Between 20 °C and -20 °C the MOR increased 5–22% and the MOE 3–27%. Only the MOE of the solid wood panel in fibre direction decreased by 6%. The work to maximal load ranged between a reduction by 19% and an increase by 10%.     

Prediction of the mechanical properties of lumber by stress-wave velocity and Pilodyn penetration of 36-year-old Japanese larch trees

The objective of this study was to obtain basic knowledge for the prediction of the mechanical properties of Japanese larch lumber (Larix kaempferi) on the basis of tree properties, such as the stress-wave velocity (SWV) and Pilodyn penetration value (Py). The values of the correlation coefficient between the SWV of a standing tree and the dynamic Young’s modulus (DMOE) of logs, which were obtained at various heights, gradually decreased with an increase in the log sampling height, indicating that the SWV of a tree is affected by wood properties at the measuring position. A significant correlation between the SWV of trees and the average modulus of elasticity (MOE) of lumber was found (r =0.834). A significant negative correlation between the Py of a tree and the average modulus of rupture (MOR) of lumber was also found (r=-0.859). A high coefficient of determination for an obtained regression curve was found when both the SWV and Py of a tree were used for evaluating the average MOE or MOR of lumber. These results indicate that the average MOE and MOR of lumber can be predicted by using the SWV and Py of the Japanese larch tree.     

Untersuchungen zur Anwendung der Schallgeschwindigkeitsmessung für die Ermittlung der elastomechanischen Eigenschaften von Spanplatten

Sound speed transmission in laboratory and industrial particleboards was studied. The boards had different densities and adhesive content. Bending strength (MOR) and module of elasticity (MOE) were determined according to DIN-standards. On the same test pieces sound speed transmission parallel to board surface was determined. A correlation between MOR and MOE with the speed of the sound transmission was calculated. An important effect of board density and amount of adhesive on the transmission was found.     

Mitteldichte Faserplatten (MDF) aus gebrauchten Oriented Strandboard (OSB)

Zusammenfassung Die Ergebnisse zeigen, dass durch den alkalischen Aufschluss von Oriented Strand Boards (OSB), die in den Mittelschichten PMDI und in den Deckschichen MUPF als Bindemittel enthalten, Fasern gewonnen werden, die bei der MDF-Herstellung zur Verringerung der Dickenquellung und zur Erhöhung der Querzugfestigkeit führen. Die Biegefestigkeit der MDF nahm bei Zusatz von 25% OSB-Recyclingfasern kaum ab. Erst bei einer Ersatzmenge von 50% verringerte sich die Biegefestigkeit von ca. 60 N/mm² auf rund 50 N/mm².

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Medium density fibre boards (MDF) from recovered oriented strand boards (OSB)

Fibres for medium density fibre boards (MDF) were made from oriented strand boards (OSB) bonded with PMDI in the core and MUPF in the surface. Chips from OSB were pulped with sodium hydroxide. The fibres obtained therefrom were used for partial substitution of fresh fibres in MDF. The preliminary results reveal that recycled fibres decrease the thickness swelling enormously and has also a remarkable positive effect on the internal bond strength as well. However, the use of higher amounts (50%) of recycled fibres negatively impacts the bending strength.

     

Mechanical properties of medium density fiberboard reinforced with metal and woven synthetic nets

This research was planned to study the influence of reinforcement with metal and woven synthetic nets on the mechanical properties of medium density fiberboard (MDF). Sample boards were manufactured according to common practice. However, reinforcements were placed in the boards at one fourth of their thicknesses. Urea formaldehyde resin was used in the boards. However, some metal nets were embedded in an epoxy resin prior to board manufacture. Bending and tensile strengths were determined according to ASTM D 1037-99, impact load resistance according to ASTM D 256-04 and board’s creep according to ASTM D 6815-02. Results revealed that bending properties (MOE and MOR), tensile strength and impact load resistance were significantly increased due to the reinforcement. Boards reinforced with thin metal nets showed the highest MOR as 105% increase; while the highest MOE and impact load resistance were determined in the boards reinforced by thick metal nets, which were embedded primarily in the epoxy resin as 112% and 79%, respectively. The highest tensile strength was also determined in boards reinforced by thick metal nets. Boards reinforced by woven synthetic nets showed lower strengths than those of the metal nets.     

Mechanical and physical properties of cement-bonded OSB

The objective of this paper was to evaluate the mechanical and physical properties of oriented strand board (OSB) using cement as binder. It was found that an increase of cement-wood ratio resulted in an increase of all, but MOR values. A lower cement-wood ratio than for particleboards is required in order to manufacture acceptable OSB and this may be due to the strands geometry.     

Mechanical and physical properties of cement-bonded OSB

The objective of this paper was to evaluate the mechanical and physical properties of oriented strand board (OSB) using cement as binder. It was found that an increase of cement-wood ratio resulted in an increase of all, but MOR values. A lower cement-wood ratio than for particleboards is required in order to manufacture acceptable OSB and this may be due to the strands geometry.     

Zusammenhänge zwischen Eigenschaften,Rohstoffkomponenten und dem Dichteprofil von Spanplatten

Modulus of elasticity (MOE) and bending strength (MOR) are particleboard properties which characterize their suitability for definite specifications. During pressing and curing of the binding agent a density distribution over the cross-section of the boards, typical of prevailing production conditions, is achieved. These density profiles have a decisive influence on board properties. Based on test results various mathematical profile evaluation methods and regression analyses are described, with which to improve the knowledge of how to influence board properties. This provides an extension, at reduced cost and material consumption, of ways and means to adapt several distinctive properties to certain specifications.     

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 a function of the temperature (ranging between 10 and 30 °C) and also the moisture content (from an oven-dry sample up to a moisture 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, a clear 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 content.     

The influence of compression failure on the bending, impact bending and tensile strength of spruce wood and the evaluation of non-destructive methods for early detection

Bending strength (MOR) and bending Young’s modulus (MOE) according to DIN 52186 and MOE calculated on the basis of eigenfrequency and sound velocity were tested on small clear wood specimens of Norway spruce wood with and without compression failure. One group of specimens was climatised in a normal climate of 20°C and 65% relative humidity, while the other group was stored for one month under water before testing. The MOR of specimens with compression failure decreased about 20% on average (normal climate and wet) compared with the specimens without compression failure. The MOE of the specimens with compression failure was reduced only minimally compared with the specimens without compression failure stored in a normal climate, but very distinct differences (more then 30%) were found under wet conditions. The MOE of the specimens with compression failure calculated on the basis of eigenfrequency and sound velocity were not reduced or only minimally compared with the specimens without compression failure. It is therefore not possible to detect compression failure and to determine reduction in MOR using eigenfrequency or sound velocity. In addition, impact bending (DIN 52189), tensile strength and tensile MOE (DIN 52188) were tested on small clear wood specimens of Norway spruce wood with and without compression failure. The specimens with compression failure revealed an average reduction in impact strength of about 40% and an average reduction in tensile strength of about 20% compared with the specimens without compression failure, whereas tensile MOE of the specimens with compression failure was not reduced compared with the specimens without compression failure. The detection of compression failure by computer tomography (CT) was tested on Norway spruce wood boards 10 cm in thickness, and detection by optical scanner was tested on planed Norway spruce wood boards. CT recognised large compression failures easily, whereas the scanner was not able to detect them.     

Comparison of the in-plane shear strength of OSB and plywood using five point bending and EN 789 steel plate test methods

In order to assess the interlaminar shear strength of spruce plywood and oriented strand board (OSB) five point bending tests and shear tests according to EN 789 were performed. Additionally, a linear elastic finite element analysis of both test set-ups was performed to visualise the distribution of shear stresses. While shear stress was homogeneously distributed in EN 789 samples, typical s-shaped stress fields were observed in beam sections of five point bending specimens. Experiments showed a higher shear strength for plywood compared to OSB. In addition, apparent shear strength measured by five point bending was higher than values obtained using EN 789, the difference being significantly more pronounced for plywood (_5-pt/_EN789 = 1.7) than for OSB (_5-pt/_EN789 = 1.3). It is concluded that differences in the structure of OSB and plywood lead to a bias in the measured apparent shear strength of plywood by means of five point bending tests. Since apparent shear strength values determined by five point bending tests are, therefore, not only dependant on span to thickness ratio, but also on composite structure, EN 789 is recommended for interlaminar shear testing of wood composites.     

Thermal modification of consolidated oriented strandboards: effects on dimensional stability, mechanical properties, chemical composition and surface color

The objective of this paper was to propose a thermal post-treatment to improve the dimensional stability of oriented strandboard (OSB). Commercial OSB panels were obtained from an industrial batch and thermally treated in a single opening hot-press at two temperature levels (190 and 220 °C) and three duration times (12, 16 and 20 min). Dimensional stability, mechanical properties, chemical composition and surface color were studied. The results pointed-out that the proposed treatment can be applied to significantly improve the OSB dimensional stability by reducing thickness swelling, water absorption, and equilibrium moisture content in comparison to the untreated board. The mechanical properties were partially affected with reduction in modulus of rupture and without any adverse effect on the other properties. Chemical degradation occurred, mainly in relation to hemicelluloses contents, reducing equilibrium moisture content. The board surface became darker and this characteristic was correlated with the observed properties improvement. Dimensional stability properties were affected by both temperature and duration of the treatment, while the others mainly by temperature. The proposed thermal treatment can be recommended as a post-treatment to improve the OSB performance.     

Dynamic mechanical thermal analysis (DMTA) of aqueous phenol formaldehyde (PF) resin modified by nano copper oxide (CuO)

To improve the bio-resistance of engineered wood composites products via gluing process, aqueous phenol formaldehyde (PF) resin was modified using nano CuO containing alkane surfactant and polyvinyl alcohol (PVA) 17-99. The modified PF system was analyzed by dynamic mechanical thermal analysis, and the mechanical properties of the bonded plywood panels including tensile strength, modulus of rupture (MOR), modulus of elasticity (MOE) and shear strength under five test conditions were also evaluated. The results indicated that the addition of nano CuO incorporating PVA 17-99 separated the gel point and vitrification point in the curve of tan δ, which is related to the delaying of moisture loss in modified PF resin during the curing process. The modification showed adverse effect on tensile strength but only a minimal influence on MOR and MOE. Additionally, PVA 17-99 reduced the water resistance of cured PF resins. However, with the test conditions of dipping in 100 °C water for 6 h, then drying for 20 h at 63 °C in air, followed by dipping in 100 °C water for 4 h, PVA consolidated the re-curing effect on the PF resin and compensated the strength loss from hydrolysis. Thus, the modified PF system not only guaranteed bio-resistance of glued wood composites via CuO, but also has the potential for developing self-curing wood composites being applied as structural construction materials.