Investigation of physical and mechanical properties of oil palm wood core sandwich panels overlaid with a rubberwood veneer face

Low-density sandwich panels consisting of an oil palm wood core overlaid with a rubberwood veneer face were manufactured. Effects of two types of grain orientation of the oil palm wood core (parallel and perpendicular to board surface) and three different veneer thicknesses (0.7, 1.8 and 2.7 mm) and core densities (223 ± 14, 301 ± 35 and 418 ± 33 kg/m³) on some physical and mechanical properties of the boards were investigated. Results showed that higher core density increased the values of thermal conductivity, screw withdrawal resistance, modulus of rupture and modulus of elasticity but decreased the value of water absorption without effect on thickness swelling of the boards. Boards with the core grain direction oriented perpendicular to panel’s surface possessed lower value of thickness swelling but higher values of thermal conductivity and strain at fracture when the board failed in a mode of core shear under bending test than those of the others. Finally, the relationship between board density and the measured physical and mechanical properties of the oil palm wood core sandwich panels overlaid with a rubberwood veneer expressed as mathematical equations could be used to predict and design the expected properties of this type of sandwich board.     

Creep behaviour of commercial wood based boards under long-term loading at room conditions in Taiwan

The purpose of this study was to investigate the creep behaviour of commercial wood based boards (sanded and laminated) under long-term loading at room conditions in Taiwan. Ten types of commercial wood based boards were used to test their physical and mechanical properties in this study. Four types of these boards were used for the same test after laminating with red oak (Quercus spp.) veneer or balanced paper. The bending creep was measured at room conditions with central concentrated loading. The values for creep deflection of commercial wood based boards 18 mm thick decreased from 1.06–1.19 mm ti 1.00–1.12 mm after laminating veneer or balanced paper. The relative creep (120 days) of those specimens decreased from 1.71–3.17 to 1.43–2.04 after laminating with veneer or balanced paper in four months’ loading. The creep deflections of specimens increased with increasing loading time. The linear regression function ist/y=a+bt, wheret is time,y is deflection. When theb value is larger, the boards displayed good creep resistance. The residual bending strength of wood based boards after creep test would be retained at about 80–95%, and the residual bending strength between particleboard proved more significant than between fiberboard.     

Influence of veneer thickness on the properties of LVL from Paricá (Schizolobium amazonicum) plantation trees

The work aimed at evaluating the influence of the veneer thickness on physical and mechanical properties of laminated veneer lumber (LVL) boards made from Schizolobium amazonicum plantation trees. It is a fast growing species (20 m³/ha/year), having a straight trunk almost without any branch and producing a white-yellowish low density hardwood: usually <0.40 g/cm³. The boards were manufactured with the following thicknesses: 1.54, 2.32 and 2.71 mm. Seven LVL boards were produced for each thickness, totaling 21, all according to the following characteristics: PVAc adhesive (200 g/m²), pressed (1.0 N/mm²) at room temperature for 12 h. The following mechanical and physical properties were then evaluated: static bending modulus of elasticity (E _M ), modulus of rupture (f _M ), compression strength parallel to grain (f _c,0 ), shear strength parallel to glue-line (f _v,0 ), shear strength perpendicular to glue-line (f _v,90 ), water absorption and thickness swelling for 2 and 24 h of water immersion. The results pointed out that the utilization of thinner veneers implied improving mechanical properties, while thicker veneer reduced the water absorption. Nevertheless, in contrast, the efficiency was lower than that observed when thicker veneer was used.     

Development of selectively densified surface laminated wood based composites

An attempt was made to develop selectively densified surface laminated wood based composites. Two types of wood composites were produced (veneer laminated Medium Density Fiberboard, MDF and wafer overlaid particleboard, PB) in this study. Veneer or wafer plasticized by NaClO₂ treatment and PF resin impregnated were laminated on both sides of the MDF or PB and compressed at ordinary pressure. The main observation was that overlaying plasticized veneer on MDF before hot pressing is a promising method for improving mechanical properties and dimensional stability of commercial MDF. The MOR and MOE of surface laminated MDF attained 177 MPa and 18 GPa, respectively. The water absorption percentage of laminated MDF decreased from 160.7 to 7.2%. Furthermore, it is interesting to note that NaClO₂ treated and resin impregnated wafer or powder laminated particleboards showed excellent performance especially in stiffness. The MOR and MOE reached 40 MPa and 7 GPa which is more than two times higher compared to untreated wafer laminated board and three times higher than particleboard. This value is comparable to commercial lauan plywood having a density of 0.78 g/cm³. The processing technique of the composite is simple and can be easily applied by the industry.     

Phosphate bonded wood composite products from invasive <Emphasis Type="Italic">Acacia</Emphasis> trees occurring on the Cape Coastal plains of South Africa

The feasibility of manufacturing phosphate bonded wood composite board products from four locally occurring invasive acacia tree species (Acacia cyclops, A. saligna, A. mearnsii and A. longifolia) was studied using a formulated magnesium oxide (MgO) and monopotassium phosphate (KH₂PO₄) binder system. The optimization for the manufacturing process was studied using a central composite statistical design, whereupon the following factors were considered, i.e. KH₂PO₄: MgO ratio, the fly ash content as partial replacement for the binder and the wood content as a ratio of wood to the total inorganic content. A fitted response surface plot was used to show the effect of the main factors and their interactions on the measured board properties. A response surface model was developed to predict the parameters leading to the best board properties. All physical properties evaluated met or exceeded the minimum requirements for low density particleboards. The results showed that the variables considered have significant effects on the physical properties of the boards. The optimum composite manufacturing process for making durable products within the scope of the studied species was found to be a KH₂PO₄/MgO ratio of 1.66, an ash content of 2.7% and a wood/inorganic ratio of 0.96 for the selected wood species.     

Material properties and nondestructive evaluation of laminated veneer lumber (LVL) made from Pinus oocarpa and P. kesiya

This study aimed at evaluating the mechanical, physical and biological properties of laminated veneer lumber (LVL) made from Pinus oocarpa Schiede ex Schltdl (PO) and Pinus kesiya Royle ex Gordon (PK) and at providing a nondestructive characterization thereof. Four PO and four PK LVL boards from 22 randomly selected 2-mm thickness veneers were produced according to the following characteristics: phenol-formaldehyde (190 g/m²), hot-pressing at 150°C for 45 min and 2.8 N/mm² of specific pressure. After board production, nondestructive evaluation was conducted, and stress wave velocity (v ₀) and dynamic modulus of elasticity (E _Md ) were determined. The following mechanical and physical properties were then evaluated: static bending modulus of elasticity (E _M ), modulus of rupture (f _M ), compression strength parallel to grain (f _c,0), shear strength parallel to glue-line (f _v,0), shear strength perpendicular to glue-line (f _v,90), thickness swelling (TS), water absorption (WA), and permanent thickness swelling (PTS) for 2, 24, and 96-hour of water immersion. Biological property was also evaluated by measuring the weight loss by Trametes versicolor (Linnaeus ex Fries) Pilát (white-rot) and Gloeophyllum trabeum (Persoon ex Fries.) Murrill (brown-rot). After hot-pressing, no bubbles, delamination nor warping were observed for both species. In general, PK boards presented higher mechanical properties: E _M , E _Md , f _M , f _c,0 whereas PO boards were dimensionally more stable, with lower values of WA, TS and PTS in the 2, 24, and 96-hour immersion periods. Board density, f _v,0, f _v,90 and rot weight loss were statistically equal for PO and PK LVL. The prediction of flexural properties of consolidated LVL by the nondestructive method used was not very efficient, and the fitted models presented lower predictability.     

Effect of laminated structure design on the mechanical properties of bamboo-wood hybrid laminated veneer lumber

The effects of veneer orientation and loading direction on the mechanical properties of bamboo-bundle/poplar veneer laminated veneer lumber (BWLVL) were investigated by a statistical analysis method. Eight types of laminated structure were designed for the BWLVL aiming to explore the feasibility of manufacturing high-performance bamboo-based composites. A specific type of bamboo species named Cizhu bamboo (Neosinocalamus affinis) with a thickness of 6 mm and diameter of 65 mm was used. The wood veneers were from fast-growing poplar tree (Populus ussuriensis Kom.) in China. The bamboo bundles were obtained by a mechanical process. They were then formed into uniform veneers using a one-piece veneer technology. Bamboo bundle and poplar veneer were immersed in water-soluble phenol formaldehyde (PF) resin with low molecular weight for 7 min and dried to MC of 8–12 % under the ambient environment. All specimens were prepared through hand lay-up using compressing molding method. The density and mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR), and shearing strength (SS) of samples were characterized under loading parallel and perpendicular to the glue line. The results indicated that as the contribution of bamboo bundle increased in laminated structure, especially laminated on the surface layers, the MOE, MOR and SS increased. A lay-up BBPBPBB (B-bamboo, P-poplar) had the highest properties due to the cooperation of bamboo bundle and poplar veneer. A higher value of MOE and MOR was found for the perpendicular loading test than that for the parallel test, while a slightly higher SS was observed parallel to the glue line compared with perpendicular loading. Any lay-up within the homogeneous group can be used to replace others for obtaining the same mechanical properties in applications. These findings suggested that the laminated structure with high stiffness laid-up on the surface layers could improve the performance of natural fiber reinforced composites.     

Herstellung von zementgebundenen Fichten- und Pappelspanplatten: Weschselwirkungen von fünf Einflußfaktoren und ihre Wirkung auf die Plattenfestigkeit

Comparisons were made between the effects of cement classes, accelerator (Al₂(SO₄)₃+Ca(OH)₂), hardening temperature, pressing time and water-cement ratio on the strength properties of cement bonded particleboards made from spruce and poplar and between the interactions of these parameters. Remarkable differences between the two wood species were revealed. Cement strength class was of only little importance for spruce particleboards, but had a significant effect on poplar particleboard strength properties. The effect of the accelerator, on the other hand, proved decisive for spruce board strength. In contrast, its effect was almost neutralized in the interaction with poplar particles and can therefore be considered more or less negligible for boards made from this wood species. The influence of heat had a substantially reducing effect on accelerator action and thus proved fatal for the strength properties of cement bonded spruce boards. Heat treatment could, however, be advantageous for poplar boards. Prolonged pressing time generally improved the strength properties of boards. The optimum water-cement-ratio should be determined selectively for any given combination of manufacturing conditions.     

Zum Stand der Bauspanplattenherstellung

The situation of the raw material markets throughout the world is also enforcing a structural change in the wood industry: Whereas in 1950 the relation between the consumption of solid wood and wood-based materials was 20∶1, the relation today is 2∶1. In the building industry this trend is accompanied by the advance of special particle-boards (instead of veneer and fibre board) for structural use, namely boards with special gluing, particle dimension or special structure, such as flakeboard, wafer and strandboard, Comply etc. After comparative studies of the most important physical-mechanical properties of the above-mentioned types of board, urgent present-day problems of processing in the manufacture of flakeboard, wafer-board, and OSB are described. With special reference to OSB, the requirements regarding density, swelling behaviour, and resistance against weathering are compared with the possibilities of improved gluing with modified urea resins; the prospects of the various types of structural boards on the US and European market are discussed.     

The influence of material properties on the amount of twist of spruce wood during kiln drying

The development of twist in Norway spruce boards (Picea abies Karst.) during normal temperature kiln drying was researched. Tangentially oriented boards were sawn from diametrical radial planks, from which the basic wood properties, i.e. linear shrinkage and grain angle, were determined. The unrestrained boards were kiln dried using a selected drying schedule. During the controlled drying process the moisture content (MC) and twist of the boards were measured. Twist was generally induced by the shrinkage of wood below the fibre saturation point, and increased in proportional to the decrease in MC. The earlier appearance of twist, with regard to MC and drying time, was confirmed in the case of boards sawn from the central part of logs. The final twist amounted to between 10 and 20°/m in the case of boards close to the pith, and decreased to less than 4°/m in the case of boards sawn at a radius of 70 mm from the centre of the logs. Ring curvature had the highest impact on the final twist of the dried boards, followed by grain angle and tangential shrinkage.     

Crack formation in unfinished siding of aspen (Populus tremula L.) and Norway spruce (Picea abies (L.) Karst.) during accelerated weathering

Crack formation is a serious defect that may reduce the lifetime of unfinished wood in service. An accelerated weathering test was carried out to study crack formation of solid wood board specimens of aspen (Populus tremula L.) and Norway spruce (Picea abies (L.) Karst.). The influence of the boards' distance from the pith was also studied. The aspen specimens developed a higher number of cracks than the spruce specimens. However, these cracks were shorter and less injurious than those propagating in spruce wood. It is concluded that a solid wood siding of aspen will show at least as good a performance as spruce regarding crack injuries. For both aspen and spruce, boards taken from near the pith had a lower proportion of long cracks than boards taken further out. This supports the rule that boards with a high proportion of annual rings perpendicular to the surface (the boards near to the pith) have a higher resistance to crack formation than boards with a high proportion of horizontal annual rings.     

Model predicted and CT scanned moisture distribution in aPinus radiata board during drying

Pinus radiata sapwood boards of 100 × 40 × 1200 mm were dried in a tube dryer at Luleå University, using a computer tomography (CT) scanner to scan the wood during drying. The CT-scanned wet wood density can illustrate moisture distribution within wood when the wood basic density profile is known. The CT-scanned results were used to validate a 2-D single board drying model developed at the New Zealand Forest Research Institute. The validation has shown that the model is not only capable of predicting the average moisture content but also moisture content gradients in board thickness, width and within growth rings. To investigate the effects of sawing pattern and intrinsic wood properties on drying, the input parameters for the model include within-ring variations of wood density, green moisture content and wood permeability. The model can assist in understanding the causes of some drying defects and has potential for the development of drying schedules.     

NIR detection of non-recoverable collapse in sawn boards of Eucalyptus globulus

NIR predictions of cellulose content and stiffness (modulus of elasticity, MOE) from spectra collected from the radial longitudinal surface of Eucalyptus globulus wood were found to be reliable indicators of zones of non-recoverable collapse associated with the presence of tension wood. Radial sections from 25 quarter-sawn boards cut from plantation-grown E. globulus trees in Spain were scanned to generate radial profiles of NIR-predicted wood properties at 2 mm increments. These boards manifested a range of non-recoverable collapse features, from no collapse to one or more severe collapse bands. Collapse bands occurred where NIR-predicted cellulose content and MOE exceeded threshold levels of 50 % and 25 GPa, respectively for more than four consecutive millimetres. A non-recoverable collapse indicator provided a clear predictor of non-recoverable collapse. A NRCI value ≥100 for a consecutive interval of at least 4 mm successfully predicted all ten NRC bands with shrinkage ≥10 % of board thickness. The potential applications of this tension wood detection method are discussed.     

Physical and mechanical properties of oriented strand lumber made from an Asian bamboo (Dendrocalamus asper Backer)

The study was conducted to determine the physical and mechanical properties as follows: modulus of rupture, modulus of elasticity, internal bond, thickness swelling and water absorption of oriented strand lumber (OSL) made from the Asian bamboo Dendrocalamus asper Backer. Thirty-six lab boards were produced from these bamboo strands with two manufacturing parameters varying, i.e., four resin types (MF, MUPF, PF, and pMDI) and three levels of resin content (7, 10, and 13%). The results indicate that OSL made from bamboo strands exhibits superior strength properties compared to the commercial products made from wood for the building sector. The resin type has a?significant effect on board properties. Moreover, all properties of the board improve generally with increasing resin content. With regard to the internal bond, bamboo-based OSL shows less strength than wood-based boards. The best results were obtained by using 13% pMDI content at 750?kg $ / $ m³ density.     

Algorithmen und Anwendungsprogramm zur Kontrolle und Steuerung der Qualitätsparameter von Spanplatten

Algorithms for the determination of a complex quality number have been developed. A BASIC program using these algorithms enables considerable improvement of the quality of particle boards. The on-line control of the production process based on the quality numberQ _p allows the optimization of the process and reduction of production costs ensuring a high quality level of the end product. The approach proposed for particle board production may also be applied to the production of other types of wood based materials and to other industrial processes.     

Evaluation of strength properties of parallel splint lumber (PSL) and its comparison with laminated veneer lumber (LVL), rubber wood and teak

( Heavea brasiliensis ) and an exterior type of adhesive were evaluated in air-dry condition. Block shear tests were also carried out in wet and dry condition. Comparisons of these strength values were made with those of laminated veneer lumber (LVL), solid rubber wood and standard teak. The results show that PSL has slightly lower values of strength properties compared to teak, solid rubber wood and quite inferior ones to those of LVL. On the basis of the data obtained in the present study, PSL made from rubber wood can be utilised as a structural material for different purposes like door and window frames, rigs and trusses.

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Evaluation of strength properties of parallel splint lumber (PSL) and its comparison with laminated veneer lumber (LVL), rubber wood and teak

Heavea brasiliensis ) and an exterior type of adhesive were evaluated in air-dry condition. Block shear tests were also carried out in wet and dry condition. Comparisons of these strength values were made with those of laminated veneer lumber (LVL), solid rubber wood and standard teak. The results show that PSL has slightly lower values of strength properties compared to teak, solid rubber wood and quite inferior ones to those of LVL. On the basis of the data obtained in the present study, PSL made from rubber wood can be utilised as a structural material for different purposes like door and window frames, rigs and trusses.     

Glued-in rods in beech laminated veneer lumber

Beech laminated veneer lumber is a new engineered wood product with superior mechanical properties and high density. In order to take advantage of this superior mechanical performance in the case of connections with glued-in rods a series of pull compression tests with different angles to the grain have been performed applying both polyurethane and epoxy resin as adhesives. No influence of the grain angle on the load carrying capacity could be found. In addition, a survey on design rules and their acceptance in practice has been carried out, showing a clear need for further standardization.     

The manufacture of particleboards using mixture of reed (surface?layer) and commercial species (middle layer)

This research was conducted to investigate the suitability of reed (Arundo donax) as a substitute for wood in laboratory made 3-layer particleboard in order to supplement the supply of raw material for the Iranian particleboard industries. The ratio of the mixture of reed and wood particles were 20:80, 30:70, and 40:60, respectively, in the surface and middle layers. Press temperatures were chosen at two levels of 165 and 185?°C. Three levels of urea formaldehyde resin were selected for the surface layers, namely: 8, 10, and 12 percent. The experimental panels were tested for their mechanical strength including modulus of elasticity (MOE), modulus of rupture (MOR), internal bonding (IB) and physical properties (thickness swelling and water absorption) according to the procedure in DIN 68763. In general, the results show that reed has a positive effect on the mechanical and physical properties of boards. In this research, the treatment with 40% reed, 12% resin in the surface layers and a 185?°C press temperature has resulted in an optimum reed board product.     

The influence of certain factors on thickness loss after the hot gluing of cut lamellas into solid wood layered boards

An experimental laboratory investigation has been carried out into the hot gluing of solid wood layered boards made out of 5.3 mm thick solid-wood lamellas, the latter being produced by the lengthwise veneer cutting technique, the object of the research being to determine some of the reasons (humidity of wood before heating, temperature of wood before cutting into lamellas, and temperature and pressure during the gluing of boards) for the permanent thickness loss which occurs during gluing. Spruce wood (Picea abies (L.) Karst.) was used in the experimental tests. Before cutting into lamellas, this wood was classified into two humidity groups, and heated to three different temperatures. The dried lamellas were used, after suitable preparation, for the two outer layers, which were glued, together with a middle layer of sawn lamellas, by the hot gluing process. A total of 162 laboratory boards, of length 500 mm, width 475 mm and thickness from 24 to 25 mm, were hot glued, using melamin-urea-formaldehyde glue, at three different gluing temperatures and three different gluing pressures. Regression analysis of the measured results of thickness loss showed that the influence of the studied factors on thickness loss was linear, and that thickness loss depends the most on gluing pressure, followed by gluing temperature. It was also found that a higher wood humidity results in a slightly greater thickness loss than the wood’s temperature before cutting into lamellas.