Properties of laboratory made yellow poplar (Liriodendron tulipifera) laminated veneer lumber: effect of the adhesives

Four different commercial resin formulations namely cross-linked polyvinyl acetate (XPVAc), melamine urea formaldehyde (MUF), urea formaldehyde (UF) and melamine formaldehyde (MF) were used to produce laminated veneer lumber (LVL) from yellow poplar veneers in the laboratory. Physical and mechanical properties were evaluated using ASTM (D 1037, D 906, D 5456) standards and compared. Internal bond, tensile shear and block shear strengths of specimens subjected to accelerated (boiled water) and cyclic (repeated cold water) conditions were also determined. Strength properties of yellow poplar LVL were improved compared with the solid wood. The properties of XPVAc bonded LVL were superior or comparable to the thermosetting adhesives. This study clearly indicated that cross-linked PVAc can be used to manufacture LVL with acceptable properties.     

Effects of cold setting adhesives on properties of laminated veneer lumber from oil palm trunks in comparison with rubberwood

In this study, the properties of laminated veneer lumber (LVL) made from oil palm trunks (OPT) were evaluated in comparison with rubberwood using cold setting adhesives, namely, emulsion polymeric isocyanate (EPI) and polyvinyl acetate (PVAc). The evaluations were based on either dry or after cold water, hot water and cyclic pre-treatment. The density of the OPT LVL was slightly higher than that of solid OPT. Thickness swelling and water absorption of OPT LVL were greater than of rubberwood LVL. Pre-treatment increased the water absorption and thickness swelling. The OPT LVL bonded with EPI without toluene showed greater water absorption and thickness swelling than EPI with toluene. Pre-treatment significantly reduced the tensile strength of OPT LVL. The OPT LVL bonded with EPI without toluene showed higher tensile shear strength, but a greater reduction of tensile shear strength after pre-treatment, than the OPT LVL bonded with EPI and toluene. The PVAc adhesive had greater wettability than the EPI. The EPI without toluene showed a lower contact angle than the EPI with toluene. The loose side of the OPT veneer was found to have greater wettability than the tight side.     

Hydroxymethylated resorcinol (HMR) priming agent for improved bondability of wax-treated wood

The effects of hydroxymethylated resorcinol (HMR) on the tensile shear strength of wood joints treated with montan ester wax were studied with polyvinyl acetate (PVAc) and melamine formaldehyde (MF) adhesives. Untreated specimens which were bonded with MF and PVAc had similar bond strength properties under dry conditions, but MF bonded specimens’ tensile shear strength values were higher than that of PVAc glued specimens under wet conditions. With both adhesives tested, dry tensile shear strengths of wax-treated specimens were in a comparable range to those of untreated wood, while under wet conditions the strength values of wax-treated specimens were significantly lower than those of the controls. HMR priming increased the shear strength of PVAc bonded specimens under wet conditions and of MF-bonded specimens under dry and wet conditions. The effect on MF-bonded specimens, however, was much more pronounced under wet conditions.     

A comparative study on some physical and mechanical properties of Laminated Veneer Lumber (LVL) produced from Beech (Fagus orientalis Lipsky) and Eucalyptus (Eucalyptus camaldulensis Dehn.) veneers

Laminated Veneer Lumber (LVL) panels made from eucalyptus (Eucalyptus camaldulensis Dehn.) and beech (Fagus orientalis Lipsky.) veneers were tested for physical and mechanical strength properties in this study. Urea formaldehyde (UF) and Polyvinyl acetate (PVA) adhesives were used for eucalyptus LVL panels and UF adhesive for beech LVL panels. The effect of veneer wood species on some physical and mechanical properties was found statistically significant. Also, different glue species caused the differences in strength properties of LVL panels.

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Über einige Eigenschaften von Furnierschichtholzplatten hergestellt aus Buchen- und Eukalyptusfurnieren

Zusammenfassung In diesem Beitrag werden einige physikalische und mechanische Eigenschaften von Schichtholzplatten, hergestellt aus Buchen- (Fagus orientalis Lipsky.) und Eukalyptusfurnieren (Eucalyptus camaldulensis Dehn.) untersucht. Für die Herstellung von Schichtholzplatten wurden die Buchenfurniere mit UF und die Eukalyptusfurniere mit UF und PVA verleimt. Die Ergebnisse zeigen, dass sowohl die Art des Bindemittels als auch die Holzart der Furniere die Eigenschaften der Schichtholzplatten signifikant beeinflussen.

     

Accelerated curing of PVAc adhesive on plasma-treated wood veneers

In this study the effect of plasma treatment at atmospheric pressure of wood veneers on the curing behaviour of a PVAc adhesive was investigated. Time-dependent shear bond strength tests on untreated and plasma-treated maple (Acer pseudoplanatus), oak (Quercus sp.), beech (Fagus sylvatica) and teak (Tectona grandis) veneers were carried out. The results confirm that plasma treatment accelerated curing of the PVAc adhesive on the wood veneers.     

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.     

Natural decay resistance of LVL made of veneers from durable and non-durable wood species

Laminated veneer lumber (LVL) was laboratory manufactured using veneers from decay and non decay resistant species in order to evaluate changes in the durability as a result of the LVL manufacturing process, and to test if the mixing of decay resistant species and non decay resistant species can improve durability. Laboratory soil block test and field test were conducted. The durability of solid wood was comparable to that of LVL made using the same species. For LVL made using veneer from durable and non-durable wood species, durability was improved when two faces and one core veneers were from decay resistant species.     

Hydroxymethylated resorcinol (HMR) priming agent for improved bondability of silicone modified wood glued with a polyvinyl acetate adhesive

A hydroxymethylated resorcinol (HMR) was used as a coupling agent to improve glueability of silicone (aminofunctional polydimethylsiloxane) modified pine sapwood (Pinus sylvestris) with polyvinyl acetate (PVAc). Priming with HMR did not significantly increase tensile shear strength of unmodified and silicone treated wood under dry conditions. Under wet conditions, tensile shear strength of the control specimens was increased by 37% and of the silicone modified specimens by 13%. Despite of higher shear strength under wet conditions, the primed silicone treated specimens displayed lower degree of wood failure than the unprimed treated specimens.     

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.     

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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Inhibited wood degradation of cement-coated beech Laminated Veneer Lumber (LVL) for temporary in-ground applications

This paper investigates the long-term tensile properties of laminated veneer lumber (LVL) beech sections coated with cement and exposed to fungal decay. A set of LVL coupon (dog-bone) samples was stored in compost, tested in tension after 6 and 12 months and compared to reference samples stored at 20 °C and 65% relative humidity. Results showed that after 26 weeks of compost exposure, a fungus of the Ascomycota genus was identified in cement-coated samples using a molecular biology polymerase chain reaction (PCR) technique, which analyses the internal transcribed spacer (ITS) region of the ribosomal DNA. However, no visual deterioration was noticed. Still in cement-covered samples and after 12 months of exposure, a common white rot fungus was determined by DNA chip technology, but no fungal wood decay was visible in areas where the applied coating had a thickness of at least 5 mm. Decay in uncoated LVL samples was significant with the samples having an average residual strength equal to 7%. This compares to the tensile strength of coated samples, which only decreased by 65% relative to the reference samples. Strength and stiffness of coated samples did not differ significantly between 6 and 12 months of exposure. Preliminary investigations tend to show that the strength reduction in cement-coated samples is due to an alkaline degradation of the wood. The observed influence of the coating thickness on the visual fungal decay can probably be ascribed to the protection mechanism due to a physical fungal barrier with a high pH.     

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.     

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.     

Adhesive bonding of beech wood modified with a phenol formaldehyde compound

Untreated (controls) and phenol–formaldehyde (PF)-modified beech wood (10 and 25?% solid content) were glued with phenol resorcinol formaldehyde (PRF) and polyvinyl acetate (PVAc). Shear strength of PRF-bonded specimens was higher than that of PVAc-bonded ones under dry and wet conditions irrespective of the pre-treatment. Under dry conditions, only PVAc-bonded specimens exhibited reduction in shear strength due to PF-modification with 25?% PF concentration as compared to the controls. PF treated wood provided inferior bonding under wet conditions with the exception of 25?% PF concentration specimens glued with PRF adhesive. Modification with PF resulted in a decrease of adhesive penetration into the porous network of interconnected cells, especially at 25?% PF concentration.     

An investigation of the cell wall ultrastructure of the sapwood of ten Greek wood species by means of chemical modification

The aim of this study was to investigate the cell wall ultrastructure of the sapwood of ten Greek wood species using chemical modification. Reactions with different sized anhydride molecules were performed on oven-dry samples in the presence of water-free xylene, which does not swell the cell wall. Reactions were also performed under identical conditions, but on wood samples that had been dried under solvent exchange conditions, thereby retaining the swollen cell wall pore structure. The results indicated that the diameters of the micropores in the cell wall of oven dried ash and elm are smaller than 0.80 nm and larger than 0.74 nm, those of beech, fir, Douglas fir, hornbeam and pine (Pinus nigra) smaller than 0.74 nm and larger than 0.66 nm, whereas those of maple, poplar, pine (Pinus sylvestris) are smaller than 0.66 nm.     

Natural decay resistance of LVL made of veneers from durable and non-durable wood species

Laminated veneer lumber (LVL) was laboratory manufactured using veneers from decay and non decay resistant species in order to evaluate changes in the durability as a result of the LVL manufacturing process, and to test if the mixing of decay resistant species and non decay resistant species can improve durability. Laboratory soil block test and field test were conducted. The durability of solid wood was comparable to that of LVL made using the same species. For LVL made using veneer from durable and non-durable wood species, durability was improved when two faces and one core veneers were from decay resistant species.

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Natürliche Fäulnisresistenz von Brettschichtholz aus haltbaren und nicht haltbaren Holzarten

Zusammenfassung Aus fäulnisunbeständigen und -beständigen Holzarten wurde in einem Labor Brettschichtholz hergestellt, um Veränderungen in der Dauerhaftigkeit auf Grund ihres Herstellungsverfahrens zu evaluieren, und um zu prüfen, ob das Mischen von fäulnisunbeständigem mit fäulnisbeständigen Holzarten die Dauerhaftigkeit von LVL verbessern kann. Bodentests wurden im Labor und als Freilandversuche durchgeführt. Bei Verwendung derselben Spezies war die Dauerhaftigkeit von massivem Holz vergleichbar mit derjenigen von LVL. Bei Brettschichtholz, welches aus resistenten und nicht resistenten Arten gefertigt war, wurde die Dauerhaftigkeit verbessert, wenn zwei Aussenschichten und eine Innenschicht aus einer fäulnisbeständigen Holzart war.

     

Modification of beech veneers with lignin phenol formaldehyde resins in the production of laminated veneer lumber (LVL)

Rotary cut beech (Fagus sylvatica L.) veneers were treated with four different lignin phenol formaldehyde (LPF) solutions using dimethyl sulfoxide (DMSO) as a solvent. Four of these veneers were bonded with PF adhesive to produce four-layer laminated veneer lumber (LVL). To synthesize the LPF solutions, a commercial phenol formaldehyde resin (PF resin) was individually mixed with three different technical lignins (Indulin AT, BioChoice lignin, organosolv lignin) and lignin cleavage products (LCP) at a ratio of 3:2 (60%:40%). Differential scanning calorimetry showed an increased curing temperature for the LPF resins in comparison to the PF resin. The mechanical and water-related properties of the LPF-modified LVL were shown to be similar or slightly improved compared to PF-modified LVL. Fungal degradation experiments with white-rot fungus (Trametes versicolor) and brown-rot fungus (Coniophora puteana) exhibited no significant differences in the mass loss of the LPF-modified and PF-modified samples except in one case: LVL made from veneers treated with Indulin AT exposed to the white-rot fungus. The resistance to weathering of LVL samples made from veneers treated with technical lignins was low; however, specimens treated with LCP and the reference PF resin displayed a higher resistance to weathering. It is concluded that technical lignins or LCP can, to a certain extent, be used as a substitute for crude-oil based PF resin.     

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.     

Characterization of water-soluble extracts from hot-pressed poplar

Thermal modification of wood constituents occurs upon hot-pressing of flakes during consolidation of oriented strand board (OSB). Hence, the effects of hot-pressing of hybrid poplar on water-soluble extractives were studied. Poplar veneers were pre-conditioned to 0 or 8 % moisture content and subsequently hot-pressed at 150, 200 or 250 °C. Aqueous extracts were characterized by conventional chemical methods in conjunction with chromatography (HPLC and SEC), mass spectrometry (ESI–MS) and spectroscopy (FTIR) analysis. Water-soluble fractions were markedly influenced by thermal compression treatment at 250 °C compared to the lower temperatures. Chromatographic results indicate that water-soluble extractives content increases with temperature while the degree of polymerization decreases with detection at low temperature levels. FTIR spectroscopic analysis indicates changes in aqueous-extracts composition of wood monosaccharides (hemicelluloses), meanwhile ESI–MS detected xylo-oligosaccharides. These results clearly show that heat treatment dictated the changes in each water-soluble extractive component and they respond independently with different treatment.     

Compressive strength and stiffness of Radiata Pine laminated veneer lumber

This paper describes results of experimental testing of compressive strength and stiffness of laminated veneer lumber (LVL) manufactured in New Zealand from Radiata Pine. It evaluates material properties of 45, 63 mm LVL and 36 mm crossbanded LVL in the three different material directions. Testing has been performed according to Australian/New Zealand Standards and European Standards. Results from experimental testing according to both standards are compared and a newly proposed method for strength increase due to stress spreading has been verified. Recommended design values for strength and stiffness are given.