Effect of Some Chemicals on Thermal Conductivity of Impregnated Laminated Veneer Lumbers Bonded with Poly(vinyl acetate) and Melamine–Formaldehyde Adhesives

Thermal conductivity is a very important parameter in determining heat transfer rate and is required for the development of drying models and for the industrial operations such as adhesive cure rate. The objective of this research was to investigate the effects of impregnation on the thermal conductivity of six-layered laminated veneer lumber (LVL) made of beech and pine. Boric acid, zinc chloride, and ammonium sulfate were used as impregnation chemicals and poly(vinyl acetate) (PVAc) and melamine-formaldehyde (MF) adhesives as bonding agent were used to produce LVLs. The veneers were impregnated by using the vacuum-pressure method. The thermal conductivity test was performed based on ASTM C 1113-99 hot-wire method. Results showed that the impregnation chemicals increase the thermal conductivity. As impregnation chemicals the highest values were obtained with boric acid and zinc chloride. In addition, the thermal conductivity of LVL made of beech was higher than that of LVL made of pine. The thermal conductivity of LVL bonded with PVAc was absolutely higher than LVL bonded with MF in both wood species.     

Effect of steam on bonding strength and dimensional stability of laminated veneer lumbers manufactured using different adhesives

Laminated veneer lumbers (LVLs) manufactured from wood with different adhesives are being increasingly used in the construction of furniture frames and buildings. Yet there is little information available concerning the dimensional stability and shear strength of LVLs after being exposed to steam. In this study, LVLs were manufactured from poplar and beech veneers with phenol/formaldehyde (PF), poly(vinyl acetate) (PVAc), Desmodur-VTKA (D-VTKA) and urea/formaldehyde (UF) adhesives. Dimensional stability of LVLs was measured after being exposed to steam for 2, 6, 12, 24, 48 and 96 h, according to the Turkish Standard (TS) 3639, and also shear strength was measured (according to BS EN 205). The highest initial density of 0.93 g/cm³ was for beech LVL with VTKA adhesive. After exposure to steam for 96 h, the highest weight increase of 65.7% was for poplar LVL with PVAc, the highest radial swelling of 5.7% was for beech LVL with UF, the highest tangential swelling of 7.9% was for beech LVL with PF and the highest longitudinal swelling of 0.5% was for beech LVL with VTKA. The highest shear strength value of 15.8 N/mm² among all samples without exposure to steam was obtained for beech LVL with PVAc adhesive and the lowest shear strength was obtained as 4.48 N/mm² for poplar LVL with UF adhesive.     

The effect on shear strength of different surfacing techniques in Oriental beech (Fagus orientalis Lipsky) and Scotch pine (Pinus sylvestris L.) bonded joints

The selection of the most appropriate surfacing technique is influential in the success of bonding, painting and varnishing processes. The objective of the study was to determine which surfacing technique was the most appropriate when applied as the final process in the production of structural wood members, which were subjected to shearing. The study also includes the effect on shear strength of the variables, such as type of wood, plane of cut, type of adhesive and pressing pressure, as they are directly related to the main objective of the study. In view of this objective, the changes in shear strength on radial and tangential cut surfaces of Oriental beech (Fagus orientalis Lipsky) and Scotch pine (Pinus sylvestris L.) woods having different roughness values as a result of sawing with a circular ripsaw, planing and sanding, and bonded with polyurethane (PU) and poly(vinyl acetate) (PVAc) adhesives at 3, 6 and 9 MPa pressure, were studied. The 936 specimens prepared with the objective of determining the effects of variables on bond performance were subjected to a shear test in a universal test equipment in accordance with the ASTM D 905-98 standard. The highest shear strength (13.85 N/mm²) was obtained for the Oriental beech specimens cut from their tangential surfaces with a circular ripsaw, which were glued with PVAc adhesive by applying a pressure of 9 MPa. The lowest value (4.22 N/mm²) was obtained in the specimens planed from their tangential surfaces, which were glued with PU adhesive by applying a pressure of 3 MPa. The specimens obtained from Oriental beech wood showed a higher shear strength compared to the specimens obtained from Scotch pine. In general, in both species of wood, the specimens glued with PVAc adhesive, both on the tangential surfaces and on the radial surfaces, produced higher shear strengths compared to the specimens glued with PU adhesive.     

Bond strength/disbonding behavior and dimensional stability of wood materials with different adhesives

In this study, we aimed to describe the effects of adhesives [poly(vinyl acetate) (PVAc), Desmodur vinyl trie ketonol acetate, and urea formaldehyde (UF)] on wooden materials (Scotch pine and oriental beech) cut tangentially and radially impregnated with Protim Solignum, chromate copper arsenate (CCA), and Celcure AC 500 and exposed to humidity and water and heat‐resistance, heating, and cooling tests. For the adhesives, the highest swelling (4.3%) was obtained for oriental beech bonded with UF and cut radially, and the lowest swelling (1%) was obtained for Scotch pine bonded with PVAc and cut radially. For the control samples, the humidity‐resistance, water‐resistance, heat‐resistance, and heating and cooling tests decreased the bonding strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Magnetic Resonance Imaging of Water Distribution in Welded Woods

This study was performed for a better understanding of water effect on welded wood and improving its water resistance. In this article, we have also attempted to demonstrate the feasibility of using Magnetic Resonance Imaging technology to study water movement in welded woods. Water distribution in welded woods of Scots pine (Pinus sylvestris) and beech (Fagus sylvatica) was investigated by Magnetic Resonance Imaging. Axial specimens were cut from beech and sapwood of Scots pine in longitudinal direction of wood grain. Two pieces of each wood species were welded together by a linear vibration machine. Sub-samples measuring 30 mm × 20 mm × 100 mm were cut from the welded specimens for Magnetic Resonance Imaging. The results showed that weldline of Scots pine was more resistant to water than weldline of beech. Pine joint was still holding after 40 h immersion in water, while a rapid wetting of the beech joint resulted in breakage of the joint in even less than an hour. This preliminary study also showed that MRI is a powerful tool to measure water distribution in welded woods and highlighted the potential of this technique to enhance understanding of wood welding.     

Fire performance of bolted connections in laminated veneer lumber

This paper describes an investigation into the fire performance of bolted tensile connections in laminated veneer lumber (LVL) made from radiata pine. The capacity of the bolted connections depends on the embedment strength of the wood and on the yield moment of the bolts. The purpose of the research was to develop a prediction method for the time to failure of the connections when exposed to fire. An experimental investigation was carried out on the axial tensile strength of three types of bolted connections that utilized either wood or steel splice plates. Some specimens were tested at ambient temperatures while similar specimens were tested in fire conditions with a constant applied load. In addition, single‐bolted connections were tested under constant elevated temperature conditions to determine the embedment strength of the LVL. Connections with no steel plates, or with steel plates slotted between the timber members, performed better than those with exposed steel. A simplified design approach is proposed, using an extension of the Johansen formulae, such that the embedment strength of the LVL depends on the temperature in the bolt. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of Outdoor Exposures and Boron Compounds on Bonding Strength of Desmodur-VTKA Adhesive

This study was carried out to determine the shear strength of an adhesive on weathered wood, impregnated with a boron compound, using a long term dipping method. The shear strength of D-VTKA adhesive on two types of wood species each containing one of two types of the impregnated material, under different weathering conditions, was measured. The results showed that the highest shear strength (11.01 N/mm²) was obtained with the control samples of untreated, oriental beech wood, and the lowest was obtained for Scots pine impregnated with boric acid after two seasons of exposure (six months). Weather conditions affected the shear strength in a negative way. Finally the results showed that if the boron compounds were supported with non-leaching chemicals, they could be recommended as fire-retardant additives and would extend the life of wood bonded with D-VTKA adhesive.     

Impacts of impregnation with Timbercare Aqua on the red and yellow color tone of some woods and varnishes

This study has been performed for determining the effects of impregnation with Timbercare Aqua (Tc) on the red and yellow color tone of some woods and varnishes. For this purpose, the test samples prepared from Oriental beech, European oak, Scotch pine, Oriental spruce, and Uludag fir woods, which met the requirements of ASTM D 358, was impregnated with Tc according to ASTM D 1413 and producer's definition. After impregnation, wood surfaces have been coated by Sayerlack parquet varnish (Sp), Sayerlack interior varnish (Si), and Sayerlack exterior varnish (Se) varnishes in accordance with the ASTM D 3023 standards. According to ASTM D 2244, the red and yellow color tone of samples after varnishing process was determined. As a result, the value of red color tone was the highest in Oriental beech (15.21) and the lowest in Uludag fir (5.38). For the wood material, impregnation material, and varnish interaction, the red color tone value was the highest in Oriental beech + Tc + Sp (18.43) and the lowest in Uludag fir + Tc + Si (3.92). The value of the yellow color tone was the highest in pine (34.45) and the lowest in Oriental beech (26.50). For the wood material, impregnation material, and varnish interaction, the yellow color tone value was the highest in Oriental spruce + Tc + Sp (42.12) and the lowest in Oriental beech + Tc + Si (21.47). This effect may be due to the impacts of impregnation chemical on wood extractives and color pigments in varnish. Accordingly, it should be taken into care for applications where the red and yellow color tone value is important. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effects of dowels produced from various materials on withdrawal strength in MDF and Pb

Wood dowels are commonly used in the construction furniture, but little information is available about the additive effects of dowels on the ultimate withdrawal strength of single or multidowel joints. This study was carried out to determine the tensile strength of 10‐mm‐diameter dowels produced from medium‐density fiberboard (MDF), plywood, scotch pine (Pinus sylvestris L.), and beech (Fagus orientalis lipsky), bonded parallel and vertical to the surface of MDF and particleboard (Pb) with poly(vinyl acetate) (PVAc) and Desmodur‐VTKA (D‐VTKA). Tensile strength was applied to the dowels according to the procedure in the ASTM‐D 1037 standard. The effects of dowel species, direction of tensile, composite material, and type of adhesive on tensile strength were determined. The results showed that the highest tensile strength was obtained in beech dowels bonded vertically with PVAc adhesive to the surface of MDF at 7.91 N/mm². If the dowels used in furniture production are subjected to great tensile strength, beech dowels bonded with PVAc adhesive on MDF should be used. However, when dowels produced from MDF and plywood waste are used, they also can produce positive results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 531–535, 2003     

New Ammonium- and 1,2,4-Triazolium-Based Ionic Liquids for Wood Preservation

Biological activity of new potential wood preservatives—ammonium- and triazolium-based ionic liquids—was determined employing screening agar-plate, agar-block, and perlite-block methods. Experiments were carried out on Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.) wood. This study examined the effect of the ionic liquid structure on anti-fungal efficacy, depth of penetration, and fixation in wood. It was stated that the fungicidal value of new ammonium compounds depended, above all, upon the cation structure; for Coniophora puteana, it ranged from 2.7 kg m^?3 to 4.6 kg m^?3. These compounds effectively protected Scots pine wood against the action of mold fungi. Ammonium ionic liquids with a nitrite anion were characterized by strong fungitoxic properties, stronger than ammonium nitrates. The application in the amount of 15 g m^?2 caused an insignificant growth of mold fungi on the surface of Scots pine wood. For the mixture of 7.5% tebuconazole and 7.5% propiconazole dissolved in ionic liquids, the synergistic effect against mold fungi at the application of 15 g m^?2 was found. Dissolving tebuconazole in didecyldimethylammonium nitrate repeatedly lowered the fungicidal value against brown-rot fungi, as well as increased penetration of the ionic liquids in wood. This was associated with reduced viscosity of this ionic liquid caused by the addition of 1,2,4-triazole derivatives. Quaternary derivatives of 1,2,4-triazoles showed very high activity against blue stain and wood-decaying fungi. Additionally, most of the test compounds were well-fixed in Scots pine wood. The spectral study in infrared confirmed that nitrite, nitrate anions, and didecyldimethylammonium cation were retained in the treated wood.     

The Improvement of Bond Strength Properties and Surface Characteristics of Resinous Woods

Apitong (Dipterocarpus spp.) and Caribbean pine (Pinus caribaea Morelet) contain high amounts of extractives that contribute to poor bonding. To reduce, if not to eliminate, the effects of these extraneous substances, surfaces of small wood blocks were Soxhlet-extracted for 8 hours by different solvents. Wettability of the wood surfaces was then measured by droplet and dynamic methods using water and dilute NaOH as liquids. Tensile shear strengths of extracted wood bonded with aqueous vinyl polymer isocyanate (API), resorcinol formaldehyde (RF) and polyvinyl acetate (PVAc) resin adhesives were also measured. Results revealed that although Caribbean pine had much higher resin content than Apitong, the former had better wettability than the latter. Solvent extraction of the adherend with either hexane or ethanol-benzene (1:2) for 8 hours was not enough to improve its wettability but enough to improve its gluability. However, successive extraction with hexane, methanol and ethanol benzene rendered the wood satisfactorily wettable. Generally, a direct relationship between wettability and bond strength could not be observed. In a separate experiment to improve bonding strengths, test specimens were either overheated or autoclaved for 4 minutes at 125°C during the pressing period. Autoclave treatment was found to be useful in increasing the bond strengths of API, RF, PVAc and urea formaldehyde (UF)-bonded Apitong and Caribbean pine.     

The effects of surface roughness on varnish adhesion strength of wood materials

In this study, the effects of surface roughness of wood material on the adhesion strength of varnish layers have been tested. For this purpose, test samples of beech (Fagus orientalis L.), Scots pine (Pinus sylvestris L.), and cherry (Prunus cerasus) wood species were prepared and sanded with 80, 120, and 180 grit abrasives. The surface roughness values of specimens were determined using a stylus-type profilometer TIME TR 200 according to the ISO 4287 standards. Then, water-based, polyurethane, and acrylic varnish were applied to the surfaces of the samples in accordance with ASTM-D 3023. Layer adhesion strength was determined to the TS EN ISO 4624 standards. As a result, the highest adhesion strength value (2.52 N/mm²) was found in cherry, while the Scots pine had the lowest value (2.32 N/mm²). For the varnish types, polyurethane varnish types gave the highest value (3.15 N/mm²), while the lowest value was obtained from the water-based varnish. Looking at interactions between adhesion strength and surface roughness, the water-based varnish had the strongest correlation with adhesion strength (69%) and acrylic varnish also had a similar result (67%), while polyurethane varnish had the weakest result (33%) in this interaction.     

Impacts of impregnation with boron compounds on surface roughness of woods and varnished surfaces

This study determines the effects of the process of impregnation of boron compounds on the surface roughness of Oriental beech, Scotch pine, Oriental spruce, and Uluda? fir woods and varnished surfaces. For this purpose, samples are prepared according to ASTM D 358 and impregnated according to ASTM D 1413‐99 with a 5.5% solution of boric acid (Ba), borax (Bx), and Ba with Bx (Ba + Bx) and varnished with synthetic varnish (Sv) and water‐based varnish (Wb) in accordance with ASTM D 3023. The surface roughness is determined according to ISO 4287 and TS 930 standards. The results indicate that the surface roughness is the highest in Uluda? fir, Wb, and Bx and the lowest in Oriental spruce, Sv, and Ba + Bx. For the combination of wood, impregnation material, and varnish, the surface roughness is the highest in Oriental beech with Bx and Wb and the lowest in Scotch pine with Ba + Bx and Sv. The surface roughness is less in impregnated samples than unimpregnated samples and in impregnated and varnished samples than impregnated and unvarnished samples. According to these results, boron compounds decrease the surface roughness of varnishes and wood materials. Thus, impregnation of wood with boron compounds decreases the surface roughness. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4952–4957, 2006     

Emission of corrosive volatiles from wood. III. Effect of treatment with propylene oxide

A study has been made of the release of corrosive volatiles when wood shavings are sterilised by propylene oxide. Sterilisation of sweet chestnut (Castanea sativa), beech (Fagus sylvatica), Norway spruce (Picea abies), Sitka spruce (Picea sitchensis), Douglas fir (Pseudotsuga taxifolia) and Scots pine (Pinas sylvestris) with propylene oxide at varying relative humidities and subsequent incubation at 48° and 100% R.H. gave a variable release of corrosive volatiles but usually tended to increase the amount of acid released.     

Drought Stress Alters the Concentration of Wood Terpenoids in Scots Pine and Norway Spruce Seedlings

Drought is known to have an impact on the resistance of conifers to various pests, for example, by affecting resin flow in trees. Little is known, however, about the quantitative and qualitative changes in resin when trees are growing in low moisture conditions. We exposed Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings to medium and severe drought stress for two growing seasons and analyzed the monoterpenes and resin acids in the main stem wood after two years of treatment. In addition to secondary chemistry, we measured the level of nutrients in the needles and the growth response of seedlings. After the first year of treatment, drought stress did not affect the growth of seedlings, but in the second year, shoot growth was retarded, especially in Scots pine. In both conifer species, severe drought increased the concentrations of several individual monoterpenes and resin acids. Total monoterpenes and resin acids were 39 and 32% higher in severe drought-treated Scots pine seedlings than in the controls, and 35 and 45% higher in Norway spruce seedlings. In Scots pine needles, the concentrations of nitrogen and phosphorus increased, while magnesium and calcium decreased compared to controls. In Norway spruce needles, nutrient concentrations were not affected. The results suggest that drought stress substantially affects both the growth of conifers and the chemical quality of the wood. We discuss the potential trade-off in growth and defense of small conifer seedlings.     

The Improvement of Bond Strength Properties and Surface Characteristics of Resinous Woods

Apitong (Dipterocarpus spp.) and Caribbean pine (Pinus caribaea Morelet) contain high amounts of extractives that contribute to poor bonding. To reduce, if not to eliminate, the effects of these extraneous substances, surfaces of small wood blocks were Soxhlet-extracted for 8 hours by different solvents. Wettability of the wood surfaces was then measured by droplet and dynamic methods using water and dilute NaOH as liquids. Tensile shear strengths of extracted wood bonded with aqueous vinyl polymer isocyanate (API), resorcinol formaldehyde (RF) and polyvinyl acetate (PVAc) resin adhesives were also measured. Results revealed that although Caribbean pine had much higher resin content than Apitong, the former had better wettability than the latter. Solvent extraction of the adherend with either hexane or ethanol-benzene (1:2) for 8 hours was not enough to improve its wettability but enough to improve its gluability. However, successive extraction with hexane, methanol and ethanol benzene rendered the wood satisfactorily wettable. Generally, a direct relationship between wettability and bond strength could not be observed. In a separate experiment to improve bonding strengths, test specimens were either overheated or autoclaved for 4 minutes at 125°C during the pressing period. Autoclave treatment was found to be useful in increasing the bond strengths of API, RF, PVAc and urea formaldehyde (UF)-bonded Apitong and Caribbean pine.     

Impact of impregnation with boron compounds on the surface hardness and abrasion resistance of some varnished woods

This study was performed to determine the impact of impregnation with boron compounds on the surface hardness and abrasion resistance of some varnished woods. For this purpose, test specimens prepared from Oriental beech, White oak, Scotch pine, and Uludag fir, which met the requirements of ASTM D 358, were impregnated according to ASTM D 1413‐99 with boric acid (Ba), borax (Bx), and boric acid + borax (Ba+Bx) by the vacuum technique. After impregnation, the surfaces are coated with synthetic (Sn), water‐borne (Wb) and acid hardening (Ah) varnishes in accordance with ASTM D 3023. the surface hardness of specimens after the varnishing process was determined in accordance with ASTM D 4366. The abrasion resistance of specimens after the varnishing process was determined in accordance with TS 4755. According to the wood type, impregnation material and varnish type, the surface hardness was the highest for Oriental beech impregnated with borax + boric acid and acid hardening varnish and the lowest for Uludag fir impregnated with borax + boric acid and synthetic varnish. According to the wood type, impregnation material and varnish type, the abrasion resistance was the highest for Oriental beech impregnated with borax + boric acid and acid hardening varnish and the lowest for Scotch pine impregnated with borax + boric acid and synthetic varnish. Those results should be taken into account for applications like parquet, flooring etc., where the surface hardness and abrasion resistance values are very important. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of edge banding thickness of white oak bonded with different adhesives on withdrawal strengths of beech dowels in composite materials

Dowel joints are widely used in furniture frame construction as a load-bearing connection structure, as well as a simple locator for parts. Joints constructed with dowels were subjected to withdrawal, bending, shear, and tensile forces. The aim of this study was to determine the withdrawal strengths of 6, 8, 10 mm diameter beech dowels embedded into matching holes drilled into the edges of medium-density fiberboard (MDF) and particleboard (PB) with solid wood edge banding of white oak with 5, 10 and 15 mm thickness, bonded with hot-melt, poly(vinyl acetate) (PVAc) and Desmodur-VTKA (D-VTKA), a polyurethane-based one-component adhesive. The effects of edge banding thickness, dowel dimension, type of composite material and type of adhesive used for edge banding on the withdrawal strength were determined. According to the interaction results from the Duncan test the highest withdrawal strength (7.019 N/mm²) was obtained in beech dowels with 6 mm diameter for MDF with solid wood edge banding of white oak with 10 mm thickness bonded with the hot-melt adhesive. Should the dowels be subjected to withdrawal, it is advised that a beech dowel should be used for MDF with solid oak edge banding with 10 mm thickness bonded with a hot-melt adhesive in furniture production and decoration applications.     

Effects of Veneer Treatment with Copper-Based Preservatives on the Decay Resistance and Mechanical Properties of Poplar LVL

To improve the durability of poplar laminated veneer lumber (LVL), the veneers were impregnated with alkaline copper quaternary (ACQ) and copper azole (CA) at four retention levels, and the effects of the treatments on the LVL properties were examined. The results demonstrated that the treatments substantially improved the decay resistance of LVLs, with the decreases in mass losses ranging from 42.6% to 87.3%. However, retention levels greater than the specified standard values for Use Category C4.1 might be required for sufficient protection of poplar LVL against decay fungi. The bending and shear properties of all treated LVLs met the requirements for high-grade products specified in the LVL standard GB/T 20241. No significant effects of the treatments were observed on the mechanical properties of LVLs, and the LVLs did not display any visible delamination after boil-dry treatment. These results imply that the treatments significantly improved the decay resistance of poplar LVL products and had no appreciable impact on their mechanical and physical properties.     

In situ emulsion polymerization and characterization of PVAc nanocomposites including colloidal silica nanoparticles for wood specimens bonding

Polyvinyl acetate (PVAc) nanocomposites for wood adhesives containing different amounts of colloidal silica nanoparticles (CSNs) were synthesized via in situ one-step emulsion polymerization. The adhesion strength of wood specimens bonded by PVAc nanocomposites was investigated by the tensile test. Thermal properties of PVAc nanocomposites were also characterized by differential scanning calorimetry and thermogravimetric analysis. Rheological and morphological properties of the PVAc nanocomposites were investigated using rheometric mechanical spectrometry and field emission scanning electron microscopy (FESEM), respectively. The obtaining results showed that the shear strength of PVAc nanocomposite including 1 wt. % CSNs has the highest shear and tensile strength about 4.7 and 3.2 MPa, respectively. A small increment of T_g (~3 °C) and considerable increment of the ash content proved the enhancement of PVAc thermal characterization in the presence of CSNs. FESEM results showed uniform dispersion of nanoparticles throughout the PVAc matrix due to using the in situ emulsion polymerization process. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48570.