Birch Veneer Research Articles

Weathering Stability and Durability of Birch Plywood Modified with Different Molecular Weight Phenol-Formaldehyde Oligomers.

This study investigated the effect of phenol-formaldehyde (PF) resin treatment on the weathering stability and biological durability of birch plywood. Silver birch (Betula pendula) veneers were vacuum-pressure impregnated with four different PF resins with average molecular weights (Mw) of 292 (resin A), 528 (resin B), 703 (resin C), and 884 g/mol (resin D). The aging properties of PF resin modified birch plywood were analyzed using artificial weathering with ultraviolet (UV) light, UV and water spray, and weathering under outdoor conditions. The same combinations of PF-treated plywood specimens were then tested in soil-bed tests to determine their resistance against soft-rot wood decay. It was not possible to compare weathering processes under artificial conditions to processes under outdoor conditions. However, the weathering stability of birch plywood treated with PF resins A, B, and C, scored better than plywood treated with commercial resin D (regardless of solid content concentration [%]). Results from unsterile soil bed tests showed improvements in resistance to soft-rot wood decay compared to untreated plywood and solid wood. Mass loss [%] was lowest for birch plywood specimens treated with resin of highest solid content concentration (resin D, 20%). Provisional durability ratings delivered durability class (DC) ratings of 2–3, considerably improved over untreated solid wood and untreated birch plywood (DC 5).

Functionality of Surface Mycelium Interfaces in Wood Bonding.

Filamentous fungi have been considered as candidates to replace petroleum-based adhesives and plastics in novel composite material production, particularly those containing lignocellulosic materials. However, the nature of the role of surface mycelium in the adhesion between lignocellulosic composite components is not well-known. The current study investigated the functionality of surface mycelium for wood bonding by incubating Trametes versicolor on yellow birch veneers and compared the lap-shear strengths after hot-pressing to evaluate if the presence of surface mycelium can improve the interface between two wood layers and consequently improve bonding. We found that the lap-shear strength of the samples was enhanced by the increase of surface mycelium coverage up to 8 days of incubation (up to 1.74 MPa) without a significant wood weight loss. We provide evidence that the bottom surface of the mycelium layer is more hydrophilic, contains more small-scale filamentous structure and contains more functional groups, resulting in better bonding with wood than the top surface. These observations confirm and highlight the functionality of the surface mycelium layer for wood bonding and provide useful information for future developments in fully biobased composites manufacturing.

Effect of Different Hardwood Species and Lay-Up Schemes on the Mechanical Properties of Plywood

In Estonia, hardwoods form approximately 50% of all forest area, where the main species are birch (30%), gray alder (9%), aspen (6%) and black alder (4%). Birch has been extensively used by the veneer-based industry, but species like black alder, gray alder and aspen have not been commonly used by the veneer-based products industry due to the lower quality of this resource. The aim of this research is to determine the effect of different lay-up schemes and usages of gray alder, black alder and aspen on the mechanical properties of plywood, by replacing birch veneer in the plywood core with alternative wood species. The main veneer and plywood characteristics will be evaluated according to the current standards, e.g., veneer strength perpendicular to grain, plywood bonding and bending strength, and modulus of elasticity. All processing parameters will be kept similar to those used generally by birch plywood manufacturers. The results showed that birch and black alder plywood panels had generally the highest bending strength properties, followed by grey alder and aspen. It was also found that, for proper gluing, birch veneers had the lowest glue consumption, 152 g/m2, and aspen had the highest glue consumption, 179 g/m2. It was found that when lower density wood was used in the plywood, the product density increased. Low density wood veneers had higher glue consumption, and also higher compaction in thickness than birch veneers under the same pressure. Overall, it was shown that the wood species used in this study have slightly lower strength properties, but with proper lay-up schemes, these wood species could be successfully used by the veneer-based products industry.

Influence of Site Conditions and Quality of Birch Wood on Its Properties and Utilization after Heat Treatment. Part II—Surface Properties and Marketing Evaluation of the Effect of the Treatment on Final Usage of Such Wood

This work is a follow-up contribution to the characteristics of Betula pendula (silver birch) wood from different habitats and the impact of the subsequent heat treatment. Specifically, it focuses on the surface properties of birch wood in the form of veneers, namely color, hardness, roughness and wetting, and in particular on the marketing evaluation of the attractiveness of colored birch wood and, thus, its possible use in practice in the Czech Republic. Three heat treatment steps at 170, 190 and 200 °C were used. The resulting values of the properties of the treated birch veneers were compared with the untreated reference veneers and also with beech veneers. These properties were the wood density, the colorimetric parameters, the roughness parameters, the wetting parameters, the hardness and density, and none of the parameters studied showed negative changes due to the temperature adjustment. Overall, both in terms of properties and in terms of marketing appraisal, there is the potential for birch to replace, for example, beech, especially in the furniture industry, by application in the form of heat-treated veneers after suitable heat treatment. The conclusions of the marketing analysis resulting from the questionnaire survey conducted on a sample of respondents show the significant preference for the heat-treated birch wood compared to reference birch samples without heat treatment.

Effects of Selected Parameters on the Bonding Quality and Temperature Evolution Inside Plywood During Pressing.

This research optimizes the process of plywood production to determine its effectiveness in reducing energy and adhesive consumption for more efficient production with the required quality. The influence of selected parameters including veneer treatment (non-densified and densified), plywood structure, temperature, time and pressure of pressing, on the bonding quality and temperature evolution within the veneer stacks during hot pressing was investigated. Rotary-cut, non-densified and densified birch veneers and phenol formaldehyde (PF) adhesive were used to manufacture plywood samples. The effect of pressure and time of pressing on bonding quality of the plywood was determined. Bonding quality was evaluated by determining the shear strength of the plywood samples. The temperature evolution inside the veneer stacks was measured for birch veneers for different pressing temperatures and pressures for different numbers of veneer layers. The heating rate of the veneer stacks increased as the pressing temperature increased and decreased markedly with an increasing number of veneer layers. At a high pressing pressure, the heating rate of the densified veneer stacks was faster than that of non-densified veneers at the same pressure. The use of densified veneers for the production of plywood can lead to a shorter pressing time (17–50% reduction), lower glue consumption (33.3% reduction) and a lower pressing pressure (22.2% reduction) without negatively impacting the bonding strength of the plywood.

Properties of modified wood according to treatment technology and thermo-vacuum process for birch (Betula pendula Roth) veneers

Thermally modified birch (Betula pendula Roth) veneers that had been subjected to wood treatment technology (WTT) or thermo vacuum (TV) processes were compared in this study. After modification of veneers in the range of temperatures from 160 °C to 218 °C and times from 0.5 h to 3 h, the color, mass loss, density, tensile strength, hygroscopicity, and decay resistance against brown rot fungus Coniophora puteana were determined. Treatment regimes with the greatest mass loss were at 217 °C for 3.0 h in TV (7.8%) and 160 °C for 0.8 h in the WTT (6.7%). As expected, wood mass loss correlated well with moisture exclusion efficiency (MEE) in all relative humidity (RH) environments (r = 0.95 to 0.99). Strength loss in the WTT was considerable compared to the TV process (57% and 40%, respectively). The resistance against brown rot fungus was moderate with a mass loss of 12% to 33%. Among the investigated samples, the regime 217/3.0/TV showed the best resistance against brown rot fungus and acceptable other properties.

On the Origin of Changes in the Adhesive Interaction between Veneer and Glue under Glue Polarization in Plywood Manufacture

The possibilities of using an electrostatic field in the technology for manufacturing plywood by the example of birch veneer with the use of carbamide–formaldehyde epoxy or polyvinyl acetate glues have been considered. It has been shown that preliminary treatment of the glue in an electric field results in a decrease of the glue viscosity and leads to an increase in the plywood strength under chipping, whereas the polarization of plywood samples in the course of the gluing procedure causes the ultimate strength under chipping to increase. The results can be explained as being due to the orientation of the glue macromolecules owing to an electric field, which leads to hardening of the material. This effect may be caused by a double electric layer occurring at the veneer–glue interface, increasing the adhesion of the glue to the veneer, by lowering glue viscosity and improving veneer surface wettability, as well as by an increase in the free surface energy of glues in the course of polarization thereof.

Influence of Fiber Deviation on Strength of Thin Birch (Betula pendula Roth.) Veneers.

The currently pursued implementation of wood into novel high performance applications such as automotive parts require knowledge about the material behaviour including ultimate strength. Previous research has shown that fiber deviation seems to be the dominating factor influencing the strength of thin veneers. This study aims to further investigate and quantify the influence of fiber deviation in two dimension and different hierarchical levels on the tensile strength of thin birch veneers. The fiber deviation in- and out-of-plane as well as the micro fibril angle were assessed by means of wide-angle X-ray scattering. Tensile strength was determined in laboratory experiments. Results show a high variability for in-plane fiber deviation mainly constituted by knots and other growth influencing factors. Pearson correlations between strength and fiber deviation ranged from −0.594 up to −0.852. Best correlation (r = −0.852) was achieved for maximum in-plane fiber deviation directly followed by a combined angle of in- and out-of-plane fiber deviation (r = −0.846). Based on the results it was shown that fiber deviation in- and out-of-plane is the dominating factor influencing ultimate tensile strength of thin birch veneers. Further research in regard to non-destructive strength prediction is necessary.

Effect of Veneer-Drying Temperature on Selected Properties and Formaldehyde Emission of Birch Plywood.

In this study, the effect of the veneer-drying process at elevated temperatures on selected properties and formaldehyde emission of plywood panels was determined. We assume that during the veneer drying at high temperatures, more formaldehyde is released from it, and therefore, a lower formaldehyde emission can be expected from the finished plywood. Prior to bonding, birch veneers were dried at 160 °C (control) and 185 °C in an industrial veneer steam dryer (SD) and at 180 °C, 240 °C and 280 °C in an industrial veneer gas dryer (GD). Two types of adhesives were used: urea–formaldehyde (UF) and phenol–formaldehyde (PF) resins. Bonding quality, bending strength and modulus of elasticity in bending, water absorption and thickness swelling of plywood samples were determined. The formaldehyde emission level of samples was also measured. It was concluded from the study that the effects of veneer-drying temperatures on the bonding strength and physical and mechanical properties of plywood panels were significant. Veneer-drying temperatures of 185 °C/SD, 180 °C/GD and 240 °C/GD negatively affected the bending strength and the modulus of elasticity along and across the fibres for both UF and PF plywood samples. Bonding strength mean values obtained from all test panels were above the required value (1.0 MPa) indicated in EN 314-2 standard. The lowest formaldehyde emissions for the UF and PF plywood samples were observed in the samples from veneer dried in a steam dryer at 185 °C/SD.

Mechanical properties of transparent high strength biocomposites from delignified wood veneer

Transparent wood (TW) based on delignified birch veneer and thermoplastic poly(methyl methacrylate) (PMMA) is investigated by uniaxial tensile tests and full-field strain analyses based on digital image correlation techniques. TW is considered as a composite of unidirectional fibers (wood veneer) in a matrix (PMMA). Four in-plane elastic constants along the material axes are reported to enable the usage of continuum mechanics and lamination theory. Longitudinal composite strength is as high as 270 MPa at a reinforcement content of only 25 vol%. The failure behavior is interpreted based on strain field development. Strong reinforcement effects were observed from delignified birch veneer. Despite the fragility of delignified veneers, this constituent provides unexpectedly high reinforcement due to the high cellulose content and favorable stress transfer mechanisms.

Experimental research on the molecular-topological structure of oak (Quercus robur L.) and birch wood (Betula pendula Roth) and its shape-memory effect

Features and characteristics of wood as a natural smart material allow us to use it to create new smart biocomposite materials, intelligent systems and environments. The shape-memory effect of oak (Quercus robur L.) and birch (Betula pendula Roth) veneers was investigated. Thermomechanical spectrometry was used to study these two species, which makes it possible to establish the relationship between the deformation transformations and the nature of intermolecular interactions and the interchain organization of wood polymers. The quantitative and molecular relaxation characteristics of the topological structure were obtained for the characterization of the shape-memory effect for the permanent, temporary and after recovery shapes of birch and oak wood samples. The results showed a relationship between the quantities of shape-memory effect and changes in the molecular-topological structure. A reversible transformation of a topological structure was experimentally confirmed for birch and oak woods, with the formation of a temporary deformation and the recovery of the original permanent shapes.

ТЕПЛОПРОВОДНОСТЬ ДРЕВЕСНЫХ МАТЕРИАЛОВ ЯЧЕИСТОЙ КОНСТРУКЦИИ

A physical model is developed for heating a set of laminated cellular structure formed from peeled veneer, dependences for determining its thermal conductivity under conditions of non-stationary heat transfer are proposed. It was found that for a package of 11 layers of birch veneer 2 mm thick, the thermal diffusivity is 1.93∙10–6 m2/s. Based on the fundamental theory of thermal conductivity of the wood substance, dependencies are obtained for calculating the duration of bonding of heat-insulating materials of a cellular structure. It has been established that the duration of gluing of a 22 mm thick plywood mesh slab of peeled birch veneer under pressure exposure is 14.5 minutes at a temperature of press plates 110 °C. The thermotechnical characteristics of the new wood-based cellular structure material were determined: the thermal conductivity coefficient of a cellular plywood board with a density of 530 kg/m3 was 0.081 W/(m·K), the strength under static bending of the board parallel to the fibers of the outer layers was 14 MPa, and perpendicular to the fibers was 10 MPa. The use of underutilized soft broadleaved species with low operational properties as a heat-insulating material, where high strength indicators are not required, is justified, since its thermal conductivity is two times lower than that of a similar material – solid plywood board. For citation: Lukash A.A., Lukutsova N.P. Thermal Conductivity of Wood-Based Cellular Structures. Lesnoy Zhurnal [Russian Forestry Journal], 2020, no. 1, pp. 146–153. DOI: 10.37482/0536-1036-2020-1-146-153

Non-destructive testing of thin birch (Betula pendula Roth.) veneers

In technical applications of wood-based composites, the predictability of elasticity and strength is important. The aim of this study was to predict the static modulus of elasticity and tensile strength of thin (0.55 mm ± 0.05 mm) birch veneers. Based on the dynamic modulus of elasticity estimated via means of wave transmission time the observed dynamic modulus of elasticity was on average 14% lower than the corresponding static modulus of elasticity. This difference could be explained by a decreased measuring area during the tensile testing or by defects within the samples. The dynamic modulus of elasticity correlated well with the static modulus of elasticity (r = 0.821). Therefore, using wave transmission time to non-destructively predict the elasticity of veneers proves to be a promising tool. The dynamic modulus of elasticity showed a significant and positive correlation with the tensile strength (r = 0.665), but this correlation was weaker than with the static modulus of elasticity. Therefore, the wave transmission time or the static modulus of elasticity must be combined with additional strength-influencing properties, such as fiber angle or density, to allow for a highly accurate prediction of tensile strength.

The accuracy of holes drilled in the side surface of plywood

Dimensional accuracy of machining translates into susceptibility to defects in assembly of furniture elements. In the initial drilling phase, the tip of the drill may slip due to the properties of the workpiece, which may result in inaccurate machining. Taking this into account, it was decided to investigate this phenomenon for drilling in the side of the plywood board. Samples for testing were made of 18 mm thick, 13 layer birch-alder plywood, covered with melamine film, glued with phenol-formaldehyde glue. With the use of an industrial dowel drilling machine, 30 holes in each of three examined layer were made. All holes were made parallel to the layers – on the side of the plywood board, and their axes were located in three adjacent layers: the birch veneer layer, the adhesive layer, and the alder veneer layer. Two types of geometric accuracy of holes were analyzed: the distance between the real center of the hole and the nominal position and also the inclination of the hole axis from the nominal axis. The holes made in the adhesive layer showed approximately twice larger deviations compared with the holes made in two adjacent layers of veneer. There was no significant relationship between the deviations of the angle of holes axis and the inaccuracies in the position of their centers. Main conclusion: When drilling in the side surface of the plywood board, less accurate holes are obtained if the hole axis is located in the adhesive layer, and there is more accuracy if the hole axis is located in the veneer layer.

The effect of diammonium phosphate and sodium silicate on the adhesion and fire properties of birch veneer

Abstract In built environments the combustibility of wood is a great concern, which limits the use of wood as a building material due to legislation. The reaction-to-fire properties of wood can be altered with the use of fire-retardant chemicals, and most of the commonly used fire retardants already have a long history of use. However, only limited information is available on the impact of different fire retardants on the adhesion properties of wood. Additionally, comparative studies between chemicals from different groups of fire retardants is scarce. The objective of this study was to investigate and compare the effects of two commonly used fire retardants, sodium silicate (SS) and diammonium phosphate (DAP), on veneer properties, the focus being especially on thermal behavior and adhesion. Thermal properties and combustibility were studied using thermogravimetric analysis (TGA), flame test and calorimetry. Glue bond strength was analyzed with an automated bonding evaluation system (ABES) and the leaching of chemicals was determined according to EN84. Additionally, the surface characteristics of modified veneers were imaged with scanning electron microscopy (SEM). Results revealed notable differences in the thermal properties of SS and DAP, with DAP having better fire-retardant performance in all thermal testing. SS also affected thermal properties and combustibility of modified veneers, but the effect was only moderate compared to DAP. Neither SS or DAP had any significant resistance against leaching but ABES testing showed a notable increase in the glue bond strength of DAP modified veneers.

Comparison of Birch and Beech Wood in Terms of Economic and Technological Properties for Plywood Manufacturing

The aim of this study was to investigate the use of birch wood, one of the most important wood species used in the plywood industry, especially in Europe, the Nordic countries, Poland, Belarus and Russia as an alternative to beech wood. For this purpose, comparison was made of their economic and technological properties. In five-ply plywood manufacturing, beech (Fagus orientalis Lipsky) and birch (Betula pendula) veneer sheets were used with melamine urea formaldehyde (MUF) and urea formaldehyde (UF) resins. Some mechanical properties such as shear strength, bending strength and modulus of elasticity of plywood panels were conducted according to EN 314-1 and EN 310, respectively. Mean mechanical strength obtained for birch plywood panels was quite above the limit values specified in the related standards. When taking into consideration the annual increment of beech and birch trees in 1 ha and the time they need to reach suitable diameters for the manufacturing of rotary cut veneers, it was calculated that birch trees provide 2.46 times more physical harvesting than beech trees.

Novel Lightweight Semi-Finished Products Made of Poplar Veneer Plywood with Basalt Fibre Reinforcement

Veneer plywood is established in building construction, interior finishing and vehicle construction. Particularly in automotive or ship interior applications, the requirements with regard to strength and stiffness properties are increasing. At the same time, the weight of the panel materials used is to be reduced. The development presented here is a new type of lightweight basalt fibre-reinforced poplar veneer plywood and at the same time rigid alternative to the established birch veneer plywood. By adapting the adhesive and the reinforcing semi-finished products, the material and manufacturing costs are comparatively low. The bonding of the fibre reinforcement to the carrier material is achieved by means of adapted wood adhesives (e.g. polyvinyl acetates), which are also used as matrix material for the fibre reinforcement. An application of the reinforcement layer is integrated into the coating process (e.g. with High Pressure Laminate HPL decorative fabrics) of the carrier material. Essential advantages compared to conventional board materials are shown in this paper. The research results were achieved at the Institute for Structural Lightweight Construction of the TU Chemnitz in cooperation with the company Toms Gerber GmbH within the ZiM cooperation project FuBa.

Исследование физико-механичес- ких и рентгенозащитных свойств деревокомпозиционного слоистого материала «Фанотрен Б»

Physical and mechanical and x-ray protection properties of new wood-based composite material “Fanotren B”, which consist of alternating layers of peeled birch veneer and reinforcing x-ray protective layers, are studied. The x-ray protective layer is nonwoven fabric – sintepon impregnated with x-ray protective composition; consist of barium sulfate, adhesive based on polyvinyl acetate dispersion and water. The material is recommended to be used in construction and decoration of premises in the areas with high radiation background. A distinctive feature of the developed material is the absence of lead and materials based on it. We had the following research objectives: to study the stress strain behavior of the material; to determine the balanced formulation of saturating composition for the x-ray protective layer; to evaluate its physical and mechanical properties. The stress – strain ratio of the ma-terial was simulated by the finite element method, the physical and mechanical properties were evaluated by the standard methods, the protective properties of the x-ray protective layer were measured by the lead equivalent of the image transparency on the radiograph with the use of lux meter. Theoretical studies have shown that the behavior of metal faced plywood under external load is described by the Sophie Germain’s equation with acceptable accuracy. The modeling was carried out on a solid model, which took into account mechani-cal properties of the materials included in the design and scheme of laying out the veneer layers. The developed model of the stress strain behavior has showed that the decrease of the protective layer thickness leads to the increase of deflections and stresses in it. Computer simulation revealed the stress increase in the areas of bonding the material protective layer and outer side of veneer. The impregnating composition was determined experimentally: mineral filler content is 51 %, binder content is 26 %, and water content is 23 %. The technological modes of composite laminated material formation were determined: binder consumption is 176 g/m2; pressing temperature is 50 oС; gluing time is 8 min. The material with the thickness of 9.5 mm has density of 1600 kg/m3; a lead equivalent is 0.54 mm Pb/mm; cross-breaking strength along the outer layers is 39 MPa; shear strength along the adhesive layer is 1.34 MPa; tensile strength along the fibers is 53 MPa.For citation: Yatsun I.V., Gorokhovskiy A.G., Odintseva S.A. Study of Physical and Mechani-cal and X-Ray Protection Properties of Wood-Based Composite Laminated Material “Fanotren B”. Lesnoy Zhurnal [Forestry Journal], 2019, no. 3, pp. 110–120. DOI: 10.17238/ issn0536-1036.2019.3.110

Core configuration and panel reinforcement affect compression properties of wood-based 2-D straight column lattice truss sandwich structure

To investigate the effects of the core configuration on the out-of-plane compressive behavior of a wood-based 2D straight column lattice truss sandwich structure, structures with different types of core configurations made of oriented particleboard (OSB) and birch (Betula) dowels were manufactured by using a simple slotting and adhesive bonding approach. An out-of-plane compression experiment was conducted to measure the structural load capacity, equivalent compressive strength, and modulus of elasticity (MOE). Numerical and theoretical analyses were conducted to verify the experimental results. The results show that the ultimate strength in the out-of-plane compression of eight different configurations followed a linear relationship with the relative density of the core (the ratio of the section area of the core to the bottom surface). Type IV (four columns with a diameter of 6 mm) and type V (one column with a diameter of 12 mm) with identical density (both 3.14%) showed similar compressive strength. The compressive MOE of type IV and type V differed greatly. The theoretical displacement is less than the actual displacement because the panel is weak. Therefore, 5 mm birch veneers were used to enhance the OSB panel. The compressive MOE of the reinforced structure could be increased by up to 78%.

Water Related Properties of Birch Wood Modified with Phenol-Formaldehyde (PF) Resins

In this study, Silver birch (Betula pendula) wood veneers and solid wood blocks were treated with commercial phenol-formaldehyde (PF) resin water solutions. Birch veneers and solid wood blocks of different size were impregnated with PF resin solutions in water with concentrations of 10, 20 and 30 wt%. The weight percent gain (WPG) and bulking after drying and curing of resin treated wood specimens were determined to evaluate the impact of specimen sizes and density. The leaching procedure according to EN 84 was performed to evaluate the PF resin fixation stability. The anti-swelling efficiency (ASE) of untreated and treated specimens during seven soaking-drying cycles was examined. Higher WPG values were obtained for specimens with lower density, but no correlation was found between the specimen size and WPG. The WPG of veneers and solid wood was 8.7 - 17.7% and 8.5 - 24.4%, respectively. The ASE of wood blocks treated with PF resins after the 1st cycle was in the range of 37 - 51% depending on the resin loading in the wood. However, the ASE values decreased after every next soaking-drying cycle, reaching 33 - 48% after the 7th cycle. After leaching, the WPG of specimens decreased by 2.3 - 3.0%.