Wood Veneer Research Articles

Bending Performance and Failure Behavior of Wooden Sandwich Panels with Corrugated Cores

Wooden sandwich panels with a corrugated core have not been the subject of scientific research so far. The anisotropic properties of the wood make it challenging to form corrugated shapes. Therefore, it is decided to determine the effect of geometric imperfections of the corrugated core made of wood veneers on the stiffness and strength of sandwich panels and the core elasticity modulus. The beams are manufactured in industrial conditions and subjected to three‐point bending. The research is carried out in the form of tests and numerical calculations. It is demonstrated that geometric imperfections of the core affect the stiffness and strength of sandwich panels. The modulus of elasticity can reach values lower by up to 37% and the strength by up to 24% compared with reference panels with an ideal, symmetrical core geometry. However, their average linear elasticity modulus (1449 MPa) indicates excellent construction properties. Under the tests, four stages of beam bending are revealed. The last stage means that panels can increase stiffness even after the core is destroyed. The corrugated core's modulus of elasticity is also determined.

State-of-the-art luminescent materials based on wood veneer with superior strength, transparency, and water resistance

Current energy and luminescent materials utilize polymers to encapsulate fluorescent carbon nanodots and dyes but they usually lack stability and biodegradability. Here, we introduce an alternative wood nanotechnology to produce luminescent films (veneer) with UV resistance and tailorable surface energy. First, fluorescent and transparent wood (FTW) is shown as a support of aggregation-induced fluorescent emission (AIE) by in-situ Hantzsch reaction of acetoacetate delignified wood (AA-DW). Highly aligned cellulose nanofibers present in AA-DW facilitate FTW densification, ensuing exceptional mechanical performance (tensile strength and Young's modulus of up to 422 MPa and 45 GPa, respectively). Simultaneously, the conjugated structures display high transparency (83 %), haze (80 %) and optical anisotropy. The new luminescent system is demonstrated to be biodegradable and effective in optical (fluorescent) windows as well as encrypted films.

The Russian forest industry: declining wood production and emerging opportunities in bioenergy

The aim of the study is to describe the main trends and possibilities in Russian forestry. Based on statistical data, the authors analyze general trends in the Russian forest industry like woodworking, roundwood and wood pellets production. Russia's output of roundwood, sawnwood, wood pellets, wood-based panels and veneer sheets has been growing steadily over the past 5 years. The production of only two wood-based panel types – hardboard and other fiberboard – is either absent or in decline. The results include decline in roundwood export and the growth rates in wood pellets, sawnwood, wood-based panels, and veneer sheets exports. The Russian forest industry has room to grow its export of forest products. This requires technology upgrading, which could be facilitated by proactive government policies. Keywords: forest industry, woodworking industry, bioenergy, Russia

Расчетно-экспериментальная оценка применимости экструдированного пенополистирола бытового назначения в трехслойных конструкциях корпуса маломерного судна

Object and purpose of research. This paper is an integrated study of extruded polystyrene foam (XPS) practicability for three-layered composite hull structures of small craft. Subject matter and methods. Mechanical properties of composite materials and their components are determined experimentally (three-point bending, longitudinal tension/compression). Elastic properties and limit-state characteristics are obtained from beam theory, mixed model of composite beam, finite-element method, as well as solution of geometrically non-linear contact problems as per Newton-Raphson iterative technique. Main results. The study illustrates final diagrams for structural responses of investigated composite beam, filler and binder as functions of pre-defined displacement of test rigging. It also gives the estimates for equivalent Young’s moduli, as well as preliminary positive opinion about the practicability of XPS as a substitute for the conventional wood veneer in composite structures of small ships. The paper also presents a structurally similar FE model suitable for prediction calculations of large complex structures that can be tested only when the whole full-scale hull is available. Conclusion. This study formulates and solves the elastic problem for the investigated XPS-based sandwich panels. The results give an idea about the practicability of this material for shipbuilding applications.

In Situ Lignin Sulfonation for Highly Conductive Wood/Polypyrrole Porous Composites

AbstractTo address the rising need of sustainable solutions in electronic devices, the development of electronically conductive composites based on lightweight but mechanically strong wood structures is highly desirable. Here, a facile approach for the fabrication of highly conductive wood/polypyrrole composites through top‐down modification of native lignin followed by polymerization of pyrrole in wood cell wall. By sodium sulfite treatment under neutral condition, sulfonated wood veneers with increased porosity but well‐preserved cell wall structure containing native lignin and lignosulfonates are obtained. The wood structure has a content of sulfonic groups up to 343 µmol g−1 owing to in situ sulfonated lignin which facilitates subsequent oxidative polymerization of pyrrole, achieving a weight gain of polypyrrole as high as 35 wt%. The lignosulfonates in the wood structure act as dopant and stabilizer for the synthesized polypyrrole. The composite reaches a high conductivity of 186 S m−1 and a specific pseudocapacitance of 1.71 F cm−2 at the current density of 8.0 mA cm−2. These results indicate that tailoring the wood/polymer interface in the cell wall and activating the redox activity of native lignin by sulfonation are important strategies for the fabrication of porous and lightweight wood/conductive polymer composites with potential for sustainable energy applications.

Double-interpenetrating nanostructured networks of marine polysaccharides possessing properties comparable to synthetic polymers

Sustainable circular economy requires materials that possess a property profile comparable to synthetic polymers and, additionally, processing and sourcing of raw materials that have a small environmental footprint. Here, we present a paradigm for processing marine biopolymers into materials that possess both elastic and plastic behavior within a single system involving a double-interpenetrating polymer network comprising the elastic phase of dynamic physical cross-links and stress-dissipating ionically cross-linked domains. As a proof of principle, films possessing more than twofold higher elastic modulus, ultimate tensile strength, and yield stress than those of polylactic acid were realized by blending two water-soluble marine polysaccharides, namely alginic acid (Alg) with physically cross-linkable carboxylated agarose (CA) followed by ionic cross-linking with a divalent cation. Dried CAAlg films showed homogeneous nano-micro-scale domains, with yield stress and size of the domains scaling inversely with calcium concentration. Through surface activation/cross-linking using calcium, CAAlg films could be further processed using wet bonding to yield laminated structures with interfacial failure loads (13.2 ± 0.81 N) similar to the ultimate loads of unlaminated films (10.09 ± 1.47 N). Toward the engineering of wood-marine biopolymer composites, an array of lines of CAAlg were printed on wood veneers (panels), dried, and then bonded following activation with calcium to yield fully bonded wood two-ply laminate. The system presented herein provides a blueprint for the adoption of marine algae-derived polysaccharides in the development of sustainable high-performance materials.

Nonlinear Finite Element Analysis of Flexural Laminated Veneer Lumber (LVL) Sengon Slender Beam

Laminated Veneer Lumber (LVL) is one of the engineered wood products consisting of wood veneers that are glued and pressed together. In this study, the behavior of LVL Sengon slender beam is numerically investigated by means of nonlinear finite element analysis (FEA), where only half of the experimental beam was modeled due to symmetry of the load configuration. The LVL Sengon wood material used Hill failure criterion with isotropic hardening rules, and its mechanical properties in both tension and compression are modelled according to its mechanical properties in tension obtained from the clear specimen test. The contact analysis is defined for each contacting and contacted elements. The FEA results well agreed with the experimental results in term of the load-deflection curve and failure mode of the beam. It is found that the lateral support has no effect on the stiffness of the beam. The beam stiffness and ultimate load increase by the increase of beam height-to-width ratio (𝑑/𝑏).

Overlaying performance and bonding mechanism of wood-based panels decorated by EVA film reinforced decorative wood veneer

ABSTRACT In order to understand the bonding mechanism of thermoplastic film reinforced wood veneer and broaden its application to wood-based panels, EVA film reinforced decorative wood veneer (EVA-RDV) was prepared and used for decoration of medium density fiberboard (MDF) and plywood (PW) respectively in this study. Decorative veneered wood-based panels were prepared by hot pressing followed by cold pressing, and their surface bonding strength and immersion peel performance were tested. The results showed that both veneered panels prepared in optimized hot-pressing parameters met the requirements of interior materials in GB/T 17657-2013. But due to the different surface properties between MDF and PW, their bonding effect with EVA-RDV was slightly different. Generally, the surface bonding strength of veneered MDF was higher than that of veneered PW, while its immersion peel performance was weaker. When the EVA film thickness was 0.3 mm, the surface bonding strength of veneered MDF and veneered PW was 1.74 and 1.30 MPa, respectively. Due to the low surface roughness of MDF and the existence of a pre-curing layer, cold pressing played a much more important role in the manufacturing process of veneered MDF.

Wood-based electrodes enabling stable, anti-freezing, and flexible aqueous zinc-ion batteries

• 3D hierarchical Zn electrode is prepared by using wood veneer as the raw material. • The wood-based electrode owns large electrical conductivity and tensile strength. • The desolvation, Zn deposition kinetics, and deposition uniformity can be promoted. • The wood-based electrode can inhibit Zn dendrites and harmful side reactions. • The wood-based battery shows high tolerance to deformations and low temperatures. As the treasure on the earth, forest resources should be utilized in a high value-added and efficient way. Herein, a wood-based quasi-solid-state aqueous zinc ion battery (AZIB) is developed to address the issues of AZIBs, i.e. , low Zn stripping/plating reversibility and poor tolerance to low-temperature environments. Particularly, the anode is fabricated by ultraviolet light irradiation-assisted delignification of wood veneer and subsequent decoration of metallic Ni and Zn. This wood-based electrode exhibits large electrical conductivity, good affinity to aqueous electrolyte, high tensile strength, and can combine the advantages of unique structure and cellulose framework from wood. It is found that this electrode can considerably restrict two-dimensional diffusion of Zn 2+ ions, facilitate desolvation process, improve Zn deposition kinetics, and inhibit Zn metal corrosion, thereby significantly stabilizing Zn deposition behavior. Thanks to that, the Zn//Zn cell with wood-based electrodes can deliver a long lifespan of 900 h at 2 mA cm −2 and 2 mAh cm −2 . Besides, wood-derived current collector and nanocellulose are used to construct cathode and hydrogel electrolyte, respectively. The assembled wood-based AZIB delivers superior performances even at −20 °C and under bending. The strategy in this work could be extended in other flexible energy storage systems.

Novel Biobased Polyester Resins for Wood Applications: Morphological, Thermal, and Chemical Characterization

AbstractThe present study focuses on the interaction of recently synthesized unsaturated polyester resins (UPRs) with wood. The UPRs are prepared from succinic acid, maleic anhydrite, and ethylene glycol or poly(ethylene glycol) as biobased monomers and crosslinked with acrylic acid. In this framework, small 3‐ply composite specimens (0.1 × 2.5 × 10 cm) of wood veneers are prepared with such binders to investigate their interaction with wood. The produced experimental specimens are studied with Fourier transform infrared spectroscopy, thermogravimetry, and scanning electron microscopy to explore their morphological and thermal degradation characteristics, as well any chemical changes from the interaction of the UPRs with wood. The experimental results indicate no chemical changes from their interaction with wood.

Fibre–Wood Laminate Biocomposites: Seawater Immersion Effects on Flexural and Low Energy Impact Properties

The present paper explores a new concept of a hybrid eco-composite by substituting the natural fibre plies with thin wood veneers. The new composite, named Fibre–Wood Laminate (FWL), is inspired by fibre–metal laminate materials. The studied FWL configuration consisted of a single thin pinewood veneer at each of the outer layers of a flax woven fabric reinforced bio-epoxy composite manufactured by infusion. Three-point bending results showed that wood veneer gives a highly anisotropic nature to the FWL. In the best case, with the grain of the wood at 0°, the stiffness and the strength increased by 28 and 41%, respectively, but reduced the strain-at-break by 27% compared to the flax fibre reinforced bio-epoxy (FFRB). The penetration and perforation energy thresholds and the peak force of the FWL obtained by falling weight impact tests were 32, 29, and 31% lower than those of the FFRB, respectively. This weakening was due to using single wood veneers, so the challenge for improving impact properties will be to explore thicker FWLs with different stacking sequences and orientations. The effect of immersing the FWL in seawater also showed considerable differences. The epoxy matrix filled the cellular structure of the wood veneers, creating a barrier effect and reducing the amount of water absorbed by the flax fibres.

Functionalized Wood Veneers as Vibration Sensors: Exploring Wood Piezoelectricity and Hierarchical Structure Effects.

Functional wood materials often rely on active additives due to the weak piezoelectric response of wood itself. Here, we chemically modify wood to form functionalized, eco-friendly wood veneer for self-powered vibration sensors. Only the piezoelectricity of the cellulose microfibrils is used, where the drastic improvement comes only from molecular and nanoscale wood structure tuning. Sequential wood modifications (delignification, oxidation, and model fluorination) are performed, and effects on vibration sensing abilities are investigated. Wood veneer piezoelectricity is characterized by the piezoresponse force microscopy mode in atomic force microscopy. Delignification, oxidation, and model fluorination of wood-based sensors provide output voltages of 11.4, 23.2, and 60 mV by facilitating cellulose microfibril deformation. The vibration sensing ability correlates with improved piezoelectricity and increased cellulose deformation, most likely by large, local cell wall bending. This shows that nanostructural wood materials design can tailor the functional properties of wood devices with potential in sustainable nanotechnology.

Potential Use of Transparent Wood in Spatial Folded Structures

Transparent wood is a relatively new material, the manufacturing starts with removing the lignin from wood veneer and infiltrating the delignified wood by a polymer thereafter. Transparent wood usually proves better mechanical properties than original wood and polymer. The article presents the potential use of transparent wood in bearing structures. The transparent wood could be used as I-beams structures, box beams, trusses, or folded structures. A spatial folded structure was numerically analyzed. Various types of transparent wood or transparent plywood were used. A comparison with commonly used materials, such as glass and other wood-based materials were made. The comparison shows that transparent wood has great potential in the use as a structural material. The plywood made from transparent wood veneer with the alternating direction of wood fibers acts as a laminate and allows a biaxial load transfer, which can be successfully used in a thin plate of the spatial folded structure while maintaining relatively good transparency.

Thermophysical Molding Treatments on Thick Wood Veneer.

Thermophysical molding (TPM) treatments can significantly improve the surface properties of thick wood veneer. To understand the effects of TPM treatments on the surface properties of thick veneer, the roughness, contact angles, and chemical changes were determined. The results indicated that the roughness of the thick veneer decreased when the temperature and the duration increased. The contact angles decreased when the temperature increased, resulting in better wettability. X-ray photoelectron spectroscopic (XPS) results provided information about the significant chemical changes in the surface with different TPM temperatures of 160–190 °C and durations of 5–11 min. Increases in temperature and duration increased the C content and decreased the O content during the treatment process. The most significant changes in the thick veneer that resulted from increasing the temperature and the duration were the increase in the C1 component and the decrease in the C2 component. Thus, the oxygen to carbon (O/C) ratio decreased and the ratio of aromatic carbon to aliphatic carbon (C1/C2) notably increased with the increasing TPM temperature. The TPM duration slightly affected the O/C ratio, but it had a stronger linear relation with the C1/C2 ratio. Additionally, the C1/C2 ratio and the O/C ratio had a linear statistical relationship with the initial wettability. These findings could provide useful information for the future utilization of thick veneers treated with TPM.

The effect of reinforcement on the mechanical properties of veneered wood fiber/polypropylene composites assembled with chlorinated polypropylene

Wood fiber/polypropylene (WF/PP) composites are environmentally friendly materials with high dimensional stability and mechanical properties. However, the applications of WF/PP composites are limited by an unattractive surface texture. In this study, the WF/PP composites were decorated with poplar wood veneer using chlorinated polypropylene (CPP) as a hot melt adhesive, the bonding strength is over 1.18 MPa. Surface bonding strength tests and scanning electron microscopy (SEM) were performed to analyze the quality of the CPP bonding layer. The physical and mechanical properties of the veneered WF/PP boards and unveneered controls were examined to determine the effects of reinforcement. The result shows that after veneered the tension strength and modulus of the whole composite board were increased over 30% and 10%; the flexural strength and modulus were increased over 10% and 20%. Low-velocity impact testing was performed to determine the impact resistance properties of the composites. Higher ratios of wood fiber in the WF/PP composite led to a higher surface bonding strength, which was evident in the SEM images. Wood veneer decoration increased the mechanical strength of the whole composite board. A tighter bond along the CPP layer would provide additional reinforcement of the veneered composite’s mechanical properties.

A Method for Measuring the Quality of Graphic Transfer to Materials with Variable Dimensions (Wood).

The transfer of graphics to a product’s surface is a widely known technology. Printing, engraving, and etching are used every day in production processes with countless types of materials. This paper deals with quality control for laser engraving on surfaces with variable dimensions via optical sensors. The engraving process, apart from colour changes, can induce volume and moisture changes, which lead to dimension changes in some materials. Natural materials and biomaterials are among the ones most affected. Combined with the porous and inhomogeneous structure of such a material, it can be difficult to measure the quality of graphic transfer, especially for shaded products. The quality control of laser-engraved photographs on thin layers of wood veneer was selected as a suitable problem to solve. A complex method for the quality measurement of the specified production was designed and tested. We used an affine transformation to determine the system behaviour and to determine the transfer function of material changes during the production process. Moreover, there is a possibility to compensate the image deformation of the engraved product.

Determination of epoxy resin usability for mass production of reinforced laminated veneer lumber

This study is part of a comprehensive study on the industrial production of reinforced laminated wood composites. The main aim of the study is to determine the production parameters of reinforced laminated wood composite board under an optimal production cycle time under temperature and pressure, using epoxy resin cured at room temperature for 24 h. For this purpose, 1.2 mm thick Samsun Poplar (Populus Deltoides I-77/51) veneer layers, three different pressing cycle times (15, 20, and 25 min), three different temperatures (100°C, 120°C, and 140°C), and three different amounts of adhesive (100, 150, and 200 g/m²) were used also 200 g/m² density twill woven glass–carbon fiber fabric was used as the reinforcement layer. In order to determine the production quality of reinforced laminated wood composite boards, the adhesion strength between the reinforcement layer and the wood veneer layer was determined according to TS EN 3969 314-1. Considering the adhesion strengths in terms of production parameters, the best results were observed at 100°C press temperature, 20 min press cycle time, 200 g/m² adhesive amount, and the use of glass fiber woven fabrics for reinforcement. Under these conditions, the best adhesion strength was found to be 4.17 N/mm². When the samples were examined, it was seen that almost all of the failures occurred as a result of the fracture in the wood layer. This indicates that sufficient adhesion can be achieved between the reinforcement layer and the wood layer.

Comparative Study of Plywood Boards Produced with Castor Oil-Based Polyurethane and Phenol-Formaldehyde Using Pinus taeda L. Veneers Treated with Chromated Copper Arsenate

Plywood is widely used in civil construction. Due to the importance of preservation and gluing in bio-composites, this study compares the influence of a chemical treatment with CCA (chromated-copper-arsenate) on Pinus taeda L. wood veneers to produce two plywood types using phenol-formaldehyde (PF) and castor oil-based polyurethane (PU). Four different treatments were performed to analyze both varieties’ physical and mechanical properties. As a result, an improvement in the properties of the treated panels was observed. Lower moisture contents and better interactions caused by less thickness swelling and water absorption were identified in the PU-based plywoods. The treatment with CCA was efficient, improving these properties when they were compared to the reference panels. Most treatments evidenced increases in the modulus of elasticity and modulus of rupture for both adhesives when the CCA treatment was applied to the veneers. Comparing the resins, the PF showed the best values of modulus of elasticity. All treatments met the requirements defined by the Brazilian standard document for the glue line shear.

Evaluation of Selected Mechanical Properties of Blighia sapida K. Koenig Wood

Over exploitation of economic tree species in the forest due to their high demand has made wood loggers shift their attention to Lesser Used Species such as Blighia sapida as alternative source of wood in Nigeria. The knowledge on the quality of the wood would to a long extent enhance the utilization of the wood. However, little information is provided on the mechanical properties of the wood species and the general belief among most wood users is that it is not a good timber species and that it cannot be utilized for any wood-based products that require strength. Therefore, investigating the mechanical properties of the timber species for better acceptability in the timber market becomes necessary. Three standing trees of Blighia sapida were purposively felled in the University of Ibadan community, Ibadan, Nigeria. 500 mm billets were gotten from wood dics at the top, middle, and base of the tree and each partitioned into three, the outerrwood, middlewood and the innerwood, in line with specified standard for each selected mechanical property test (Modulus of Elasticity, Modulus of Rupture, Impact bending strength, and Compressive strength parallel to grain) were all evaluated. Modulus of rupture with mean value 118.47 ± 1.96 N/mm2, ranged from 103.67 ± 3.42 to 144.26 ± 3.68 N/mm2. Modulus of Elasticity with mean value 10649.99 ± 167.51 N/mm2, ranged from 9237.14 ± 399.22 to 12877.35 ± 284.61 N/mm2. Compressive strength parallel to grain with the average value 52.86 ± 0.81 N/mm2, ranged from 42.88 ± 1.32 to 62.62 ± 1.65 N/mm2. Mean impact bending strength was 28.05 ± 0.58 N/mm2, ranged from 24.56 ± 0.86 to 35.09 ± 1.71 N/mm2. The average Modulus of Rupture and Modulus of Elasticity of Blighia sapida wood indicated that the wood falls within the category of medium construction strength timbers. The maximum compressive strength value for Blighia sapida wood revealed that it compared well with other economic tree species that are widely known for various structural applications. Therefore, the general belief among wood users that it is not a good timber species and that it cannot be utilized for any wood-based product that requires strength is far from the truth. It can therefore be concluded that the timber can be used for some building constructions, sheeting and lining, furniture, carpentry, veneer wood production, cabinet work, and so on.

Gloss of Varnished MDF Panels Veneered with Sanded and Thermally Compressed Veneer

The objective of this study was to investigate the gloss of different types of commercially manufactured varnish systems, including water-based (WB), polyurethane (PUR) and UV-cured (UV), applied on veneered MDF panels with sanded and thermally densified alder and birch wood veneers. The varnishes were applied at various numbers of layers on veneered panels. The gloss was measured at three angles of incident light: 20°, 60° and 85°. Statistical analysis showed that the type of varnish, the number of layers, the pre-treatment process, the wood species and direction of wood fibers significantly affect gloss of the coatings of veneered MDF panels. The type of varnish had a dominant effect on gloss. The highest gloss values were measured for the UV-varnished surface, and the lowest for WB- and PUR-varnished surfaces. Gloss was enhanced with an increase in the number of layers. Birch veneer provided higher gloss values compared to alder veneer. The gloss values measured along the wood fibers were higher than those measured across the fibers. No significant differences were found between the coatings created on sanded and thermally densified veneers for the average gloss values measured along the fibers at angles 60° and 85°. This study could have practical applications for producing value-added furniture elements using low-value wood species pre-treated by thermal compression.