Effect of Veneer Initial Moisture Content on the Performance of Polyethylene Film Reinforced Decorative Veneer

The flexible modification of decorative veneer by plastic film is an effective method to broaden its applications. In order to understand the effect of initial veneer moisture content on the performance of plastic film reinforced decorative veneer, Fraxinus mandshurica veneers with different initial moisture contents were composited with polyethylene film. The overlaying performance of the decorative veneer and its interface morphology with MDF substrate were evaluated. The results showed that when the initial moisture content increased from 10% to 50%, the cavity proportion of PE film reinforced decorative veneer increased from 7.23% to 18.48%, while all of the minimum steel rod diameters remained at 7.6 mm. When the initial moisture content fluctuated between 10% and 20%, the optimum surface bonding strength (1 MPa) and immersion peel strength (0 mm) of the decorative veneer could be obtained. The strength of the decorative veneer significantly decreased when the initial moisture content was more than 20%, which was caused by the cavities and the poor interfacial bonding. The veneer surface was easy to crack under low moisture content conditions. Based on the overall performance and the cost of decorative wood-based panels, initial veneer moisture content was suggested to be 15% to 20%.

Influence of technological cracks of peeled vener on the shear strength of ultralam bars

The aim of the research is to study the shear strength of laminated veneer lumber (LVL) when working on shear in four different planes. To determine the influence of the presence of technological cracks formed in the peeling process, an experiment was carried out for which four types of samples were used. The load was applied parallel and perpendicular to the glue line and the direction of the peeled veneer fibers. As tests have shown, the technological weakening of peeled veneer reduces the strength properties of a multilayer glued veneer bar, especially for shear along the glue lines and perpendicular to the direction of the peeled veneer fibers, where the maximum number of microcracks is located. The analysis of these microcracks is carried out and their widths are determined. The width of the studied cracks was from 152 to 94 μm. There is no adhesive layer in the microcracks of this building material, which may indicate insufficient wetting of the veneer surface with the adhesive material, or the difficulty of penetration of high-molecular phenol-formaldehyde glue into the cavity of microcracks.

Laminated veneer lumber from spindleless rotary-peeled veneers produced from short rotation, small Hevea plantation logs: Effects of lamination pressure

The invention of spindleless lathe technology has enabled veneers to be produced from small logs, such as logs from short rotation Hevea plantations, with low recovery loss. However, for structural laminated products, such as laminated veneer lumber (LVL), manufacturers are highly selective regarding the veneers for their conventional production. During the peeling process of small logs (< 18 cm), deeper and higher frequency of lathe checks were induced on veneer surface compared to the common log size used (> 30 cm). In this study, spindleless rotary-peeled veneers made from small rubber logs were processed into LVL using different lamination pressures: 7, 8, 9, and 10 kgf/cm2. The effects of lamination pressures on the physical and mechanical properties of the produced LVL were evaluated. Based on the findings, the specific gravity increased from 0.73 to 0.83 with increased lamination pressure. In terms of mechanical properties, all the values increased with lamination pressure, but with a sudden drop with 10 kgf/cm2. Understanding the effect of lamination pressure on the physical and mechanical properties can shed light on optimizing the usage of spindleless rotary-peeled veneers from small logs for the production LVL and other lamination products.

Fabrication of flexible thin veneer for electromagnetic interference shielding and decoration through simple electroless plating

A widely applicable electromagnetic interference (EMI) shielding and decorative thin veneer containing copper was prepared with simple electroless technology. Copper was used as the structural and EMI reflection component to reinforce the mechanical strength and EMI shielding effectiveness. Both the texture and structural properties of copper deposited on poplar wood were characterized. The X-ray diffraction patterns indicated that the copper deposited on poplar wood had a crystallite size between 7.9 nm and 15.9 nm, and the copper crystallites grew rapidly as the number of electroless runs increased, which was consistent with the resistivity and microscopy analyses. The mechanical and EMI shielding effectiveness results showed that after two electroless runs, the wood veneer surface was completely covered, which improved the EMI shielding effectiveness and mechanical properties of wood veneer. The material could be bent 360° without being damaged and had a good decorative effect.

Addition of Polyurethane Foam Waste to Polymeric Diphenyl Methane Diisocyanate to Improve Plywood Binder Performance

The objective of this study was to investigate the feasibility of using polyurethane (PU) foam waste obtained from automobile shredder residue (ASR) in plywood production. The PU foam waste from ASR was cleaned by water and acetone, ground into powder, dried, and mixed with polymeric diphenyl methane diisocyanate (pMDI) resin at various ratios (2.5%, 5%, 7.5%, and 10%, based on the weight of pMDI). The mixed adhesives were examined with Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric (TG) analysis, and evaluated as plywood binders (measured in accordance with Chinese National Standard GB/T 17657-2013). The results indicated that the addition of PU powder into pMDI resin increased adhesive viscosity and efficiency, and also helped solve the problem of deficiency of pMDI on the veneer surface. FTIR results showed various reactions between pMDI and PU powder. This potential cross-linking might contribute to the cohesive strength of the cured adhesive. TG analysis results showed the possible increased thermal stability of the cured mixed adhesive at a temperature range of 150°C to 300°C. The best PU addition ratio was 7.5 percent of the pMDI weight, considering both the bond strength and production practice of plywood. Plywood testing showed that both the dry and wet bond strength reached the peak value at the optimal mixing ratio. The use of PU powder in plywood manufacturing provided a possible way of recycling PU foam waste while improving or maintaining the performance of plywood.

Effect of knots and holes on the modulus of elasticity prediction and mapping of sugi (Cryptomeria japonica) veneer using near-infrared hyperspectral imaging (NIR-HSI)

Naturally occurring knots reduce the mechanical strength of wood. Veneers from sugi (Cryptomeria japonica) served as research material to study the effect of knots and holes. Veneer samples were first subjected to a three-point bending test to obtain measured modulus of elasticity (MOE) values. Then, near-infrared (NIR) hyperspectral imaging (HSI) was used to construct a prediction model and map the predicted MOE values. This is the first attempt for MOE prediction from the entire veneer surface based on NIR-HSI technology, while the mathematical part relies on chemometrics and cross-validation partial least squares regression (CV-PLSR). Maps of MOE prediction values could distinguish between latewood (LW) and earlywood (EW), as well as between a sound knot and a dead knot.

Enhancing resin efficiency in plywood production via DBD plasma treatment and atomized air spray of UF resin

To improve resin efficiency in plywood production, the veneer surface was modified by dielectric barrier discharge (DBD) plasma and the resin was applied by air spray atomization. The droplet size and coverage of resin droplets were evaluated by image analysis. This novel approach improved the resin efficiency. The shear strength of the produced plywood was improved along with a higher gluing speed. The surface energy of poplar veneer altered after plasma treatment, resulting in an increased size of resin droplets and increased resin coverage. Plywood produced at a plasma-processing power of 4.5 kW exhibited the highest shear strength and a 6 kW plasma-processing power did not bring about advantages. Under these circumstances, the lowest amount of resin necessary for fabricating quality products can be reduced to 50 g m−2.

Research on the Gradual Process of the Metallization Structures and Mechanical Properties of Wood Veneer

In order to improve the mechanical properties of the wood surface and explore the mechanical effect of wood veneer surface metallization, the 31-year-old Pinus sylvestris is taken as the research object and Cu is deposited on the wood surface by magnetron sputtering to achieve wood veneer metallization. Based on X-ray diffraction (XRD) and nanoindentation, a research on the gradual process of the structures and mechanical properties of wood veneer metallization was carried out. The results indicate that wood veneer metallization does not affect the crystallization zone of wood, there are still wood cellulose characteristic peaks and the crystalline structure of the wood cellulose is not damaged; the thickness of the copper thin film increases with the increase of the deposition time, the cellulose characteristic peak strength gradually decrease, and the relative crystallinity also decreases; the characteristic diffraction peaks of Cu (111), Cu (200), and Cu (220) appear near the diffraction angle 2θ which is equal to 43.3°, 50.4°, and 74.1°, and the diffraction peak intensity increases with increase of deposition time, the copper film of the metal wood veneer crystallizes well; the load–displacement of wood veneer decreases significantly with the increase of deposition time, while the moduli of elasticity and hardness increase rapidly. The load–displacement of the samples which were coated for 15 min decreased by 80%, while the moduli of elasticity and hardness of these samples increased by 24.1 times and 17.3 times, respectively. From the results of Scanning Electron Microscope (SEM) measurement of the metallization of wood veneer, it can be seen that the uniform and continuous copper film can be formed on the wood veneer surface by using the magnetron sputtering method. This paper provides a basis for wood veneer surface metallization, which is of great significance for the functional improvement of wood, the expansion of wood application fields, and the enhancement of added value.