CHARACTERISATION OF EUCALYPTUS HYBRID PLYWOOD PRODUCED IN GHANA, A POTENTIAL SUBSTITUTE FOR THE EUROPEAN BIRCH PLYWOOD

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Absztrakt (kivonat)

This study evaluated the mechanical, physical, bonding, and biological durability of plywood manufactured from juvenile Eucalyptus pellita produced in Ghana. Panels of five nominal thicknesses (9, 12, 15, 18, and 21 mm) were produced using two commercial adhesives, phenol formaldehyde (PF) and melamine–urea–formaldehyde (MUF), and tested using relevant EN and BS standards. Mechanical characterization (3-point bending: modulus of elasticity, MOE; modulus of rupture, MOR) used specimens prepared and conditioned to 12% moisture content (EN 310/326-1); physical tests measured density (EN 323) and 24-h thickness swelling (EN 317); bonding quality employed shear tests and wood-failure assessment (EN 314-1); biological durability comprised a 7-month field test against subterranean termites (EN 350 / BS EN 252) and a 16-week laboratory decay test with Coriolus versicolor (CEN/TS 15083-1). Data were analyzed with ANOVA/Tukey, correlation and multiple regression. Mechanical properties, primarily the MOE and MOR, decreased with increasing panel thickness; longitudinal properties exceeded those in the transverse direction. PF-bonded panels consistently recorded higher MOE/MOR than MUF across thicknesses (e.g., PF longitudinal MOE ≈ 7,096 ± 1,567 N/mm² at 9 mm vs ≈4,627 ± 842 N/mm² at 21 mm). Orientation and thickness effects were statistically significant in most comparisons (p < 0.05–0.01). Physical properties results showed that the mean density declined with thickness for both adhesives; PF panels were denser than MUF (e.g., PF: 785 → 709 kg·m⁻³; MUF: 731 → 648 kg·m⁻³). Thickness swelling decreased with thickness and was lower for PF (5.90 mm → 3.62%) than MUF (7.92 mm → 3.11%); a multiple regression model (R² - 0.699) identified significant adhesive × density and adhesive × thickness interactions affecting swelling. Bonding PF produced higher and more consistent shear strength (1.58–1.67 N·mm⁻² for 9–15 mm, dropping to 1.12 N·mm⁻² for 18–21 mm) and high wood-failure percentages (78–83%), while MUF showed greater variability (bonding strength 1.24–1.67 N·mm⁻²; wood failure 53–72%); correlations between bonding strength and wood failure were stronger in thinner panels. Biological termite field trials ranked materials: control Triplochiton scleroxylon failed (mean mass loss 71.5%); birch plywood was not durable (40.6% mass loss); E. pellita PF panels were classified as Durable (9.4% mass loss, DC1), whereas MUF panels were Moderately Durable (14.0%, DC3). In laboratory decay tests, all tested plywood types (PF and MUF, birch and E. pellita) exhibited very low mass loss (2.6–3.1%) and were classified as Very Durable (DC1). In contrast, the beech control failed (≈35.7%, DC5) as expected. Overall, juvenile E. pellita plywood, particularly when bonded with PF and produced as thinner laminates, demonstrates promising mechanical performance, dimensional stability, and biological resistance, making it suitable for demanding applications. MUF remains a cost-effective option for interior uses but exhibits greater variability and reduced moisture/termite resistance. The results emphasize the importance of selecting the right adhesive, ensuring veneer quality, and controlling pressing to optimize plywood performance; further long-term field studies and targeted process optimization are recommended

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