Potential of Quebracho Tannin to Substitute Urea-Formaldehyde Adhesive in Plywood: Comparative Technical and Environmental Performance

The construction sector is facing significant challenges in transitioning to a defossilised system. While wood-based products have considerable potential, reliance on adhesives derived from fossil fuels poses significant sustainability concerns. Tannin-based adhesives present a compelling bio-based alternative, offering advantageous bonding properties with the potential to reduce toxicity, minimise fossil resource use, and enhance end-of-life scenarios. Despite extensive research demonstrating the technical potential of tannin-based adhesives, industrial adoption remains limited—partly due to the paucity of studies addressing their environmental impacts. The present study investigates the use of tannin-based adhesives in the production of interior-grade plywood, employing urea-formaldehyde (UF) adhesive as reference. The evaluated formulations incorporate quebracho tannin with hexamine or novel protein-containing ingredients, namely soy protein isolate, soy flour, and tara germ powder. Technical tests assessed bonding quality, bending strength, and modulus of elasticity in five-layer plywood. A cradle-to-grave life cycle assessment (LCA) was conducted, with the novelty of using plywood as the functional unit. One formulation, combining tannin and hexamine, exhibited performance comparable to UF-bonded plywood, meeting EN 310 and EN 314 Class 1 standards. Environmental benefits were notable, with carcinogenic human toxicity reduced by 47%, even without accounting for formaldehyde emissions during the use stage. Fossil resource depletion decreased by up to 13%, and global warming potential from fossil sources fell by 10%, in accordance with EN 15804:2012+A2:2019. These findings provide a foundation for further optimisation, broader application in wood-based panels, and enhanced sustainability in construction.