Enhancing the Performance of Layered Wood Composites Through the Non-Food Application of Dietary Fiber in Their Bonding Matrix

Rye flour is a commonly used filler in plywood production, made from finely ground rye grains. It enhances glue viscosity, ensuring even distribution and better adhesion, which improves the plywood's mechanical properties, dimensional stability, and resistance to warping. Additionally, rye flour increases the plywood's strength and durability, making it more resistant to mechanical damage and external factors. Its affordability and availability further support its widespread use in plywood production. However, the growing availability of new raw materials has sparked interest in alternative fillers, especially considering food waste challenges caused by low demand or poor household management. This study explores the potential of spirulina, bamboo flour, lupine flour, and coconut flour as alternative fillers to rye flour, being part of the food chain, in three-layer plywood production. Plywood panels were manufactured using birch and pine veneers, urea-formaldehyde resin, and varying filler contents (10, 15, and 20 parts by weight/pbw). Key mechanical properties were evaluated, including modulus of elasticity (MOE), modulus of rupture (MOR), shear strength, density profile, and filler water absorption. The highest MOE for hardwood plywood was observed with coconut flour (20 pbw, 17,228 N mm-2). Conversely, the lowest MOE values were recorded for coniferous plywood with spirulina (8440 N mm-2). For MOR, the best performance in softwood was achieved using lupine flour (10 pbw, 113 N mm-2), while coconut flour yielded the highest MOR in hardwood plywood (20 pbw, 177 N mm-2). Spirulina exhibited the lowest MOR (72 N mm-2, 15 pbw). Shear strength peaked with lupine and coconut flour. The filler composition determines adhesive properties and bond performance through water absorption, structural interactions, and filler content optimization. These findings emphasize the potential for fine-tuning alternative fillers to achieve desired mechanical performance, ensuring sustainable and efficient plywood production. These also demonstrate the potential of certain alternative fillers, particularly coconut and lupine flours, excluded from the food value chain, in improving specific properties of plywood.