Physical and mechanical performance of hybrid beech–alder laminated veneer lumber (LVL): Effects of layering configuration and adhesive type

This study investigates the physical and mechanical performance of hybrid laminated veneer lumber (LVL) produced from oriental beech ( Fagus orientalis ) and black alder ( Alnus glutinosa ) veneers. The interacting effects of adhesive type (phenol-formaldehyde (PF) and melamine-urea-formaldehyde (MUF)) and layering configuration (0%, 25%, and 50% alder by layer count) were examined. The evaluated properties included density, water absorption, thickness swelling (TS), modulus of rupture (MOR), modulus of elasticity (MOE), impact strength (IS), hardness, screw holding capacity, and glue line thickness. Increasing alder content significantly reduced LVL density, primarily due to the lower inherent density of alder ( A. glutinosa , 0.50–0.55 g/cm 3 ) compared to beech ( F. orientalis , 0.62–0.64 g/cm 3 ) and the limited densification of alder layers under the applied hot-pressing conditions. PF-bonded LVLs exhibited superior dimensional stability, with the 50% alder configuration (PF-50A) showing the lowest TS. Mechanically, PF-bonded panels generally outperformed MUF-bonded ones in MOR, MOE, IS, and hardness. The effect of hybridisation varied with adhesive type: incorporation of alder improved MOE and IS in MUF-bonded LVLs but reduced MOE in PF-bonded ones; nevertheless, the PF-50A configuration maintained high MOR values. Glue line thickness increased with alder content only in MUF-bonded panels. Pure beech PF-LVL is recommended for high-performance structural applications. For cost-effective interior uses requiring a balance between performance and cost, MUF-bonded LVL with 25% alder offers a viable alternative. The PF-50A hybrid configuration shows considerable potential for further industrial optimisation.