Bonding performance and surface characterization of cold-bonded acetylated beech (Fagus sylvatica L.) laminated veneer lumber

Acetylation of wood with acetic anhydride reduces the wood-moisture interaction, improves the dimensional stability and resistance against biodegradation. However, the adhesive bonding is affected by the modification, which is crucial to manufacture engineered wood products, such as laminated veneer lumber (LVL). In this study we report the bonding of 8-layered acetylated beech (Fagus sylvatica L.) LVL boards to 2-layered LVL beams. The beams were glued together at room temperature adding three common load-bearing construction adhesives: melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF), and one-component polyurethane (PUR). The bonding performance was tested by assessing its dry and wet tensile shear strength (TSS) and wood failure percentage (WF). Also evaluated were the material's density and moisture content (MC). The surface was characterized prior to bonding by its pH, roughness, and contact angle (CA). The adhesive penetration was observed by fluorescence microscopy. Aside from MUF, applying PRF and PUR adhesives achieved good bonding performance on acetylated LVL and references. Acetylated LVL displayed a more hydrophobic behaviour, a higher pH, a somewhat smoother surface, and an increased density.