Mechanical and bonding performance of cross-laminated timber manufactured from heat-treated wood

Abstract

The chemical and surface changes induced by heat treatment can affect wood-adhesive interactions; however, limited attention has been given to the role of silane-based surface modification in enhancing the bonding and mechanical performance of heat-treated cross-laminated timber (CLT). Heat-treated Pinus sylvestris (Scots pine) and Abies bornmülleriana (Uludağ fir) were used as outer layers in the manufacture of three-layer CLT panels, and their mechanical properties were evaluated in this study. Heat treatment (HT) was carried out at 200 °C for 4 hours according to the Thermo-wood method. Layers were joined using one-component polyurethane-based adhesive. Some samples were treated with a silane-based coupling agent before bonding to improve bonding performance, and the effects of silane on bonding and mechanical properties were studied. Within this frame, tensile shear strength (TSS), bending shear strength (BSS), modulus of elasticity in bending (MOE), and tensile strength perpendicular to the surface (PTS) were measured. According to the results, silane modification generally improved mechanical performance, leading to a significant 74 % increase in PTS in Scots pine, while also affecting BSS (13 %) and MOE (7 %) in fir. In contrast, HT mainly altered bending-related behavior, most notably in Uludağ fir (BSS ≈ 10 %). Uludağ fir samples showed a higher BSS performance when compared to Scots pine ones. Overall, this study emphasizes that HT and silane modification can improve the mechanical performance of CLT, with effects varying by wood species and mechanical properties, providing valuable insights for the enhancement of low-durability wood.