Study of Properties and Mechanism of Bonding Line in Three-Layer Hybrid Cross-Laminated Timber

The physical and chemical properties of three kinds of laminations relative to the bonding properties of three-layer hybrid cross-laminated timber (CLT) were studied. The density of the parallel layer lamination of CLT was 640.47±61.85 kg/m3, and the perpendicular layer laminations for CLT larch wood, poplar, and oriented strand board (OSB) were 392.51±40.14, 343.73±17.16, and 384.41±12.93 kg/m3. Block shear bond strength (BBS), wood failure percentage (WFP), and delamination rate (DR) of the hybrid CLT specimens were also determined. The results showed that the three kinds of hybrid CLT prepared with polyurethane (PUR) adhesive had good bonding properties under 1.2 MPa of bonding pressure. The BBS values of CLT with larch wood, poplar hybrid, and OSB hybrid were 2.32, 2.41, and 1.98 MPa, respectively; furthermore, their WFPs were all greater than 80%, and their DRs were 9.32%, 0.37%, and 0.11%, respectively. Regarding the relationship between perpendicular layer material properties and bonding properties, analysis revealed that delamination performance was strongly correlated with pH, buffer capacity, and the surface free energy of the perpendicular layer, whereas the WFP and BBS values had a strong correlation with pH and buffer capacity. Density was determined to be unrelated to bonding performance in the CLT prepared in this experiment. Microscopic analysis of the bonding line proves that the PUR adhesive can effectively penetrate into three different laminations under a bonding pressure of 1.2 MPa and form enough nails to ensure bonding strength.