Longitudinal tensile shear properties of polyurethane-bonded preservative-impregnated Eucalyptus grandis laminates subjected to varied simulated climatic conditions
A A Alade, C B Wessels
Bonding process adaptations have yielded improvements in the adhesive bonding of Eucalyptus grandis wood for manufacturing hardwood laminates. However, there are still concerns over the adhesive-bond performance, particularly preservative-impregnated E. grandis laminates, under exposure to varying climatic conditions. These concerns could limit the implementation of E. grandis laminates, especially in exterior structural applications. Therefore, this study investigated the suitability of polyurethane (PUR)-bonded E. grandis laminates pre-impregnated with copper and boron-based preservatives for use in various pre-defined exposure conditions. The investigation focused on the determination of the longitudinal tensile shear properties according to the EN 302-1:2013 standard. The effect of sapwood vs. heartwood on the tensile shear properties was also evaluated. The main effect of the preservative impregnations resulted in up to 14% reduction of the tensile shear strengths of the PUR-bonded E. grandis laminates. Relative to the standard climate, 20 ±2 °C at 65% relative humidity, exposures to varying pre-defined climatic conditions resulted in up to 45% reduction in the tensile shear strength and up to 31% reduction in the tensile modulus. Reconditioning the submerged laminates to the initial dry state facilitated substantial recoveries of the tensile shear strengths. The sapwood-heartwood/preservative impregnation interaction had a significant effect (p > 0.05) on the tensile modulus. The overall outcome of the study indicated that PUR-bonded preservative-impregnated E. grandis laminates are better suited for applications not involving shear stress loading under prolonged wet states.