Bonding surface-modified Karri and Jarrah with resorcinol formaldehyde

A series of abrasive papers were used to sand machined regrowth karri (Eucalyptus diversicolor) and regrowth jarrah (E. marginata) wood surfaces. Shear test specimens were then prepared by gluing sanded wood blocks with resorcinol-formaldehyde and pressing them at 1500 kPa and 20°C for 7 hours. Wettability measurements on sanded wood surfaces and strength tests on shear test specimens were used to assess the ability of the sanding treatment to improve adhesive performance. The effect of sanding on wettability and shear strength varied according to the abrasiveness of the sanding treatment. Application of the coarsest abrasive (80 grit) significantly improved wettability and shear (adhesive) strength in both dry and wet conditions. A positive correlation between wettability and shear strength occurred only after sanding. SEM observations revealed different morphological structures of the glueline in sanded and non-sanded surfaces.