SURFACE ACTIVATION WITH LITHIUM AND SODIUM HYDROXIDES ON REGROWTH KARRI AND JARRAH

Abstract

Surface activation using lithium and sodium hydroxides was examined to determine its effect on wettability and gluebond strength of regrowth karri (Eucalyptus diversicolor) and jarrah (E. marginata). Wood blocks were treated with three different concentrations of each hydroxide prior to gluing with resorcinol formaldehyde resin. Glued blocks were pressed at 1500 kPa and 20°C for 7 h. Contact angle and shear strength were measured to assess the effectiveness of the treatment. Both lithium and sodium hydroxides significantly increased wettability and dry shear strength of the two regrowth eucalypts. These effects varied according to wood type, solution concentration and type of hydroxide. Bond strengths of treated specimens increased to a greater degree in jarrah than in karri. Increases in solution concentration significantly increased dry bond strength, but in most cases also increased the strength loss during wetting. Lithium hydroxide gave higher improvement in both dry and wet bond strengths than sodium hydroxide. Treatment using 0.5 M lithium hydroxide was the most effective method to protect strength loss on wetting.