Lathe check characteristics of fast growing sengon veneers and their effect on LVL glue-bond and bending strength

Fast growing sengon (Paraserianthes moluccana) is largely rotary-cut to produce veneer for core plywood production. In order to provide better information on veneer production and utilization, in this study the effects of wood juvenility and veneer thickness on lathe checks of rotary-cut sengon veneers were evaluated. Before veneer manufacturing, sengon logs were boiled at 50 °C and 75 °C for 4 and 8 h, respectively. The boiled logs were peeled to produce veneer of 1, 1.5, and 2 mm in thickness. Lathe checks of veneers were measured on the loosed side at every 5 mm veneer length under an optical video microscope and their frequency, depth, and length were characterized. Twenty sampling points of 5 mm veneer length were prepared from each segmented ring of 1 cm width from pith to bark. Isocyanate resin adhesive were used to produce laminated veneer lumber (LVL) of 20 mm thick, which consisted of 24-ply of 1 mm veneer thick, 14-ply of 1.5 mm veneer thick, and 11-ply of 2 mm veneer thick, for glue bond and bending strength test. Results showed that wood juvenility and veneer thickness determined the frequency, depth and length of lathe checks for the sengon rotary-cut veneers. In general, the frequency of lathe checks of the veneer increases with increasing veneer thickness, and also increases from pith to bark. Boiling of logs before rotary-cutting could decreases the frequency of lathe check of the veneer. The results indicated that boiling of logs at 50 °C for 8 h and at 75 °C at least 4 h before peeling the logs could minimize the frequency of lathe check in manufacturing rotary cut veneer thickness of 1, 1.5, and 2 mm from juvenile wood of fast growing sengon. The frequency of lathe check affects significantly the glue bond and bending strength, in which the glue bond, modulus of elasticity (MOE), and modulus of rupture (MOR) decrease as the frequency of lathe checks increases.