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

Abstract

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 8h, respectively. The boiled logs were peeled to produce veneer of 1, 1.5, and 2mm in thickness. Lathe checks of veneers were measured on the loosed side at every 5mm veneer length under an optical video microscope and their frequency, depth, and length were characterized. Twenty sampling points of 5mm veneer length were prepared from each segmented ring of 1cm width from pith to bark. Isocyanate resin adhesive were used to produce laminated veneer lumber (LVL) of 20mm thick, which consisted of 24-ply of 1mm veneer thick, 14-ply of 1.5mm veneer thick, and 11-ply of 2mm 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 8h and at 75°C at least 4h before peeling the logs could minimize the frequency of lathe check in manufacturing rotary cut veneer thickness of 1, 1.5, and 2mm 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.