Formaldehyde emission, surface roughness, and some properties of plywood as function of veneer drying temperature

The drying of veneer is an essential part of the veneer-producing process to aid the gluing during the manufacture of the plywood and LVL. Determining the optimum veneer drying temperature without loss of bonding strength is also very important from an industrial viewpoint. Increased temperatures are being used in veneer drying to reduce the overall drying time and increase capacity. In this study, 2-mm-thick rotary-cut veneers obtained from alder (Alnus glutinosa barbata) logs were used as materials. After rotary cutting, veneer sheets were classified into four groups and dried at 20, 110, 150, and 180 degrees C. Three-ply and 6-mm-thick plywood panels were manufactured with area formaldehyde (UF) adhesive. Surface roughness and color variations of veneer sheets and shear strength, bending strength, equilibrium moisture content, and formaldehyde emission of plywood panels were determined based on veneer drying temperatures. According to the results, the smoothest surfaces were obtained for 20 degrees C drying temperature while the highest values of surface roughness were obtained for 180 degrees C. Total color change value (Delta E*) increased linearly with increasing drying temperature. Shear strength values of plywood panels decreased clearly with increasing veneer drying temperature. While the least bending strength mean value was obtained for 20 degrees C drying temperature, no clear difference was found for bending strength of plywood panels manufactured from veneers dried at 110, 150, and 180 degrees C. Equilibrium moisture content (EMC) of plywood panels decreased with increasing veneer drying temperature and as the veneer drying temperature was increased, formaldehyde emission values of plywood panels increased.