Formaldehyde emission values of plywood panels as function of veneer drying temperature were shown in Fig. 3.
As can be seen from Fig. 3, the least formaldehyde emission value was obtained for 20_C veneer drying temperature while the highest value was obtained for plywood panels manufactured from veneers dried at
180_C. As the veneer drying temperature was risen, formaldehyde emission values of plywood panels increased evidently. It was indicated in the literature that organic emissions during the thermal drying process
are strongly dependent on the drying temperature[32] and the amount of organic compound emission increased with increasing temperature.[33] The basic emission mechanisms in wood drying are direct evaporation
(i.e., vapor pressure of pure components increases as the temperature increases), steam distillation, and thermal degradation. In thermal degradation, high-molecular-mass organic compounds split into lowermolecular-
mass organic compounds in increasing temperature