The Effects of Heat Treatment, Wood Species and Adhesive Types on Screw Withdrawal Strength of Laminated Veneer Lumbers

Aim of study: The objective of this study was to evaluate the effects of heat treatment temperature on the screw withdrawal strength on laminated veneer lumbers (LVL). Material and Methods: The LVL samples were prepared in the form of ten layers that 2 mm thickness from the European oak (Quercus petreae L.), Oriental beech (Fagus orientalis L.), scotch pine (Pinus sylvestris L.) and poplar (Populus nigra L.) veneers bonded with two-component polyvinyl acetate (PVAc-D4), melamine formaldehyde (MF) and polyurethane (PU) adhesives and then heat treatment was applied to the prepared samples. The test samples were subjected to heat treatment at 185 and 212 degrees C for 2h. Main Results: Consequently, according to wood type, the highest screw withdrawal strength was determined in Oriental beech, with respect to the adhesive type in MF adhesive. The screw withdrawal strength of samples was decreased with increasing treatment temperature. In the interaction of the wood materials, type of adhesive and treatment temperature, it was the highest in control beech samples bonded with MF and the lowest in poplar samples bonded with PU which heat-treated at 212 degrees C. It was also observed that the lowest strength loss due to the treatment temperature was found in oak samples and in MF adhesive. Research highlights: Screw withdrawal strengths were directly related to wood type and density, heat treatment temperature and adhesive type.