Optimization of Press time and Properties of Laminated Veneer Lumber Panels by Means of a Punching Technique

The impact of veneer punching pattern and density (343, 356, and 1424 hole·m-2) was tested relative to selected physic-mechanical properties of 5-ply laminated veneer lumber (LVL) panels fabricated from poplar wood (Populus deltoides) under different press time (5, 6, and 7 min). Samples were made with urea-formaldehyde resin using hot press technology at a uniform pressure of 10.8 N·mm-2 and temperature of 120 °C. The results indicated that punching the inner veneers (except the core veneer) of LVL significantly improved the average values of shear strength, modulus of elasticity, and bending strength (both parallel and perpendicular to the grain). In contrast to control samples, the veneer punching technique showed an overall negative impact on the water resistance of LVL (after either 2 or 24 h of immersion in water). Nevertheless, specimens with punching densities of 1424 hole·m-2 pressed for a maximum of 5 min were more dimensionally stable than the control samples. The physic-mechanical properties of LVL were significantly affected by presstime as well. Considering the data obtained, the presstime of LVL could be reduced to nearly 16.7%, or 1 min, by using a punching density of 1424 hole·m-2 without any significant negative change in the major physic-mechanical properties.