Influence of pressing parameters on mechanical and physical properties of self-bonded laminated beech boards

Abstract

Five-ply self-bonded boards were obtained by pressing beech veneers parallel to the grain without additional adhesives, steam or pre-treatment. Fifteen different combinations of pressing parameters were tested, including temperature (200°C, 225°C and 250°C), pressure (4, 5 and 6 MPa) and pressing time (240, 300 and 360 seconds). Due to severe pressing conditions, the new product showed a higher density and different properties compared to a conventionally glued laminated wooden board. The self-bonding quality was assessed through dry shear strength tests, through a three-point bending test and a water-soaking test at 20°C. The dimensions in the cross section of the boards were measured after soaking in water. Results show that the choice of pressing parameters affects all the mechanical and physical properties tested. A statistical analysis revealed that the pressing temperature is the most influential parameter. Boards pressed at 200°C delaminated rapidly in water, whereas boards pressed at 225°C delaminated only at core-positioned layers after 48 hours and boards pressed at 250°C did not delaminate at all in water. Compared to panels pressed at lower temperatures, boards pressed at 250°C had the highest density, a higher shear and bending strength and a lower water absorption.