Water resistant plywood of increased elasticity produced from European wood species
The paper investigates the possibility of producing the water-resistant plywood of increased elasticity with use of veneers attained from European wood species, such as alder, birch, beech, pine as well as linden, poplar, willow and spruce. Plywood was produced in two variants. Variant I of plywood was made from various wood species, yet the veneers were of the same thickness. In variant II the centre layer in each case was made from 1 mm thick pine veneer and the face layers were made from 1.4 mm thick veneers of various wood species. The produced plywood was subjected to tests on modulus of rupture, modulus of elasticity and tensile strength, bond quality and compression ratio. Specific values of modulus of rupture and modulus of elasticity were also determined taking into consideration the differences in the thickness of applied veneers. Based on these investigations, the authors concluded that, regardless of the manufacturing method, the highest values of modulus of rupture as well as modulus of elasticity and bond quality are achieved for plywood made from linden, poplar, willow and spruce. The change in the plywood structure (variant II) resulted in a considerable decrease in the values of modulus of rupture and modulus of elasticity (and their specific values) both parallel and across the grain. The lowest values of these parameters were obtained for poplar, linden and willow plywood. What is more, as a result of the applied procedure the bond quality of the produced plywood increased and the compression ratio was reduced. Taking the above into account, we can assume that linden, poplar and willow wood is an optimum choice for the face veneers of plywood with increased elasticity. The centre layer of this kind of plywood can be made from pine veneer of lesser thickness.