Properties of Plywood Panels Composed of Thermally Densified and Non-densified Alder and Birch Veneers

Abstract

Ukrainian companies mainly use birch in the manufacture of plywood, but species such as black alder is not yet widely used in the manufacture of plywood due to its lower properties. It is well known that thermal compression is often used to improve the properties of solid wood. Good lay-up schemes of veneer can maximize the advantages, minimize the disadvantages of these wood species, and generally improve the utility value of the plywood. The research aimed to develop plywood panels with two wood species and two types of veneer treatments and to evaluate the influences of different lay-up schemes on the properties of the plywood. Five-layer plywood panels were formed with 16 different lay-up schemes using birch (Betula verrucosa Ehrh.) (B) and black alder (Alnus glutinosa L.) (A) veneers, non-densified (N) and thermally den-sified (D). The different lay-up schemes were to identify opportunities to improve the mechani-cal and physical properties of the plywood by replacing birch veneer in the plywood structure with alternative alder veneer. The veneer sheets were thermally densified in laboratory hot press at temperature 180 °C and pressure 2 MPa within 3 min. The conducted study showed that the bending strength, modulus of elasticity and shear strength of mixed-species plywood (BD–AN–AN–AN–BD) increased up to 31.5%, 34.4% and 16.8%, respectively, in comparison to those properties of alder plywood from non-densified veneer (AN–AN–AN–AN–AN), by positioning al-der non-densified veneers in the core layers and birch densified veneers in the outer layers. Moreover, the surface roughness of plywood panels with outer layers of birch veneer is lower than panels with outer layers of alder veneer. It was shown that non-treated alder veneer, de-spite somewhat lower strength properties than birch veneer, could be successfully used with proper lay-up schemes in the veneer-based products industry.Ukrainian companies mainly use birch in the manufacture of plywood, but species such as black alder is not yet widely used in the manufacture of plywood due to its lower properties. It is well known that thermal compression is often used to improve the properties of solid wood. Good lay-up schemes of veneer can maximize the advantages, minimize the disadvantages of these wood species, and generally improve the utility value of the plywood. The research aimed to develop plywood panels with two wood species and two types of veneer treatments and to evaluate the influences of different lay-up schemes on the properties of the plywood. Five-layer plywood panels were formed with 16 different lay-up schemes using birch (Betula verrucosa Ehrh.) (B) and black alder (Alnus glutinosa L.) (A) veneers, non-densified (N) and thermally den-sified (D). The different lay-up schemes were to identify opportunities to improve the mechani-cal and physical properties of the plywood by replacing birch veneer in the plywood structure with alternative alder veneer. The veneer sheets were thermally densified in laboratory hot press at temperature 180 °C and pressure 2 MPa within 3 min. The conducted study showed that the bending strength, modulus of elasticity and shear strength of mixed-species plywood (BD–AN–AN–AN–BD) increased up to 31.5%, 34.4% and 16.8%, respectively, in comparison to those properties of alder plywood from non-densified veneer (AN–AN–AN–AN–AN), by positioning al-der non-densified veneers in the core layers and birch densified veneers in the outer layers. Moreover, the surface roughness of plywood panels with outer layers of birch veneer is lower than panels with outer layers of alder veneer. It was shown that non-treated alder veneer, de-spite somewhat lower strength properties than birch veneer, could be successfully used with proper lay-up schemes in the veneer-based products industry.