Citation: Bekhta, P.; Pipíška, T.; Gryc, V.; Sedliaˇ cik, J.; Král, P.; Ráhel’, J.; Vanˇ erek, J. Properties of Plywood Panels Composed of Thermally Densified and Non-Densified Alder and Birch Veneers. Forests 2023, 14, 96. https://doi.org/10.3390/f14010096 Academic Editor: Antonios Papadopoulos Received: 13 December 2022 Revised: 2 January 2023 Accepted: 3 January 2023 Published: 4 January 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article Properties of Plywood Panels Composed of Thermally Densified and Non-Densified Alder and Birch Veneers Pavlo Bekhta 1,2, * , Tomáš Pipíška 2 , Vladimír Gryc 2 ,Ján Sedliaˇ cik 3 , Pavel Král 2 , Jozef Ráhel’ 2 and Jan Vanˇ erek 4 1 Department of Wood-Based Composites, Cellulose and Paper, Ukrainian National Forestry University, 79057 Lviv, Ukraine 2 Department of Wood Science and Technology, Faculty of Forestry and Wood Technology, Mendel University in Brno, Zemˇ edˇ elská 3, 613 00 Brno, Czech Republic 3 Department of Furniture and Wood Products, Technical University in Zvolen, T.G. Masaryka 24, 960 01 Zvolen, Slovakia 4 Faculty of Civil Engineering, Institute of Technology of Building Materials and Components, Brno University of Technology, 602 00 Brno, Czech Republic * Correspondence: [email protected] Abstract: Ukrainian companies mainly use birch in the manufacture of plywood, but species, such as black alder, are not yet widely used in the manufacture of plywood due to their poorer 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 and minimize the disadvantages of these wood species, and generally improve the utility value of the plywood. This research aimed to develop plywood panels with two wood species and two types of veneer treatments in order 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, which were non-densified (N) and thermally densified (D). The different lay-up schemes were used to identify opportunities to improve the mechanical and physical properties of the plywood by replacing the birch veneer in the plywood structure with an alternative alder veneer. The veneer sheets were thermally densified in a laboratory hot press at a temperature of 180 ◦ C and pressure of 2 MPa for 3 min. The conducted study showed that the bending strength, modulus of elasticity and shear strength of mixed-species plywood (B D –A N –A N –A N –B D ) increased by up to 31.5%, 34.4% and 16.8%, respectively, in comparison to those properties of alder plywood from non-densified veneer (A N –A N –A N –A N –A N ), by positioning alder 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 was lower than that of panels with outer layers of alder veneer. It was shown that non-treated alder veneer, despite exhibiting somewhat lower strength properties than birch veneer, could be successfully used with proper lay-up schemes in the veneer-based products industry. Keywords: birch; black alder; thermal densification; plywood properties; wood veneers 1. Introduction Nowadays, veneer-based products, including plywood and laminated veneer lumber (LVL), are highly effective engineering wood products for construction. The plywood manufacturing process creates products with several dimensions to suit architectural and structural purposes, and mechanical properties equivalent or superior to those of the initially solid wood [1]. However, various process variables should be considered to obtain panels with satisfactory properties, such as the wood species used, type of adhesive, density, moisture content, lay-up scheme of the veneers, etc. [2]. The choice of wood species is very important for the properties and price of the panel [3]. Ukrainian companies mainly use Forests 2023, 14, 96. https://doi.org/10.3390/f14010096 https://www.mdpi.com/journal/forests
Properties of Plywood Panels Composed of Thermally Densified and Non-Densified Alder and Birch Veneers
Jun 27, 2023
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