In Estonia, hardwoods form approximately 50% of all forest area, where the main species are birch (30%), gray alder (9%), aspen (6%) and black alder (4%). Birch has been extensively used by the veneer-based industry, but species like black alder, gray alder and aspen have not been commonly used by the veneer-based products industry due to the lower quality of this resource. The aim of this research is to determine the effect of different lay-up schemes and usages of gray alder, black alder and aspen on the mechanical properties of plywood, by replacing birch veneer in the plywood core with alternative wood species. The main veneer and plywood characteristics will be evaluated according to the current standards, e.g., veneer strength perpendicular to grain, plywood bonding and bending strength, and modulus of elasticity. All processing parameters will be kept similar to those used generally by birch plywood manufacturers. The results showed that birch and black alder plywood panels had generally the highest bending strength properties, followed by grey alder and aspen. It was also found that, for proper gluing, birch veneers had the lowest glue consumption, 152 g/m², and aspen had the highest glue consumption, 179 g/m². It was found that when lower density wood was used in the plywood, the product density increased. Low density wood veneers had higher glue consumption, and also higher compaction in thickness than birch veneers under the same pressure. Overall, it was shown that the wood species used in this study have slightly lower strength properties, but with proper lay-up schemes, these wood species could be successfully used by the veneer-based products industry.

During the rotary peeling of veneer for plywood or the laminated veneer lumber manufacture, checks are formed in the veneer that are as deep as 70–80% of the veneer thickness. The results of this study show that, during adhesive bond testing, deep lathe checks in birch (Betula pendula Roth.) veneer significantly reduce the shear strength and the percent wood failure of phenol-formaldehyde (PF) – bonded plywood. The results also show that specimens tested with the checks pulled open or closed can fail by different mechanisms. Dried rotary peeled birch veneers were sanded to create uniform surfaces with lathe check depths varying from 30% to 90% of veneer thickness. Then, 7-ply plywood was manufactured with a commercial PF resin. After the preparation of the test specimens, the check depth of each specimen was measured microscopically. Subsequently, bond quality was measured according to EN 314. The results show that veneer checking alone can bring EN 314 specimens to the brink of failure even with an excellent adhesive. These findings stress the importance of measuring the depth of lathe checks and considering the orientations of checks during the testing to get a better understanding of bond quality in veneer-based products.

The enormous potential of renewable bioresources is expected to play a key role in the development of the EU’s sustainable circular economy. In this context, inexhaustible, biodegradable, non-toxic, and carbon-neutral forest-origin resources are very attractive for the development of novel sustainable products. The main structural component of wood is cellulose, which, in turn, is the feedstock of nanocellulose, one of the most explored nanomaterials. Different applications of nanocellulose have been proposed, including packaging, functional coatings, insulating materials, nanocomposites and nanohybrids manufacturing, among others. However, the intrinsic flammability of nanocellulose restricts its use in some areas where fire risk is a concern. This paper overviews the most recent studies of the fire resistance of nanocellulose-based materials, focusing on thin films, coatings, and aerogels. Along with effectiveness, increased attention to sustainable approaches is considered in developing novel fire-resistant coatings. The great potential of bio-based fire-resistant materials, combined with conventional non-halogenated fire retardants (FRs), has been established. The formulation methods, types of FRs and their action modes, and methods used for analysing fireproof are discussed in the frame of this overview.