The valorization of tree bark through chemical treatment into valuable products, such as bark acid, leads to the formation of process residues with a high solids content. Since they are of natural origin and are able to be suspended in water and acid, research was carried out on the recycling of suberic acid residues (SAR) as a bi-functional component of binder mixtures in the production of plywood. The 5%–20% (5%–30% for curing time) mass content of SAR has been investigated with urea-formaldehyde (UF) resin of about 66% of dry content. The results show that the curing time of the bonding mixture can be reduced to about 38% and 10%, respectively, for hot and cold curing, of the initial curing time for the lowest SAR content. The decreasing curing time of the tested binder mixtures with the increase in SAR content was caused by the increasing amount of acidic filler, since amine resins as UF require acidification hardening, and the curing dynamics are strongly dependent, among others, on the content of the acid medium (curing agent). In the case of hot curing, a SAR content of about 20% allowed us to achieve the curing time of bonding mass with an industrial hardener. Investigations into the mechanical properties of examined panels showed a significant modulus of elasticity (MOE) increase with filler content increase. Similar conclusions can be drawn when analyzing the results of the modulus of rupture (MOR) investigations; however, these were only significant regarding hot-pressed samples. The shear strength of the plywood samples increased with the SAR rise for both cold- and hot-pressed panels. The in-wood damage of samples with SAR filler, hot-pressed, rose up to about 30% for the highest SAR filler content. For cold-pressed samples, no in-wood damage was found. The positive effect of veneer impregnation limiter by resin was identified for SAR acting as a filler. Moreover, a higher density of SAR-containing bonding lines was reached for hot-pressed panels. Therefore, the results confirmed the ability to use the SAR as an upcycled component of the bonding mixture for plywood production.

Post-extraction birch bark residues as a potential binder in particleboards. Nowadays, in the wood-based composites industry, aspects such as ecology and joining the current circular economy play a very important role. However, user safety is also very important. Formaldehyde is one of the hazardous substances which, if emitted too high, can harm human health. Unfortunately, binders containing formaldehyde still reign supreme in the wood-based panels' industry. Therefore, this paper concerns the possibility of using post-extraction residues obtained during the extraction of suberinic acid, as a formaldehyde-free and ecological binder in the production of particleboards. The main component, suberinic acid, is a colorless, crystalline solid used in the synthesis of drugs and the production of plastics. The aim of the research was to answer the question: since suberinic acid itself is a good binder in the production of particle boards, as described in other publications, it is worth checking whether the post-extraction residues also have similarly good properties of joining particles in particle boards, depending on the size of the wood particles? In addition, the use of post-extraction residues of bark, and thus the elimination of synthetic adhesives in the wood-based composites production process, allows the reuse of wood raw material, which fits perfectly with the idea of upcycling. The tests showed that using post-extraction residues of birch bark, using 10% and 20% resination, the requirements of the EN 312: 2010 standard were met only in the case of the modulus of elasticity for boards made of the largest wood particles used in the tests. The resination and the size of wood particles contributed to the improvement of the properties of the tested boards.

Compression strength and other mechanical properties of particleboards induced by density. The aim of the paper was to investigate the contractual compression strength and modulus of elasticity under compression of six types of commercially available particleboards of various thickness, density and surface finish. The basic mechanical and physical characteristics of the tested panels (modulus of elasticity and modulus of rupture during bending, density and density profile) were also performed. The studies showed that the compression strength raises linearly with panels’ density raise, and the modulus of elasticity under compression is linearly opposite, depending on the panels’ density.

Compression strength-focused properties of wood composites induced by density. The aim of this study was to analyse the contractual compression strength and modulus of elasticity under compression of ten commercially available wood composites of various thickness, density, structure and surface finish. Density and density profiles have also been performed. The tests showed that there is no significant dependence of the compression strength and MOEC on the density of composites.