This study examined the potential of hydrolysable tannin in comparison to condensed tannins for the production of furanic foams. The results indicate that chestnut tannin presents lower reactivity and requires a stronger acid for the polymerization. Additionally, foamability and density were found to be dependent on both surfactant concentration and tannin type, allowing lower densities for mimosa tannin and lower thermal conductivities for chestnut-based foams. Mimosa tannin was found to have the highest compression strength, followed by quebracho and chestnut, promising thermal conductivity of around 50 mW/m·K for 300 kg/m³ foams, which suggests that chestnut foams have the potential to performing highly when the density is reduced. Chemical analysis revealed that the methylene moieties of the furanics are non-specific and produces new covalent bonds with nucleophilic substrates: -OH groups and free-positions in the flavonoids. Overall, this study opens new perspectives for the application of hydrolysable tannins in polymer and material science.

In accordance with sustainable economic and social development, Europe supports the use of energy from renewable sources to decrease the use of fossil fuels. Among renewable energy sources, wood, especially production wood waste from the supply chain, represents an exploitable source in line with a circular economy development. In this context, processing of residues produced by wood companies becomes an important resource. This work deals with the possible energy recovery of glued wood wastes. Two solid biofuels were produced from glued wood wastes: pellets and briquettes. They have been produced in collaboration with a local company and analyzed according to the applicable EN ISO international standards. The results were compared with the limits imposed by the standards in order to identify their quality class and their applicability to the current market. The amount of adhesive present in the wood wastes does not negatively affect the intrinsic characteristics of the material that is suitable for the production of solid biofuels. In addition, the amount of wood waste containing cross-linked polyurethane was calculated in order not to compromise the quality of solid biofuels made therefrom.

With increasing concerns about the production of sustainable materials, the field of wood-based materials still offers a critical challenge. Indeed, a close dependence on petroleum derivatives is still required, involving high consumption of non-renewable and toxic chemicals in the assembly of wooden parts. Herein, the aim of this research was to evaluate the potentiality of an entirely renewable tannin-based adhesive for particleboard production. Industrial quebracho (Schinopsis balansae) tannin powder was selected as a raw material and analyzed in terms of polyphenols, polysaccharides, and the total condensed amount. Furfural was proposed as a bio-sourced hardener to establish crosslinking between the flavonoid units and hence produce a resin. This formulation was analyzed in terms of viscosity and curing time and then applied to laboratory-scale single-layer particleboard production. The density, mechanical properties, and thickness swelling of the panels were investigated at different glue ratios and pressing conditions. It was observed that time has a higher impact than temperature on the internal bond, and panels pressed at 160 °C for a longer pressing time (>7 min) performed better than the boards obtained at a higher temperature. The registered values at 160 °C for 11 min of pressing of internal bond (0.37 MPa) and modulus of elasticity (1417 MPa) met the required standards for P1 panels according to European norms EN 312 (2010). Conversely, the modulus of rupture (4.9 MPa) did not satisfy the requirements suggesting the need for the use of additive or post-treatments. Considering the results achieved, quebracho–furfural adhesives are an interesting base for bio-based adhesive formulations.

Wood-based products are traditionally bonded with synthetic adhesives. Resources availability and ecological concerns have drawn attention to bio-based sources. The use of tannin-based adhesives for engineered wood products has been known for decades, however, these formulations were hardly used for the gluing of solid wood because their rigidity involved low performance. In this work, a completely bio-based formulation consisting of Quebracho (Schinopsis balancae) extract and furfural is characterized in terms of viscosity, gel time, and FT-IR spectroscopy. Further, the usability as an adhesive for beech (Fagus sylvatica) plywood with regard to press parameters (time and temperature) and its influence on physical (density and thickness) and mechanical properties (modulus of elasticity, modulus of rupture and tensile shear strength) were determined. These polyphenolic adhesives presented non-Newtonian behavior but still good spreading at room temperature as well as evident signs of crosslinking when exposed to 100 °C. Within the press temperature, a range of 125 °C to 140 °C gained suitable results with regard to mechanical properties. The modulus of elasticity of five layered 10 mm beech plywood ranged between 9600 N/mm² and 11,600 N/mm², respectively, with 66 N/mm² to 100 N/mm² for the modulus of rupture. The dry state tensile shear strength of ~2.2 N/mm² matched with other tannin-based formulations, but showed delamination after 24 h of water storage. The proposed quebracho tannin-furfural formulation can be a bio-based alternative adhesive for industrial applicability for special plywood products in a dry environment, and it offers new possibilities in terms of recyclability.

One of the major challenges currently in the field of material science is finding natural alternatives to the high-performing plastics developed in the last century. Consumers trust synthetic products for their excellent properties, but they are becoming aware of their impact on the planet. One of the most attractive precursors for natural polymers is tannin extracts and in particular condensed tannins. Quebracho (Schinopsis balansae) extract is one of the few industrially available flavonoids and can be exploited as a building block for thermoset resins due to its phenol-like reactivity. The aim of this study was to systematically investigate different hardeners and evaluate the water resistance, thermal behavior, and chemical structure of the quebracho tannin-based polymers in order to understand their suitability as adhesives. It was observed that around 80% of the extract is resistant to leaching when 5% of formaldehyde or hexamine or 10% of glyoxal or furfural are added. Additionally, furfuryl alcohol guarantees high leaching resistance, but only at higher proportions (20%). The quebracho-based formulations showed specific thermal behavior during hardening and higher degradation resistance than the extract. Finally, these polymers undergo similar chemistry to those of mimosa, with exclusive reactivity of the A-ring of the flavonoid.