Development of Quebracho (Schinopsis balansae) Tannin-Based Thermoset Resins

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

Comparing condensed and hydrolysable tannins for mechanical foaming of furanic foams

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 center dot K for 300 kg/m(3) 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

Quebracho-based wood preservatives: Effect of concentration and hardener on timber properties

Tannin polyphenols are produced by plants to protect themselves against natural decay. It is expected that impregnating low-durable timber with tannin extracts of more durable species such as quebracho (Schinopsis balansae) will enhance the durability of the specimens. This biomimetic approach combined with the in situ polymerization of quebracho–hexamine formulations can be a valid alternative to synthetic wood preservatives. In this work, we aim to evaluate the impregnation mechanism as well as the impact of tannin and hardener concentration on the mechanical and leaching resistance properties of treated wood. Compression resistance, surface hardness and leaching resistance of four different common non-durable wood species: spruce (Picea abies), pine (Pinus spp.), poplar (Populus alba) and beech (Fagus sylvatica) impregnated with different concentrations of extract and hexamine are presented. The results show that the mechanical properties of tannin-impregnated timber are enhanced, especially for timber with lower densities. Tannin and hardener concentrations tendentially do not contribute significantly to further increase MOE (modulus of elasticity), MOR (modulus of rupture) and Brinell hardness. Similar results are also obtained when the specimens are tested against leaching: tannin is significantly more water-resistant when cured with hexamine, but higher amounts of hardener do not further improve its water resistance. These findings suggest that quebracho tannin–hexamine formulations are already effective at low concentrations (5 to 10% extract with 2.5 to 5% hexamine)

Quebracho Tannin Bio-Based Adhesives for Plywood

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

Thermal valorization and elemental composition of industrial tannin extracts

Due to their natural origin and broad availability, industrial tannin extracts are extending their application field from the classical, and still principal, application in tannery, to oenology, pharmacy, adhesives and material science. Despite the growing interest, not much is known about the thermal valorization of these biomolecules. In this article we present the thermal properties of the eight most common commercial tannin extracts and their elemental chemical composition to shed light on the end-life of the bio-materials based on these polyphenols. Results have shown that hydrolysable tannins can be managed similarly to wood, while condensed tannins have higher heating values but also generally higher chlorine content. Sumac and gambier leaf extracts registered contained heating values and significant amounts of ashes rich in calcium and sulfur. The high chlorine content observed for the extracts of mimosa (Acacia Mearnsii) does not hinder the combustion of its derived products which can still be thermally valorized. Mimosa tannin-based materials can also be added up to 2% to wood pellets and briquettes without significantly affecting the overall quality of the biofuels according to the in-force standards

Quality assessment of pellets and briquettes made from glued wood waste

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 afect the intrinsic characteristics of the material that is suitable for the production of solid biofuels. In addition, the amount of wood waste containing crosslinked polyurethane was calculated in order not to compromise the quality of solid biofuels made therefrom

Produzione e caratterizzazione di pannelli truciolari incollati con bio-adesivi a base di tannino

In un’ottica di uno sviluppo sostenibile e indipendente da risorse fossili, le foreste e la gestione di esse, giocano un ruolo chiave e imprescindibile. Versatilità e rinnovabilità permettono a legno e derivati di ricoprire un ruolo da protagonisti in diverse aree, dalla bio-raffineria al settore energetico fino alla produzione di diversi tipi di prodotti legnosi. In particolare, la produzione di pannelli prevede l’assemblaggio delle componenti legnose attraverso l’applicazione di adesivi. Tradizionalmente i pannelli a base di legno sono assemblati utilizzando resine di origine sintetica. È quindi chiaro come la loro produzione sia attualmente vincolata a risorse non rinnovabili, e sebbene la comunità scientifica abbia studiato e sviluppato alternative più sostenibili, non si è ancora verificata un’inversione di rotta. È quindi evidente che ulteriori ricerche e sviluppi siano necessari al fine di ottenere materiali con proprietà competitive con gli attuali adesivi sintetici. Il presente studio punta alla valorizzazione di una bio-risorsa che, come il legno, vanta caratteristiche quali versatilità e rinnovabilità, il tannino. I tannini grazie alla loro capacità antiossidante trovano da tempo applicazione in enologia, in cosmetica, nell’industria animale e farmaceutica. La loro naturale conformazione chimica, la buona reattività e un processo di estrazione rispettoso dell’ambiente hanno spinto la ricerca ad aprire nuove strade a questi composti, tra le quali di particole interesse vi è quella degli adesivi. Lo studio è stato svolto in collaborazione con l’azienda Silva (Cu, Italia), leader mondiale nella produzione di tannini, che ha fornito un estratto di quebracho, sottoposto a specifico trattamento di estrazione ottimizzandone le proprietà per l’applicazione come adesivo. Cinque principali induritori (formaldeide, esamina, gliossale, furfurale e alcohol furfurilico) sono stati selezionati e l’interazione induritore-tannino è stata stu diata. Esamina e furfurale risultano tra gli induritori più performanti a seguito di una approfondita caratterizzazione chimico-fisica (test di lisciviazione, analisi termo-meccanica - TMA, analisi termo-gravimetrica - TGA, spettroscopia 13C-NMR e FT-ATR). La produzione di pannelli truciolari e il confronto di parametri quali, profilo di densità, test meccanici e resistenza all’umidità, con pannelli simili incollati con una resina sintetica industriale, offrono una reale prospettiva del possibile utilizzo del tannino per lo sviluppo di colle industriali. Le potenzialità del tannino di quebracho modificato come bio-adesivo per il legno sono state studiate per la produzione di pan nelli truciolari, ma ulteriori lavori sono necessari per ampliare l’applicazione ad altri prodotti legnosi (plywood,LVL, fiberboard, ecc.)

Biocompatible and Printable Ionotronic Sensing Materials Based on Silk Fibroin and Soluble Plant-Derived Polyphenols

The emergence of ionotronic materials has been recently exploited for interfacing electronics and biological tissues, improving sensing with the surrounding environment. In this paper, we investigated the synergistic effect of regenerated silk fibroin (RS) with a plant-derived polyphenol (i.e., chestnut tannin on ionic conductivity and how water molecules play critical roles in regulating ion mobility in these materials. In particular, we observed that adding tannin to RS increases the ionic conductivity, and this phenomenon is accentuated by increasing the hydration. We also demonstrated how silk-based hybrids could be used as building materials for scaffolds where human fibroblast and neural progenitor cells can highly proliferate. Finally, after proving their biocompatibility, RS hybrids demonstrate excellent three-dimensional (3D) printability via extrusion-based 3D printing to fabricate a soft sensor that can detect charged objects by sensing the electric fields that originate from them. These findings pave the way for a viable option for cell culture and novel sensors, with the potential base for tissue engineering and health monitoring