Extraction and Characterization of Tannins from the Barks of Four Tropical Wood Species and Formulation of Bioresins for Potential Industrial Applications

The use of renewable plant resources for the formulation of adhesives is increasingly promising, thanks to their availability at an affordable price and their high content of biomolecules such as polyphenols. The study of tannins therefore remains an active and ongoing area of research. This article presents a recent characterization of tannins extracted from the barks of four types of tropical trees (Entandophragma candolei, Entandophragma cylindricum, Afzelia africana and Dacryodes klaineana) and their application in the development of bioresins. Tannin extraction with hot water yielded between 25% and 40%. Tannin from Entandophragma candolei produced the highest yield. Chemical analysis confirmed the high presence of condensed tannins, with the identification of several new monomers in each tannin type, underlining their uniqueness. The most chemically stable tannins, Dacryodes klaineana and Afzelia africana, demonstrated their ability to withstand temperatures of 525 °C and 375 °C, respectively, with carbon residues of 45.05% and 43.18%. As for the resins, Entandophragma candolei tannin resin stood out for its thermal properties, notably a degradation temperature of 500 °C and a carbon residue rate of 36.72%. As for E. cylindricum resin, it boasted the highest modulus of elasticity (5268 MPa). Characterized tannins can be exploited in the technological sector.