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

This study explores the extraction of tannins from the barks of four tropical wood species (Entandophragma candolei, Entandophragma cylindricum, Afzelia africana and Dacryodes klaineana) and their use in formulating bio-resins. The tannin extraction yield varied between 25 and 40%. The tannins were characterized by 13C Nuclear Magnetic Resonance (13C NMR), Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight (MALDI-TOF) and Thermogravimetric Analysis (TGA). The associated bio-resins, formulated with an Acacia nilotica hardener, were evaluated in terms of thermal stability, gel time, and modulus of elasticity. The results reveal significant chemical and thermal variability depending on the wood species. The tannin-based resin from E. candolei exhibits the best thermal stability (final residue 36.72% at 600°C), while the one based on E. cylindricum shows the best modulus of elasticity (5268 MPa). These tannins represent promising alternatives for bio-based adhesives.