Biobased Adhesives from African Mahogany Tannins: Characterization by 1H and 13C NMR and Physicochemical Properties
A. Bikoro Bi Athomo1,2, S.P.M. Engozogho Anris1,2, R. Safou Tchiama2,3, F. Eyma4, P.L. de Hoyos-Martinez5 and B. Charrier1
1CNRS/ Université de Pau et es Pays de l’Adour, Institut des sciences analytiques et de physico-chimie pour l’environnement et les matériaux – Xylomat, UMR5254, 40004, Mont de Marsan, France; 2Laboratoire de Recherche et de Valorisation du Matériau Bois (LaReVa Bois). Ecole Normale Supérieure d’Enseignement Technique (ENSET), BP. 3989 Libreville (Gabon); 3Laboratoire des Substances Naturelles et de Synthèses Organométalliques (LASNSOM). Unité de Recherche en Chimie, BP 941, Université des Sciences et Techniques de Masuku, Franceville (Gabon); 4Institut Clément Ader (ICA), Université de Toulouse, CNRSUMR 5312-INSA-ISAE-Mines Albi-UPS, Tarbes, France; 5Chemical and environmental engineering department, University of the Basque Country UPV/EHU, Plaza Europa, 1, 20018, Donostia-San Sebastian, Spain
Abstract: The study of the development of tannin-based adhesives from the African mahogany Khaya ivorensis A. Chev tannins condensed hexamine was carried out. Tannins from the bark, sapwood, and heartwood were extracted employing the industrial method (NaOH/Na2SO3/NaHSO3) and they were used to synthesize different formulations of biobased adhesives. Tannins/hexamine/water adhesives obtained were characterized by differential scanning analysis (DSC) to know their physical changes under heat action. Polymerization temperatures were between 90°C and 153°C. These adhesives heat resistance was studied by thermogravimetric analysis (TGA). Results showed good thermal stabilities properties for adhesives with degradation temperatures between 225°C and 250°C. Besides, a thermomechanical analysis (TMA) shows a high value of elasticity modulus for these adhesives. Finally, 2D HSQC NMR analysis was performed to confirm the good reactivity between African mahogany tannins and hexamine linked with strong bounds.
Keywords: Bark, Sapwood, Heartwood, Khaya ivorensis, Tannins, Thermal stability.