Synthesis of Green Adhesive with Tannin Extracted from Eucalyptus Bark for Potential Use in Wood Composites

Recently, the exploitation of renewable plant resources in the formulation of adhesives is very promising for their availability at low coast, as well as their richness in biomolecules such as polyphenols. In this way, many research studies tannins extracted from different sources such as mimosa, quebracho, and pine have been the subject of very satisfactory recent studies. In this paper, a new complete characterization of the tannins extracted from the bark of eucalyptus globulus harvested from two regions in Algeria was achieved. The structural characterization enabled us to confirm the richness in condensed tannins, particularly in procyanidin and prodelphinidin units. The most reactive tannins obtained during extraction at 70°C (yield: 27.1%) have a Stiasny number of 75.92%. This extract was used for the formulation of adhesives (tannin/hexamine). The thermal characterizaction of the adhesives showed higher stability for the tannin formulation of eucalyptus/hexamine as well as an excellent mechanical performance with a MOE of 2807 MPa at 180°C and shear strength of 689.4 N/mm2.