Quantification of the bark Myrcia eximia DC tannins from the Amazon rainforest and its application in the formulation of natural adhesives for wood

Abstract

The bark of the Myrcia eximia DC., tree which occurs in the Brazilian Amazon, was studied. The aim was to determine the yield of condensed tannins and their quality on formulation of natural adhesives for wood bonding. The extraction performance of tannins in water and sodium sulfite solution was compared. The tannins were characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Adhesives based on Myrcia eximia tannins were produced and evaluated for their physicochemical properties and shear strength in the wet and dry glue line. The extracts of Myrcia eximia bark presented 25.2% of condensed tannins in water extraction and 32.6% in sodium sulfite solution (Na2SO3). In these two extraction conditions, the Stiasny index values indicated that Myrcia eximia tannins can be used in wood adhesive formulations. The properties of the natural adhesives allowed for good application on wood and the glue line shear tests showed important bonding properties of the adhesive with the wood in both evaluated conditions, reaching a resistance of 5.3 MPa and 87.5% of ruptures in the wood. We conclude that Myrcia eximia bark is a source of high levels of condensed tannins with quality for application in natural adhesives.