Tannin-based extracts of Mimosa tenuiflora bark: features and prospecting as wood adhesives
Pedro Jorge Goes Lopes, Leandro Calegari, Wagner Alex de Medeiros Silva, Darci Alberto Gatto, Pedro Nicó de Medeiros Neto, Rafael Rodolfo de Melo, Ivonete Alves Bakke, Rafael de Ávila Delucis, André Luiz Missio
Abstract
Abstract Mimosa tenuiflora (Willd.) Poir. (MT) is an underutilized plant specie since its wood is mostly used for energy production. Nonetheless, the bark from this forest plant has a high amount of tannins and other valuable compounds. Tannins have high worldwide importance and, because of that, there is an increasing number of researches on biorefinery systems aiming at maximizing their exploitation. The present study evaluated tannins extracted from the MT bark and their use for producing wood adhesives. Three types of powdered tannins were extracted using different solvents: a pure aqueous solution, a 5% sodium hydroxide (NaOH) aqueous solution, and a 5% sodium bisulfite (NaHSO 3 ) aqueous solution. Distilled water, wheat flour, and formaldehyde were also used as a solvent, a glue extender, and a catalyst, respectively. These adhesives were applied for bonding pine wood joints and their shear strengths were determined. All the MT-based adhesives showed high viscosities and, yielded glue lines with similar shear strengths and similar shear deformations if compared to each other. That tannin-based glue incorporated with the tannin extracted using NaOH or NaHSO 3 stood out and yielded similar bonding performances if compared to a commercial adhesive applied as a positive control.