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Adhesives based on vegetable tannins are already a reality in the market. However, their use is still limited due to their low mechanical resistance and weak humidity resistance. Cellulose nanofibrils (CNFs) are being used as reinforcing materials in various composites, resulting in an improvement of mechanical proprieties in general. The objective of this work was to evaluate the incorporation of CNFs in adhesives made of tannins obtained from the Angico tree (Anadenanthera peregrine). Concentrations of nanofibrils at 1, 5, and 10% were added to the adhesives on a dry basis. Tests of viscosity, pH, solids content, and gel time were performed to determine the physical proprieties of the adhesives. The Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Raman spectra measurements were also determined to understand the interaction between tannins and CNFs. Thermogravimetric analyses (TGA) were carried out to determine the thermal resistance of the composite. The FTIR and Raman characterization identified some differences in the peaks in the chemical composition of the adhesives with different percentages of CNFs. The adhesives showed no different decomposition in the thermogravimetric analyses. The shear strength in the glue line of the adhesive with 5% of CNFs in Toona ciliata woods was determined. Among all the adhesives analyzed, the one with 5% of CNFs produced an improvement in the mechanical resistance and humidity resistance on the glue line.

This study evaluated the quality of plywood panels bonded with adhesives produced with tannins from the bark of Acacia mangium Wild. trees and compared their bonding performance with commercial adhesive formulations. Crude hot-water extract from the bark of A. mangium was employed to synthesize the adhesive formulation for plywood bonding. Twelve plywood panels with five layers were produced, four with each type of adhesive. Static bending strength, modulus of elasticity, modulus of rupture and Janka hardness were evaluated. Water absorption percentages were determined after immersion for 2 and 24 hours. Regarding mechanical properties, there was no statistical difference among the adhesive based on A. mangium and the commercial formulations. However, based on the water absorption results, plywood panels bonded with A. mangium tannins were found to be suitable only for indoor uses due to higher absorption compared to the other adhesives.

This study aimed to assess the influence of time and sodium sulfite concentration on tannin yield in Curupay bark and propose better extraction conditions. The extractions were performed using 100 g of dried bark and 1500 mL of water at 70 °C, with extraction times of 2, 3, and 4 h and amount of extractor salt at the concentrations of 0, 1, 2, 3, and 4%. The following parameters were evaluated: content of total solids, total yield of solids, Stiasny index, and gravimetric yield of condensed tannins and non-tannins. Results show that the higher the concentration of sodium sulfite, the higher the content and yield of solids, as well as the higher the extraction of non-tannin compounds. Three-hour extraction time at 3.0% sodium sulfite concentration was the best condition to extract tannins from Curupay bark, under which a condensed tannin yield of 20.46% was obtained.