Adhesives from Anadenanthera peregrina tannin for plywood production: effect of sodium bisulfite concentration on gluing quality

Applying different salt concentrations during extraction can increase the yield and improve the properties of tannic adhesives. The objective of this study was to develop natural polyphenol adhesives extracted with different concentrations of sodium bisulfite (NaHSO₃) for the production of plywood panels. The polyphenols were extracted from the bark of Anadenanthera peregrina with 0, 3, and 5% NaHSO₃. The adhesives were produced with solids contents of 45% and 6% paraformaldehyde and tested on plywood panels. The adhesives were characterized by FTIR and thermogravimetric analysis. Gravimetric yield, viscosity, gelation time, solids content, and pH of the tannins were measured to evaluate their use as adhesives. The plywoods were evaluated based on the physical, mechanical, and microstructural properties. The tannins extracted from the bark of A. peregrina, under different concentrations of NaHSO₃, reached high Stiasny values; the adhesives produced showed suitable physicochemical properties. However, increasing the concentration of bisulfite resulted in greater water absorption by the panels, restricting their use to indoor environments. Panels bonded with the adhesive extracted with 3% NaHSO₃ stood out for better mechanical properties, especially in static bending, in addition to meeting shear strength requirements. The bisulfite concentration indicates a viable option for increasing tannin yield, making it an environmentally sustainable alternative for the partial or total replacement of commercially formulated phenol-formaldehyde adhesives.