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

## TL;DR

This study explores using tannins from a tree species to create eco-friendly adhesives for plywood, finding that a specific sodium bisulfite concentration improves performance.

## Contribution

The study introduces a method to optimize tannin-based adhesives using sodium bisulfite for sustainable plywood production.

## Key findings

- Adhesives extracted with 3% sodium bisulfite showed better mechanical properties in plywood panels.
- Higher bisulfite concentrations increased water absorption, limiting use to indoor environments.
- Tannin yield and adhesive properties improved with sodium bisulfite treatment.

## Abstract

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.