Desenvolvimento e avaliação de adesivos biobaseados a partir de taninos de Stryphnodendron adstringens e ácido cítrico para colagem de madeira

Abstract

This study investigated the technological potential of bioadhesives based on barbatimão tannins (Stryphnodendron adstringens), crosslinked with citric acid and formaldehyde, resulting in a partial reduction in the use of synthetic adhesives. The methodology comprised aqueous extraction of tannins from the bark (70 °C/3 h) with 3% sodium sulfite, resulting in an extract with 59.56% solids, 75% Stiasny index, and 44.72% condensed tannins. The adhesives were formulated with 50% solids and different proportions of citric acid/formaldehyde, and were characterized in terms of pH, viscosity, and gel time. Pinus sp. plywood was produced (140 °C; 12 kgf/cm²) and subjected to shear strength tests (NBR 9534/86) and Raman spectroscopy analysis. The results showed that treatment T4 (10% citric acid and 90% formaldehyde) presented the highest reactivity, with a gel time of 55 seconds and viscosity of 904.33 cP. In the dry mechanical test, T4 obtained a resistance of 7.75 MPa, statistically surpassing the 100% formaldehyde treatment (5.59 MPa). Raman analysis confirmed the formation of stable polymer networks via ester bonds, although high concentrations of citric acid (T2 and T3) compromised moisture resistance. It is concluded that the incorporation of citric acid as a partial cross-linking agent is technically feasible, resulting in high-performance adhesives with lower environmental impact, consolidating barbatimão as a strategic raw material for the production of sustainable wood adhesives.