Harnessing polyphenols from pulp industry residues of juvenile eucalyptus wood: potential for adhesive applications

Approximately 1-2% of the wood processed for pulp production is converted into sawdust and pinchips, which are commonly burned for energy in industries that already produce excess power. This material, juvenile wood only containing sapwood, poses challenges for its valorization. This study explores the extraction of polyphenols from Eucalyptus wood residues generated by a pulp industry in Uruguay, aiming to evaluate their suitability as partial replacements in phenol-formaldehyde (PF) adhesives. Using solid-liquid extraction with sodium hydroxide and sodium sulfite, the extractions conditions were optimized through an experimental design considering sodium hydroxide and sodium sulfite charges, along with temperature as variables. The extracts were characterized based on phenolic content, condensed tannins content, antioxidant activity, and Stiasny number, to assess the adhesive potential. Adhesives formulated with 10%, 20%, and 30% PF resin substitution demonstrated a progressive reduction in tensile shear strength, with the 10% substitution achieving acceptable strength. While higher substitution levels compromised adhesive performance, the results suggest that formulation adjustments may improve performance at moderate substitution ratios. Furthermore, the high antioxidant capacity of the extracts opens up potential for their use in other high-value applications where natural antioxidants are increasingly sought after as safer and more sustainable alternatives to synthetic additives.