Biorefining of Wood Feedstock: Production of a Hemicellulose-Based Bioadhesive

Abstract

A resource-efficient biorefining technology for lignocellulosic feedstock has been developed to obtain a wood dehydration resin (WDR) as a bio-adhesive. The process is implemented directly from hemicelluloses via steam-phase hydrolysis followed by drying in an oxygen-containing atmosphere and is suitable for industrial scale. It was demonstrated that when drying of the hydrolysate mass, acid-catalyzed dehydration of pentoses occurs with the formation of reactive carbohydrate intermediates and their subsequent oligomerization/ carbonization (“humic-like” condensates); the average molecular weight of water-soluble products increases from ~195 to ~296 Da. FTIR data register signatures of dehydration of the carbohydrate phase (attenuation of OH bands at 3350–3400 cm⁻¹ and C–O/C–O–C bands at 1150–1040 cm⁻¹) and an increase in carbonyl groups (1705–1710 cm⁻¹), while ¹³C NMR shows increased contributions of C=O and O-alkyl centers without distinct aromatic or furan signatures, consistent with the formation of a condensed humic-like network. The resin gelating was observed at 180 °C within 22–27 s; upon addition of H₂SO₄ ≥ 6 % (based on resin solids) the gel becomes water-insoluble. High-density fiberboards (HDF) produced with the resin exhibited enhanced water resistance (thickness swelling 6–21 % after 24 h), which is comparable to modern bio-adhesives and outperforms typical starch-based formulations in water resistance. Formaldehyde emission by the WKI method was as low as 1.7 mg/100 g. These results align with current trends in lignin-, tannin-, and polysaccharide-based bioadhesives, demonstrating the possibility of eliminating formaldehyde while maintaining acceptable physico-mechanical properties.