Modified kraft lignin as sustainable consolidants for waterlogged archaeological wood

This study evaluates lightened kraft lignin: modified via acetylation and encapsulation, as a sustainable consolidant for waterlogged archaeological pine (Pinus sp.) from the Biskupin site (Poland). Lignin was acetylated with acetic anhydride/pyridine and, in a separate route, converted into colloidal capsules by tetrahydrofuran/water self‑assembly; both modifications were characterized and then applied to waterlogged archaeological wood by 2‑week immersion. Effectiveness was assessed by Fourier‑transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), colourimetry, linear dimensional change (LDC), anti‑shrink efficiency (ASE), and water‑uptake tests. Acetylated lignin penetrated more deeply and reduced water uptake (from > 240% to ~ 96%) with moderate improvements in dimensional stability; encapsulated lignin showed limited penetration but lowered shrinkage (tangential: from 6.78 to 4.21%; radial: from 3.36% to 2.37%) through a surface‑barrier effect and was better in preserving the natural colour. These results indicate that modified kraft lignin, particularly the encapsulated formulation, can complement or partially replace petroleum‑based consolidants and motivate further optimization of capsule size/distribution to enhance mechanical performance and treatment uniformity.