Characterization of delignified woods modified with ε -caprolactone

This study explores the use of deep eutectic solvents (DES) for selective lignin removal from wood, followed by in situ polymerization of ε-caprolactone (ε-CL) to enhance structural and functional properties of wood. Scots pine ( Pinus sylvestris L. ) and beech ( Fagus orientalis ) were treated with DES formulations based on choline chloride (ChCl) combined with oxalic acid (OA) or glycerol (GL) at molar ratios of 1.5:1 or 1:1, respectively. Post-treatment, ε-CL was grafted onto the delignified wood via ring-opening polymerization. Beech specimens treated with OA-based DES exhibited high mass loss and low weight percent gain (WPG: 60%) which was different for Scots pine where lower mass loss and higher WPG (143.45%) was observed, possibly indicating a more efficient CL grafting. The modified wood of both the species, exhibited improved water resistance and dimensional stability, with swelling values below 10% and remarkably reduced water uptake rates. Anti-swelling efficiency exceeded 54% in beech and 35% in pine. FTIR confirmed successful CL grafting through ester carbonyl bands, while XRD indicated reduced crystallinity, suggesting increased amorphous character; potentially justifying the use of DES-assisted delignification and CL polymerization for functional wood modification. • DES pretreatment selectively removes lignin from wood cell walls. • ε-Caprolactone grafting improves water resistance and dimensional stability. • Scots pine shows higher polymer uptake than beech after ε-Caprolactone modification. • FTIR and XRD confirm successful chemical integration and structural changes. • DES + CL synergy offers a sustainable route for advanced wood modification and wood based composites.