Plasticization and locking through lignin reprogramming for high-strength and dimensionally stable densified wood

Densified wood is a promising sustainable structural material but is severely limited by moisture-induced shape recovery, which restricts its practical application. Herein, we report a lignin macromolecular reprogramming strategy to achieve high-strength densified wood with shape fixation via a ternary deep eutectic solvent (DES) combined with microwave-assisted pretreatment and hot pressing. Compared with the binary DES, the ternary DES containing ethylene glycol better regulates lignin condensation and preserves more mobile lignin fragments, thereby facilitating their redistribution and network formation during subsequent hot pressing. Microwave-assisted pretreatment (3 min) achieves comparable dimensional stabilization performance to conventional oven heating (90 °C, 8 h) under the tested conditions, while markedly shortening the pretreatment time. During hot pressing, stabilized lignin fragments undergo controlled recondensation and redistribution, forming a densely cross-linked aromatic network within the cell wall. DES pretreatment efficiently plasticizes the cell wall, while the cross-linked network provides shape fixation through both covalent bonding and physical confinement. The resulting densified wood exhibits a bending strength of 132.89 MPa, a modulus of elasticity of 14.15 GPa, and an ultralow water-induced recovery of only 2.59%. This work provides a scalable and sustainable approach to upgrade fast-growing wood into high-performance, dimensionally stable wood-based materials.