Deep eutectic solvents-assisted wood densification: A promising strategy for shape-fixation

Densified wood is preferable for structural applications because of its excellent mechanical properties and sustainability, but the fixation of its compression deformation and the prevention of water-induced mechanical deterioration remain challenging. Herein, an eco-friendly and highly efficient method was designed for producing dimensionally-stable densified wood, including deep eutectic solvent (DES) pretreatment and subsequent temperature-assisted compression. Hemicellulose, amorphous cellulose, and lignin were in-situ depolymerized or modified by DES pretreatment, and then they were repolymerized or recondensed by temperature-assisted compression to form a crosslinking network to achieve deformation fixation. This DES-assisted densified wood showed a lower set recovery rate (4.7% vs. 69.8%) and higher bending strength (173.7 MPa vs. 69.2 MPa) than densified natural wood. Moreover, its surface hardness could be maintained at a higher level even after a water-soaking/boiling test due to its excellent dimensional stability. DES pretreatment could be considered as a suitable and green strategy for producing high-strength structural wood with excellent dimensional stability.