Integrated surface densification and furfurylation for enhancing mechanical performance and dimensional stability of fast-grown Chinese fir

Abstract Surface densification combined with bio-based polymer impregnation offers a sustainable approach for enhancing the performance of fast-growing softwoods. In this study, a one-step and a catalyst-assisted two-step furfuryl alcohol (FA) modification strategy were applied to Chinese fir ( Cunninghamia lanceolata ) prior to thermal surface densification. The effects of FA concentration (10 %, 30 %, and 50 %) and treatment route on density distribution, weight percentage gain, colorimetric change, mechanical properties, dimensional stability, and chemical structure were systematically evaluated. The one-step treatment with 50 % FA produced the high MOR (123 MPa), compressive strength (65 MPa) accompanied by improved surface darkening and reduced thickness swelling (4.3 % and 22.8 %) under 65 % and 98 % humid conditions. Scanning electron microscopy revealed progressive cell wall deformation and densification, while FTIR analysis (1738 and 1715 cm −1 ) confirmed in situ FA polymerization and crosslinking. Compared to untreated and water-treated controls, FA-modified samples exhibited superior performance with reduced set recovery (28.2 %) and enhanced structural rigidity (MOE:13.6 GPa). The results demonstrate that FA-assisted surface densification is a tunable and resource-efficient method for upgrading low-density plantation wood for structural and decorative applications.