Effect of supercritical carbon-dioxide pretreatment on the permeability and plant dyeing performance of three wood species

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Abstract

Supercritical carbon dioxide (SC-CO2) pretreatment is known for its environmental friendliness and low energy consumption, drawing interest in wood processing. This study examined the effects of SC-CO2 pretreatment on permeability and plant dyeing performance of oak, poplar, and Chinese fir. Using an orthogonal experimental design, optimal parameters were identified (20 MPa, 70 °C, 60 min). Results showed that SC-CO2 pretreatment significantly increased water uptake and weight gain in all species, with Chinese fir over a 30% increase. Fourier-transform infrared spectroscopy and X-ray diffraction analyses indicated reductions in hydrophilic functional groups and crystallinity. Scanning electron microscopy confirmed a more porous structure with enhanced pore connectivity in treated wood, favoring dye penetration. Ultrasonic dyeing experiments with camphor fruit extract revealed that SC-CO2 pretreatment significantly improved color fastness and dye adsorption in all species. Poplar showed the greatest improvements: + 12.6% in color difference (ΔE), + 16.4% in color intensity (K/S), and +6.5% in dye uptake. Oak and Chinese fir also gained in these metrics. Reflectance in the 400–600 nm range decreased by ∼18% after pretreatment, confirming enhanced dye-binding capacity. By altering wood microstructure, SC-CO2 pretreatment improves dye uniformity and adsorption efficiency, supporting development of environmentally friendly, high-performance wood dyeing.

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