Dyeing of Poplar Wood through High-Pressure Processing: Performance Evaluation

Dyeing of poplar wood through high-pressure (HP) processing was evaluated at different pressure levels (40 to 130 MPa) and compared with conventional hot dip treatment. Dyeing performance was evaluated based on external surface color, fractal color dimension, dye uptake, internal color, elemental composition, and subsequent ultraviolet aging of the wood. The internal microstructure of the treated wood was also examined by scanning electron microscopy (SEM). Results showed that the external surface color difference and change in brightness were significantly greater with HP treatment than with hot dip treatment. The hue angle of HP treated wood surfaces was 1.27 to 4.01 higher and the fractal color dimension was significantly (p < 0.05) lower than that of hot dip treated wood, demonstrating more intense and more uniform distribution of color with HP treatment. The internal color of HP treated wood was also more evenly distributed and more intense, while the hot dip treated wood had no internal dye uptake (zero penetration). SEM analysis showed that the wood structure was damaged by HP treatment, which allowed the dye solution to penetrate into the wood more easily. Among the different pressure levels, the higher pressures resulted in better dyeing performance; however, considering the treatment cost, time, and energy efficiency, 100 MPa treatment may be more economical.