Enhancing dyeing efficiency of bamboo culm through surface sanding: modifying microstructure and permeability for improved dyeing performance

Abstract

Bamboo products are increasingly popular among consumers; however, their monotonous surface coloration and inherent natural defects limit their economic value. To address these issues, this study investigated the dyeing performance of bamboo culms after surface sanding treatment. The experimental factors examined included sandpaper grit size, sanding removal amount, and dyeing duration for unsanded and sanded samples, while the measured responses included surface morphology, roughness, wettability, chemical composition, dye penetration depth, color parameters, gloss, and lightfastness. Sandpaper grit size primarily governed surface roughness characteristics, whereas sanding removal amount controlled the extent of hydrophobic barrier removal; both parameters were systematically examined for their individual and interactive effects on dyeing performance. The results demonstrated that sanding treatment reduced the surface silicon content of bamboo by 22.9% and increased its surface roughness by 16.81%. As the sandpaper grit size increased, the surface roughness decreased, cell structural damage was reduced, and pits on the cell walls remained observable. After dyeing, the bamboo culms showed distinct color differences compared with undyed bamboo. Both prolonging the dyeing time and increasing the sanding removal amount enhanced dye penetration depth and darkened the surface color. Sanding improved the surface wettability of bamboo, promoted more uniform surface dyeing and improved dyeing efficiency, but reduced surface gloss. The dye adhered via physical adsorption without new chemical bonds. Lightfastness tests showed that dyed bamboo faded after 124 h of xenon lamp irradiation. Overall, sanding pretreatment negatively affected lightfastness, but this trade-off was offset by substantial improvements in dyeing efficiency and uniformity. Among the tested samples, unsanded bamboo dyed for 4 h, sanded bamboo dyed for 30 min and bamboo with a sanding removal amount of 3–4 g showed better lightfastness, with grades of 3–4, 4 and 3–4, respectively. This research provides a new strategy for bamboo dyeing in eco-friendly construction and decoration.