Dye fading of dyed rayon fibers containing titanium oxide-silica complex photocatalyst

Excellent antibacterial properties and self cleaning performance have been reported for rayon fibers containing titanium oxide silica complex photocatalyst. However, when these fibers are dyed, photocatalysis may also decompose the dye. In this study, a direct dye and a reactive dye were used to dye these fibers in order to examine the dye fading of the dyed these fibers. First, the dyed these fibers were subjected to UV irradiation in air. Neither the direct dye nor the reactive dye faded at all and the color hue of the dyed these fibers was very stable to ultraviolet light. Subsequently, the dyed these fibers were subjected to UV irradiation in water. Although both dyes were found to fade, the direct dye faded more readily than the reactive dye. The difference was more pronounced when these fibers were dyed in light colors. The difference was believed to show up because cellulose molecules making up rayon fibers bond with direct dye molecules through hydrogen bonds whereas cellulose molecules bond with reactive dye molecules through covalent bonds. Finally, to examine the photocatalytic function of the dyed rayon fibers containing titanium oxide silica complex photocatalyst, the dyed these fibers were subjected to UV irradiation while immersed in an methylene blue aqueous solution. Methylene blue underwent dye decomposition, showing that the dyed these fibers maintained an dequate photocatalytic function.