A Novel Natural Dye Derivative for Natural Fabric Supercritical Carbon Dioxide Dyeing Technology

The supercritical carbon dioxide (SC-CO2) dyeing technology is a green dyeing technology, and the usage of natural dye makes SC-CO2 dyeing technology safer and more environment-friendly. Nevertheless, after using natural dye in SC-CO2 dyeing, the color depth and fastness of dyed natural fabric are poor. In this study, alkyl and hydroxyalkyl groups were grafted onto alizarin, which is a natural dye, to elevate the color depths and fastness of alizarin-derivative-dyed natural fabric. The results demonstrate that the color depths of alkyl-alizarin-dyed and hydroxyalkyl-alizarin-dyed natural fabrics were increased. This has to do with the increase in the solubilities of alkyl alizarin and hydroxyalkyl alizarin in SC-CO2. The hydroxybutyl-alizarin-dyed wool displayed the best color depth (K/S value: 6.44). And the hydroxyalkyl-alizarin-dyed natural fabric showed good washing fastness and rubbing fastness (about 4–5 level), because that hydroxyalkyl alizarin could be linked by a covalent bond to the natural fabric.