Exploring the requirements of reactive dyes in eco-friendly dyeing process: The relationship between dye structure, dyeing properties, and eco-friendly dyeing techniques

Herein, four heterobifunctional brilliant yellow dyes containing different numbers of sulfonic groups (MRY1-MRY-4) were designed to investigate the relationship between the dye structure, dyeing properties, and the eco-friendly dyeing technique. The solubility, stability, substantivity, reactivity, and colorimetric properties of the dyes were studied. The substantivity of the dyes was significantly reduced when the diazo component of the chromophores contained two sulfonic groups. The four dyes were then used to dye cotton fabrics using ecofriendly low liquor ratio dyeing and cold pad -batch dyeing techniques. For low liquor ratio dyeing, when the liquor ratio was 1:6, the fixation rates of MRY-1, MRY-2, and MRY-3 were 84.9 %, 71.1 %, and 75.0 %, respectively. MRY-4 was not suitable for exhaust dyeing but could be used in cold pad -batch dyeing, in which its fixation rate on cotton fabric reached 93.8 %. However, MRY-1 cannot be used to dye cotton by cold pad -batch dyeing due to its low alkali resistance and resulting poor stability. In a similar chromophore structure, increasing the number of sulfonic groups increased the brightness value of the dye but also made the dye greener and bluer. The dry and wet rubbing fastness of cotton dyed with the four reactive dyes was grade 4-5 and 3-4, respectively. The wash fastness to color change and staining reached grades 4 or 4-5, while the light fastness of MRY-1 and MRY-3 was grade 3-4 and that of MRY-2 and MRY-4 was grade 4-5.