Coupling coloration of cotton fiber modified with an aniline derivative

Coupling coloration refers to a dyeing method that forms azo chromophore in-situ on fiber through coupling reaction, where some electron-donating groups on fiber are served as coupling components, when treated with a diazonium salt. Since the generated azo chromophores connect to the fiber by covalent bonds, dyed fabrics through coupling coloration usually have excellent fastness. In this paper, a dyeing method involving a fiber modification process and a coupling coloration procedure was proposed for cotton fabric. To achieve this goal, an aniline modifier was firstly designed and synthesized through combination of aniline and triazine structures. Chemical modification of cotton fabric using the aniline modifier successfully grafted aniline units onto cotton fiber. The modified cotton fiber was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and X-ray diffraction. Coupling coloration of the modified cotton fabric utilizing 2,6-dichloro-4-nitroaniline, p-nitroaniline or 2-amino-5-nitrothiazole diazonium salts successfully presented deep shades of orange, red or blue color, respectively, with good levelness property. The dyed fabric exhibited good color firmness property. For example, the dyed fabric showed good resistance to organic solvent extraction with color fixation values of higher than 90%. The color fastnesses to soaping and rubbing of the dyed cotton fabrics reached higher than grade 4. The dyed cotton fabrics also had excellent washing stability after 20 washing cycles. Besides, the migration values of the cotton fabrics through coupling coloration were lower than 3%, indicating excellent anti-migration property.