A Three-Bath Process for Dyeing Cotton with Bis-Azo Bi-Functional Reactive Dyes Based on Diazonium Salts

Mono-azo dyes possessing a primary aromatic amino group have been shown to react with cotton by diazotization followed by treatment with soda ash at 60–65 °C thereby acting as monofunctional reactive dyes. Bis-azo dyes bearing two amino groups are expected to act as bi-functional reactive dyes and exhibit enhanced dye-cellulose fixation. This work shows that the difference in fixation exhibited by mono-azo and bis-azo dyes is statistically significant at 95 % confidence level in favor of the latter group. This work describes a three-bath dyeing process which reduced the amount of consumed water by 60.6 % and the environment factor by 62.2 %. The newly developed three-bath process also conserves energy by 74.1 %. Hence, a new class of bifunctional reactive dyes without externally attached reactive systems is, in principle, available. It will have the advantage of reducing raw materials and manufacturing costs. It also employs a sustainable reactive dyeing process.