Effect of PH on cotton dyeing with reactive dyes

Reactive dye are so called because their molecules react chemically with the fiber polymers of some fiber to from a covalent bond between the dye molecules and fiber polymer. Reactive dye is a class of highly colored organic substances, primarily utilized for tinting Textiles that attach themselves to their substrates by a chemical reaction that forms a covalent bond between the molecule of dye and that of the fiber. The dyestuff thus becomes a part of the fiber and is much less likely to be removed by washing them are dyestuffs that adhere by adsorption. The very first fiber-reactive dyes were designed for cellulose fibers, and are still used mostly in this way. There are also commercially available fiber-reactive dyes for protein and polyamide fibers. In theory, fiber-reactive dyes have been developed for other fibers, but these are not yet practical commercially. The dyes contain a reactive group that, when applied to a fiber in a weakly alkaline dye bath, form a chemical bond with the fiber. Reactive dyes can also be used to dye wool and nylon, in the latter case they are applied under weakly acidic conditions.

A fiber-reactive dye will form a covalent bond with the appropriate textile functionality is of  great interest, since, once attached, they are very difficult to remove.

The first fiber-reactive dyes were designed for cellulose fibers, and they are still used mostly in this way. There are also commercially available fiber-reactive dyes for protein and  polyamide fibers. In theory, fiber-reactive dyes have been developed for other fibers, but these are not yet practical commercially.

Although fiber-reactive dyes have been a goal for quite some time, the breakthrough came fairly late, in 1954. Prior to then, attempts to react the dye and fibers involved harsh conditions that often resulted in degradation of the textile.
The first fiber-reactive dyes contained the 1, 3-5-triazinyl groups, and were shown by Rattee and Stephen to react with cellulose in mild alkali solution. No significant fiber degradation occurred. ICI launched a range of dyes based on this chemistry, called the Portion dyes. This new range was superior in every way to vat and direct dyes, having excellent wash fastness and a wide range of brilliant colors. Portion dyes could also be applied in batches, or continuously. The general structure of a fiber-reactive dye is shown below:

  For More Please Click Here