Reactive dye s are dye s which usually have the basic struc-
ture of acid, direct , or mordant dyes but which in addition have a reactive
group capable of covalent bond formation with the fiber. Since the fiber
must have reasonable reactivity toward the dye reactive group, application
of these dyes has been limited to cellulosic , protein, and nylon fibers for
the mos t pa rt.
The fastness of reactive dyes covalently bound to the fiber is excellent . Reactive functional groups have been selected for incorporation into reactive dyes which will react readily with the fiber after diffusion into the
structure but which will not hydrolyze (decompose) in the water solvent
used in dye application. Acidic or basic conditions are necessary for
successful and rapid reaction of the reactive dye with the fiber, so dye
appl ication is carried out at either sl ightly acid or basic pH (hydrogenion concentration). Procion dyes are the best known of the reactive dyes.
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