The best guide to the dyeing performance of a reactive dye can be obtained from two sources of information: the SERF profile and migration properties under application conditions. The SERF profile is constructed by the determination of substantively factor, exhaustion factor, fixation percentage and rate of fixation.
The performance of a reactive dye can also be defined by the Reactive Dye Compatibility Matrix (RCM). The critical measures of performance are the substantivity equilibrium (S), the migration index (Ml), the level dyeing factor (LDF) and an index of the reactivity of the dye (T50).
Evaluation of these four measures of performance provides a measure of the compatibility of the dye to provide right first-time production. Right first-time production is maximized if these fundamental measures of performance within the RCM are set at the following illustrated values:
Some of the important characteristics of reactive dyeing, namely exhaustion, migration, levelness, fixation and colour yield, washing-off, dye-fibre bond stability, and fastness properties are discussed as under:
There are two types of exhaustion that relate to the application of reactive dyes: primary exhaustion and secondary exhaustion. Primary exhaustion occurs before the addition of the alkali, while secondary exhaustion takes place after the addition of the alkali. Both the rate of exhaustion and the extent or degrees of exhaustion are important.
The rate of exhaustion can be increased by selecting dyes of high substantively, increasing the temperature and increasing the electrolyte concentration.
The degree of exhaustion can be increased by selecting dyes of high substantivity, lowering the temperature and increasing the electrolyte concentration.
The intrinsic properties of a reactive dye that affect migration are substantivity, molecular structure, physical chemistry and stereo chemistry. The higher the dye substantivity, the lower is the migration. The external factors that affect migration are: concentration of the dye, temperature, time, liquor ratio, liquor circulation and the form of textile material.