Daffodil International University
Science & Information Technology => Science Discussion Forum => Topic started by: naser.te on March 08, 2015, 12:37:06 PM
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Dyeing Mechanism of Reactive dye
Exhaustion phase
During this stage of dyeing, some reactive dye will be absorbed by the fibers, the amount depending upon its substantivity. This dye is capable of migration to promote level dyeing. Salt should be present initially or be added gradually to the dye bath during this phase to promote exhaustion. The temperature of the dye bath may also be gradually increased for penetration of dye into the fibers and to assist migration.
Fixation phase
After the initial exhaustion phase, the pH of the dye bath is increased by gradual addition of the appropriate type and amount of alkali. This causes the reaction of dyes with fiber. The fixation process then results in additional dye absorption, to re-establish the dyeing equilibrium. Dye absorption from solution and reaction with the fiber then in progress.
Post-dyeing washing
The rinsed dyeing contains dye bonded to the cellulose, absorbed but un-reacted dye, as well as hydrolyzed dye. There will also be residual alkali and salt. The latter are relatively easy to remove by successive rinsing in cold and then warm water. As much unfixed dye as possible must be washed out of the dyeing.
For details, see http://textilelearner.blogspot.com/2012/01/dyeing-mechanism-of-reactive-dye.html