http://ntupk.academia.edu/AAzeem/ Function of Salt in the Textile Wet Processing Why Salt is Used in Dyeing? The textile substrate and dye molecule, not necessarily should have of homogeneous characteristics to combine with each other. In such case, we require some catalyst to facilitate dyeing action on fabric. Salt plays this crucial role of catalyst. Salt has an extremely high affinity for water. Broadly speaking, Salt is necessary in three ways, firstly, to drive dye into textile during the dyeing process in textile. Secondly, use of salt leads to maximum exhaustion of dye molecules during dyeing process in textiles. Thirdly it is used as an electrolyte for migration, adsorption and fixation of the dyestuff to the cellulose material. Salts plays important role in reactive dyeing by improving the affinity of the dyestuff towards the fibre and acceleration of the dyestuff's association and lowering its solubility. Normally, Glauber's salt or common salt/ vacuum salt is used for this purpose. The presence of chlorine ion in the common salt may cause corrosion of the equipment. Hence, Glauber's salt is always preferred over common salt. Glauber's salt is a common name for sodium sulfate decahydrate, Na2SO4.10H2O; it occurs as white or colorless monoclinic crystals. Upon exposure to fairly dry air it effloresces, forming powdery anhydrous sodium sulfate. Johann Glauber’s was the first to produce the salt (from Hungarian spring waters). Glauber's salt is water soluble, has a salty, bitter taste, and is sometimes used in medicine as a mild laxative; it is also widely used in dyeing. Vacuum salt is the common name of sodium chloride (NaCl). Role of Inorganic Salt in Reactive Dyeing: Inorganic salts have two main functions in exhaustion dyeing with reactive dyestuffs: 1. Improving the affinity of the dyestuff 2. Acceleration of the dyestuff's association and lowering of its solubility. Generally reactive dyes contains sulphonic acid (- SO3H) group which is insoluble in water. During the manufacturing of the reactive dyes these sulphonic acid groups are converted into the sodium salt of sulphonic acid (- SO3Na) which is soluble in water. Reactive dye – SO3H + Na⁺ → Reactive dye SO3Na Generally when the reactive dye goes in the water, it is solublised giving dye anions and sodium cations Reactive dye-SO3Na + Water → Reactive dye – SO3⁻ + Na +