Sodium Sulfate in The Printing and Dyeing Industry

Chemical Formula

Na2SO4

Molecular Weight

142.04214

Stability

Stable. Incompatible with strong acids, aluminium, magnesium, strong bases. Hygroscopic.

Application

The application of direct dyes as silk dyeing retarders to protein fibers is mainly seen in the dyeing of silk, and the resulting dyeing fastness is better than that of ordinary acid dyes.

Some direct dyes also have excellent discharge dyeability, so they are often used as discharge ground colors in silk fabric printing. Direct dyeing of silk with dyes often involves adding a small amount of sodium sulfate, but the role of sodium sulfate in the printing and dyeing industry here is different from that of cotton dyeing, and it only acts as a dyeing retarder.

Note: 1. When dyeing silk with direct dyes, the principle of the retarding effect that will occur after the addition of sodium sulfate is as follows: The direct dye R SO3Na is dissociated into sodium ions Na+ and the pigment anion R SO3- in water using the following formula: R SO3Na (mutual conversion arrow in parentheses) Na+R SO3 and sodium sulfate Na2SO4 are dissociated into sodium ions Na+ and sulfate ions SO4 in water using the following formula: Na2SO4 (mutual conversion arrow in parentheses) 2Na+RSO4: in the dyeing bath, The dye anion RSO3 can be directly dyed onto silk. When sodium sulfate is added, it dissociates and produces sodium ions, which affect the dissociation of the dye due to the increase of sodium ions.

In other words, due to the existence of an ionic equilibrium relationship and the influence of Na+, the dissociation of the dye is reduced, which plays a slow dyeing role in silk dyeing.