Sulfur dyes | Properties | Limitation of the Sulfur dyeing process

 

Sulfur dyes

Sulfur dyes are called sulfur dyes because it contains disulfide linkage in their chemical structure and the dyeing process are carried out in alkaline condition. These dyes have the best light fastness and low price among the dyes applied to natural fibers.

Properties of Sulfur dyes

i. Sulfur dyes are highly water-insoluble, and some are partially soluble.

ii. Excellent dyeing properties and economical dyeing.

iii. Colourfastness properties are good overall such as perspiration fastness, wash fastness, lightfastness, etc.

iv. These dyes are used to dye only for dull shades

v. Its shade range is limited.

vi. There is no red dye found in sulfur dyes.

vii. It can be applied by the semi-continuous, exhaust, continuous dyeing method.

viii. These are available in liquid, granule, and powder forms.

ix. The main black dye used worldwide for cellulose dyeing is sulfur black.

x. The conventional dyeing process is not environmentally friendly due to the contamination problem of sodium sulfide.

xi. These are suitable for heavy & durable shades

xii. It is available in powder and soluble form

xiii. These are exclusively amorphous, some of them also show crystallinity.

xiv. Not suitable for chlorine bleach.

xv. It is applied in alkaline conditions.

Dyeing procedure

First, the dye solution is taken in the dye bath and the fabric is immersed in the product. Then it is heated for 10-15 minutes. Half of the total NaCl solution is then added and the temperature is increased to boil and then the remaining amount of NaCl is added. At this temperature, the dyeing continues for about 30 minutes. The steaming is then stopped and the application is continued in the cool for another half hour. This vapor helps to disperse the fix before fixing the color of the fix. Colored dye liquor should be washed off the surface of the fabric immediately.

Dyeing Recipe-

Sulpher Dye - 10% (On the weight of the fabric)

Na₂S (Reducing Agent) - 1.5 % (on the weight of the Dye)

Salt - 8 gm. /liter (NaCl)

Soda Ash (NaCO₃) - 7 gm. /liter

Temperature - 100

Time - 90 minutes

Material: Liquor - 1:20  

Limitations of the Sulfur dyeing process

i. In the application of sulfur dyes, dye baths should not contain Ca-salts. If they are present in the form of inviolable compounds with sulfur dyes which spread easily in closed machines and form sludge while limiting the circulation of dye alcohol.

ii. Should be dissolved with colored soda.

iii. Great care should be taken during the reduction process as the transmission of dye per excess reduced fiber should be reduced. As a result, dull shades will appear and large amounts of dyestuff will be lost.

iv. The fabric must not be exposed to air during dyeing to prevent precipitation & oxidation. This will cause uneven color.

v. In the case of jigger dyeing machines, large amounts of N₂S or NaOH and salt should be added to prevent uneven dyeing of the fabric.

vi. Dye liquor should not be too hot to prevent bronzes.

vii. Colored products should be treated with a solution of K₂Cr₂O₇ after washing with Sulfur Black. This will prevent sulfur from black tendering.