Sulfur dye
Encyclopedia
Sulfur dyes are the most commonly used dye
s manufactured for cotton
in terms of volume. They are cheap, generally have good wash-fastness and are easy to apply. The dyes are absorbed by cotton from a bath containing sodium sulfide
or sodium hydrosulfite and are made insoluble within the fiber by oxidation. During this process these dyes form complex larger molecule
s which is the basis of their good wash-fastness.
These dyes have good all round fastness except to chlorine. Due to the highly polluting nature of the dye-bath effluent
, slowly sulfur dyes are being phased out. Sulfur dyes are primarily used for dark colors such as blacks, browns, and dark blues. The deep indigo blues of denim
blue jeans
are a product of sulfur dyes.
Recent advances in dyeing technologies have allowed the substitution of toxic sulfide reducing agents. Glucose
is now used and both low sulfide and zero sulfide products are available.
Future developments in the field of reducing dye levels by means of electro-chemical processes are promising. This work is just in the research stage but is expected to come to industry very soon. This may eradicate the problems of polluting sulfides.
Sulfur dyes are water insoluble. They have to be treated with a reducing agent and an alkali at temperature of around 80 degrees Celsius where the dye breaks into small particles which then becomes water soluble and hence can be absorbed by the fabric.
Heating and adding a substance like common salt facilitates the absorption. After this the fabric is removed from the dye solution and then taken for oxidation. During the oxidation step the small particles of dye once more form the parent dye which is insoluble in water.
This oxidation can be done in air or by using oxidizing agents like hydrogen peroxide
or sodium bromate
in a mildly acidic solution. Now as the dye has become water insoluble in fiber so it will not bleed in water when washed and will not stain other clothes. However the dye may have poor fastness to rubbing, that is the dye from the fiber may come out gradually if the fabric is rubbed against. Also the fastness to hypochlorite bleach is poor because hypochlorite breaks the color imparting group in the dye and hence the colored part becomes colorless.
Sulfur dyes are very inexpensive and very important to the dyeing industry. Out of all the sulfur dyes perhaps 50% of production is of the sulfur black color as black is the most popular fabric color.
Sulfur dyes do not have any pure red color in its shade range. A pink or lighter Scarlet
color is available.
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
s manufactured for cotton
Cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. The botanical purpose of cotton fiber is to aid in seed dispersal....
in terms of volume. They are cheap, generally have good wash-fastness and are easy to apply. The dyes are absorbed by cotton from a bath containing sodium sulfide
Sodium sulfide
Sodium sulfide is the name used to refer to the chemical compound Na2S, but more commonly it refers to the hydrate Na2S·9H2O. Both are colorless water-soluble salts that give strongly alkaline solutions...
or sodium hydrosulfite and are made insoluble within the fiber by oxidation. During this process these dyes form complex larger molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s which is the basis of their good wash-fastness.
These dyes have good all round fastness except to chlorine. Due to the highly polluting nature of the dye-bath effluent
Effluent
Effluent is an outflowing of water or gas from a natural body of water, or from a human-made structure.Effluent is defined by the United States Environmental Protection Agency as “wastewater - treated or untreated - that flows out of a treatment plant, sewer, or industrial outfall. Generally refers...
, slowly sulfur dyes are being phased out. Sulfur dyes are primarily used for dark colors such as blacks, browns, and dark blues. The deep indigo blues of denim
Denim
Denim is a rugged cotton twill textile, in which the weft passes under two or more warp threads. This produces the familiar diagonal ribbing identifiable on the reverse of the fabric, which distinguishes denim from cotton duck. Denim has been in American usage since the late 18th century...
blue jeans
Blue Jeans
"Blue Jeans" is a sentimental popular song written by Harry D. Kerr and Lou Traveller in 1920. In the song, the singer is reminiscing about a long-ago young love that happened somewhere in the "hills of the old Cumberland." The chorus echoes the singer's longing:* The Parlor Songs Collection.* by...
are a product of sulfur dyes.
Recent advances in dyeing technologies have allowed the substitution of toxic sulfide reducing agents. Glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
is now used and both low sulfide and zero sulfide products are available.
Future developments in the field of reducing dye levels by means of electro-chemical processes are promising. This work is just in the research stage but is expected to come to industry very soon. This may eradicate the problems of polluting sulfides.
Sulfur dyes are water insoluble. They have to be treated with a reducing agent and an alkali at temperature of around 80 degrees Celsius where the dye breaks into small particles which then becomes water soluble and hence can be absorbed by the fabric.
Heating and adding a substance like common salt facilitates the absorption. After this the fabric is removed from the dye solution and then taken for oxidation. During the oxidation step the small particles of dye once more form the parent dye which is insoluble in water.
This oxidation can be done in air or by using oxidizing agents like hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
or sodium bromate
Sodium bromate
Sodium bromate, the inorganic compound with the chemical formula of NaBrO3, is the sodium salt of bromic acid. It is a strong oxidant, mainly used in continuous or batch dyeing processes involving sulfur or vat dyes and as a hair-permagent, chemical agent, or gold solvent in gold mines when used...
in a mildly acidic solution. Now as the dye has become water insoluble in fiber so it will not bleed in water when washed and will not stain other clothes. However the dye may have poor fastness to rubbing, that is the dye from the fiber may come out gradually if the fabric is rubbed against. Also the fastness to hypochlorite bleach is poor because hypochlorite breaks the color imparting group in the dye and hence the colored part becomes colorless.
Sulfur dyes are very inexpensive and very important to the dyeing industry. Out of all the sulfur dyes perhaps 50% of production is of the sulfur black color as black is the most popular fabric color.
Sulfur dyes do not have any pure red color in its shade range. A pink or lighter Scarlet
Scarlet (color)
Scarlet is a bright red color with a hue that is somewhat toward the orange. It is redder than vermilion. It is a pure chroma on the color wheel one-fourth of the way between red and orange. Scarlet is sometimes used as the color of flame...
color is available.