Sulfur dyes
Sulfur
dyes are non-ionic, possess sulfur bonds, are water-insoluble, produce
shades that are reasonably cheap and washable, and have moderate fastness
properties. The dyes are applied to the cellulosic in the reduced and dissolved
anionic state. These dyes are mainly used in the cellulosic fabric. It gives
different types of dark shades like black. Examples of sulfur dyes are
indophenol, sulfur black, sulfur blue dye, sulfur brilliant green, etc.
Description of Sulfur dyes
Sulfur
dyes made for cotton are the most widely used dyes in terms of volume. These
are inexpensive, usually have wash fastness, and are easy to apply. Sulfur dyes
are mainly black, brown, and dark blue. Red sulfur dyes are unknown, although
pink or light scarlet colors are available.
The sulfur dye is usually heated by sulfur or sodium sulfide together with specific
aromatic amines, amino phenols, and other organic compounds. During dyeing, the sulfur dye should be dissolved in sodium sulfide solution or alkaline
hydrosulfite solution to reduce its hidden color and then absorbed and oxidized
by fiber to show the color.
i.
Sulfur dyes are commonly used for black, blue, brown, khaki, and green.
ii.
Sulfur dyes are applied to cellulosic fibers and to cellulosic blends with
polyester, nylon, and acrylics.
iii.
Sulfur dyes can be applied with great results with little difficulty and
relatively low cost.
Sulfur
dyes are compounds of high molecular weight that are obtained from the reaction
of sulfur or sulfide with phenols and amines. There are plenty of colorants on
the market that contain sulfur but only those dyes that are soluble in water
after reacting with sodium sulfide in alkaline conditions are known as sulfur
dyes.
Sulfur
black dye is available in powder, granules, and liquid form and has a higher degree
of properties than other cotton colors on the market. Good color fastness
properties like lightfastness, wash fastness, and cost-effectiveness make
sulfur black an important class of dye. This dye can be applied by clothing,
fabric extraction, semi-continuous, or continuous dyeing methods.
Sulfur dyes manufacturing process (Navy Blue)
i.
The first step in this process is-
The
preparation of para-nitroso phenol is formed by the action of sodium
nitrite in the phenol in an acid solution at a temperature of around 0 °C.
These para-nitroso phenols are filtered, grated in an extractor, analyzed, and
stored in a cool place. It is quite flammable and combustible and must be used
with care to manage and preserve it.
ii.
The second step is-
Prepare the color base or indo-phenol by the concentration at low temperatures
in a solution of sulfuric acid, para-nitroso phenol, and ortho-toluidine. When
this extremely delicate reaction is complete, the mass is driven into a mixed solution of soda ash, and the acid is neutralized with the resulting
precipitation of indo-phenol that is filtered and analyzed but not dyed, as the color base is quite unstable and must be used fresh.
iii.
The third step is-
Prepare sodium polysulphide by heating the solution and some amount of sodium
sulfide together in sulfur. Indo-phenol is dissolved in sodium polysulphide,
the solution is brought to a certain boiling point by evaporation or reduction
and is run in a boiling state in a closed tank or kettle equipped with a reflux
condenser for a period of 12 to 100 hours. During the fusion cycle, substantial
evolution of hydrogen sulfide occurs. The strength, ratio of polysulphide from
sulfide to sulfur, temperature, and fusion reaction times are different to
create all the desired shades. Also, specific solvents and fusion auxiliaries
are sometimes employed to produce specific shade or solubility results. These
include assistant’s alcohol, glycerin, and their derivatives.
iv.
In the fourth step, is completed the fusion-
The
dissolution of the dyestuff from the mixture and the sulfide solution means
that the dyestuff continues to flow through the air using acid, acid
salts, or a solution of oxidation of sulfide.
v.
The fifth step is filtering-
The
precipitated dyestuff drying, grinding, aging, and standardization by mixing
different batches and diluting with salt, sodium sulfate, etc., and then
marketing.
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