2. INTRODUCTION
A dye is a colored substance that has an affinity to
the substrate.
Dyes are soluble in water.
Dyes are colored, because they absorb only some
wavelength of visible light.
It may requires a mordant to improve the fastness
of the dye on the fiber.
Mordant-Substance used to set dyes on fabrics by
forming a coordination complex with the dye.
3. SYNTHETIC VS NATURAL DYES
Most dyes used are synthetic, i.e., are made from
petrochemicals.
Majority of the natural dyes are derived from plant
sources such as roots, berries, bark, leaves etc..
4. TYPES OF DYES
Dyes are classified according to their solubility and
chemical properties as:
o Reactive dyes
o Disperse dyes
o Azo dyes
o Sulfur dye
o Direct dye
o Acid dye
o Basic dye
o Mordant dye
o Vat dye
5. REACTIVE DYE
Reactive dyes utilize a chromophore attached to a
substituent that is capable of reacting directly with
fiber.
The covalent bond between reactive dye and
natural fiber makes it the most permanent among
all the dyes.
Most of them like Procion MX, Cibacron F can be
applied at room temperature.
Reactive dyes are the best option for dyeing
cellulose fibers.
6. DISPERSE DYES
Disperse dyes are water insoluble and were
developed for dyeing cellulose acetate.
The dyes are finely ground in the presence of a
dispersing agent and sold as paste or powder.
A dyeing temperature of 130°C and a pressurized
dyebath is required.
The very fine particle size gives a large surface
area that helps in dissolution to allow uptake by
fibers.
7. The dyeing rate can be significantly influenced by the
choice of dispersing agent used in grinding.
Disperse dyes are widely used to dye polyester, nylon,
acrylic fibers.
A disperse dye molecule is based on an azobenzene or
anthraquinone molecule with nitro, amine, etc. groups
attached.
8. AZO DYES
Azo dyes are organic compounds bearing the R-
N=N-R’ functional group.
They are mainly salts, the colored component being
anionic usually.
The dyeing of leather and wool is an ion exchange
reaction, the proteins being cationic and is through
electrostatic forces.
They have excellent coloring properties and good
light fastness.
e.g.: Direct blue 1, Basic red 18
9. SULFUR DYES
Sulfur dyes are insoluble, inexpensive and are
extensively used in dyeing cotton.
They have good wash-fastness and are easy to
apply.
Application : reducing agent, alkali pH, elevated
temperature around 80°C→dye particle disintegrate
and become water soluble→absorbed by
fiber→oxidized to regenerate the dye, which is
insoluble.
They are mainly black, brown and dark blue.
e.g.: sulfur black 1
10. DIRECT DYES
Direct or substantive dyes adheres to its substrate
by non-ionic forces.
These dyes works best with cotton and other
cellulosic fibers.
It almost replaced the mordant dyes.
They are set in a slightly basic or neutral
environment near its boiling point.
It forms aggregate within the interstices of the
fibers.
e.g: Direct blue 14, Direct blue 15
11. ACID DYES
Acid dyes are water-soluble anionic dyes applied to fibers
such as silk,wool,..
Salt formation is attained between anionic groups in the
die and cationic groups in the fiber.
Most of the synthetic food colours fall in this type.
e.g.: Acid red 88
12. BASIC DYES
Basic dyes are water soluble cationic dyes, mainly
applied to acrylic fibers.
Acetic acid is usually used to the dye bath to help
the uptake of the dye onto the fiber.
Basic dyes are used in the coloration of paper.
e.g.: crystal violet, safranin,..
13. MORDANT DYES
Dyes which have no affinity toward textile fibers are
attached with fibers with the help of mordants.
The mordant is chosen carefully as it affect the final color
significantly.
The most important dyes are the synthetic dyes or
chrome dyes, used for wools.These comprise of about
30% of the dyes used for wool.
14. VAT DYES
Vat dyes are insoluble in water and incapable of
dyeing fibers directly.
So it is made water soluble, but becomes colorless
and is referred to as Leuco dyes and has an affinity
to fiber in the dye bath.
When the fiber is taken out from the dye bath,
colour is imparted to it as a result of oxidation and
the dye become insoluble again.
e.g.: The colour of denim is due to indigo, the
original vat dye.
