DYES
AND ITS
CLASSIFICATION
Dr Bushra Nisar
Introduction
• Dyes are colored organic compounds that are used to
impart color to various substrates, including paper,
leather, fur, hair, drugs, cosmetics, waxes, greases,
plastics and textile materials.
• A Dye is a colored compound, normally used in solution,
which is capable of being fixed to a fabric.
• To be of use, dyes must possess the following four properties:
• 1. Colour
• 2. Solubility in water
• 3. Ability to be absorbed and retained by fibre (substantivity)
or to be chemically combined with it (reactivity).
• 4. Ability to withstand washing, dry cleaning and exposure
to light.
• The dye has a colour due to the presence of chromophore and
its fixed property to the acid or basic groups such as OH,SO3H,
NH2, NR2, etc.
• The polar auxochrome makes the dye water-soluble and binds
the dye to the fabric by interaction with the oppositely
charged groups of fabric structure.
Classification
• There are several ways for classification of dyes.
• Each class of dye has a very unique chemistry, structure
and particular way of bonding. While some dyes can
react chemically with the substrates forming strong
bonds in the process, others can be held by physical
forces. Some of the prominent ways of classification are:
• Classification based on the source of materials
• classification of the Dyes- Based on the nature of their
respective chromophores.
• Classification by methods of application.
Classification based on the
source of materials
• A very common classification of the dyestuff is based on the
source from which it is made. Accordingly the classification
could be:
• Natural Dyes
• Synthetic Dyes
Natural Dye
• Natural dyes are dyes or
colorants derived from plants,
invertebrates, or minerals.
• The majority of natural dyes are
vegetable dyes from plant
sources. E.g. roots, berries, bark,
leaves, and wood.
• Other organic sources include
fungi and lichens.
Synthetic Dyes
• Almost all the colors that you see today are Synthetic dyes.
Synthetic dyes are used everywhere in everything from
clothes to paper, from food to wood. This is because they are
cheaper to produce, brighter, more color-fast, and easy to
apply to fabric.
• E.g. Acid Dyes, Azo Dyes, Basic Dyes, Mordant Dyes, etc
Azo dye testing
Classification based on the
Chromophore present
• Dyes may be classified according to the type of chromophores
present in their structures.
1. Nitro and Nitroso Dyes
2. Azo Dyes
3. Triarylmethane Dyes
4. Anthraquinone Dyes
5. Indigo dyes
Nitro and Nitroso Dyes
• These dyes contain nitro or nitroso groups as the
chromophores and –OH as auxochrome.
• A few examples are:
Mordant green 4
Naphthol yellow S
Azo Dyes
• Azo dye is a large class of synthetic organic dyes that contain
nitrogen as the azo group −N=N− as primary chromophore
their molecular structures. More than half the commercial
dyes belong to this class. These dyes are highly coloured and
are prepared by diazotizing an aromatic amine and coupling
with suitable aromatic compound.
Para Red
Methyl Orange
Bismarck Brown
Congo Red
Azo dyes account for approximately 60-70% of all dyes used in
food and textile manufacture. In theory, azo dyes can supply a
complete rainbow of colours, but yellow/red dyes are more
common as blue/brown dyes.
Triarylmethane Dyes
• Triarylmethane dyes are synthetic organic
compounds containing triphenylmethane backbones. These
compounds are intensely colored and are produced
industrially.
• In triarymethane dyes a central carbon is bonded to three
aromatic rings, one is in the quinoid form. Auxochromes
areNH2, NR2 and OH.
Malachite Green
Phenolphthalein
• Malachite Green is used as a direct dye for wool and silk.
• Phenolphtalein is used as acid base indicator
Anthraquinone Dyes
• Anthraquinone dye, any of a group of organic dyes having
molecular structures based upon that of anthraquinone.
Alizarin
• Alizarin is the main ingredient for the manufacture of the
madder lake pigments known to painters as Rose
madder and Alizarin crimson.
• Alizarin is also used commercially as a red textile dye.
Indigo Dyes
• Indigo dye is an organic compound with a distinctive blue color
Historically, indigo was a natural dye extracted from plants. But
today nearly all indigo dye is produced synthetically.
• It contains carbonyl chromophore.
Indigo
• The primary use for indigo is as a dye for cotton yarn, which is
mainly for the production of denim cloth for blue jeans
• Small amounts are used for dyeing wool and silk.
Classification by methods of
application
• Method used for application depends on the nature of
both….Dye and Fabric.
• They are classified on the basis of technique employed for
their application.
Direct Dyes
• Carried out in a neutral or slightly alkaline dye solution.
• It contains acidic or basic auxochromes.
• Polar in nature.
• Used on cotton, paper, leather, wool, silk and nylon.
Martius yellow
Acidic Auxochrome
Fiber-NH2 + HO-Dye Fiber-NH3+……….-O-Dye
Vat dyes
• Insoluble in water.
• Soluble in sodium hydrosulfide (Na-S-H).
Great affinity for cotton and fibers
• Indigo is a good example of Vat dyes.
• -OH binds the dye fast to cellulose fiber that contains
ethereal oxygen and –OH group.
Mordant dyes
• No natural affinity………used with the help of salts.
• Mordants – Al or Cr oxides salts.
• Fiber is first treated with mordant & then with dye solution.
(insoluble coordination complex between fiber and dye)
• Most suitable for wool and nylon.
Azoic dyes
Azoic dyes
• Water insoluble.
• two components react to produce the dye-usually Phenol or
Napththol or Aniline.
• This method of dyeing cotton is declining in importance due to
the toxic nature of the chemicals used.
aniline Phenyl azo 2-napthol
Orange-red dye
Disperse dye
• Insoluble in water……..but colloidal form can be formed.
• These colloidal fine particles are absorbed into the crystal
structure of fabric.
• Used to dye nylon,orlon,polyesters and cellulose acetate.
