The document discusses mordants and mordant dyes. It defines a mordant as a substance used to set dyes on fabrics by forming a coordination complex between the dye and mordant. Common mordants include tannic acid, alum, and various metal salts. Mordant dyes require a mordant to bond the dye to fibers. There are three mordanting methods: pre-mordanting, meta-mordanting, and post-mordanting. Chromium is often used as a mordant for wool, resulting in strong colorfastness. The mordant and dyeing process influence the hue and properties of mordant dyes

1. Presentation on: Mordant & Mordant dye
Prepared By:
Tanvir Ahammed Rana
Id. 2012000400038
19th Batch, Textile Department.
SouthEast University.

2. Mordant
A mordant is a substance used to set dyes on fabrics or
tissue sections by forming a coordination complex with the
dye which then attaches to the fabric or tissue. It may be
used for dyeing fabrics, or for intensifying stains in cell or
tissue preparations. The term mordant comes from the
present participle of French mordre, "to bite". In the past, it
was thought that a mordant helped the dye bite onto the fiber
so that it would hold fast during washing. A mordant is often
a polyvalent metal ion. The resulting coordination complex
of dye and ion is colloidal and can be either acidic or
alkaline.

3. Common dye Mordants
Mordants include tannic acid, alum, urine, chrome
alum, sodium chloride, and certain salts of
aluminum, chromium, copper, iron, iodine,
potassium, sodium, and tin.
Iodine is often referred to as a mordant in Gram
stains, but is in fact a trapping agent.

4. Dyeing methods
The three methods used for mordanting are:
i. Pre-mordanting (onchrome): The substrate is
treated with the mordant and then dyed.
ii. Meta-mordanting (metachrome): The mordant is
added in the dye bath itself.
iii. Post-mordanting (afterchrome): The dyed
material is treated with a mordant.

5. The type of mordant used changes the shade obtained
after dyeing and also affects the fastness property of the
dye. The application of mordant, either pre-mordant,
meta-mordant or post-mordant methods, is influenced
by:
i. The action of the mordant on the substrate: if the
mordant and dye methods are harsh (for example, an
acidic mordant with an acidic dye), pre-mordanting or
post-mordanting limits the potential for damage to the
substrate.
ii. The stability of the mordant or dye lake or both: the
formation of a stable dye lake means that the mordant
can be added in the dye without risk of losing the dye
properties (meta-mordanting).

6. Mordant dye
A dyestuff that requires the use of a mordant. There are very few
synthetic dyestuffs currently in use that require a separate mordant,
except for some dyes for wool, where mordant dyes are still quite
popular. Since chromium is almost exclusively used as the mordant on
wool, chrome dye has become essentially synonymous with mordant
dye. Many natural dyes require a mordant. The mordant used can
significantly influence the hue produced with a particular dyestuff.
These are special acid dyes in which certain metal atom can be
introduced during dyeing. These are water soluble dyes and affinity for
silk, wool and polyamides. Mordant dyes requires a mordant in their
application and these dyes upon combination with the mordant deposit
on the fiber in the form of insoluble color. Most commonly dyes have
hydroxyl or carboxyl groups and are negatively charged in nature.

7. Properties of Mordant dyes
1. These dyes are economical dyes and are generally used to
produce dark shades such as dark greens, dark blues and blacks.
2. These dyes have good leveling and color fastness properties.
3. The interaction between fiber and dye is established through
very strong ionic bonds, which are formed between the anionic
groups of the colorant and ammonium cations on the fiber.
Chromium or the metal ion acts as bridge between the dye and
fiber, which gives rise to a very strong linkage, resulting into
excellent fastness properties.
However there are disadvantages of the chrome dyes also such as
longer dyeing cycles, difficulties in shading, risk of chemical
damage to the fiber and the potential release of chromium in the
waste water.

8. Mechanism of dyeing
Since these are a special class of acid dyes , which are
soluble in water and applied to the fiber from an acidic bath.
When a solution of an acid mordant dye is mixed with a
solution of potassium dichromate in the presence of sulfuric
acid , chromium ion from dichromate forms a complex with
the dyes , this complex is insoluble in water ,and hence
precipitates on the fiber.
There are three different methods of application of chrome
dyes on the fiber:
1. Chrome – Mordant method
2. After chrome method
3. Meta chrome method

9. Application of Mordant dyes
1. Chrome-Mordant Process
In chrome mordant process, the fiber is first treated with
potassium dichromate in the neutral bath or in the presence of
either sulfuric or formic or oxalic acid. When sufficient amount
of chromium is taken up by fiber , it is taken out , squeezed and
entered in the dye bath containing acid mordant dye. The dye
form an insoluble complex with chrome present on the fiber .
2. After Chrome Method
In this method the substrate is first treated with the dye , the dye
is exhausted by the addition of an acid , and after complete
exhaustion the material is taken out squeezed and then run in a
solution containing potassium dichromate and an acid. Metal dye
complex is formed on the fiber , which is insoluble.

10. 3. Meta Chrome Process
This is a single bath process , in which the material is treated
with in a bath containing acid mordant dye , potassium
dichromate and ammonium Sulphate.
The dye along with potassium dichromate and ammonium
Sulphate got absorbed by the fiber and evenly distributed
but no complex is formed because the pH is not suitable for
the chemical reaction to take place.
In the second step of the meta chrome process, when the dye
bath is heated , ammonium sulphate is converts into
ammonia and Sulphuric acid , which makes the bath
strongly acidic and potassium dichromate in the presence of
strong acid now react with the dye molecule forming an
insoluble complex on the fiber.

11. A dyeing cycle for dyeing of wool with chrome dyes
Dyeing cycle of Wool
Here,
A= Glauber salt+Acetic acid+Leveling agent
B= Dye
C= Potassium Dichromate
D=Acid