Mordant for Dyes - 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.
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.
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.
The three methods used for mordanting are -
Pre-mordanting (onchrome): The substrate is treated
with the mordant and then dyed.
Meta-mordanting (metachrome): The mordant is added
in the dye bath itself.
Post-mordanting (afterchrome): The dyed material is
treated with a mordant.
Mordants
are compounds that are used often in the production of various textile
products. The main purpose of a mordant is to interact with the fibers of a
given material and the dye solution. This interaction helps to ensure that the
dye sets properly, without splotching or running. Mordants are employed at
several different points in the production process, depending on the type of
material used and the desired effect that the manufacturer wishes to achieve.
There
are a number of different mordants that may be employed as part of the process
of dyeing and setting the color of a given fabric. If there is a desire to
achieve what is referred to as a gram stain, iodine is often used to create the
desired result. A number of metallic related compounds qualify for use as
mordants, including such salts of aluminium, copper, tin, and chromium. Sodium,
potassium and tannic acid are other agents that may be used as mordants.
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