Sunday, 22 December 2013

Mordant for Dyes

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.

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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