Introduction of mordant dyes
- The Latin word "model," which means "to bite" or "to take hold of," is the root of the English word "mordant."
- An organic or inorganic material called a mordant is used to bind a mordant dye to a textile fibre. Because of how frequently chromium is employed, mordants are also referred to as chrome dyes.
- Natural protein fibres, especially wool, are the ones that mordant dyes can colour the most easily. Additionally, mordant dyes have been used to colour nylon and modacrylic, two synthetic fibres.
Inorganic mordants | Organic mordants |
(1) Most commonly used mordant | (1) It is used to a much less extent |
Properties of Mordant Dyes:
- The lightfastness rating of mordant dyes is usually about 5.
- The presence of chromium within the dye molecule contributes to the excellent light fastness of mordant-dyed textile material.
- The presence of chromium also adds to the steadiness of the chromophores and leads to added resistance to the ultraviolet component of sunlight.
- The washing fastness rating of mordant dyes is mostly about 4-5.
- The excellent washing fastness of textile material dyed with mordant dyes is because of the big size of the dye molecules or 'lakes' that are formed within the polymer system of the fibre.
- These molecules, in additionally to being large and difficult to get rid of, are held within the macromolecular system of the fibre using hydrogen bonds and van der Waals' forces.
- The range of colours within the mordant dye class is restricted and available people also are relatively dull in appearance.
- The presence of chromium is assumed to be chargeable for the limited colour range and therefore the dullness of shade.
Classification of Mordant Dyes:
(A) Azoic.(B) Anthraquinone
(C) Triphenylmethane
Mechanism of the Dye chromium lake formation:
Typically, the mordant dyes can create "lakes" with metal hydroxides or oxides. When textile fibres create lakes, they exhibit excellent fastness in future wet treatments. Good mordants include aluminium, chromium, copper, iron, and zinc salts that produce poorly soluble hydroxides.
However, as chromium salts are the sole ones that matter within the process of dying wool, the dyes used as a mordant for wool have also been noted as chrome dyes.
If a metal salt is cost-effective, it is used as a mordant. Additionally, it should be able to create coloured lakes that are bright and quick to light, acids, and alkalis inside the molecular structure of wool when heated, forming a compound with the fibre. In the illustration below, the chromium cation encompasses a valency of 6, meaning its six bonds.
The six lines pointing in the chromium cation's direction represent these bonds. Three of the six bonds are connected to the anion of the mordant dye, while the opposite three are connected to water molecules. The three water molecules may only be there as a short-lived measure
before being gradually replaced by another anion of a mordant colour. Thus, a "lake" or dye-chromium complex is created when two mordant dye molecules combine with the chromium cation. Mordant dyes have excellent washing fastness due to the creation of those comparatively massive complexes.
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| Formation of a mordant dye Complex |
The dye-chromium lake formation requires,
(i) The presence of a gaggle necessary for the synthesis of the metallic salt, often a hydroxyl (although it'd alternatively be nitrous) group.
(ii) The ketonic (-C=O), carboxylic (-COOH), azoic (-N-N), and other groups of the dye contain unsaturated atoms, like oxygen or nitrogen, which can make covalent bonds.
These atoms, which must be within the ortho position in relevance to the group that constitutes the salt, act as electron donors for the metallic atom by providing it with 6 electrons from the dye molecules, saturating its "coordination number," which within the instance of Cr is 6.
Because the dyes diffuse before the complex forms, when their size is significantly smaller and they are consequently substantially more mobile, chrome dyes have good fastness. As a result, they will reach areas of the fibre that the metal-complex dye of greater dimensions wouldn't be able to reach.
The considerably bigger molecule that results from the creation of the dye combination inside the fibre structure is nearly unable to exit the fibre. This explains the mordant dyes' high we: fastness.
Questions -
- What are the mordant dyes?
- What are the properties of mordant dyes?
References
How to mordant. (2017, February 21). Botanical Colors. https://botanicalcolors.com/how-to-mordant/
Kennedy, L. (2020, October 30). Mordants for natural dyes - what you need to know. Little Yellow Wheelbarrow. https://www.littleyellowwheelbarrow.com/mordants-for-natural-dyes/
Mordants and fixatives - natural dyeing. (2012, September 3). All Natural Dyeing. https://allnaturaldyeing.com/mordants-fixatives/
The MAIWA BLOG: Natural dyes - mordants part 1. (n.d.). The MAIWA BLOG. from https://maiwahandprints.blogspot.com/2013/01/natural-dyes-mordants-part-1.html
Victoria. (2020, November 18). The importance of using a mordant in natural dyeing. La Creative Mama. https://lacreativemama.com/mordant-natural-dyeing/
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