Metal complex dye introduction
Pre-metallised acid dyes are another name for metal complex dyes. this is often because of the dye molecule incorporating a metal during manufacture, typically chromium.
The presence of metal within the dye molecule makes it easier to use the dye on the fibre, which aids a rather quick dying process.
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| Metal complex dyed fabric |
Properties of metal complex Dyes :
(1) Metal complex dyes are rated as having a light fastness of around 5.
(2) a washing fastness of 4 to 5. A large number of van der Waals forces between the relatively large dye molecules and the macromolecules of the fibre makes it challenging for the dye fibre bonds, such as ionic bonds, hydrogen bonds, and coordinate bonds also play a significant role in this regard.
(3) The main component of these dyes, chromium, only offers a small selection of rather dull colours.
Classification of Metal complex Dyes :
The dyes can be classified in two groups in two groups depending on their constituents - All dyes are held in the fibre by coordinate & electrovalent bonds.
(A) 1:1 Metal Complex Dyes
(B) 1:2 Metal Complex Dyes
These dyes are further classified into two groups -
(a) Unsulphonated 1:2 Metal Complex Dyes (conventional)
(b) Sulphonated 1:2 Metal Complex Dyes
Characteristics of metal complex Dyes :
(A) 1:1 Metal Complex Dyes :
These dyes are often said to dyestuff pre-metallised dyes since they combine one molecule of an acid dye with one metal atom, typically chromium.
The metal in 1:1 Complex dyes are made of azo dyes that have two hydroxyl groups within the two ortho positions relative to the chemical group and have -SO3H groups present within the molecule (making it water soluble), such as o, o' dihydroxy azo compounds, o-amino-o' -hydroxyazo compounds, and derivatives of 2-hydroxybenzoic acid. Its figure is provided below.
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| Metal Complex Dyes |
Chromium can form stable Complexes with certain azo dyes that have hydroxyl groups in each of the ortho positions that are connected to the group.
One molecule of the dye dihydroxy azo will be accustomed to create a less complicated complex since the chromium atom's stable outer shell has 12 electrons, or a coordination number of 6. the 2 initial -OH groups undergo salt
The formation, converting Cr3+ to Cr+. Two electrons are donated by the loan pair of nitrogen atoms from the azo links, and also the remaining six electrons come from the loan pairs of oxygen atoms from three different water molecules. We discuss these donor atoms or groups as ligands.
(B) 1:2 Metal complex Dyes :
These colours, which contain one metal complex, are often noted as neutral dyeing pre-metallized colours.
Chromium, a metal atom, forms the centre of an anion in dyes.
This results from the initial Cr3+ being changed to Cr by the four hydroxyl or other Acidic groups.
The twelve election systems are completed by the 2 azo groups functioning as ligands, as indicated below:
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| Metal Complex Dyes |
Mechanism of dyeing protein fibre with complex Dyes :
The following figure shows the several types of bonds that connect protein fibres to metal complex dyes.
The presence of hydrogen bonds, coordination bonds, and ionic or salt couplings should be noted.
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| Different types of bonds between a metal Complex Dye and protein fibres |
References
Chakraborty, J. N. (2011). Metal-complex dyes. In Handbook of Textile and Industrial Dyeing (pp. 446–465). Elsevier.
Parkes, D. T. (n.d.). Ethical Clothing, Heavy Metals Content, heavy metals in Reactive Dye, Fibre2fashion.com. Fibre2fashion.com. from https://www.fibre2fashion.com/industry-article/3539/metals-in-reactive-dyes-for-cellulose
(N.d.). Textilelearner.net. from https://textilelearner.net/metal-complex-dyes/
Link for the certain dye explanation -
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Part 1 Introduction of metal complex dyePart 2 Application of Metal Complex Dyes
Writer - Rushikesh Patil (Textile Engineer)
