Introduction of direct dyes
Because of their excellent substantivity for cellulosic textile materials like cotton and viscose, direct dyes also are remarked as substantive dyes.
This class of dyes gets its name from the very fact that they need an instantaneous affinity for cellulosic fibre when used from a solution.
Chemically speaking, direct dyes are sodium salts of aromatic sulphonic acids, and therefore the majority of them have a group as their primary chromophore.
Direct dyes are sold by different producers under various trade names; some examples are given below.
Manufacturer | Trade name |
Indokem | Incomine |
Hindustan Ciba Geigy | Chlorantine,solophenyl |
Clariant | Solar |
Atul products | Atual Direct |
ICI | Chlorazol |
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| Direct dye |
(i) A prohibition on the utilisation of several azo dyes has been in situ in Germany since 1996, though. Since comparable laws are in situ in other European nations, the utilization of direct dyes is now severely constrained.
This is often so because many direct dyes are supported by dangerous amines like benzidine and other things.
Therefore, it's imperative to work out if direct dyes are environmentally beneficial before utilising them in the routine mass dyeing of textiles.
(ii) Official listings of the direct dyes on the red list are available to assist with this. Note the -N=N- (azo) and -SO3Na groups within the structure of an on-the-spot dye, which is illustrated below.
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| Structure of direct dyes |
(iii) An alkaline or neutral dye bath is employed to use a sort of dyestuff referred to as dyestuff onto the substrate.
(iv) direct dyes are among the only affordable forms of dyes accustomed to colour cotton and other cellulosic textiles.
(v) They are often used on rayon, silk, and wool and produce good shades without the necessity for mordanting on cotton and linen.
Direct dyes produce vibrant colours but have low wash fastness. The term "after-treated direct colours" refers to dyes that have undergone various treatments to extend their wash fastness.
(vi) Direct Dyes are molecules that bind to the molecules of the material by themselves, without the help of additional chemicals.
(vii) Normally, dye is applied using an aqueous dyebath with an electrolyte, like binary compound (NaCl) or sodium sulphate (Na2SO4).
Properties of Direct Dyes -
(1) Direct dyes are soluble in water.
(2) It has an affinity for protein and cellulose fibres, particularly wool.
(3) Chemically, the dyes are represented as sodium salts of acid (DSO3Na).
(4) The dye molecules dissociate into ions (DSO3- and Na+) once they are dissolved in water.
Textiles absorb coloured anions from the dye solution after they are dyed.
This was followed by the molecules diffusing into the fibre, where they were subsequently held or attached by physical forces.
(5) due to their solubility in water, the bonds between the dyes weaken and make it easier for them to be removed after washing, which is noted as having low wash fastness qualities.
(6) Light fastness properties of Direct Dyes are moderate.
(7) The fastness properties of these dyes can be improved slightly using certain treatments.
Classification of Direct Dyes -
The direct dyes classification is based on the effect of electrolyte and temperature-
(B) Self-Controllable dyes or class B
(C) Temperature-controllable dyes or Class C
(A) Self-levelling dyes or class A | (B) Self Controllable dyes or Class B | (C) Temperature-controllable dyes or Class C |
(1) During using these dyes, the resultant dyeing may be uneven in the initial stages but they get levelled on prolonged dyeing because of migration properties. | (1) These dyes do not migrate well and require salt addition for increased exhaustion If uneven dyeing takes place initially, it is very difficult to correct the dyeing. | (1) Similar to B, the levelling properties of these dyes are poor. They are also sensitive to salt and their exhaustion cannot be controlled with salt alone. |
(2) These dyes do not require salt for exhaustion. | (2) It required salt to Increase exhaustion. | (2) These dyes required their exhaustion to be controlled by a controlled rise in dye bath temperature. |
(3) Typical examples of these groups are C.I. Direct Yellow 50, C.I. Direct Red 31 and C.I. Direct Blue 67 and maximum exhaustion are reached at 60–80°C. | (3) The standard dyes of this group are C.I. Direct Red 26, C.I. Direct Blue 8 and C.I. Direct Violet 1. Maximum exhaustion is obtained at 80–100°C in presence of 5 g/l salts and when dyeing is carried without salt, the exhaustion is markedly inferior. |
When more than one dyestuff is required to match a given shade, dyes belonging to the same class should be preferred.
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| Applied direct dye on yarn |
Questions -
- What are direct dyes and their application?
- Which properties of direct dyes are useful as textile materials?
- Give a classification of direct dyes.
References
Chakrabarti, R., & Mehta, N. (2008, November 8). Quick Level Dyeing of Direct Dyes. Fibre2fashion.com; Fibre2Fashion. https://www.fibre2fashion.com/industry-article/3742/quick-and-level-dyeing-of-direct-dyes-dyrite-process
Clark, M. (2011). Handbook of textile and industrial dyeing: Principles, processes and types of dyes (Matthew Clark, Ed.). Woodhead Publishing.
Hasin, S. (2020, July 16). All about direct dyes. Textile Property. https://www.textileproperty.com/direct-dyes/
Sayed, A. (n.d.). Direct dye: An overview [A to Z]. Blogspot.com. from https://textileapex.blogspot.com/2015/01/direct-dye.html
The Editors of Encyclopedia Britannica. (1998). direct dye. In Encyclopedia Britannica.
Trivedi, Y. (2020, November 18). Dyeing of cotton fabric with direct dyes. Textilesphere.com. https://www.textilesphere.com/2020/11/dyeing-of-cotton-with-direct-dyes.html
(N.d.). Textilelearner.net. from https://textilelearner.net/direct-dye-classification/
Further read,
Part 2 Mechanism and effects of Dyeing
Part 3 Application of direct dyes
Part 4 Direct dyes for certain fibres
Part 5 After treatment of Direct Dyed Goods
Part 6 Other treatment of direct dyed goods and stripping
Writer - Rushikesh Patil (Textile Engineer)
