What is Dyes?
Dyes are substances those are used to color various materials, including textiles, plastics, paper, and other materials. They are soluble, coloured organic compounds that are usually applied to textiles from a solution in water. Dyes can be natural or synthetic. They are designed to bond strongly to the polymer molecules that make up the textile fibre. A dye is used to impart color to materials of which it becomes an integral part. Dyes are widely used in many industries, including textiles, printing, and cosmetics, to add color to products and materials. Some common types of dyes include acid dyes, basic dyes, disperse dyes, reactive dyes, and vat dyes, each with its own specific properties and uses. In this article I will discuss dyes classification and explain important types of dyes.
Classification of Dyes:
Dyes can be classified into various categories based on their origin, chemical structure, solubility, application method, and other factors. Some common classification of dyes include:
1. Classification of dyes based on origin:
- Natural dyes
- Synthetic dyes
2. Dyes classification based on chemical structure:
- Azo dyes
- Anthraquinone dyes
- Triphenylmethane dyes
- Phthalocyanine dyes
- Quinoline dyes
- Nitroso dyes
- Indigoid dyes
- Natural dyes
3. Classification of dyes based on application method:
- Direct dyes
- Reactive dyes
- Acid dyes
- Basic dyes
- Disperse dyes
- Vat dyes
4. Dyes classification based on solubility:
- Water-soluble dyes
- Oil-soluble dyes
- Solvent dyes
5. Classification of dyes based on use:
- Textile dyes
- Food dyes
- Ink dyes
- Leather dyes
- Hair dyes
- Medical dyes
Each type of dye has its own unique properties, advantages, and disadvantages, and is used for specific applications depending on its characteristics.
Important types of dyes are briefly discussed below:
1. Synthetic dyes: Synthetic dyes are man-made chemical compounds used to add color to a variety of materials, including textiles, plastics, paper, and food. They are often preferred over natural dyes due to their wider range of colors, greater consistency, and lower cost. Synthetic dyes are classified based upon their chemical composition and the method of their application in the dyeing process.
2. Basic / cationic dyes: Basic dyes are water soluble and are mainly used to dye acrylic fibres. They are mostly used with a mordant. A mordant is a chemical agent which is used to set dyes on fabrics by forming an insoluble compound with the dye. With mordant, basic dyes are used for cotton, linen, acetate, nylon, polyesters, acrylics and modacrylics. Other than acrylic, basic dyes are not very suitable for any other fibre as they are not fast to light, washing or perspiration. Thus, they are generally used for giving an after treatment to the fabrics that have already been dyed with acid dyes.
3. Acid dyes: Acid dyes are a type of water-soluble synthetic dyes that are used to color protein fibers such as wool, silk, and nylon. They are called “acid” dyes because they require an acidic environment, typically with acetic acid or citric acid, to effectively bond with the fibers. Acid dyes have acidic groups that enable them to bond with the amino groups in the protein fibers, resulting in bright, vibrant colors. They are particularly suitable for wool and silk, which are difficult to dye with other types of dyes. Acid dyes have excellent color fastness properties, making them a popular choice in the textile industry.
4. Direct dyes: Direct dyes colour cellulose fibres directly without the use of mordants. They are used for dyeing wool, silk, nylon, cotton, viscose, etc. These dyes are not very bright and have poor fastness to washing although they are fairly fast to light.
5. Mordant or chrome dyes: Chrome dyes are acidic in character. Sodium or potassium bichromate is used with them in the dyebath or after the process of dyeing is completed. This is done for getting the binding action of the chrome. They are mostly used for wool which gets a good colorfastness after treatment with chrome dyes. They are also used for cotton, linen, silk, viscose and nylon but are less effective for them.
6. Reactive dyes: Reactive dyes react with fibre molecules to form a chemical compound. These dyes, they are either applied from alkaline solution or from neutral solutions which are then alkalized in a separate process. Sometimes heat treatment is also used for developing different shades. After dyeing, the fabric is washed well with soap so as to remove any unfixed dye. Reactive dyes were originally used for only cellulose fibres but now their various types are used for wool, silk, nylon, acrylics and their blends as well.
7. Disperse dyes: Disperse dyes are water insoluble. These dyes are finely ground and are available as a paste or a powder that gets dispersed in water. These particles dissolve in the fibres and impart colour to them. These dyes were originally developed for the dyeing of cellulose acetate but now they are used to dye nylon, acetate and acrylic fibres too.
8. Sulphur dyes: Sulphur dyes are insoluble and made soluble by the help of caustic soda and sodium sulphide. Dyeing is done at high temperature with large quantities of salt so that the colour penetrates into the fibre. After dyeing, the fabric is oxidized for getting desired shades by exposure to air or by using chemicals. Excess dyes and chemicals are removed by thorough washing. These dyes are fast to light, washing and perspiration and are mostly used for cotton and linen.
9. Nitro Dyes: Nitro dyes are polynitro derivatives of phenols containing at least one nitro group ortho or para to the hydroxyl group. They are of relatively little importance industrially, because the colours are not very fast. Examples of this class are picric acid (2,4,6-trinitrophenol), Maritus yellow (2, 4-dinitro-1-naphthol), and Naphthol yellow S (2,4-dinitro-1-naphthol-7-sulphonic acid).
10. Pigment dyes: Although pigments are not dyes in a true sense, they are extensively used for colouring fabrics like cotton, wool and other man-made fibres due to their excellent light fastness. They do not have any affinity to the fibres and are affixed to the fabric with the help of resins. After dyeing, the fabrics are subjected to high temperatures.
11. Fluorescent dyes: Fluorescent dyes are a type of dye that emit visible light when exposed to ultraviolet light or other sources of energy. They are commonly used to create bright, vibrant colors in highlighters, paints, inks, and other products where high visibility is desired.
12. Solvent dyes: These dyes are soluble in organic solvents such as benzene, toluene, and acetone. They are commonly used to color petroleum-based products, plastics, waxes, and other hydrocarbon-based materials. Solvent dyes are valued for their high solubility, color strength, and stability, making them ideal for use in a wide range of industrial applications.
13. Natural dyes: Natural dyes are dyes derived from plants, animals, or minerals. They have been used for thousands of years to color textiles, leather, and paper. Natural dyes are valued for their beautiful colors, eco-friendliness, and non-toxicity. However, they can be less colorfast than synthetic dyes and require more effort to extract and use.
14. Vat dyes: Vat dyes are insoluble in water and cannot dye fibres directly. However, they can be made soluble by reduction in alkaline solution which allows them to affix to the textile fibres. Subsequent oxidation or exposure to air restore the dye to its insoluble form. Indigo is the original vat dye. These dyes are the fastest dyes for cotton, linen and viscose. They are used with mordants to dye other fabrics such as wool, nylon, polyesters and acrylics.
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