Fundamentals of Dyes and its applications
- 1. Unit - I Fundamental of Dyes Unit - I Fundamental of Dyes M.Sc. Semester - III M.Sc. Semester - III Presentation by Dr. Nandan C. Pomal Assistant Professor, Faculty of Science, Sigma University, Vadodara, Gujarat, India
- 3. Dye • Dye, substance used to impart colour to textiles, paper, lather, and other materials such that the colouring is not readily altered by washing, heat, light, or other factors to which the material is likely to be exposed. • Dyeing textiles dates back to the Neolithic period (around 10,200 BC). • Dyes were primarily extracted from plants, animals, and minerals. • India, Phoenicia, and Egypt were early centers of dyeing. • Indigo (blue), madder (red), and saffron (orange) were popular choices. History Definition
- 4. • A revolutionary discovery: William Perkin accidentally creates the first synthetic dye in 1886, named mauve, while experimenting with coal tar. • Rapid development: This breakthrough sparks a surge in synthetic dye production. • Advantages: Synthetic dyes offer a wider range of colors, better colorfastness, and are often cheaper than natural dyes. • Impact: Synthetic dyes revolutionize the textile industry and lead to advancements in other fields like medicine. Age of Synthetic Dye
- 5. Introduction As per the report of unlike the most organic compounds, dyes possess colour because; 1. They absorb light in the visible spectrum (400–700 nm) 2. Have at least one chromophore (colour-bearing group) 3. Have a conjugated system, i.e. a structure with alternating double and single bonds 4. Exhibit resonance of electrons, which is a stabilizing force in organic compounds.
- 6. • When any one of these features is lacking from the molecular structure the colour is lost. • In addition to chromophores, most dyes also contain groups known as auxochromes (colour helpers), examples of which are carboxylic acid, sulfonic acid, amino, and hydroxyl groups. • Examples carboxylic acid, sulfonic acid, amino, and hydroxyl groups. • While these are not responsible for colour, their presence can shift the colour of a colourant and they are most often used to influence dye solubility.
- 7. Visible Region – Colour – Wavelength
- 9. Classification Based on Structure Azo Dyes: Most commercially important class, containing azo group (-N=N-). Wide color range, good fastness. Ex: Methyl Orange, Congo Red Anthraquinone Dyes: High fastness to light, heat, and chemicals. Used for cotton, wool, and synthetic fibers. Ex: Alizarin, Indanthrone Triphenylmethane Dyes: Brilliant colors but poor light fastness. Used in paper, inks, and some textiles. Ex: Malachite Green, Crystal Violet Phthalocyanine Dyes: Excellent light and weather fastness, copper complex structure. Used in paints, inks, and textiles. Ex: Copper Phthalocyanine Blue
- 10. Classification Based on Application Direct Dyes: Directly applied to cellulose fibers without mordants. Good substantivity but moderate fastness. Ex: Congo Red, Direct Blue Acid Dyes: Applied to wool and silk in acidic medium. Good levelness and fastness properties. Ex: Acid Red, Acid Blue Basic Dyes: Cationic dyes, applied to acrylic and modified polyester fibers. Brilliant colors but poor fastness. Ex: Basic Red, Basic Blue Vat Dyes: Insoluble dyes reduced to soluble leuco forms, then oxidized back to insoluble color. Excellent fastness properties. Ex: Indigo, Indanthrone Reactive Dyes: React with fiber forming covalent bonds. Good fastness properties and wide color range. Ex: Reactive Red, Reactive Blue Disperse Dyes: Insoluble in water, applied to polyester fibers at high temperature. Good fastness properties. Ex: Disperse Red, Disperse Blue
- 11. Classification Based on Solubility Water Soluble Dyes: Most common, used in textile dyeing, paper, and ink industries. Oil Soluble Dyes: Soluble in organic solvents, used in printing inks, plastics, and oil-based coatings. Pigments: Insoluble dyes, dispersed in a binder to form paints and coatings.
- 12. Theories of dye Structure
- 13. • Understanding the structure of dyes is fundamental to the field of chemistry. This knowledge is essential for developing new dyes with desired properties, predicting color, and understanding the interaction between dyes and substrates. This response will delve into the key theories underpinning dye structure. • Chromophores and Auxochromes: • The foundation of dye structure lies in the concepts of chromophores and auxochromes. • Chromophores: These are groups of atoms responsible for the color of a compound. They typically contain conjugated systems of double bonds, allowing for the absorption of visible light. Common chromophores include: • Azo (-N=N-) • Nitro (-NO₂) • Carbonyl (C=O) • Azomethine (-CH=N-) • Quinoid structures
- 14. • Auxochromes: These groups enhance the color intensity and modify the color produced by the chromophore. They do this by increasing the electron density on the chromophore. Common auxochromes include; • -OH, -NH2, -NHR, -NR2, X (Cl, Br or I), COOH. • 1,3-Dinitronapthalene (Figure 1) is pale yellow but the dye Martius Yellow (2,4-Dinitro-1-naphthol) is orange-red (Figure 2). (Figure 1) (Figure 2)
- 19. • The color of a dye is directly linked to its molecular structure. Key factors influencing color include: • Conjugation: An extended conjugated system in a chromophore leads to a bathochromic shift (red shift), resulting in deeper colors. • Auxochromes Effect: The presence of auxochromes can intensify color (hyperchromic effect) and alter the hue. • Resonance: The ability of a molecule to delocalize electrons through resonance contributes to color depth and stability. • Steric Hindrance: The spatial arrangement of atoms can affect conjugation and color. Colour and Structure Relationship
- 20. • Theories Explaining Colour and Structure • Several theories provide insights into the relationship between dye structure and color: 1. Witt's Theory • Proposed by German chemist Otto Witt in 1876. • Introduced the concepts of chromophores and auxochromes. • Successfully explained the color of many dyes. • However, it lacked a quantitative explanation for color.
- 21. 2. Valence Bond Theory (VBT) • Describes the electronic structure of molecules in terms of covalent bonds. • Explains color based on the energy difference between ground and excited states. • Provides a qualitative understanding of color but has limitations in predicting exact wavelengths.
- 22. 3. Molecular Orbital Theory (MOT) • Offers a more accurate and quantitative description of electronic structure. • Explains color in terms of electronic transitions between molecular orbitals. • Allows for calculations of absorption spectra and prediction of color shifts. • This theory is widely used in modern dye research.
- 23. • Colorimetry: The quantitative measurement of color is essential for dye characterization and quality control. • Dyeing Processes: The interaction between dyes and fibers is influenced by dye structure and properties. • Environmental Impact: The development of environmentally friendly dyes requires a deep understanding of dye structure and reactivity.
- 24. TO BE CONTINUE…