Dyes

• Dyes


  Organic compounds widely used for imparting color to textiles, produced from natural or synthetic resources
• Dyes


  • They do not build upon the material's surface but are absorbed in the fibers' pores
  • The dye molecules are smaller than the size of the pores of the fibers
  • The planar shape of its molecules with a little thickness helps to slip into the fiber's polymer system
  • There is an affinity between the dye and the fiber due to the force of attraction
• Chromophore


  Color-bearing group
• Conjugated system


  A structure with alternating double and single bonds
• Resonance of electrons is the stabilizing force in organic compounds
• Resonance structure of Malachite Green

  • Colorless compound (chromophore not in conjugated system)
  • Orange color (chromophore in conjugated system)
• Auxochromes


  Color helpers that can shift the color of the dye, attach the dyes to the fibers, and influence dye solubility
• Bathochromic shift (redshift)


  The position shift of a peak or signal to a longer wavelength (lower energy), increases absorption and intensity (darker) of the color
• Hypsochromic shift (blue shift)

  The position shift of a peak or signal to a shorter wavelength (high energy), decreases absorption and intensity of the color
• Factors that can intensify the color of the Dye

  • Doubling the length of the conjugated system causes a bathochromic effect
  • Adding groups of electron-donating (auxochromes) has a bathochromic effect
  • Electron-donating (NH2) and electron-accepting (NO2) provide a bathochromic effect
  • Increasing the number of electron-attracting groups (chromophores) conjugated with electron-donor (auxochromes) has a bathochromic effect
  • The electron-donating effect of an amino group is enhanced by adding alkyl groups to the N-atom
• Natural Dyes


  Obtained from natural sources like vegetable matter, mineral, insects or manufactured in the factory from petrochemical feedstock
• Natural Dyes


  • Mauveine – first synthetic dye made from coal tar
  • Indigo – brilliant blue color made from fermented leaves of a plant
  • Red Lac dye – extracted from lac, a resinous protective secretion of a tiny insect
  • Iron oxide – gives a brown color
  • Buff – derived from ferrous sulfate
• Synthetic Dyes


  Acid Dyes (Anionic Dyes), Basic Dyes (Cationic Dyes), Disperse Dyes
• Acid Dyes (Anionic Dyes)


  • Suitable substrates: polyamides like nylon and proteins like wool, silk, and leather
  • Acid dyes carry a negative charge (anionic) are used to polyamides and proteins that carry a positive charge (cationic) during the dyeing process
  • Applied in acidic conditions
  • Inexpensive, lightfast but not wet fast
• Acid Dyes


  • Acid Black 1
• Basic Dyes (Cationic Dyes)

  • Suitable substrates: polyacrylics
  • Basic dyes carry a positive charge (cationic) are used to polyacrylics that carry a negative charge (anionic) during the dyeing process
  • The basic dyes derived their name from the fact that they possess a cationic group
  • Good fastness and bright shades
• Basic Dyes


  • Mauveine (first synthetic dye), Basic Red 18
• Disperse Dyes


  • Suitable substrates: Hydrophobic substrates like polyesters and acetate
  • Involve dissolving the dye in a polymer matrix to form a solid-solid solution
  • They are dispersed in water rather than fully dissolved to carry out the dyeing process
  • Since polyesters are hydrophobic and have crystalline content, high temperature, pressure, and carrier assistance lead to satisfactory dyeing
• Disperse Dyes


  • Disperse Blue 165
• Direct Dyes


  • Suitable substrates: cellulosic polymers like cotton, viscose rayon, and vegetable fibers
  • Water-soluble and applied in the absence of a binding agent, mordant
  • Water-soluble and low fastness
  • Gain proximity to the cellulose chain to maximize the effects of intermolecular interactions such as H- bonding
  • Cheap, easy to apply but low fastness quality
• Direct Dyes


  • Benzidine-based direct dyes
• Vat Dyes and Sulfur Dyes

  • Suitable substrates: cotton, linen, rayon
  • Used to enhance wet fastness of cellulosic substrates (prevent color removal upon water exposure)
  • Water-insoluble dye, but made soluble by the use of sodium hydrosulfite dissolved in a sodium hydroxide
  • Vat dyes: Name derived from the vatting process during application
  • Sulfur dyes: Name derived from the essential use of sulfur in their synthesis
  • Expensive and also called hot water dyes
• Vat Dyes and Sulfur Dyes

  • Vat dye - Natural dye indigo (dye for denim fabric)
• Azoic Dyes (Naphthol dye)


  • Suitable substrates: cotton and nylon
  • The color development takes place in a coupling reaction between naphthol and diazo component
  • Wet fast but low lightfast
  • Bright and high-intensity colors
  • Also called cold water dyes
• Azoic Dyes


  • Tie-dye (Fast dye or jobus)
• Reactive Dyes


  • Suitable substrates: natural and synthetic cellulosic fibers
  • Undergo chemical reaction with cellulose to form a covalent bond
  • Excellent and bright wet-fast shades on cellulosic fibers
• Reactive Dyes


  • Reactive Blue 19