Textile Dyeing- Common terms used and Dyes classification

Classification of Dyes

There are two ways in which dyestuff can be classified

  • According to use: This classification is important for practical point of view.
  • According to chemical constitution: Synthetic dyes and Natural dye.

The use-view classification of dyestuff that are available in colored form as ‘ready-made’ dyes. Natural dyes are from animal and plant origin which is used for dyeing wool, cotton and silk.

Common terms used in dyeing:

  • Substantivity/Affinity: It is defined as the attraction between the fiber and the dye under given dyeing condition, where the dye is selectively extracted from an application medium by the fiber. In simple terms, affinity or substantivity indicates the ability of a dye to go from the solution phase to fiber.
  • Exhaustion: It is defined as the proportion of dye absorbed by the fiber in the relation to that remaining in the dye bath. It is expressed in terms of a percentage. For example, if the exhaustion of the dye bath is 50% then it means that 50% of the dye in the dye bath has moved from the dye solution into the fiber.
  • Material to liquor ratio: This expression refers to the weight: volume between the fiber to be dyed and the total volume of dye bath.
  • Shade percentage: Shade percentage refer to the quantity of dye taken for dyeing expressed as a percentage of the dry weight of the fiber to be dyed.
  • Dye Assistants: Dyeing assistant are chemicals that facilitate, in one way or another, the production of the required shades in dyeing. They are also called dyeing auxiliaries.
  • Water softening: These are the compounds used where hard water is used in the process od dyeing. These agents when react with metallic ions and become a complex ion. One of the commonly used softening agent is EDTA.
  • Exhausting agents: Exhausting agents facilitate the movement of the dye molecules to the fiber and thereby “exhaust” the dye bath. The most commonly used exhausting agent is Glauber’s salt (sodium sulphate).
  • Dispersing agents: Dispersing agent is described as an aromatic sulphonic acid condensation product, a naphthalene sulphate acid condensation product and a highly condensed NS acid.
  • Levelling agents: These agents are used to produce uniform dyeing on the textile materials. Some dyes can rush on to the fiber due to the high affinities they possess, in such cases to gain uniform dyeing the levelling agents are used.
  • Retarding agents: Retarding agents are used as levelling agents to retard the sudden rushing of dye to and into the fiber. In some cases where the dyeing rate is very high due to the high affinities. Retarding agents basically slows down the dyeing process.

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