Acid dye

An acid dye is a dye that is typically applied to a textile at low pH. They are mainly used to dye wool, not cotton fabrics.[1] Some acid dyes are used as food colorants,[2][3] and some can be used to stain organelles for medical microscopy.

Acid dyes are anionic, soluble in water and are essentially applied from acidic bath. They possess acidic groups, such as SO3H and COOH and are applied on wool, silk and nylon when an ionic bond is established between a protonated –NH2 group of the fibre and acid group of the dye. Overall wash fastness is poor, although lightfastness is quite good. As dye and fibre contain opposite electrical natures, strike rate and uptake of acid dye on these fibres is faster; electrolyte at higher concentration is added to retard dye uptake and to form levelled shades. Acid generates cations on fibre and temperature helps to substitute the negative part of the acid with anionic dye molecules.[4]

  1. ^ Booth, Gerald (2000). "Dyes, General Survey". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a09_073. ISBN 3527306730.
  2. ^ Trowbridge Filippone, Peggy. "Food Color Additives". Archived from the original on April 5, 2015. Retrieved September 8, 2016.
  3. ^ Klaus Hunger, ed. (2003), Industrial Dyes: Chemistry, Properties, Applications (in German), Weinheim: WILEY-VCH Verlag, pp. 276ff, ISBN 978-3-662-01950-4
  4. ^ A K Roy Choudhary, “Textile Preparation and Dyeing”, Science Publishers, USA (2006)
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