Necessity of Auxiliaries in Textile Dyeing

Auxiliaries in Textile Dyeing
A chemical or formulated chemical product which enables a processing operation in preparation, dyeing, printing or finishing to be carried out more effectively, or which is essential if a given effect is to be obtained’.
Dyeing auxiliaries
Necessity of Auxiliaries in Textile Dyeing

(a) To prepare or improve the substrate in readiness for coloration by

(b) To modify the sorption characteristics of colorants by
  •  acceleration
  •  retardation
  •  creating a blocking or resist effect
  •  providing sites for sorption
  •  unifying otherwise divergent rates of sorption
  •  improving or resisting the migration of dyes
(c) To stabilize the application medium by
  •  improving dye solubility
  •  stabilizing a dispersion or solution
  •  thickening a print paste or pad liquor
  •  inhibiting or promoting foaming
  •  forming an emulsion
  •  scavenging or minimizing the effects of impurities
  •  preventing or promoting oxidation or reduction
(d) To protect or modify the substrate by
  • creating or resisting dye ability
  • lubricating the substrate 
  • protecting against the effects of temperature and other processing conditions
(e) To improve the fastness of dyeings, as in
  •  the after treatment of direct or reactive dyes
  •  the after treatment of acid dyes on nylon
  •  the chroming of mordant dyes on wool or nylon
  •  giving protection against atmospheric influences, as in UV absorbers or inhibitors of gas-fume fading
  •  back-scouring or reduction clearing
(f) To enhance the properties of laundering formulations (fluorescent brightening agents).

Some have more than one purpose :
An auxiliary to improve dye solubility may also accelerate (or retard) a coloration process, or an emulsifying agent may also act as a thickening agent; pH-control agents may both stabilize a system and also affect the rate of dye sorption. Undesirable effects during handling, through effluent discharge to surface waters, through discharge to the atmosphere (e.g. via stenter gases), through consumer contact with the finished product (e.g. skin sensitivity) or during the eventual disposal of solid wastes (e.g. incineration or landfill)

Classification
A) Non-surfactants
B) Surfactants,

Non-surfactants
Simple electrolytes, acids and bases, both inorganic and organic. E.g., sodium chloride, sodium acetate, sulphuric acid, acetic acid and sodium carbonate, together with complex salts (such as sodium dichromate, copper(II) sulphate, sodium ethylenediaminetetra-acetate, sodium hexametaphosphate), oxidizing agents are.

  • Oxidising agents(hydrogen peroxide, sodium chlorite)
  • Reducing agents (sodium dithionite, sodium sulphide).
Anionic polyelectrolytes such as sodium alginate or carboxymethylcellulose, used mainly as thickening agents and migration inhibitors, also fall within the class of nonsurfactants; So too do sorption accelerants such as ophenylphenol, butanol and methylnaphthalene, although they normally require an emulsifier to stabilise them in aqueous media. Fluorescent brightening agents (FBAs) form another large class of nonsurfactant auxiliaries 
 
Surfactants:
Organic in nature and more complex structures ‘An agent, soluble or dispersible in a liquid, which reduces the surface tension of the liquid’ In coloration processes this reduction in surface tension usually takes place at a liquid/liquid or liquid/solid interface, although liquid/gas interfaces are also occasionally important.

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