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Home » Dyestuff » Direct Dyes

Direct Dyes

Direct Dyes
Direct dyes offered by us are anionic dyes that come with substantively for cellulosic fibres. These are normally applied from aqueous dye bath that contain an Electrolyte, either:
  • Sodium chloride (NaCl)
  • Sodium sulfate (Na2SO4)

With the dyeing process with direct dyes being very simple, the dyeing is carried out in neutral/slight alkaline dye bath at/near boiling point. But, here a separate after treatment like cationic dye fixing that helps in enhancing wet fastness is also required for most direct dyeing processes. Being salts of complex sulfonic acids, chemically more than 75% of all direct dyes are un-metalized Azo structures with a great majority being:
  • Disazo type
  • Polyazo type

With ionic nature being anionic and soluble in water, these have affinity for wide variety of fibers like:
  • Cotton
  • Viscose
  • Silk
  • Jute
  • Linen

Further, these are also used as pH indicators and as biological stains. As these do not make any permanent chemical bond with cellulosic fibers, here, these are attached to it using:
  • Week hydrogen bonding
  • Van der waals force

The flat shape and length of these dyes also enable them to:
  • Lie along-side cellulose fibers
  • Maximize Van-der-Waals, dipole and hydrogen bonding

Solving wash fastness issue for Direct Dyes:
The quality of wash fastness is poor unless it is treated with suitable:
  • Dye fixing agent
  • Fastness improving finishing agent

For overcoming this, a special after treatment process is used. Under this process, a cationic bulking agent ‘RETAYNE’ is used where this agent glues dyes into fibers.

Major types of Direct Dyes:

Anionic Direct Dyes:
These are used for:
  • Coloring papers
  • Controlling tint and shade
  • Correction of two sided paper color

Structural features:
The main structural features of Anionic Direct Dyes are:
  • Planar vary from each other
  • Structural single & double bonds are much extended
  • Containing one/more than one sulfonate groups that make them soluble in the water

Cationic Direct Dyes:
The main structural features of cationic direct dyes are:
  • Structural single & double bonding are extended
  • Molecular structure is planar
  • Positive charges more than negative charges

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