Optical Brightening Agents (OBA) | Properties of Fluoroscent Whitening Agents for Textiles

Optical brightening agents:
The coloring matter, whether it is natural or present as a contaminant in the fiber is generally decolorized by different bleaching methods. However the appearance of the textile substrate is somewhat creamish after the bleaching, therefore chemical treatments are become necessary to neutralize the yellow tint of the textile fibers.

Optical brightening agents
Optical brightening agents
There are two methods ,which are generally used for this purpose. By using a blue tinting agent , which absorbs the yellow part of the light and reflected light appears to be of bluish tint. The total light reflected by this mean is less than the total incident light.

By using fluorescent optical brightening agents :

The OBA s (optical brightening agents ) are most widely used in textiles , paper, detergents and plastics . The optical brightening effect is obtained by the addition of light , which means that the amount of light reflected by the Fluorescent Whitening Agents (also called optical brightener) absorb high energy radiation in the ultraviolet to violet region (330nm-380nm) on the part of characteristic molecules and emit lower energy radiation in blue region in visible spectrum (400nm-450nm), which yields the counteracting the yellowing appearance. FWA should be transparent on the substrate and should not absorb the visible region of the spectrum. The OBAs are effective only when the incident light has a significance proportion (such as daylight) of UV rays. When material treated with OBAs are exposed to UV black light source , it glows in the dark.Anionic OBA’s exhaust on cotton, wool and silk., cationic OBA’s exhaust on acrylic and certain polyesters and nonionic OBA’s are exhaust on all synthetics.

Desired Properties of Fluoroscent Whitening Agents for Textiles Use:
Before selecting an optical brightener for textile application we must look for following properties,

  1. It should have good solubility , should not have its own color and good substantivity for the textile substrate under OBA application.
  2. OBA’s should have good light as well as wet fastness properties.
  3. Its rate of strike on the substarte.
  4. Build up and exhaustion properties.
  5. Requirement of electrolytes and its sensitivity towards different exhausting agents.
  6. Effect of temperature on the exhaustion and build up properties.
  7. Application pH range and sensitivity towards change in pH.
  8. Effect of water hardness.
  9. It should have good leveling and penetrating properties.
  10. Should not decompose to colored products on exposure to atmospheric conditions as well as storage, and it should not absorb light in the visible region.
  11. It should be compatible and stable with finishing chemicals, auxiliary and process such as heat and temperature.
  12. It should be stable and fast to the common oxidative and reductive bleaching chemicals and bleaching systems.
 

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