Types and Properties of Fluorescent Brightening Agents
Fluorescent brightening agents (FBA) or fluorescent whitening agent are the white dyes that have the potential to absorb UV region, light of electromagnetic region and emit back the blue light region. The chemical is suitable for silk, wool, paper, cellulose, nylon and other polymers. fluorescent whitening agents are usually colorless dues that also remit the blue light.
Textile fibers, detergents, printing paste etc in their raw state are undesirably creamish and the reason can be attributed to the presence of natural dyes and pigments. In case of manmade material, this can be the due to thermal decomposition. The coloring matte, whether natural or a contaminant in the fiber is usually decolorized by using various bleaching method. However, repeated bleaching can degrade the quality of substrate. Virtually all the white fabrics are incorporated or applied with OBA during processing.
Desired Properties of Fluorescent Whitening Agents for Textiles Use:
It must have a good solubility and should not have a color of its own.
OBAs must have good light and wet fastness properties
Building up and exhaustion properties
Rate of strike on substrate
Effect of temperature on exhaustion
Build up properties
Water hardness effects
Application and sensitivity towards change in pH
Good leveling and penetration properties
Should necessarily not decompose on colored products while on exposure to atmospheric condition
Should not absorb light in visible regions
Should be stable and very fast to usual oxidative and reductive bleaching chemicals or bleaching systems
Disulfonic / Divalent: Two sulfonic acid groups. They are good for hydrophobic fiber like Nylon, Silk, Wool etc.
Tetrasulfonic / Tetravalent: It constitutes four Sulfonic group, have good solubility and is ideal for paper applications, cellulosic fiber at alkaline or neutral pH.
Hexasulfonic / Hexavalent: It constitutes of 6 sulfonic groups, have great solubility for surface coating application.
Conclusion:
OBA or Optical Brightening Agents (OBA) or Fluorescent Whitening Agents (FWA) are added to many substrates in order to reduce yellowing of material, enhance brightness and improve whiteness of products. Optical whiteners absorb the UV radiations and re-emit the blue light. The emitted blue light in turn reduces the yellow color of substrate. This imparts a pleasing white and sometimes whiter appearance. Optical brighteners give more intensity to some colors as well.
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