Whiteness in substrates can be improved by
- increasing reflection (reflectance) or
- offsetting the blue defect.
Bleaching does both of these to some extent, but invariably leaves behind part of the yellowish cast. Even the most thorough bleach cannot remove all traces of yellowing.
Bleaching agents are actually oxidizing agents or reducing agents, which use their oxidative or reductive effects to fade the colored impurities in the fibers. Clearly, this bleaching damages fibrous tissue to varying degrees.
It’s a chemical process.
The whitening of the fluorescent whitening agent(FWA) is an optical effect, so it will not cause damage to the fibrous tissue.
It’s a physical process.
