Abstract
This chapter describes the chemistry and mechanism of optical brightening agents as well as their applications to various kinds of fibers. The optical brighteners counteract the yellowness of the fabric by increasing the reflection of blue light rays. They convert invisible short-wave ultraviolet rays of sunlight into visible blue light and have a degree of whiteness that is comparatively more intense. Over-bleaching may reduce the fibre strength. Even well bleached fabrics possess a slight yellowish appearance. This yellowish hue of the materials can be eliminated by whitening with optical brightenering agents (OBA) or fluorescent brightening agents (FBA). Sometimes blueing agents are also used. In blueing, the initial yellowish shade of the textiles is covered by the blue dye and bluish white results. However, the corresponding blue dye itself absorbs in visible light and thus, the total amount of reflected light is smaller than in the case of unblued material, so that the blued material is less bright—that is, it is dull, or greyish.
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