Textile fibres do not appear perfectly white due to the presence of certain coloured impurities. Whitening with optical brighteners or fluorescent brightening agents can eliminate the yellowish hue of the materials. The optical brightening agents counteract the yellowness of the fabric by increasing the reflection of the blue light rays. They convert invisible short wave ultraviolet rays of sunlight into visible blue light and effectively neutralize the pale yellow or cream colour of the white materials; hence a degree of whiteness, which is comparatively more intense, is achieved. The greatest use of brighteners is in detergents, and almost every commercial detergent contains one or more brighteners, in the proportion of 0.05-0.3%.
The fluorescent substance to act as a whitening agent must essentially emit light in the blue region so that it effectively neutralizes the normal pale yellow or cream colour of the so-called white materials. OBA is based on the addition of light, whereas the bluing method achieves its white effect through the removal of light.
About the authors
Dr. Ruma Chakrabarti is Associate Professor with Kumaraguru College of Technology, Coimbatore & Mr. A. Vignesh is Technical Compliance Manager with Hohenstein India Pvt. Limited.