How Do Optical Brightening Agents Work?

By Author: Ryan Hancock
Total Articles: 1
Comment this article

Apart from its vast use in whitening and brightening laundry, optical brightening agents find use in manufacture of textiles, paper, plastics, printing inks, paint, and cosmetics. Different types of fiber and increase in number of fibers has increased the various application methods of optical brightening agents. All round fastness properties and a good yield along with different shades of white are desired by both processors and consumers. You can hardly find any white textile or white paper industry without the use of optical brightening agents. They not only prove to be useful in medical diagnostic procedures, but also had remarkable use in maintaining crops as biological pesticides and detecting waste water leakages.

Function of Optical Brightening Agents

< a href="http://www.valblanc.com/optical-brightener.html">Optical brightening agents absorb ultraviolet light and emit it back as visible blue light. From the visible range of the spectrum, fluorescent colors will reflect more light than they can absorb. Absorption of radiation having a high energy on the part of the molecule causes fluorescence, which ...
... re-emits this radiation in the form of lower energy that is of longer wavelength. The difference in energy is transformed into kinetic energy. This blue light minimizes the yellowing that may be present in the clothes and make them appear whiter, brighter, and cleaner. To enable a molecule to fulfill this function, optical brightening agents must be manufactured according to some standard principles. The fluorescence mechanism of optical brightening agents depends on the structure and the condition of the molecule. Many brightening agents fluoresce in powder form, few in solution, and few only in contact with fiber. Differences in hue can be detected on comparing different textile fabrics.

Categorization of Optical Brightening Agents

The classification of optical brightening agents can be done based on the chemical structure of the brightener and the method of application.

Based on the application method, they can be largely categorized into two groups:

• Direct Optical Brightening Agents: They are soluble in water. They are mostly used for brightening of natural fibers. Their use in synthetic materials such as polyamide is very rare.
• Disperse Optical Brightening Agents: They are insoluble in water, and are applied either to color from an aqueous dispersion or for mass coloration. They are majorly used in synthetic materials such as acetate, polyamide, polyester, and occasionally on paper.
Based on the chemical structure, optical brightening agents are classified into derivatives of coumarin, naphthalene dicarboxylic acids, stilbene, 1, 3 diphenylpyrazoline, cinnamic acids, heterocyclic dicarboxylic acids, and substances belonging to other chemical systems.

Chemistry of Optical Brightening Agents

The chemistry of optical brightening agents mostly contains stilbene derivatives. They absorb the ultraviolet regions at 342 nm. They can be present in two isomeric forms: the Cis configuration and the Trans configuration. The Cis isomer is not optically active, unlike the Trans isomer. The Trans form is present both in powder and liquid form. Optical brightening agents suitable for cotton are mostly derivatives of diaminostilbene disulphonic acid, and others are derivatives of heterocyclic compounds containing nitrogen atoms.