Optical brighteners also called fluorescent whitening agents (FWAs) are hydrophilic water-soluble compounds that can absorb UV light and emit visible (blue violet) light. They are mainly anionic diamino stilbene (DAS) or distyrylbiphenyl (DSBP) derivatives displaying a low aquatic toxicity.
Mechanism of Optical Brightener
Fluorescent activity is a short-term or rapid emission response, unlike phosphorescence, which is a delayed emission. These additives are often used to enhance the appearance of color of fabric, paper, and polymers causing a "whitening" effect, making materials look less yellow by increasing the overall amount of blue light reflected. Once deposited on products, they enhance the whiteness or brightness appearance of white or lightly colored products. Although they are used at low levels in products, their contribution to the overall whiteness performance is not negligible.
Fig 1. Natural polymers with and without optical brighteners.
(A) Natural polymers without optical brighteners. (B) Natural polymers with optical brighteners.
Applications of Optical Brightener
Optical brighteners can be used into detergents, textile industry, papers, synthetics & plastics, and others (lacquers, ultraviolet tracer and pigmented lacquers), by end-users into consumer products, security & safety, textiles & apparel, packaging. We list three main applications as following.
The biggest requirement of OBAs is in whitening the clothes and therefore, it's no surprise that the detergent industry is the largest user of the fluorescent brighteners. As we all have experienced, clothes lose their natural whiteness over the course of time. That is where optical brighteners come in not just to protect that whiteness, but also to enhance it by converting low-density colors to the ones with higher density.
Fig 2. Application in detergent
Another significant usage of the OBAs is in the textile industry where every cloth needs to be bleached before being processed as the raw material is full of impurities that come from pesticides, dust stuck to the fabric while transportation. And in fabrics sourced from animalsimpurities like animal fats, secretions, etc. need to be removed. However, bleaching does not offer complete whitening, which leads to the necessary usage of Optical Brightening Agents (OBAs).
Fig 3. Application in textile
We all want our papers to be as white as possible. Well, that's where optical brightening agents come in. The raw material of paper often consists of impurities such as snippets of bamboo sticks and wood. These impurities dampen the brightness of the paper and that is why this sector creates a lot of opportunity for optical brightening agent manufacturers.
Fig 4. Application in paper