Fluorescent whitening agents are a general term for a class of compounds that brighten and whiten the appearance of cloth and paper (the fluorescent whitening agents used in the paper industry are sodium salts).

Principle

Fluorescent whitening agents absorb light in the ultraviolet and violet regions of the visible spectrum (typically wavelengths of 340-370 nanometers) and re-emit light in the blue region of the visible spectrum (typically wavelengths of 420-470 nanometers). This is a phenomenon known as fluorescence. Because fluorescent whitening agents emit more blue light, they can make objects that originally appear yellow or orange appear less yellow.

Function

According to the national standard GB/T6687-2006 "Terminology of Dyes," fluorescent whitening agents are colorless fluorescent dyes that, when exposed to ultraviolet light, emit blue or violet light, which complements the yellow light emitted by the substrate, resulting in a whitening effect. In layman's terms, fluorescent brighteners (FBAs) use optical color-matching to whiten, brighten, or enhance the color of white or light-colored items (such as soaps, detergents, textiles, plastics, and paper). They do not chemically react with the material, but instead rely on optical effects to increase the whiteness of the object, using fluorescence to enhance the visual perception of whiteness. Therefore, FBAs are also called "optical brighteners" or "white fluorescent dyes."

Usage

FBAs can be used in plastics through dry whitening, wet whitening, and masterbatch whitening. In paints, FBAs can be added by grinding the paint and FBA together, or by directly grinding the FBA into a fine powder and then adding it to the paint using a high-speed disperser.

In plastics, the dosage of FBA is often expressed as a percentage of the plastic's mass. For transparent plastics, the dosage is typically 0.0001%-0.001%, while for white plastics, the dosage is typically 0.05%-0.1%.

In paints and inks, the dosage of fluorescent brighteners is typically between 0.02% and 0.05%. Regarding the specific dosage, it's recommended to obtain small samples from the fluorescent brightener manufacturer. Too little fluorescent brightener can result in unsatisfactory whitening effects, while too much can cause the brightener to precipitate. Therefore, before determining the dosage, it's important to test a small sample to ensure the desired effect is achieved.

Safety

The safety of fluorescent brighteners is closely related to their structure and cannot be generalized. Different industrial sectors have specific requirements for the use of fluorescent brighteners, so consumers don't necessarily assume fluorescent brighteners are unsafe. For example, "Fluorescent Brighteners for Detergents" (QB/T2953-2008) stipulates that distyryl biphenyl and bistriazine aminostyrene fluorescent brighteners can be added to various laundry detergents.

As early as 1999. the European Chemical Industry Council (CEFIC) and the European Detergent Association (A.I.S.E.) launched the "Human and Environmental Risk Assessment of Ingredients of Household Cleaning Products in Europe" (HERA) project, and completed the safety evaluation and risk assessment of diphenylethylene fluorescent whitening agents commonly used in laundry detergents such as Fluorescent Brightener 71. and concluded that they would not cause adverse effects on humans and the environment.