Optical Brightener
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Optical brighteners, optical brightening agents (OBAs), fluorescent brightening agents (FBAs), or fluorescent whitening agents (FWAs), are chemical compounds that absorb light in the
ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
and violet region (usually 340-370 nm) of the
electromagnetic spectrum The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...
, and re-emit light in the blue region (typically 420-470 nm) through the phenomenon of
fluorescence Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colore ...
. These additives are often used to enhance the appearance of color of
fabric Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, and different types of fabric. At first, the word "textiles" only referred to woven fabrics. However, weaving is no ...
and
paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses, Feces#Other uses, herbivore dung, or other vegetable sources in water. Once the water is dra ...
, causing a "whitening" effect; they make intrinsically yellow/orange materials look less so, by compensating the deficit in blue and purple light reflected by the material, with the blue and purple optical emission of the fluorophore.


Properties

The most common classes of compounds with this property are the stilbenes, e.g., 4,4′-diamino-2,2′-stilbenedisulfonic acid. Older, non-commercial
fluorescent Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with color ...
compounds include
umbelliferone Umbelliferone, also known as 7-hydroxycoumarin, hydrangine, skimmetine, and ''beta''-umbelliferone, is a natural product of the coumarin family. It absorbs ultraviolet light strongly at several wavelengths. There are some indications that this c ...
, which absorbs in the UV portion of the spectrum and re-emit it in the blue portion of the visible spectrum. A white surface treated with an optical brightener can emit more visible light than that which shines on it, making it appear brighter. The blue light emitted by the brightener compensates for the diminishing blue of the treated material and changes the hue away from yellow or brown and toward white. Approximately 400 brightener types are listed in the international Colour Index database, but fewer than 90 are produced commercially, and only a handful are commercially important. The Colour Index Generic Names and Constitution Numbers can be assigned to a specific substance. However, some are duplicated, since manufacturers apply for the index number when they produce it. The global OBA production for paper, textiles, and detergents is dominated by just a few di- and tetra-sulfonated triazole-stilbenes and a di-sulfonated stilbene-biphenyl derivatives. The stilbene derivatives are subject to fading upon prolonged exposure to UV, due to the formation of optically inactive cis-stilbenes. They are also degraded by oxygen in air, like most dye colorants. All brighteners have extended conjugation and/or aromaticity, allowing for electron movement. Some non-stilbene brighteners are used in more permanent applications such as whitening synthetic fiber. Brighteners can be "boosted" by the addition of certain
polyols In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups (). The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, thre ...
, such as high molecular weight
polyethylene glycol Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular wei ...
or
polyvinyl alcohol Polyvinyl alcohol (PVOH, PVA, or PVAl) is a water- soluble synthetic polymer. It has the idealized formula H2CH(OH)sub>''n''. It is used in papermaking, textile warp sizing, as a thickener and emulsion stabilizer in polyvinyl acetate (PVAc) a ...
. These additives increase the visible blue light emissions significantly. Brighteners can also be "quenched". Excess brightener will often cause a greening effect as emissions start to show above the blue region in the visible spectrum.


Common uses

Brighteners are commonly added to
laundry detergent Laundry detergent is a type of detergent (cleaning agent) used for cleaning dirty laundry (clothes). Laundry detergent is manufactured in powder (washing powder) and liquid form. While powdered and liquid detergents hold roughly equal share of ...
s to make the clothes appear cleaner. Normally cleaned laundry appears yellowish, which consumers do not like. Optical brighteners have replaced bluing which was formerly used to produce the same effect. Brighteners are used in many papers, especially high brightness papers, resulting in their strongly fluorescent appearance under UV illumination. Paper brightness is typically measured at 457 nm, well within the fluorescent activity range of brighteners. Paper used for banknotes does not contain optical brighteners, so a common method for detecting
counterfeit A counterfeit is a fake or unauthorized replica of a genuine product, such as money, documents, designer items, or other valuable goods. Counterfeiting generally involves creating an imitation of a genuine item that closely resembles the original ...
notes is to check for fluorescence. Optical brighteners have also found use in
cosmetics Cosmetics are substances that are intended for application to the body for cleansing, beautifying, promoting attractiveness, or altering appearance. They are mixtures of chemical compounds derived from either Natural product, natural source ...
. One application is to formulas for washing and conditioning grey or blonde hair, where the brightener can not only increase the luminance and sparkle of the hair, but can also correct dull, yellowish discoloration without darkening the hair. Some advanced face and eye powders contain optical brightener microspheres that brighten shadowed or dark areas of the skin, such as "tired eyes". End uses of optical brighteners include: # Detergent whitener (instead of bluing agents) # Paper brightening (
internal Internal may refer to: *Internality as a concept in behavioural economics *Neijia, internal styles of Chinese martial arts *Neigong or "internal skills", a type of exercise in meditation associated with Daoism * ''Internal'' (album) by Safia, 2016 ...
or in a
coating A coating is a covering that is applied to the surface of an object, or substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. powder coatings. Paints ...
) # Fiber whitening (internal, added to polymer melts) # Textile whitening (external, added to fabric finishes) # Color-correcting or brightening additive in advanced cosmetic formulas (
shampoo Shampoo () is a hair care product, typically in the form of a viscous liquid, that is formulated to be used for cleaning (scalp) hair. Less commonly, it is available in solid bar format. (" Dry shampoo" is a separate product.) Shampoo is use ...
s, conditioners, eye makeup)


Misuse

From around 2002 to 2012, chemical brighteners were used by many Chinese farmers to enhance the appearance of their white mushrooms. This illegal use was mostly eliminated by the Chinese Ministry of Agriculture.


References

* {{DEFAULTSORT:Optical Brightener Fluorescent dyes Cleaning product components Luminescence Papermaking Process chemicals