Fluorescent brightening agent also known as optical bleaches or fluorescent whitening agents that are fluorescent white dyes which absorb ultraviolet region (340 – 370 mm) light of electromagnetic region emit back to visible blue region that is at 420- 470 nm. 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 off a fabric and paper causing a "whitening" effect, making materials look less yellow by increasing the overall amount of blue light reflected. Treated material remits more light in the visible region than does an untreated white sample and thus appear ‘whiter than white’.
Main used of this agent is in laundry detergents and textile finishing, they are also generally found in domestic waste waters that have a component of laundry effluent. Major usage is in laundry detergent that is to replace whitening agents removed during washing and to make the clothes appear cleaner. Before the use of FBA, common practice was to apply small amounts of blue or violet dyes called bluing to boost the visual impression of whiteness. But since at the same time they shift the shade of the yellowish material towards blue, the human eye receives an increase of whiteness. Unlike blue dyes, optical brighteners offset the yellowish cast and at the same time improve the lightness because their bluing effect is not based on subtracting yellow-green light but rather on adding blue light. Some brighteners can cause allergic reactions when in contact with skin, depending on the individual.
HISTORY OF FLUORESCENT BRIGHTENING AGENTS
In the early twentieth century a class of chemicals was identified that could increase whitening by the action of fluorescence. These materials, often called colourless dyes, are known as fluorescent whitening agents, optical bleaches or optical brighteners. Optical brighteners are a group of molecules that absorb light predominantly in the ultra-violet range and emit light in the visible range, thereby causing a brightening of the substrate by emitting more than one hundred percent of the incident visible light.
These materials were first used in food packaging and x-ray film enclosures to prevent deterioration caused by ultraviolet light. Soon their whitening properties were exploited, and brighteners were added to numerous commercials materials, fostering a taste for “whiter than white” papers and textiles and non-yellowing plastics.
Numerous materials especially natural and synthetic fibre, are not completely white and efforts have been made since ancient time to free from their yellowish tinges. When Optical brighteners first came up they were regarded as bleaching auxiliaries, which enabled a shorter or a milder bleach when used in very small quantities Cotton and linen bleachers knew 200 years ago the effect of bleaching could be improved with the help of horse chestnut extracts. This is due to the fact the inner bark of the horse chestnut contains aesculin or esculinic acid, a glucoside which is derivative of coumarin and which has ultra violet fluorescence.
CLASSIFICATION OF FLUORESCENT BRIGHTENING AGENTS
They can be classified into two large groups:
a) Direct (substantive) brightener
b) Disperse brightener
a) Direct (substantive) brightener
Direct optical brightening agents are predominantly water soluble substance used for the brightening of natural fibers and occasionally for synthetic material such as polyamide.
b) Disperse brightening
Disperse optical brightening agents are mainly water insoluble and as with disperse dyes they are applied either to coloured from an aqueous dispersion on they can be used for mass colouration. They are used for synthetic materials such as polyamide, polyester, acetate.
From the chemical point of view they are classified according to either...