Whitening Agent: Properties, Function, Mechanism and Usages (Part-1)

Whitening Agent: Properties, Function, Mechanism and Usages (Part-1)
Authors: Md. Mosharaf Hossain
Kiriti Kingkar Mondal
Tawhidul Islam

Dept. of Textile Engineering
Primeasia University, Dhaka 

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Abstract:
Man's earliest endeavors to enhance the brightness of white objects in everyday use, especially clothing, led to the invention of various bleaching processes. KRAIS'S discovery in 1929 that the natural substance esculin could be applied to textiles to give whites of unprecedented brilliance led to the industrial development of fluorescent whitening agents (FWA's). Fluorescent whiteners are colorless to weakly colored organic compounds that, in solution or applied to a

Substrate, absorb ultraviolet light and re-emit most of the absorbed energy as blue-violet light between 400 and 500 nm. These compounds are included in commercial detergents formulation in order to increase whiteness and intensifying the colors. The aim of this work was to study several industrial situations related with color changes after domestic washing. In order to achieve that, the effect of optical brighteners on white and colored textiles was considered. The action of eight of the most known commercial detergents, on different colors, was tested. Among the selected washing agents, three of them were more specific products: a ‘color protector’, ‘for black and dark colors’ and ‘with active oxygen’. Fabrics with and without pre-brightening were tested. In all the cases, color fastness tests to washing (with ECE detergent and standard soaps) and to rubbing were done in order to conclude about the influence of these parameters on final results.

Keywords: Optical brighteners, whitening effect, brightness, color fastness.

Introduction:
The use of whitening agent in the textile chemical processing is rapidly gaining globally recognition because of their non-toxic and eco-friendly characteristics with the increasingly important requirements for textile manufacturers to make the fabric white at a desired level in textile production. One kind of whitening treatment is anti - biotic. The appearance and handle of cotton knits can be significantly improved by treatment with cellulose and such treatment leads to improve brightness of dyed fabric.

What is whitening agent
A optical brightener ( sometimes called optical bleaches or fluorescent whitening agents ) agent is a compound which, when applied to a textile material, absorbs the short wavelength electromagnetic radiation (300-400 nm) which is invisible to the human eye, and converts it into visible light of longer wavelength between 400 and 500 nm, which is emitted either as violet, pure blue or greenish blue. Because the main use of these dyes in laundry detergents and Textile finishing, Optical Brightener are generally found in domestic waste waters that have a component of laundry effluent. Its characteristic is the incident light to generate fluorescence excitation, so that the stained material was similar fluorite sparkling effect, to the naked eye to see the material is white, especially when added to a yellowish-white material. Fluorescent whitening agents may be used to whiten or brighten a textile or paper material. Further more, well all round fastness property and a good yield are also desired. In addition to this, different shades of whites are desired, as white shades are subject to fashion trends They are requires to be used on a verity of finishing processes and they should be compatible with practically all chemicals and auxiliaries used at different stages.
whitening agent
Figure: Whitening agent
History of whitening agent
Textile material (cotton, wool, linen and silk) and synthetic (mainly polyamide, polyester and polyacrylonitrille) are not completely white and effort have been made since ancient time to free from this yellowish tings. Bleaching in the sun, bluing and mater chemical bleaching of textile and other materials increased the brightness of the products and eliminated to a certain hue or the local impurity of the original or industrially treated material.

When optical brighteners first came up they regarded as bleaching auxiliaries which enable short or milder bleach when used in very small quantities (approx 0.001 – 0.05%) they were also called as optical bleaching agents it could be improved with the help of horse chestnut extra acts. This is due to fact the inner back of the horse chestnut contains aesculin or esculinic acid, a glucoside which is derivative of coumain and which has ultra violet fluorescent. Then came the introduction of organic products based on Diaminostilbine sulphonic acid derivatives.

Historical Development of Optical Brightening Agents:
Numerous materials especially textiles, both classical (Cotton, wool, linen and silk) and synthetic (mainly polyamide, polyester and polyacrylonitrile ), are not completely white and efforts have been made since ancient times to free from their yellowish tinges. Bleaching in the sun, blueing and later chemical bleaching of textile and other materials increased the brightness of the products and eliminated to a certain extent the yellowish tinge to grayish yellow hue or the local impurity of the original or industrially treated material. 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 {Approximately 0.001 to 0.05% }. They were also called as Optical Bleaching Agents. 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 a derivative of coumarin and which has ultra violet fluorescence. Scientist recommended aesculin for improving the whiteness on the basis of theoretical considerations. An aqueous solution of a esculin proved more suitable, but had two major draw backs. Firstly it was not fast to washing and secondly aesculin on the fiber was very sensitive to light. Then came the introduction of organic products based on Diaminostilbine sulphonic acid derivatives. 


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