“Fluorescent whitening agent” is a substance that has always been controversial. Whether it is harmful or not has always been a lingering question in some people’s minds. Today, let the editor take you through this substance and explore it thoroughly. Next, its true face?
What is a fluorescent whitening agent?
British physicist George Gabriel Stokes first described the phenomenon of fluorescence in 1852. In 1929, Krais.P first discovered that 6,7-dihydroxycoumarin has a fluorescent whitening effect; in 1940, the German IG Company developed a fluorescent whitening agent with practical value and began its commercialization process.
In 1959, the former Tianjin Dye Factory produced my country’s first fluorescent whitening agent – V B L (C.I.85), which is a bistriazine amino stilbene type. In 1966, the former Ministry of Chemical Industry promulgated the chemical industry standard (ministerial standard) for this variety, numbered HG 2-382-66, which was the first industry standard for fluorescent whitening agent products in my country. Now the product standard has been upgraded to GB/T 10661-2003 “Fluorescent Whitening Agent VBL”. Fluorescent whitening agents were initially only used in the textile printing and dyeing industry in my country. In the late 1960s, optical brighteners began to be used in the synthetic detergent industry, and were only used in the paper industry in the 1970s.
Fluorescent whitening agents are used in a wide range of applications. From their initial use in textiles, they are now widely used in papermaking, detergents, plastics, coatings, inks, leather and other fields. . With the rapid development of economy, the use and dosage of optical brighteners are still expanding. At present, the textile industry is no longer the field that uses the largest amount of optical brighteners. In countries around the world, the application proportions of optical brighteners in different industries vary, but the order of usage proportions is basically the same: that is, mainly used in detergents, followed by papermaking, textiles third, and smaller amounts in plastics and other fields.
Principle of optical brightener
In the textile industry, the whiteness of the fiber itself often fails to meet people’s aesthetic requirements. Especially for natural fibers, their whiteness varies greatly due to different growth environments and growth cycles. White substances generally slightly absorb the blue light of 450-480nm in visible light, resulting in a lack of blue, making it slightly yellow and giving people an old feeling. For this reason, people have taken different measures to make items whiter and more colorful.
Before the emergence of fluorescent whitening agents, there were two main whitening methods commonly used:
① Adding blue to whiten This method can have a whitening effect, but the effect is limited, and because the total amount of reflected light is reduced, the color of the item becomes darker.
②Chemical bleaching method mainly causes substances to fade through oxidation-reduction reactions, but it will cause certain damage to cellulose, and the bleached fabrics often have a yellow color, which will affect the Whitening effect.
Fluorescent whitening agents can make up for the shortcomings of traditional whitening methods and show great advantages. Fluorescent whitening agents can absorb higher-energy near-ultraviolet light, causing their molecules to enter an excited state, and then the excited molecules transition to a lower-energy ground state and emit fluorescence.
Due to energy loss, the fluorescence wavelength of the radiation becomes longer (about 450nm blue light). The yellow color of yellowed items can be compensated by the blue light reflected by the fluorescent whitening agent. This increases the apparent whiteness of the item. Since the intensity of the emitted light exceeds the intensity of the original visible light projected on the treated fabric, a slightly colored whitening effect is produced. Fluorescent whitening agents with practical value, in addition to absorbing ultraviolet light and emitting purple-blue fluorescence and having high fluorescence efficiency, must also be close to colorless or slightly yellow and have the characteristics of ordinary dyes. For example, the fiber has good affinity, good solubility or dispersion properties, and good fastness properties such as washing, light fastness and ironing resistance.
The whitening properties of fluorescent whitening agents are determined by the special structure of their molecules. Its chromophoric group has a conjugated system that can undergo π-π* transition. The most common systems include benzene ring, naphthalene ring, triazine ring, vinyl, five-membered heterocyclic ring and other fused ring systems. Electronic systems with a small degree of conjugation generally only absorb light of very short wavelengths. As the conjugation system increases, the wavelength of absorbable light increases, the electrons are more easily excited, and the fluorescence efficiency of the whitening agent is greater, thus meeting the requirements Whitening requirements for optical brighteners.
Fluorescent reaction and fluorescent whitening agent
Fluorescence reaction refers to the process in which a substance is excited after being irradiated by ultraviolet invisible light, and then converts the excited energy into light visible to the naked eye and releases it. This is a luminescence phenomenon of photoluminescence.
Fluorescence reactions are extremely common in nature, in many animals (such as shrimps, crabs, jellyfish, etc.), foods (such as soy sauce, Pu’er tea, liquor, coffee, etc.), and drugs , plant extracts (such as Ginkgo biloba, peony, sophora flavescens alkaloids, etc.), chlorophyll, and microorganisms (bacteria, mold) can produce fluorescent reactions under UV light irradiation. This is natural fluorescence and an inherent characteristic of substances.Among the various substances that come into contact with food, food packaging paper is included, so theoretically, the possibility of consumers ingesting fluorescent whitening agents through food is very small, and is mainly ingested through the skin. Since the skin surface is covered with a stratum corneum, it can seriously hinder the ability of cells below the dermis layer to absorb macromolecular organic matter. Therefore, it is much more difficult for most substances to enter the human body through skin contact than through ingestion and inhalation. Not to mention, the fluorescent whitening agent hanging on the skin is at risk of being eluted again at any time, and cannot wait to be absorbed slowly.
Evaluating the toxic risk of a substance to the human body usually depends on three aspects: first, the toxicity of the substance itself and its degradation products; second, the potential exposure of the population to the substance The dose size; third, whether the substance bioaccumulates and whether it will accumulate in the human body with continued exposure.
Summary
Therefore, no matter Whether fluorescent whitening agents are used as dyes or as auxiliaries, as long as the fluorescent whitening agent production enterprises can produce, sell and use up-to-standard fluorescent whitening agents in accordance with the requirements of the standards, the use of fluorescent whitening agent products on textiles is safe for consumers. safe. It is not difficult to understand that it is safe to add fluorescent whitening agents to detergents to wash clothes and other fabrics.
However, with the development of my country’s economy and the improvement of living standards, the demand for fluorescent whitening agents will also keep pace with the times, and the development speed of fluorescent whitening agents will also be very fast. quick. It is necessary to continuously follow up on the development of technology and the formulation and revision of standards, strengthen safety research on new varieties, and regulate the market. No matter which industry the fluorescent whitening agent is used in, there must be corresponding safety research and standard basis for use, so that the personal health of our consumers can be guaranteed and all fields of the country’s national economy can develop in a healthy and orderly manner. </p
