Optical brightener

Optical brighteners ( colloquially: whitening, also whiteners ) are fluorescent substances whose function is to increase the whiteness, in particular by compensating the yellowness of materials.

Use

They are most often used in the detergent, textile, fiber, paper and plastics industries, to compensate for by bleaching not completely eliminated, based on residues yellowness of lightened materials.

Operation

Optical brighteners need UV light for their effect. Especially with strong sun and clear blue sky in the open or under appropriate artificial lighting (with high UV component), the white does then white.

Fluorescence is the reason for the whitening effect of the optical brightener. These are substances that absorb from the invisible ultraviolet ( 290-400 nm in ) and emit most of the absorbed energy in the visible light again after intramolecular interlude. Fluorescent materials that emit at 400-480 nm, preferably at 430-440 nm are most suitable. At the end of the 18th century, people realized that horse chestnut extracts containing the fluorescent esculin, the effect of bleaching solutions improved. Suitable groups for the molecules of modern optical brighteners are heterocyclic five-membered rings such as oxazole, triazole and imidazole residues. They have a high quantum yield of fluorescence.

The issue of additional, blue light, the reflectance increases (color- technical: chromaticity ) over 100 %, thus the base material appears brighter ( whiter than white). In addition, the additive mixing blue light results in a surplus of yellow tones. In addition, a blue (cool ) white does intense, it becomes easier associated with high white. The "gray veil " is better concealed than slightly red or greenish white.

White papers and white textiles are today usually whitened. Textiles and paper thus appear brighter. Under ultraviolet light ( "black light " ), such as in a nightclub, is perceived due to the high light intensity in the surrounding darkness, the emitted fluorescent light particularly intense, and with a color stimulus at 440 nm as a clear blue. Similar conditions are found in a tanning salon. In contrast to the normal daily environment with bound body colors and textures " radiant " light colors are seen by the emissions.

Groups of substances

Optical brighteners used today can be divided into six distinct groups

• Stilbene compounds such as Blankophore ( about 80 % of the produced optical brighteners suitable for cellulosic and polyamide)
• Ethylene, phenylethylene, and thiophene derivatives which two hetero -aromatic radicals (e.g., the benzoxazole group) include (hydrophobic, as additives in melt spinning process )
• Coumarin and Carbostyril derivatives ( are no longer used )
• 1,3- diphenyl-2- pyrazolines ( for the optical brightening of protein fibers, cellulose acetate, and polyamides )
• Naphthalimides ( the main representative of N- methyl -4-methoxy - naphthalimide, very stable)
• Compounds in which a condensed aromatic ring is directly connected to a heteroaromatic such as thiazoles, pyrazoles, oxadiazoles, or triazines (e.g., 2,4 -dimethoxy- 6-( 1'- pyrenyl ) -1,3,5- triazine)

Today, about 400 different substances are produced as optical brighteners with a total of over 33,000 t / a. n number of different application forms of the same base body are counted. From the optical brighteners, whose absorption maximum wavelength shorter than visible light, the colorful fluorescent colors to be distinguished, which fluoresce in the green and yellow ( Brillantflavin ) and in the red ( rhodamine ) and find their application for effect purposes and backup here.

Use

Detergent

In the detergents segment optical brighteners are primarily intended for washing textiles with lighter -duty detergents. The function of the detergent brightener lies in the replacement of brighteners which leached out or undergo photochemical degradation during wear. In this way an increasing yellowing and fading of fabrics is prevented, thus increasing the useful life. The content of optical brighteners in washing ranges from 0.03 % to 0.3% (dry basis ) with an average of 0.15%.

The present detergents contain almost exclusively the two stilbene DAS1 ( disodium -4 ,4 -bis- [(4 -anilino -6 -morpholino- 1 ,3,5- triazin-2- yl) amino] stilbene-2 ​​, 2 - disulfonate ), and DSBP ( disodium -4 ,4-bis (2- sulfostyryl ) -biphenyl). The market ratio of DAS1 to DSBP in Europe is about 85 % to 15%. DAS1 and DSBP are sodium salts of aromatic ( at DAS1 additional heterocyclic ) sulfonic acids. In dissolved form, they are due to the high acidity of sulfonic acid at pH values ​​of 6 to 8 as anions. The sulfonate groups are responsible for the moderate water solubility of the otherwise hydrophobic brightener.

The Lingerie Blue previously used made ​​it seem more gray linen, because the absorption of blue light by the laundry ( yellowing ) was offset by the absorption of all other light components.

Textiles

Already in the 19th century was the fluorescence of the Aesculins, or sonnenlichtbestrahlter, aqueous extracts of horse chestnut bark reported. Around 1929 watched the German chemist Paul krais ( 1866-1939 ) that textiles (wool and flax fibers ) after treatment with esculin ( from an extract of horse chestnut ) white appeared as usual, the derived from aesculin methylumbelliferone was the first industrially manufactured brighteners. This initially used optical brighteners, however, were a little light, water and wash-fast. The first well- adhered to the fiber optical brighteners were the derivatives of 4,4 ' -diamino-2, 2'- stilbenedisulfonic acid.

Paper

Optical brighteners are formulated in the preparation of certain paper grades. Papers are so " bright " white. They are applied in magazine papers and poster papers, in order to achieve a higher brightness here. White pigment is titanium dioxide for paper, this increases the degree of whiteness, optical brightening fluorescent organic substances are added. In addition, is used as a substitute for titanium dioxide today often finely ground and highly white or precipitated calcium carbonate.

In case of overdose of optical brighteners absorption can range up into the visible, so enters the opposite effect, the paper is not bright, but the color is greenish.

Fluorescent Color

Not even fluorescent colorants may be by admixture of certain optical brighteners to chromatic colors with fluorescent inks character. Due to the special Absortions and emission maxima, this composition, however, are only suitable for blue to blue-green tones. Since optical brighteners be made ​​for the absorption of ultraviolet un emission in the blue region, this limitation is inherent. This application separately for signal colors plays a certain role.

Environmental relevance

• During the washing process, the optical brightener couple to the fabric fiber. Since it is an equilibrium process, there remains a part of the washing solution and thus enters the waste water and thus further into the sewage treatment plant. In the sludge go on up to 50 % of the brightener, the rest will be entered into the waters ( receiving water ). Because of the resistance of the brightener against microbial degradation in soil and water can enter an alarming accumulation. In water bodies and ground surface occurs at a slower sunlight photolytic degradation.

• A hormonal effect of certain classes of substances is suspected. Optically brightened textiles, due to the direct contact with the skin under acquisition in the body, a damaging effect attributed. Ecologically working textile, detergent, and paper - manufacturers have therefore optical brighteners.

Figurative meaning

In a figurative sense euphemistic, distorting PR methods are also referred to as a whitener in public relations. Most conceptually more established greenwashing is meant, which stands for the natural representation of companies that want a targeted launch an environmentally conscious image.