UV light absorber

The amount of UV light absorbed is expressed as the sample s molar absorptivity (e), defined by the equation... 

Molar absorptivity (Section 14.7) A quantitative measure of the amount of UV light absorbed by a sample. 

Preservatives generally fall into four categories. There are ultravi-olet/UV light absorbers (to prevent light from creating harmful and bad-tasting toxins), color stabilizers, antioxidants, and antimicrobials. 

GC is extensively used to determine phenolic and amine antioxidants, UV light absorbers, stabilisers and organic peroxide residues, in particular in polyolefins, polystyrene and rubbers (cf. Table 61 of Crompton [158]). Ostromow [159] has described the quantitative determination of stabilisers and AOs in acetone or methanol extracts of rubbers and elastomers by means of GC. The method is restricted to analytes which volatilise between 160 °C and 300 °C without decomposition. A selection of 47 reports on GC analysis of AOs in elastomers (period 1959-1982) has been published... 

Lawrence and Ducharme [16] have described a fast, simplified method for the detection of fluorescent whiteners in polymers, in which the polymer dissolution was applied directly to the thin layer. Similarly, using fluorescent indicator-containing layers, the presence of small amounts of UV light-absorbing antioxidants in polymers could be determined. 

Phenyl salicylate (salol) is manufactured by heating salicylic acid and phenol in the presence of phosphoms oxychloride for 4—5 hours at 110—115°C. The molten product is separated, mixed with water, dried, and distilled under vacuum. Another process involves the transesterification of a salicylate such as methyl, with phenol in the presence of an alkali or alkaline-earth phenate. Medicinally, phenyl salicylate was formerly used as an intestinal antiseptic. However, the main applications of phenyl salicylate have been related to the ability to absorb uv light over the wavelengths of 290—325 nm. As an effective uv-light absorber, phenyl salicylate was incorporated in alkyd paints, waxes, and polishes, but has been largely replaced in this application by less extractable, more effective compounds. The May 1996 price was 10.60/kg (18). 

Autoxidation can lead to deterioration of food, drugs, cosmetics, or polymers, and inhibition of this reaction is therefore an important technical issue. The most important classes of autoxidation inhibitors are radical scavengers (phenols, sterically demanding amines [65, 66]), oxygen scavengers (e.g. ascorbic acid), UV-light absorbers, and chelators such as EDTA (to stabilize high oxidation states of metals and thereby suppress the metal-catalyzed conversion of peroxides to alkoxyl radicals) [67]. 

The stabilizers chosen for evaluation include different types of heat and light stabilizers selected to represent different mechanisms of action as well as chemical compositions (ArJi). Types of stabilizers evaluated include benzotriazole and benzophenone light stabilizers [ultraviolet (UV) light absorbers], hindered amine light stabilizers (HALS, catalytic radical scavengers), hindered phenol heat stabilizers (antioxidant radical scavengers), and thioester heat stabilizers (antioxidant hydroperoxide decomposers). 

Set B Based on the results of set A discussed below, a third set. Set B, was prepared (Table IV). Cyasorb 531 (a benzophenone UV light absorber) was found to be the most effective stabilizer in Set A. It was therefore rerun at an even lower add-on in Set B, and since it was the only UV light absorber included in Set A, a second type of UV absorber, Tinuvin 327 (a benzotriazole) was included in Set B. Two new non-polymeric hindered amine light stabilizers (HALS) Tinuvin 770 and Tinuvin 765 were also evaluated in Set B with the hope that they might be more effective than the polymeric HALS (Chimassorb 944LD) included in Set A which was quite detrimental to the heat stability. Combinations of these four additives were also applied in Set B. The three new compounds evaluated have been reported to be effective light stabilizers for polyester and polyamide fibers (Capocci, G., Ciba Geigy Corporation, Ardsley, NY, personal communication, 1986). 

Other additives include materials such as hindered amine light stabilizers (HALS) and UV light absorbers (UVAs) to protect the colorants from destruction due to the environment, as well as items such as defoamers and wetting or levehng agents to help improve lay down and flow out on the media. Some of these additives such as the stabilizers and the HALS and UVAs must be added in small amounts as they can also impede curing. 

The unique luminescent properties of rare earth metal clathrochelates have been used in the development of luminescent materials (luminophores and laser materials). The luminescence of these clathrochelates in solution makes their application as biological probes and concentrators of the luminescence (i.e., the antenna effect ) promising. These complexes can also serve as efficient molecular devices to convert UV light absorbed by the ligand to lanthanide ion luminescence in the visible region. Even in very dilute (10-5 mol l-i) solutions, the conversion of irradiated photons to luminescent ones has been observed to occur at a rate of approximately 1%. For rare earth metal aqua ions at the same concentration, the efficiency of conversion is equal to 4 x IQ- % [212, 390-392]. 

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