Ultraviolet light absorbers

There is the possibiUty of a chemical reaction between a plastic and a colorant at processing temperatures. Thermal stabiUty of both the polymer and colorant plays an important role. Furthermore, the performance additives that may have been added to the resin such as antioxidants, stabilizers, flame retardants, ultraviolet light absorbers, and fillers must be considered. The suitabiUty of a colorant in a particular resin must be evaluated and tested in the final apphcation after all processing steps to ensure optimum performance. 

Ubichromenol synthesis, 3, 752 Ugi reaction, 5, 830 Uliginosin B, bromo-molecular dimensions, 3, 621 Ullman and Fetvadjian synthesis quinolines, 2, 477 Ullman synthesis acridines, 2, 470-benzacridines, 2, 470 Ultraviolet light absorbers in polymers, 1, 397-398 Ultraviolet spectroscopy heterocyclic compounds reviews, 1, 78... 

Ultraviolet light absorbers will be discussed in more detail under another section. Suffice it to say that their incorporation into a polymer can provide a useful antioxidant function. 

Additives used include plasticisers such as diphenyl diethyl ether, ultraviolet light absorbers such as 5-chloro-2-hydroxybenzophenone (1-2% on the polymer) and stabilisers such as phenoxy propylene oxide. 

Small amounts of stabiliser (1-5%) are normally added to improve weather resistance. These materials are the usual ultraviolet light absorbers such as phenyl salicylate and various benzoates. Triphenyl phosphate also has a beneficial influence. 

The alternative approach is to add a photodegradant which is an ultraviolet light absorber. However, instead of dissipating the absorbed energy as heat (as with conventional ultraviolet absorbers) the aim is to generate highly reactive chemical intermediates which degrade the polymer. One such material is iron dithiocarbamate. 

Applicabdity Limitations Photolysis is appropriate for difficult-to-treat chemicals (e.g., pesticides, dioxins, chlorinated organics), nitrated wastes, and those chemicals in media which permits photolyzing the waste. The waste matrix can often shield chemicals from the light (e.g., ultraviolet light absorbers, suspended solids, solid wastes). The photolysis process typically requires pretreatment to remove suspended materials, and the by-products formed may be more toxic than the parent molecules. 

Wintergreen is used as a flavoring in foods, beverages, drugs, and candies. It is also used as a perfume in root beer, and as an ultraviolet light absorber in cosmetics. 

An ultraviolet spectrometer is a bit more complicated than a colorimeter. Different wavelengths of ultraviolet light from 200 to 400 nm are passed through the sample and the amount of ultraviolet light absorbed at different wavelengths Is recorded. The results are plotted automatically as an ultraviolet spectrum. As with a colorimeter, the absorbance Is directly proportional to the concentration of the absorbing species. 

Hao W, Fong HK 1996 Blue and ultraviolet light-absorbing opsin from the retinal pigment epithelium. Biochemistry 35 6251—6256... 

In the MALDI technique a pulsed laser beam strikes a solid sample and heats, vaporizes, and ionizes compounds with little decomposition.201-209 Proteins or other biopolymers are mixed with a "matrix" Fiat absorbs the heat of Fie laser beam. The protein sample together with Fie matrix is dried. Most proteins form crystals and Fie laser beam is directed toward individual protein crystals or aggregates. Various materials are used for the matrix. Compounds as simple as glycerol, succinic acid, or urea can be used with an infrared laser. For proteins an ultraviolet nitrogen laser tuned to 337 nm is usually employed with an ultraviolet light-absorbing matrix such as hydroxy-benzoic acid, 2,5-dihydroxybenzoic acid, a-hydroxy-... 

Polystyrene light stabilization has been achieved with a variety of ulfravioler absorbers including the benzophenones, benzotriazoles. and salicylates. While yellowing of polystyrene occurs in many applications, it is particularly noticeable in diffusers used with fluorescent lights. This problem has been effectively solved by using ultraviolet light absorbers. In this instance, superior stabilization is achieved when the ultraviolet absorber is used in conjunction wirh specific antioxidants. 

Ultraviolet Light Stabilizers. Both titanium dioxide and carbon black are strong ultraviolet light absorbers and effective in protecting the PVC. For ultraviolet light absorption in transparent PVC oi foi impiovement of pigmented systems, various derivatives of benzotnazole are used. 

Shahjahan, M., and R. P. Enever. 1992. Some parameters forthe solubilization of nitrofurazone and ultraviolet light absorbers by nonionic surfactarltet. J. Pharm. 82 223-227. 

Shahjahan M. Ultraviolet light absorbers and their uses in pharmacy. East Pharm 1989 32 37-41. 

The major use of ultraviolet light absorbers is in polyolefins, polyvinyl chloride), polyesters, cellulose esters, and polystyrene, as Table III indicates. Lesser quantities are used in polyamides, acrylics, polyacetals, and polyurethanes. 

Table III. Domestic Consumption of Ultraviolet Light Absorbers in Plastics during 1967...

It is evident that on the basis of thermochemistry all of these reactions are possible because 91,000 calories per mole is available from the ultraviolet light absorbed. All the reactions are endothermic and one can say only that the energies of activation will be at least as large as these values of AE, but they may be much larger. 

Ultraviolet Light. At least one other source of cellulose degradation should be mentioned the destruction of cellulose by ultraviolet light absorption. Under certain conditions, it might be worthwhile to consider incorporating into the manufacture of permanent paper an ultraviolet light absorber. Most papers will not be subjected to intense uv light, however, and this should not be a problem. 

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