Ultraviolet radiation-stabilizers

How does the primary mechanism of stabilization differ between ultraviolet radiation stabilizers and thermal stabilizers ... 

Hydroxybenzophenones represent the largest and most versatile class of ulbaviolet stabilizers that are used to protect materials from the degradative effects of ulbaviolet radiation. They function by absorbing ultraviolet radiation and by quenching elecbonically excited states. 

As a rule, however, most of the ESIPT dyes exhibit weak to very weak fluorescence quantum yields, i.e., the quantum yield of the nonradiative processes is near unity. Such dyes, if they show little permanent photodestruction, can be used as ultraviolet (UV)-stabilizers of polymers, such as Tinuvin (a hydroxy-benzotria-zole),(45) because they efficiently convert UV radiation, harmful for the polymer, into harmless heat. The mechanisms of these nonradiative decay paths are often linked to... 

Acrylic and modacrylic fibers have a wool-like appearance and feel, and excellent resistance to heat, ultraviolet radiation, and chemicals [Bajaj and Kumari, 1987]. These fibers have replaced wool in many applications, such as socks, pullovers, sweaters, and craft yams. Other applications include tenting, awning fabric, and sandbags for rivershore stabilization. The use of acrylic and modacrylic fibers in carpets is low since these materials do not hold up well to recycling through hot-humid conditions. This also prevents its use in the easy-care garment market. 

The role of CFCs in the destruction of ozone in the stratosphere was something of a surprise to some researchers because those compounds are normally quite stable. In fact, their stability is one of their most desirable properties for many industrial and commercial applications. But, when CFCs escape into the atmosphere and drift upward, they are exposed to ultraviolet radiation in sunlight and, as is oxygen itself, are dissociated by that radiation. In the case of Freon-12 (CCI2F2), photodissociation results in the formation of free chlorine atoms ... 

Hexamethylphosphoramide has been produced commercially in relatively small quantities in several countries of Europe, in Japan and in the United States. It is used as a solvent for polymers, a selective solvent for gases and as a thermal and ultraviolet radiation degradation stabilizer in various polymers (lARC, 1977). 

Bryce-Smith [2] in 1959. They found that benzene and maleic anhydride react to form a stable 1 2 adduct under the influence of ultraviolet radiation. The authors proposed that initially an ortho adduct is formed which could normally be expected to revert rapidly to the starting materials, but which would be stabilized by rapid addition of a further molecule of maleic anhydride to the bicyclic diene system. The stereochemistry of the 1 2 adduct was established by Grovenstein et al. [23] (who reported that they had independently discovered the same reaction) and, more firmly, by Bryce-Smith et al. [24] and Pettit et al. [25], The structure is depicted in Scheme 4. 

Of prime importance to the continued growth of polypropylene are the stabilizer systems which must be used to protect the resin during processing, and during exposure of finished products to various environmental and use conditions. The weak tertiary carbon—hydrogen bonds in polypropylene make it particularly susceptible to degradation caused by heat, oxidation, process shearing, and ultraviolet radiation (24). 

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