Degradation by UV irradiation

Already carbon black is recognized for its ability to stabilize polymers against degradation by UV irradiation. However, basically three different major classes of light stabilizers can limit and slow down the photodegradation of polymers ... 

Polyvinyl chloride has been modified by photochemical reactions in order to either produce a conductive polymer or to improve its light-stability. In the first case, the PVC plate was extensively photochlorinated and then degraded by UV exposure in N2. Total dehydrochlorination was achieved by a short Ar+ laser irradiation at 488 nm that leads to a purely carbon polymer which was shown to exhibit an electrical conductivity. In the second case, an epoxy-acrylate resin was coated onto a transparent PVC sheet and crosslinked by UV irradiation in the presence of both a photoinitiator and a UV absorber. This superficial treatment was found to greatly improve the photostability of PVC as well as its surface properties. 

Kusic, H, Koprivanac, N Srsan, L. Azo dye degradation using Fenton type processes assisted by UV irradiation A kinetic study. Journal of Photochemistry and Photobiology A Chemistry, 2006 181 (2-3), 195-202. 

Most cleavable surfactants contain a hydrolyzable bond. Chemical hydrolysis is either acid- or alkaU-catalyzed and many papers discuss the surfactant breakdown in terms of either of these mechanisms, hi the environment, bonds susceptible to hydrolysis are often degraded by enzymatic catalysis, but only few papers dealing with cleavable surfactants have dealt with such processes in vitro. Other approaches that have been taken include incorporation of a bond that can be destroyed by UV irradiation or use of a bond which is cleaved when exposed to ozone. 

None of the five compounds analyzed can be destroyed in the gas phase without UV irradiation however, both trichloroethylene and tetrachloroet-hylene were degraded under UV irradiation. In the aqueous phase, UV irradiation destroyed the five compounds tested. The degradation rates increased linearly with UV intensity. Finally, the utilization efficiency of ozone, as well as the corresponding destruction rates of organic compounds, is influenced by UV intensity. The maximum efficiency roughly occurred in light intensity ranging from 10 to 100 W/m2. 

Allard, B., H. Boren, C. Pattersson, and G. Zhang. 1994. Degradation of humic substances by UV irradiation. Environment International 20 97-101. 

Amino acids are converted into aldehydes, the most popular method being the Strecker degradation. 2 The amino acid is simply mixed with reagents such as niiihydiin and heated to form ammonia and carbon dioxide as by-products. Sodium hypochlorite can be used in a process accelerated by UV irradiation. 2 A similar reaction is the Akabori reaction where the amino acid is heated with compounds such as glucose to give aldehydes, as in the Strecker process. 2 ... 

Luse and M(iLaren (1963) have reviewed published research on the photolysis products and quantum yields tor the destruction of amino acids and have attributed the photochemical inactivation of the enzymes chymo-trypsin, lysozyme, ribonuclease, and trypsin by UV light at 254 m i primarily to destruction of the cystyl and tryptophyl residues. The destruction of these residues in proteins was suggested to be a function of the product of the number of residues present, the molecular extinction coefficient, and the quantum yield for destruction of each residue. Cysteine and tryptamine were identified among the irradiation products from cystine and tryptophan, respectively. Tyrosine, histidine, and phenylalanine were also shown to be degraded by UV, histidine yielding histamine, urocanic acid, and other imidazole derivatives, and phenylalanine yielding tyrosine and dihydroxyphenylalanine. Destruction of these three amino acids was not considered to contribute appreciably to the enzyme inactivation. 

As stated above, De Haan and co-workers did not consider photolysis of fulvic acids by UV irradiation as an important determinant of fulvic acid molecular weight distribution pattern or chemical composition. Since cleavage of fulvic acid molecules and subsequent degradation to CO2 and H2O by UV irradiation can occur especially in summer, the observed fluctuations in Tjeukemeer may be attributed to phytolysis as well as degradation by bacteria. This is supported by findings of Strome and Miller (1978) and Gilbert (1980), who demonstrated an enhanced biodegradability of fulvic acids after UV irradiation. 

Matos, J., Laine, J., and Hermann, J.M. (2001). Effect of the type of activated carbons on the photocatalytic degradation of aqueous organic pollutants by UV-irradiated titania. J. Catal, 200(1), 10-20. 

Polyethylene is known to be degraded and cross-linked by UV irradiation, and a tremendous number of investigations have been carried out, mainly from the practical point of view. Several workers have studied... 

Any plastic constituent in addition to the function it serves must have heat stability, UV light stability, weather resistance, low solubility in terms of extraction, compatibility with other constituents and good dispensability. Where plastics have to be sterilised by irradiation, certain constituents may be degraded, or even continue to degrade after irradiation. Certain antioxidants are degraded by gamma irradiation. 

Irradiation by UV Irradiation crosslinking Irradiation degradation Irrotational flow field Isocyanate-containing species Isopropenyl oxazoline (IPO)... 

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