Natural photochemical degradation

There is a substantial literature on the thermal and photochemical degradation of PS and it is well established that polymer properties are sensitive to the manner in which a particular sample of PS is prepared. For example, it has been reported that PS prepared by anionic polymerization shows enhanced stability with respect to that prepared by a radical mechanism.2 10 This has often been attributed to the presence of "weak links" in the latter polymers. However, the precise nature of the "weak links" remains the subject of some controversy. T he situation is further confused by all PS prepared by radical mechanisms often being considered as a class without reference to the particular polymerization conditions employed in their preparation. In many cases the polymers are "commercial samples" with details of the method of preparation incomplete or unstated. 

Basagran has a herbicidal activity but a high bioconcentration factor (Kinkennon, 1995). Diquat is able to undergo natural photochemical decomposition after application to plant surfaces. Studies show that 50 mg of herbicide is depleted to below 6 mg/kg within 7 days after treatment. In soil, diquat is biodegraded at a rate of 10% per year. In aqueous environments, diquat was degraded to levels that were undetectable in less than 30 days. 

Mopper, K., X. Zhou, R.J. Kieber, D.J. Kieber, R.J. Sikorski, and R.D. Jones. 1991. Photochemical degradation of dissolved organic carbon and its impact on the oceanic carbon cycle. Nature 353, 60-62. 

Ahel, M., F.E. Scully Jr, J. Hoigne, and W. Giger. 1994. Photochemical degradation of nonylphenol and nonylphenol polyethoxylates in natural waters. Chemosphere 28, 1361-1368. 

Slade, P., Smith, A.E. (1967) Photochemical degradation of diquat. Nature 213, 919. 

However, under more natural conditions, e.g. according to the methods recommended in the EPA Guidelines the rate of the photochemical degradation was found to be very low h.) In other experiments washing off of diflubenzuron from plant leaves with high amounts of simulated rainfall was found to be negligible All these results point to a high... 

Sakkas VA, Lambropoulou DA, AlbanisTA. Photochemical degradation study of irgarol 1051 in natural waters influence of humic and fulvic substances on the reaction. J Photochem Photobiol A Chem 2002 147 135-41. 

Stress and strain Nature of environment Temperature Molecular weight Molecular architecture Crystallinity Orientation > < Dissolution Softening Stress-cracking Embrittlement Chemical degradation Photochemical degradation k Biological degradation... 

Natural fibers may be adversely affected by sunlight, air pollutants, acids and alkali, bleaches and other oxidizing agents, and chemical finishing processes. However, the effects of photochemical degradation are by far the most problematic in the conservation of textiles and therefore have received the most attention. 

Photochemical degradation of natural fibers depends on the atmospheric conditions in which the textiles are exposed, stored, or displayed, on... 

Experimental data are needed regarding photolysis of tetryl in the atmosphere so that the relative contributions of photochemical degradation can be determined. Photolysis and hydrolysis are the primary mechanisms that degrade tetryl in water (HSDB 1994). It would be helpful to develop reliable data for photoreaction, hydrolysis and biodegradation rates of tetryl in natural water, and biodegradation rates of tetryl in natural soils. 

Trichloroethane may very slowly undergo abiotic degradation in soil or water by elimination of hydrochloric acid (HCl) to form 1,1-dichloroethene, which also can be considered a pollutant, or it can undergo hydrolysis to form the naturally occurring acetic acid. Direct photochemical degradation is not expected to be an important fate process. 

---