Ultraviolet light degradation

Specifically the situation may involve a patent covering a method of reducing ultraviolet light degradation of plastic materials by... 

Because of its high crystallinity, the hnmopolymer (PVDV) is insoluble in most solvents at room temperature. However, since the regularity of repeating units in the chain is decreased by copolymerization, Saran is soluble in cyclic ethers and aromatic ketones. This copolymer (100 g) is plaslicized by die addition of a-melhyl-benzyl ether (5 g), stabilized against ultraviolet light degradation by 5-chloro-2-hydroxybenzophenone (2.0 g) and heat stabilized by phenoxypropylene oxide (2.0 g). 

Simazine is virtually nonvolatile and resists ultraviolet light degradation. These characteristics result in long residual activity. Simazine is relatively insoluble, remaining within the top few inches of most soils. The amount of simazine moving downward in the soil usually increased as the rate per acre was increased. 

Persistence in the soil is generally low (half-life under aerobic and anaerobic conditions is 21 and 68 days, respectively). In sterile soil, the half-life is almost 1 year. Azinphos-methyl adsorbs strongly to soil particles and has low solubility in water. Biodegradation and evaporation are the primary routes of elimination from soil but azinphos-methyl is also degraded by ultraviolet light. Degradation is more rapid at higher temperatures. Azinphos-methyl has a short half-life in surface waters (2 days). Hydrolysis is more prominent under alkaline conditions but the compound is relatively stable in water below pH 10. The half-life on crops is 3-5 days under normal conditions. 

Poly(methyl methacrylate) depolymerizes at elevated temperature under the influence of ultraviolet light of 259.7 nm [549]. Irradiation of polyacrylonitrile, however, leads to chain scission at the acrylonitrile units. The difference between thermal and ultraviolet light degradation of polyacrylonitrile is principally in the different sites of initiation and the fact that the reaction occurs at 160°C in the presence of light and at 280°C in the darkness [550]. 

Another factor in oxidative degradation is ultraviolet radiation, of which sunlight is a rich source. The oxidation of parylene appears to be enhanced by ultraviolet radiation. 02one may play a mechanistic role in the ambient temperature exposure of parylenes to ultraviolet radiation in the presence of oxygen. For the best physical endurance, exposure of the parylenes to ultraviolet light must be minimised. 

Geotextiles may be woven, nonwoven, or knitted. AH types, woven, nonwoven, or knitted, are susceptible to degradation owing to the effects of ultraviolet light and water. Thus stabilizing agents are added to the base polymeric material to lessen the effects of exposure to ultraviolet light and water. 

EthylceUulose is subject to oxidative degradation in the presence of sun- or ultraviolet light, especially at elevated temperatures above the softening point. It must, therefore, be stabilised with antioxidants (44). EC is stable to concentrated alkah and brines but is sensitive to acids. 

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. 

Effect of UV Radiation on Sodium Pentachlorophenate. Sodium pentachlorophenate is quickly degraded in the presence of ultraviolet light as well as daylight, as shown in Table III. The degradation is almost complete after 16 hours exposure to the General Electric R.S. sunlamp. Three and one-half days of rainy and overcast skies account for the somewhat lower degradation observed in the sample exposed to daylight. 

If no references for the degradation products or impurities are available in the laboratory, the sample should be exposed to stress conditions such as heat (50-80 °C), ultraviolet light (2000 lux), acid and base (0.1-1 M HC1 and NaOH), and oxidant (3% H2O2). After incubation in the allotted time, the purity and identity of the analyte peak/spot should be proved by using DAD or MS detection (for LC), MS (for GC), or in situ UV-Vis measurement using a densitometry or TLC-MALDI MS (for TLC). 

Pseudoephedrine hydrochloride can be considered a stable compound in bulk and in formulations. After 4-weeks under fluorescent lights (2400 ft. candles) and ultraviolet light (190 pw/cm2) no discoloration or chemical degradation was observed. The bulk drug was stable for at least 6 months at 37°C and 3 months at 50°C. Tablet and syrup formulations stored at 15-30°C for 5 years showed no appreciable degradation. 13... 

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