ULTRAVIOLET DEGRADATION APPLICATION

PMMA and polyvinylidene fluoride (PVDF) form miscible blends in which PMMA acts as a polymeric plasticiser when added in low amounts. PMMA improves processing and both PMMA and PVDF are resistant to ultraviolet degradation. Applications include weatherable film [37-41]. 

Polymeric hindered amine light stabilizer is excellent for protection against ultraviolet degradation. Applications include polyolefins (polypropylene, polyethylene), olefin copolymers such as EVA as well as blends of polypropylene with elastomers. Also effective in polyacetals, polyamides, polyurethanes, flexible and rigid PVC, and PVC blends. 

Engineering thermoplastic composites are subject to both short-term and long-term outdoor applications. In such applications they are susceptible to moisture, thermal, oxidative, and photochemical (ultraviolet) degradation. 

Hypalon is a tradename for CSM chlorosulfonated polyethylene. It offers good resistance to moderate chemicals, ozone, alkaline solutions, hydrogen. Freon, alcohols, aliphatic hydrocarbons, as well as ultraviolet degradation from sunrays. Strong oxidizing acids, ketones, esters, acetic acid, and chlorinated and nitro-hydrocarbons attack Hypalon. Its temperature range for applications is from -40°C to 150°C (-40°F to 300°F). Its physical properties are presented in Table 10-16. 

Degradation of parathion in soil was by hydrolysis to p-nitro-phenol and diethylthiophosphoric acid and reduction to aminopara-thion (25,26). Chemical oxidation of parathion in soils and waters was not prevalent, although oxidation of the phosphorus-sulfur bond has been shown to occur under ultraviolet light and in oxidizing environments (26). At ordinary levels of application to soil, parathion was degraded within weeks if microbial activity was available (27). Accumulations even after repeated applications were unlikely (28). When higher concentrations were applied to soil, persistence increased. Simulated spills of concentrated parathion resulted in a 15% residue after five years (29) and 0.1% after 16 years (30). 

A major consequence of using regulatory limits based on degradant formation, rather than absolute change of the API level in the drug product, is that it necessitates the application and routine use of very sensitive analytical techniques [ 10]. In addition, the need to resolve both structurally similar, as well as structurally diverse degradants of the API, mandates the use of analytical separation techniques, for example, HPLC, CE, often coupled with highly sensitive detection modes, for example, ultraviolet (UV) spectroscopy, fluorescence (F) spectroscopy, electrochemical detection (EC), mass spectroscopy (MS), tandem mass spectroscopy (MS-MS) and so forth. 

Nylons require modification or stabilization to improve their resistance to certain environmental effects. Unstabilized nylon is degraded by ultraviolet light. The most widely used stabilizer has been approximately 2% well-dispersed carbon black, which has proved effective in the absorption of ultraviolet light. The nylons are considered adequate for outdoor applications if they are not exposed to direct sun-hght,... 

The particular absorber to be used in a given application depends on several factors. One important criterion is whether the absorber will strongly absorb that portion of the ultraviolet spectrum responsible for degradation of the plastic under consideration. Compatibility, volatility, thermal stability, and interactions with other additives and fillers are other items that must be considered. When used in food wrappings, Food and Drug Administration approval must be obtained. While one or more of these considerations may rule out a given stabilizer or influence llie choice of one class over another, the final selection must await the results of extensive accelerated and long-term tests. 

As noted earlier, poly(methyl methacrylate) plastic has excellent resistance to ultraviolet radiation. Nevertheless, in long-term outdoor applications or in lighting fixtures, small amounts of ultraviolet absorbers are employed to retard the yellowing and degradation in physical properties which would otherwise occur. 

After an extraction into methylene chloride from a methanolic pH 7.2 phosphate buffer, the ultraviolet absorbance is measured near 318 nm. This analysis measures intact indomethacin in the presence of its hydrolytic degradation products. If esterification has occurred, an ether wash prior to extraction from phosphate buffer has been used to prevent interference caused by esters(39). This procedure is also applicable to injections, suppositories, suspensions and tablets. 

The single use of vinyl chloride is in the manufacture of poly(vinyl chloride) plastic, which finds diverse applications in the building and construction industry as well as in the electrical, apparel, and packaging industries. Poly(vinyl chloride) does degrade relatively fast for a polymer, but various heat, ozone, and ultraviolet stabilizers make it a useful polymer. A wide variety of desirable properties can be obtained by using various... 

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