Weathering properties oxygen

For some applications, more than one polymer layer is desirable. For example, a food tray might need a strong, abrasion-resistant surface layer such as polypropylene combined with an inner layer such as poly(vinylidene chloride) to contribute low oxygen permeability. House siding of poly(vinyl chloride) can benefit from a surface layer of an ABS-type polymer with superior weathering properties. In order to produce laminated, multilayer film by coextrusion, several extruders can be coupled. Each will contribute a separate stream of polymer melt to be combined without mixing in a feed block from which a layered melt issues. Much better adhesion between film layers often can be achieved in this way than could be attained by coating one melt onto a previously extruded and cooled second film. 

Fluoroelastomers excel compared to aU other elastomers in heat, chemical, flame, weathering, fuel, and o2one resistance. In addition oU, oxygen, and water resistance ate very good. The fluoroelastomers, however, ate attacked by amines and some highly polar solvents. The abrasion resistance and low temperature properties ate adequate for most appHcations. 

Chlorinated polyethylene CPEs provide a very wide range of properties from soft/ elastomeric to hard. They have inherent oxygen and ozone resistance, have improved resistance (compared to PEs) to chemical extraction, resist plasticizers, volatility, and weathering. Products do not fog at high temperatures as do PVCs and can be made flame retardant. 

Freshly cast lead has a bright, silvery appearance. On exposure to the atmosphere, however, lead in the surface layer combines with atmospheric oxygen and carbon dioxide to form a dark, stable gray coating of mixed lead oxide and basic lead carbonate. This layer usually protects the metal from further oxidation and corrosion (see Fig. 38). Protected by a weathered surface layer, solid lead is stable to further corrosion. Lead is also very ductile and soft, being the softest metal known in antiquity. It is mainly because of these properties that lead was widely used for building, to make pipes and roofs, and in naval construction, for example. Solid lead flows, albeit very... 

Because of the inorganic nature inherent in the strings of sulfur atoms in their backbones, these polymers have excellent resistance to hydrocarbon solvents that can swell common hydrocarbon elastomers. They also have good resistance to moisture, oxygen, and ozone, good weatherability, and better-than-average low temperature properties.62... 

The moderate random chlorination of polyethylene suppresses crystallinity and yields chlorinated polyethylene elastomer (CPE), a rubber-like material that can be crosslinked with organic peroxides. The chlorine (Cl) content is in the range of 36 to 42%, compared to 56.8% for PVC. Such elastomer has good heat and oil resistance. It is also used as a plasticizer for PVC. They provide a very wide range of properties from soft/elastomeric too hard. They have inherent oxygen and ozone resistance, resist plasticizers, volatility, weathering, and compared to PEs have improved resistance to chemical extraction. Products do not fog at high temperatures as do PVCs and can be made flame retardant. 

Silicone rubbers are highly resistant to the action of oxygen and ozone on natural ageing. They also have resistance to the action of intense UV radiation. Silicone rubber may be regarded as one of the most weather-resistant elastomers, even though there is some decrease in the mechanical properties on storage in open air for several years (Noll, 1968). 

Photooxidation — Occurs when the sun s action on an oil slick causes oxygen and carbons to combine to form new products that may be resins. The resins may be somewhat soluble and dissolve into the water or they may cause water-in-oil emulsions to form. Some oils are more susceptible to photo-oxidation than others. In general, it is not an important process in changing an oil s properties after a spill. (See also Resins, Weathering.)... 

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