Fluorinated polymers, weathering

In a study of weathering resistance, three partially fluorinated polymers (ETFE, PVDF, and PVF) were exposed to ultraviolet light in a QUV Weather-... 

Many fluorinated polymers have excellent weathering resistance. Ethyl-ene/tetrafluoroethylene copolymers are particularly appropriate for film manufacture and developments have included examples reinforced with woven glass and perforated metal foil which can be used outdoors [41]. Fluorinated polymers reinforced with glass fibre are used for roofing applications. 

Ethylene Tetrafluoroethylene Copolymer - Thermoplastic comprised of an alternating copolymer of ethylene and tetrafluoroethylene. Has high impact resistance and good abrasion resistance, chemical resistance, weatherability, and electrical properties approaching those of fully fluorinated polymers. Retains mechanical properties from cryogenic temperatures to 356°F. Can be molded, extruded, and powder-coated. Used in tubing, cable and wire products, valves, pump parts, wraps, and tower packing in aerospace and chemical equipment applications. Also called ATFA. 

The polymer, like many fluorine-containing polymers has very good weathering resistance and may also be used continuously up to 150°C. Outside of the electrical field it finds use in fluid handling, in hot water piping systems, in packaging and in chemical plant. A widely used specific application for PVDF is in ultra-pure water systems for the semiconductor industry. 

When photosensitizers such as benzophenone are added to polymer, absorption of ultraviolet radiation results in excitation of the sensitizer followed by hydrogen abstraction fi-om the polymer to yield radical sites (Equation 1.39) available for cross-linking by combination reactions. Copolymers of vinyl esters and fluorinated monomers that can be cross-linked by ultraviolet radiation have been developed for use as weather-resistant wood coatings. In this application, the vinyl ester constitutes about 10% of the copolymer and benzophenone is added as a photosensitizer. The vinyl ester polymer also undergoes a-cleavage reaction (Equation 1.40) with subsequent cross-linldng. 

Fluoropolymers Polymers prepared Irom unsaturated fluorine-containing hydrocarbons. Has good chemical resistance, weatherability, thermal stability, antiadhesive properties, low friction, and flammability, but low creep resistance, strength, and difficulty processing. The properties vary with the fluorine content. Processed by extrusion and molding. Used as liners in chemical apparatus, in bearings, films, coatings, and containers. Also called Fluoroplastics. 

S Polyvinyl fluoride (PVF). Polyvinyl fluoride (PVF) is a crystalline polymer available in film form and used as a lamination on plywood and other panels. The film is impermeable to many gases. PVF is structurally similar to polyvinyl chloride (PVC) except for the replacement of a chlorine atom with a fluorine atom. PVF exhibits low moisture absorption, good weatherability, and good thermal stability. Similar to PVC, PVF... 

Lower crystallinity, and consequently density, are associated with higher-molecular-weight polymer. This is a useful relationship, since the normal solution methods of molecular weight determination are precluded by the insolubility of PTFE in all solvents except at temperatures above 300°C, which property is exploited in many applications. PTFE is chemically inert, attack being limited to materials such as molten sodium. It may be dissolved by highly fluorinated liquids near its melting point. It has excellent weathering resistance and is stable in air to at least 250°C for continuous service. 

The characteristics of fluoropolymers are summarized in Table 1. Thermal and chemical resistance is in general with most of plastics, elastomers and perfluorinated membranes. Weather resistance with the outdoor durability for more than 20 years is specific for fluorinated paint resins. Surface properties such as water and oil repellency are provided by acrylic polymer-based textile finishes and coatings with long-chain per-fluoroalkyl groups. Electrical properties as well as a low refractive index are important for optoelectronics applications like optical fibers. 

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