Polytetrafluoroethylene mechanical properties

Another field of application of fluorinated biomaterials is connected to lesions or evolving disease pathology of blood vessels. In particular, arteries may become unable to insure an adequate transport of the blood to organs and tissues. Polytetrafluoroethylene (PTFE) and expanded e-PTFE are the preferred materials for vascular prostheses. The interactions of blood cells and blood plasma macromolecules with both natural and artificial vessel walls are discussed in terms of the mechanical properties of the vascular conduit, the morphology, and the physical and chemical characteristics of the blood contacting surface. 

Kabin, S. P. On the dynamic mechanical properties of polyethylene and polytetrafluoroethylene. Soviet Physics Technical Physics 1, 2542—2546 (1956). 

Speerschneider CJ, Li CH (1963) A correlation of mechanical properties and microstructure of polytetrafluoroethylene at various temperatures. J Appl Phys 34 3004... 

Polymers used for seat and plug seals and internal static seals include PTFE (polytetrafluoroethylene) and other fluorocarbons, polyethylene, nylon, polyether-ether-ketone, and acetal. Fluorocarbons are often carbon or glass-filled to improve mechanical properties and heat resistance. Temperature and chemical compatibility with the process fluid are the key selection criteria. Polymer-lined bearings and guides are used to decrease friction, which lessens dead band and reduces actuator force requirements. See Sec. 28, Materials of Construction, for properties. 

Perfluoroalkylvinyl ethers form an important class of monomers in that they are used as comonomers for the modihcation of the properties of homofluoropolymers in addition to their broad nse in copolymers with TFE and other monomers. They are capable of snppressing the crystallization of PTFE efficiently, which imparts usefnl mechanical properties to lower molecular weight of polytetrafluoroethylene polymers. Copolymers of PAVEs and tetrafluoroethylene are thermally stable as PTEE homopolymers. Commercially significant monomers are perfluoropropylvinyl ether and perflnoromethylvinyl ether (PMVE), used for the production of a variety of perflnoroalkoxy resins. 

Polytetrafluoroethylene is a completely fluorinated polymer manufactured by free-radical polymerization of tetrafluoroethylene. With a linear molecular structure of repeating -CF2—CF2- units, PTFE is a crystalline polymer with a melting point of 326.7°C. Its specific gravity is 2.13—2.19. Polytetrafluoroethylene has exceptional resistance to chemicals. Its dielectric constant (2.1) and loss factor are low and stable across a wide range of temperature. It has useful mechanical properties from myogenic temperatures to 260°C. In the United States, PTFE is sold as Halon, Algoflon, Teflon, Fluon, Hostaflon, and Polyflon. ... 

Mechanical properties. Polytetrafluoroethylene retains excellent properties at very low and high temperatures. Table 3.11 provides summary of some of the mechanical properties of three different compounds containing 65% bronze, 15% carbon, and 25% glass fiber at different temperatures. Properties of unfilled PTFE have been listed for comparison. 

Ryton Polyphenylene Sulfide is a new commercial plastic which is characterized by good thermal stability, retention of mechanical properties at elevated temperatures, excellent chemical resistance, a high level of mechanical properties, and an affinity for a variety of fillers. It is produced from sodium sulfide and dichlorobenzene. Its unusual combination of properties suggests applications in a variety of molded parts such as non-lubricated bearings, seals, pistons, impellers, pump vanes, and electronic components. Tough coatings of polyphenylene sulfide can be applied to metals or ceramics by a variety of techniques and are used as protective, corrosion-resistant coatings in the chemical and petroleum industries. Incorporation of small amounts of polytetrafluoroethylene provides excellent non-stick properties in both cookware and industrial applications. 

Polymers and polymer matrix composites are increasingly replacing metals in bearings, cams, gears, and other sliding components. Polytetrafluoroethylene (PTFE) is an example of a self-lubricating polymer that is widely used for its wear resistance. Fiber reinforcement of PTFE improves other mechanical properties without sacrificing the wear performance. 

Asymmetric and composite membranes commercially known as HYFLON AD are obtained from copolymers of tetrafluoroethylene (TFE) and 2,2,4-trifluoro-5-trifluoromethoxy-l,3-dioxole (TTD) these membranes show a high hydrophobic character with contact angles to water greater than 120° (Arcella et al. 1999). Hydrophobic membranes from copolymers of polytetrafluoroethylene (PTFE) and polyvinylidenefluoride (PVDF) were prepared by a phase inversion process (Feng et al. 2004) these membranes exhibit excellent mechanical properties and good hydrophobicity (contact angle to water of about 87°). 

Polytetrafluoroethylene is extremely sensitive to radiation and exhibits marked damage to its mechanical properties. It was shown that fluoride ions evolve from the polymer not only during irradiation, but also for long periods afterward [134]. The molecular weight of the polymer drops steadily with each dose. Many double bonds form in the polymer [580]. 

Various micronized polytetrafluoroethylene powders were compounded with silicone rubber (MQ) and the mechanical properties of the composites were evaluated. At a PTFE level of only 5 wt%, the fractured surface of the composites showed layered structure morphology. This stracture effectively improved the tear strength of the MQ but it also lowered the tensile properties of the composites. The addition of fluorosUicone rubber (FMQ) as a compatibilizer, improved considerably the tensile and tear strength of the composites. Extrusion of the MQ/PTFE/FMQ composites on an electric wire indicated that the spherical PTFE powder was suitable for the extrusion process [55]. 

One other material that is used for its limited cell adhesion feature is expanded pol-ytetrafluoroethylene (ePTFE). Polytetrafluoroethylene (PTFE) was launched in the 1940s by Du Pont de Nemours as Teflon brand name. PTFE was used for the first time as a vascular prosthesis in 1963 by Edwards Lifescience and then in 1970s by Gore-Tex in expanded and microporous form (Fig. 13.12). Polytetrafluoroethylene is very stable chemically and has high hydrophobic grade that provides reduced throm-bogenicity compared to material such as PET. However, ePTFE-related mechanical properties are very poor with low compliance and elasticity. 

Tubular scaffolds fabricated by electrospinning have been extensively studied as scaffolds for small diameter (<6 mm) vascular grafts. Current artificial grafts, mainly Dacron and expanded polytetrafluoroethylene (ePTFE), have had some success when used in larger diameter grafts but are limited by issues such as thrombosis when considered for use in smaller diameter grafts. Electrospun tubular scaffolds can be fabricated with well-controlled diameters and uniform thickness across the material. The variety of polymers from which these scaffolds can be synthesised has resulted in scaffolds with mechanical properties similar to those of native vascular tissues, and hence these better support blood flow and capillaiy in-growth. 

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