A fluoropolymer is a fluorocarbon -based polymer with multiple carbon—fluorine bonds. It is characterized by a high resistance to solvents, acids, and bases. The best known fluoropolymer is polytetrafluoroethylene Teflon. While working with tetrafluoroethylene gas, he noticed that a previously-pressurized cylinder had no pressure remaining.
In dissecting the cylinder, he found a mass of white solid in a quantity similar to that of the tetrafluoroethylene gas. It was determined that this material was a new-to-the-world polymer. Tests showed the substance was resistant to corrosion from most substances and had better high temperature stability than any other plastic. By early , a crash program was making commercial quantities. Fluoropolymers share the properties of fluorocarbons in that they are not as susceptible to the van der Waals force as hydrocarbons.
This contributes to their non-stick and friction reducing properties. Also, they are stable due to the stability multiple carbon—fluorine bonds add to a chemical compound. Fluoropolymers may be mechanically characterized as thermosets or thermoplastics.
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Fluoropolymers can be homopolymers or Copolymer. The global demand on fluoropolymers was estimated at approximately 7. Search for books, journals or webpages All Pages Books Journals. View on ScienceDirect. Authors: Sina Ebnesajjad. Hardcover ISBN: Imprint: William Andrew. Published Date: 10th June Page Count: View all volumes in this series: Plastics Design Library. For regional delivery times, please check When will I receive my book?
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Discovery and History of Fluoropolymers 3. Graphite, bronze, and glass fibers also improve wear resistance and stiffness of the resin. The choice of fillers improving properties of FEP and their amounts are limited, however, because of processing difficulties of such mixtures. DuPont However, to use this property for welding of parts, the thickness of the resin must be sufficient to absorb the energy produced. Its volume resistivity remains unchanged even after prolonged soaking in water.
The dielectric constant of FEP is constant at lower frequencies, but at frequencies MHz and higher, it drops slightly with increasing frequency.
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Its dissipation factor has several peaks as a function of temperature and frequency. The absorption does not affect the resin and its properties and is completely reversible. The only chemicals reacting with FEP resins are fluorine, molten alkali metal, and molten sodium hydroxide. It occurs only by molecular diffusion, because the polymer was melt-processed.
Because of the low permeability and chemical inertness, FEP is widely used in the chemical industry. For the permeation through FEP films an inverse relationship between permeability and film thickness applies. They are considerably more transparent to the infrared and UV spectra than glass. The refractive index of FEP films is in the range 1. This subject is covered in more detail in Chapter 7.
Since they can be relatively easily processed by conventional methods for thermoplastics into film and sheets without microporosity, they have distinct advantage over PTFE in certain applications, such as corrosion protection and antistick coatings. The mechanical properties of PFA and MFA at room temperature are practically identical; differences become obvious only at elevated temperatures, because of the lower melting point of MFA. As a result, lower permeation coefficients should result because permeation occurs by molecular diffusion. This is indeed the case, but the effect levels off at higher temperatures.
In comparison with the partially fluorinated polymers, they are only slightly affected by temperature up to their maximum service temperature. The dissipation factor at low frequencies from 10 Hz to 10 kHz decreases with increasing frequency and decreasing temperature. In the range from 10 kHz to 1 MHz, temperature and frequency have little effect; while above 1 MHz the dissipation factor increases with the frequency.
This property depends on the degree of crystallinity and the crystal morphology in the polymer. For example, 0. The refractive indexes of these films are close to 1.kick-cocoa.info/components/buhenowo/kex-spiare-un.php
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They are resistant to strong mineral acids, inorganic bases, and inorganic oxidizing agents and to most of the organic compounds and their mixtures common in the chemical industry. However, they react with fluorine and molten alkali. This reaction has a practical application for improving surface wettability and adhesive bonding of perfluorocarbon polymers to other substrates. Since these resins are melt-processed, they are usually free of voids and, therefore, exhibit much lower permeability than PTFE. Permeation through PFA occurs via molecular diffusion. They have an excellent balance of physical, chemical, mechanical, and electrical properties, are easily fabricated by melt-processing techniques, but have found little commercial utility, because they exhibit a poor resistance to cracking at elevated temperatures.
Friction and wear properties are good and can be improved by incorporating fillers such as fiberglass or bronze powders. Fillers also improve creep resistance and increase the softening temperature. Its dielectric constant is low and essentially independent of frequency. Dielectric strength and resistivity are high and are unaffected by water. Irradiation and cross-linking increase dielectric loss. Strong oxidizing acids, such as nitric acid, and some organic bases cause depolymerization at high concentrations and high temperatures.
Addition of certain salts can alter the decomposition from oligomer formation to dehydrofluorination.
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Iron and other transition metal salts accelerate the dehydrofluorination. Hydrofluoric acid itself destabilizes ETFE at elevated temperatures and the degradation becomes self-accelerating. LOI depends on monomer ratio in the polymer and it increases gradually as the fluorocarbon content is increased to the alternating composition and then increases more rapidly to the LOI values for PTFE. Other major factors influencing the properties of PVDF are molecular weight, molecular weight distribution, and extent of irregularities along the polymer chain and the crystalline form.
Similar to other linear polyolefins, crystalline forms of polyvinylidene fluoride involve lamellar and spherulitic forms. The differences in the size and distribution of the domains as well as the kinetics of crystal growth are related to the method of polymerization. There are a total of four distinct crystalline forms: alpha, beta, gamma, and delta. The alpha and beta forms are most common in practical situations. Generally, the alpha form is generated in normal melt processing; the beta form develops under mechanical deformation of melt-fabricated specimens.
The gamma form arises under special circumstances, and the delta form is obtained by distortion of one of the phases under high electrical fields.
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Thus, the typical density of commercial products in the range from 1. The structure of polyvinylidene fluoride chain, namely, alternating CH2 and CF2 groups, has an effect on its properties which combine some of the best performance characteristics of both polyethylene —CH2—CH2— n and polytetrafluoroethylene —CF2—CF2— n. These exhibit somewhat different properties than the homopolymer.
The values can be substantially changed by the type of cooling and post-treatments, which determine the morphological state of the polymer. Dielectric constants as high as 17 have been measured on oriented samples that have been subjected to high electrical fields poled under various conditions to orient polar crystalline form. The structure yielding a high dielectric constant and a complex polymorphism also exhibits a high dielectric loss factor. This excludes PVDF from applications as an insulator for conductors of high frequency currents since the insulation could heat up and possibly even melt.
On the other hand, because of that, PVDF can be readily melted by radio frequency or dielectric heating and this can be utilized for certain fabrication processes or joining. To convert GPa to psi, multiply by , To convert J to cal, divide by 4. To convert Gy to rad, multiply by Source: Dohany, J. Section 7.
Technology of Fluoropolymers
This feature makes it unique among vinylidene polymers, which typically are degraded by high-energy radiation. Strong bases, amines, esters, and ketones cause its swelling, softening, and dissolution, depending on conditions. Such systems solvate the polymer as the temperature is raised during the fusion of the coating, resulting in a cohesive film.
These aspects have been studied and are reported in some detail in Reference For example, polyethyl acrylate is miscible with polyvinylidene fluoride, but polyisopropyl acrylate and homologues are not. Strong dipolar interactions are important to achieve miscibility with PVDF, as suggested by the observation that polyvinyl fluoride is incompatible with polyvinylidene fluoride. Low-molecular-weight polymer is available as oil or grease. It also has an excellent resistance to creep.
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