PVDF Polyvinylidene Fluoride

PVDF exhibits a complex crystalline polymorphism, which cannot be found in other known synthetic polymers. There are a total of four distinct crystalline forms alpha, beta, gamma, and delta. These are present in different proportions in the material, depending on a variety of factors that affect the development of the crystalline structure, such as pressure, intensity of the electric field, controlled melt crystallization, precipitation from different solvents, or seeding crystallization (e.g., surfactants). 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 

The structure of polyvinylidene fluoride chain, namely, alternating CH2 and CF2 groups, has an effect on its properties that combines some of the best performance characteristics of both polyethylene (-CH2-CH2-)n and polytetrafluoroeth-ylene (-CF2-CF2-) . Certain commercial grades of PVDF are copolymers of VDF with small amounts (typically less than 6%) of other fluorinated monomers, such as HFP, CTFE, and TFE. These exhibit somewhat different properties than the homopolymer. 

Typical values of electrical properties of the homopolymer without additives and treatments are listed in Table 3.10. 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 [74]. 

The unique dielectric properties and polymorphism of PVDF are the source of its high piezoelectric and pyroelectric activity [75]. The relationship between ferroelectric behavior, which includes piezoelectric and pyroelectric phenomena, and other electrical properties of the polymorphs of polyvinylidene fluoride is discussed in [76]. 

Melting point, crystalline, °C Specific gravity Refractive index n  

PVDF has properties similar to PTFE but is easier to fabricate. It has good resistance to inorganic acids and alkalis, and organic solvents. It is limited to a maximum operating temperature of 140°C. 

Polyvinylidene fluoride is a crystalline, high molecular weight polymer containing 50% fluorine. It is similar in chemical structure to PTFE except 

The chemicals listed are in the pure state or in a saturated solution unless otherwise indicated. Compatibility is shown to the maximum allowable temperature for which data is available. Incompatibility is shown by an X. A blank space indicates that data is unavailable. 

Source From P.A. Schweitzer. 2004. Corrosion Resistance Tables, Vols. 1-4,5th ed.. New York Marcel Dekker. 

Much of the strength and chemical resistance of PVDF is maintained through an operating temperature range of —40 to +320°F ( — 40 to +160°C). 

Approval has been granted by the Food and Drug Administration for repeated use in contact with food in food handling and processing equipment. 

Polyvinylidene fluoride (PVDF) (PVF2) is made from 1,1-difluoroethylene by polymerization in bulk, solution or dispersion with starters such as peroxides or y-radiation. Commercial PVDF products are Kynar (Pennwalt Corporation), Sole (Solvay) and Vidar (AWK Trostbergj [2]. 

The density of the a-polymorph is 1.98 g cm amorphous PVDF has a density of 1.68 g cm . Thus, commercial samples with a density of 1.75-1.78 g cm have 45% crystaUinity. The a-polymorph melts at 170 °C however, the processed polymer, because of its polymorphism, displays no sharp melting point but melts between 150 and 190 °C. The thermal decomposition becomes significant at T 300°C. Pyrolysis of PVDF yields hydrogen fluoride, the monomer C2H2F2 and C4F3H3 [12]. Up to 600 °C, pyrolysis also yields polyaromatic structures by cyclization of polyenic intermediates formed through HF ehmination [16]. This is a particular advantage over PTFE, which is less likely to yield carbonaceous products. Thus in obscurant applications, PVDF is preferred over PTFE as a fluorine source (see Chapter 11). 

The macromolecule of polyvinylidene fluoride (PVDF) consists of a linear chain in which the predominant monomer unit is [—CH —CF —] . PVDF has good weathering resistance and it is resistant to most chemicals and solvents but less inert than PTFE, PFA and FEP in the same conditions. PVDF is nonflammable and exhibits greater mechanical strength, wear and creep resistance than other fluorocarbons. PVDF is heat resistant up to 150°C. However, the material is much more workable and has been made into essentially any shape necessary for the chemical process industry. Complete pumps, valves, piping, smaller vessels, and other hardware have been made and have served successfully. The material may also be applied as a coating or as a liner. 

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Which materials are best for cell design depends essentially on the type of electrolyte used. Because HF acid is quite common in the electrochemistry of silicon, materials resistant to HF are preferable. Polyvinyl chloride (PVC), polypropylene (PP), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) can be used for the cell body. PVC is a good choice for most designs because it is inex-... 

Polyvinylidene fluoride (PVDF) Aqueous and/or organic samples resistant to common HPLC solvents... 

Polymers with flexible chains, such as natural rubber (NR), have low Tg values. The Tg is always less than the Tm> and the ratio of Tg to Tm is lower for symmetrical polymers like polyvinylidene fluoride (PVDF) than for those with unsymmetrical repeating units, such as polychlorotrifluoroethylene. Raymond Boyer has proposed a relationship of Tm — KTg, where the constant K — 2 for symmetrical and 1,4-asymmetrical chains. 

Polyvinylidene fluoride (PVDF) (Kynar) has the following repeating unit ... 

Polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF) cross-link upon irradiation, particularly with the use of prorads, such as TAG, TIAG, diallyl itaconate, ethylene bis-maleimide, and others. ... 

PVC, another widely used polymer for wire and cable insulation, crosslinks under irradiation in an inert atmosphere. When irradiated in air, scission predominates.To make cross-linking dominant, multifunctional monomers, such as trifunctional acrylates and methacrylates, must be added. Fluoropolymers, such as copol5miers of ethylene and tetrafluoroethylene (ETFE), or polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), are widely used in wire and cable insulations. They are relatively easy to process and have excellent chemical and thermal resistance, but tend to creep, crack, and possess low mechanical stress at temperatures near their melting points. Radiation has been found to improve their mechanical properties and crack resistance. Ethylene propylene rubber (EPR) has also been used for wire and cable insulation. When blended with thermoplastic polyefins, such as low density polyethylene (LDPE), its processibility improves significantly. The typical addition of LDPE is 10%. Ethylene propylene copolymers and terpolymers with high PE content can be cross-linked by irradiation. ... 

Fluoropolymers, such as copolymer of ethylene and tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), are widely used in wire and cable insulations. They are relatively easy to process and have excellent chemical and thermal resistance, but tend to creep, crack and possess low mechanical stress at temperatures near their melting points. Radiation has been found to improve their mechanical properties and crack resistance.36... 

Some construction materials, for example, polyvinylidene fluoride (PVDF), are bacteriologically resistant and it has been shown that simple rinsing without... 

All the filters used must comply with the demands made by regulatory authorities. In sterilizable systems, hydrophobic diaphragm filters made of either polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) with a diaphragm pore width of... 

H2S and S02 removal 245 Polyvinylidene fluoride (PVDF) hollow fibers and concentrated NaOH solution used... 

Polyvinylidene fluoride (PVDF) and Ethylene tetrafluoroethylene copolymer (ETFE) can be considered as diluted PTFE s, which in their structure and their properties... 

Commercial products based on copolymers of ethylene and TEE are made by free radical-initiated addition copolymerization.69 Small amounts (1 to 10 mol%) of modifying comonomers are added to eliminate a rapid embrittlement of the product at exposure to elevated temperatures. Examples of the modifying comonomers are perfluorobutyl ethylene, hexafluoropropylene, perfluorovinyl ether, and hexafluoro-isobutylene.70 ETFE copolymers are basically alternating copolymers,70 and in the molecular formula, they are isomeric with polyvinylidene fluoride (PVDF) with a head-to-head, tail-to-tail structure. However, in many important physical properties, the modified ETFE copolymers are superior to PVDF with the exception of the latter s remarkable piezoelectric and pyroelectric characteristics. 

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