Vinylidene fluoride extrusion

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

Suzuki et al. reported cloud-point temperatures as a function of pressure and composition in mixtures of poly(ethyl acrylate) and poly(vinylidene fluoride) [9], Their data in terms of p(T) curves at constant composition show that miscibility in the same system may either improve or decline with rising pressure, depending on the blend s composition. Important consequences for blend-processing ensue. A planned two-phase extrusion may easily be jeopardized by the pressure building up in the extruder. Conversely, a homogeneous melt may be turned into a two-phase system when the pressure on the blend increases. 

Extrusion-Applied Insulations. The polymers used in extrusion applications can be divided into two classes low-temperature applications and high-temperature applications. Polymers in the first category are poly(vinyl chloride), polyethylene, polypropylene, and their copolymers along with other elastomers. Polymers in the second category are mainly halocarbons such as Teflon polytetrafluoroethylene (which requires special extrusion or application conditions), fluoroethylene-propylene copolymer (FEP), perf luoroalkoxy-modified polytetrafluoroethylene (PFA), poly(ethylene-tetrafluoroethylene) (ETFE), poly(vinylidene fluoride) (PVF2) (borderline temperature of 135 °C), and poly(ethylene-chlorotrifluoroethylene). Extrusion conditions for wire and cable insulations have to be tailored to resin composition, conductor size, and need for cross-linking of the insulating layer. 

A homopol5mier of vinylidene fluoride was ex-trudedt J using a coat hanger die with a width of 590 mm to produce a sheet at a thickness of 150 pm at a die temperature of 270°C. A chill roll at a temperature of 70°C chilled the hot film. This film was biaxially oriented by four times the original length in the extrusion (machine) direction and six times in the transverse direction (perpendicular to the extrusion direction). The film was at a temperature of 100°C while it was oriented at a stretch rate of 10 mm/min in both directions. 

Polyvinylidene Fluoride Thermoplastic polymer of vinylidene fluoride has good strength, proeessability, wear, fire, solvent, and creep resistance, and weatherability, but decreased dielectric properties and heat resistance. Processed by injection and transfer molding, extrusion, and powder coating. Used in electrical insulation, pipes, chemical apparatus, coatings, films, containers, and fibers. Also called PVDF. 

Thermoplastic polymer of vinylidene fluoride and hexafluoropropylene. Has good antistick, dielectric, and antifiiction properties, and chemical and heat resistance, but decreased mechanical strength, creep resistance, and poorprocessibility. Processed by molding, extrusion, and coating. Used in chemical apparatus, containers, films, and coatings. 

Kolbeck and Uhlmann have considered the effect of high stress extrusion on the properties of several polymers - polypropylene, poly(vinylidene fluoride) and polyethylene. There was no substantial heating on deformation up to twenty-five times. Polypropylene and poly(vinylidene fluoride) could not be continuously extruded below the melting point and brittle fracture and necking was observed, while the tensile properties depend on draw ratio with yielding. Above 373 K annealing occurs but the product has a lower elongation to break. The properties of oriented nylon-6, > polyfethylene terephthalate)," - polypropylene, and polyethylene " have been widely studied. 

Poly(vinylidene fluoride) has good heat resistance and may be used continuously at temperatures up to 150°C. The polymer may be melt processed by the standard techniques of injection moulding and extrusion. The polymer has very good weather resistance. Potential applications for poly (vinylidene fluoride) are in chemical and food-processing plant, packaging film, laminates and wire covering. 

The second example concerns the crystallization of poly(vinylidene fluoride) (PVDF) during a melt spinning process. Extrusion of the melt through a... 

This book is the second of two volumes about fluoropolymers. The division of the volumes is based on the processing techniques of commercial fluoropolymers. Volume One covers the homopolymers of tetrafluoroethylene (TFE) or polytetrafluoroethylene plastics, which are processed by nontraditional techniques. The extremely high melt viscosity of TFE homopolymers precludes its processing by conventional melt processing methods such as injection molding and melt extrusion. The copolymers of TFE and other fluorocarbon polymers, which are processed by melt-processing methods, have been covered in Volume Two. This book is devoted to exploring the various perflu-orinated and partially fluorinated copolymers of tetrafluorethylene and chlorotrifluoroethylene. Polymers of vinyl fluoride and vinylidene fluoride that are, for the most part, melt-processible have been discussed in the second volume. 

Chlorotrifluoroethylene (CTFE) can also be homo-and copolymerized by suspension and dispersion methods in aqueous andnonaqueous media. The copolymer of ethylene and CTFE is ECTFE, a melt processible polymer and a counterpart of ETFE. CTFE is also copolymerized with vinylidene fluoride (VDF). Higher VDF contents generate elastomeric polymers. Methods similar to those for PTFE are used to recover the polymer in various forms. Both powder and dispersion products are available. PCTFE can be processed by both non-melt techniques such as compression molding, and melt techniques such as injection molding and extrusion. Thicker parts are usually made by non-melt methods. 

Polymerization can be designed to improve specific properties of polyvinylidene fluoride. For example, Dohany reported y" ] polymerization of vinylidene fluoride to modify the flow behavior to allow extrusion of the polymer at higher speeds. Polyvinylidene fluoride of this development was produced as a homopolymer or a copolymer containing up to 25% of a comonomer such as tetrafluoroethylene, chlorotrifluoroethylene, and... 

In this section, examples of films made from poly-vinylidene fluoride (PVDF) are discussed. Although most of the polyvinylidene fluoride film is in the form of coating on metal substrates, stand-alone PVDF films and sheets are produced by extrusion and film blow-ing.P2][23] Bientjs of PVDF and a number of other polymers such as polymethylmethacrylate are miscible. Films made from these blends have excellent piezoelectric properties that are described further in Ch. 13. 

Vinylidene fluoride homopolymers can be used to improve the extrusion of low density poly(ethylene) (5). 

S.C. Chu and R.G. Shaw, Compositions of linear polyethylene and poly-vinylidene fluoride for film extrusion, and films thereof, US Patent... 

The addition of specific fluoropolymers to polyolefins allows for improved processability, including elimination of melt fracture (sharkskin), reduced die build-up, lowered processing viscosity, reduced die pressure and abihty to increase extrusion rates [278-282]. The fluoropolymers are generally added at levels of 100-1000 ppm. Vinylidene fluoride-hexafluoro-propylene fluorocarbon elastomers are often mentioned in the patent examples, such as the commercial systems carrying the tradename Viton duPont. 

A most striking additive, which also induces slippage during extrusion of polyolefins, are fluoropolymers [68 to 72]. These include poly(vinylidene fluoride)... 

N. Ghasem, M. Al-Marzouqi, N.A. Rahim, Effect of polymer extrusion temperature on poly(vinylidene fluoride) hoUow fiber membranes Properties and performance used as gas-liquid membrane contactor for CO2 absorption, Sep. Purif. Technol. 99 (2012) 91-103. 

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