Fluoroplastic melting points

Chemically, THV Fluoroplastic (hereafter referred to as THV) is a terpolymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (VDF) produced by emulsion polymerization. The resulting dispersion is either processed into powders and pellets or concentrated with emulsifier and supplied in that form to the market.91 Currently, the manufacturer is Dyneon LLC and there are essentially nine commercial grades (five dry and four aqueous dispersions) available that differ in the monomer ratios and consequently in melting points, chemical resistance, and flexibility. 

PTFE (trade name Teflon, Fluon etc.) is probably the most well known of the fluoroplastics. It is, however, a relatively difficult material to process. The polymer is linear, with a very high molecular weight, a high density (2.2) and a high melting point (327 0 C). 

Fluoropolymers are semicrystalline polymers most do not exhibit glass transition in the conventional sense during which all crystalline structures are converted to the amorphous. The glass transitions of fluoroplastics have been described as molecular relaxation (conformational disorder) that takes place in the amorphous phase of the polymer. These temperatures are also called second order transitions their value depends on the technique and the frequency of energy addition to the polymer sample. Table 3.61 presents these temperatures and melting points of perfluorinated and partially fluorinated fluoroplastics. 

Table 3.61. Glass Transition Temperatures and Melting Points of Fluoroplastics ...

In the first molding step, half of the fluoroplastic resin was charged into the mold. Next, the bearer and core assembly was set in the mold. Then the other half of the resin was dispensed into the mold. The hold-down plate was used to compress the contents of the cavity while the mold was heated to a temperature above the melting point of the fluoroplastic resin. After cooling, the part can be removed and machined to the required specifications. 

Pressure Rating Depending on the fluoroplastic, a mold rating of 7-28 MPa at 370°C is sufficient for the highest melting point and melt viscosity fluoropolymer. 

Other melt-processable fluoroplastics include ethylene-chlorotrifiuoroethylene (ECTFE) copolymer (melting point 240°C), polyvinylidene fluoride (PVDF) (melting point 170°C), and polyvinyl fluoride (PVF), which is commercially available only as film. 

Table 9.1 Melting Point Ranges of Various Fluoroplastics...

TFE and VDF can be polymerized in any proportion, thus giving rise to a broad variety of products. The copolymers are obtained in either emulsion or suspension process. An approximate composition of TFE PVDE of 20 80 is the eutectic point in the system, with a melting point of 120 ° C. It is widely used as a technical polymer and is available under the brand names Kynar 7200 and Kynar SL (Pennwalt Corporation). A composition with the an approximate composition of TFE PVDF 29 71) is available as Fluoroplast 42 (Russia). Both copolymers are soluble in ketones and esters but are insoluble in alcohols and chlorinated hydrocarbons and are mainly processed via melt extrusion at temperatures between 190 and 260 °C [27, 28]. The low-wave-number FTIR spectrum of the copolymer is depicted in Figure 3.13. 

Fluorocarbon plastics do not actually burn when exposed to a flame. They can easily be identified by a copper wire test that indicates the presence of fluorine by a bright green-colored flame. The fluoroplastics have a very high melting point. PTFE has a waxy surface and a specific gravity of 2.15. Fluoroplastics are practically impossible to dissolve in any chemical. 

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