Melt-processible fluoropolymers, properties

Summary of Properties of Selected Melt-Processible Fluoropolymers... 

Because of its high viscosity (10 °-10 poise at 380°C), PTFE cannot be fabricated by melt-processing techniques. Melt-processible fluoropolymers have been developed by copolymerization of TFE, and FEP, a copolymer of TFE and HFP, has a lower maximum continuous use temperature than PTFE (200° C vs. 260° C) because of the deterioration of mechanical properties. Whereas, PFA, a copolymer of TFE with PPVE or PEVE, offers thermal stability, melt-processibility, and a maximum continuous use temperature of 260°C. Both FEP and PFA are considered perfluoropolymers. 

Fluoropolymers. Melt processable fluoropolymers such as Teflon FEP, Tefzel ETFE, poly(vinylidene fluoride) (Kynar), and ethylene-chlorotrifluoroethylene copolymer (Halar) are suitable for wire insulation in special applications because they combine good physical properties with low flammability. They are used for instrumentation cable in process-control rooms, as well as for computer and aircraft wiring and in military applications. The... 

The present chapter covers information published by resin manufacturers about the commercially available grades of melt processible fluoropolymers. The first two polymers are perfiuorinated resins, followed by partially fluorinated polymers ethylene-tetrafiuoro-ethylene and ethylene chlorotrifiuoroethylene, andpoly-vinylidene fluoride and polyvinylfiuoride, and finally concluding with fluoroplastics polymerized in supercritical carbon dioxide. Commercially available resins have been classified by type, grade, and manufacturer. Properties of commercial grades have been presented in this chapter based on the literature published by the manufacturers. 

Properties are similar to those of PTFE, and PFA fluoropolymers are generally considered to be the best melt-processable alternative to PTFE yet available. They are, however, more expensive than PTFE. Compared with the TFE-FEP copolymers such as Teflon I P the PFA fluoropolymers ... 

FEP and PFA despite being melt-processible are crystalline (between 50 and 70%). The crystallinity results in poor optical properties (low clarity) and a very poor solubility in organic solvents. The latter makes the preparation of thin optical coatings exceedingly difficult.10 TEFLON AF, an amorphous fluoropolymer, contains in its molecule a bulky dioxole ring, which hinders crystallization. As a result, the polymer has an exceptionally high clarity and excellent optical properties. Its refractive index is the lowest of any plastic.11... 

One of the disadvantages of PTIE is that it is not melt processable. In 1960 DuPont introduced fluorinated ethylene propylene (FEP), which was chiefly designed to provide melt processability. In 1972 DuPont introduced another fully fluorinated polymer, perfluoroalkoxy (PEA), which is also melt processable, with better melt flow and molding properties than FEP. Although PEA has somewhat better physical and mechanical properties than FEP above 3000°F (1490°C), it lacks the physical strength of PTFE at elevated temperatures and must be reinforced or designed with thickness to compensate for its softness. The heat deflechon temperature of PFA is the lowest of all fluoropolymers. PFA is used to make tubing products. 

All aspects of the fluoropolymers including monomer synthesis, polymerization, properties, applications, part fabrication techniques, safety in handling, and recycling are discussed. Homopolymers and copolymers of vinylidene fluoride, all melt processible, have been covered in Volume Two because of the close... 

PVDF polymers are partially fluorinated and melt processible. They have a lower melting point and chemical resistance than perfiuorinated fluoropolymers. Polyvinylidene fluoride resins are, in general, homo-and co-polymers of vinylidene fluoride. PVDF resins are specified by ASTM Method D3222, which also provides procedures or references to other ASTM methods for the measurement of resin properties. Commercial PVDF resins offered by major manufacturers have been listed in Tables 6.10 through 6.14. 

Thermoplastic perfluorocyclobutane arylene ether polymers offer a solvent soluble, melt processable, low dielectric alternative to conventional fluoropolymers. Relatively little time has been spent on their development, however. The bifimctional monomers have proven quite useful as comonomers in modifying the thermal and mechanical properties of high Tg thermoset copolymers. In particular, the siloxane PFCB polymer discussed earlier (Figure 3) exhibits a Tg = 16 C (DSC) thereby providing a reactive toughening or flexibilizing additive either as block type copolymers or comonomer for random incorporation (8),... 

A fully fluorinated fluoropolymer, PFA has a slightly different chemistry than PTFE, where alkoxy groups (carbon hydrogen chains) replace some of the fluorine atoms. While the properties are similar to PTFE, the biggest difference is that PEA can be melt-processed (molded, extruded, etc). 

Another fully fluorinated fluoropolymer, FEP is a copolymer of hexafluoropropylene and tetrafluoroethylene (the base material of PTFE). It was the first commercially produced material that offered the unique advantages of fluoropolymers with the melt-processing capabilities of more conventional polymers. Properties are very similar to PTFE, with a lower service temperature. 

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... 

Fluoropolymers. These form one of our oldest and most spectacular families of engineering plastics. Polytetrafluoroethylene was developed by DuPont over two decades ago, and more recently by Allied Chemical, Hoechst, ICI, Pennwalt, and other manufacturers as well. It combines unusually low adhesion and friction, high temperature and flame resistance, excellent electrical properties, and extreme chemical inertness. Its high melting point and melt viscosity make thermoplastic processing extremely difficult, so that many... 

There are two approaches to characterizing fluoropolymers for injection molding. The more fundamental methodology centers around the measurement of physical properties such as melt viscosity and thermal diffusivity to generate data for mathematical modeling (simulation) of injection molding processes. 

Monoaxially and biaxially oriented films of fluoropolymer are made by melt extrusion of the resin into flat webs or tubes. The main function of orientation is to enhance the mechanical properties of the film such as tensile break strength and tear resistance. The decision to orient is usually made according to the requirements of the end use for mechanical properties. All process surfaces that contact molten fluoropolymers must be corrosion resistant because of the formation of corrosive compounds such as HF and HCl from the high-temperature degradation of these plastics. 

Vinylidene Fluoride Hexafluoropropylene Copolymer - Thermoplastic copolymer of vinylidene fluoride and hexafluoropropylene. Has better thermal stability, antistick, dielectric, and antifriction properties, and chemical resistance, but lower mechanical strength at room temperature and creep resistance, compared to incompletely fluorinated fluoropolymers. Processing by conventional thermoplastic techniques is difficult due to its high melt viscosity. Uses include chemical apparatus, containers, films, and coatings. Also called TAM... 

The following sections will briefly explain the structures and properties of the various fluoropolymers. It is important to keep in mind there are variations of most of these polymers. The most common variation is the molecular weight, which will affect the melting point somewhat, and the viscosity of the polymer above its melting point, properties that are very important in determining processing conditions and use. 

A link between the relatively good processability of low density polyethylene (LDPE) and the excellent toughness of linear low density polyethylene (LLDPE) has been a key subject for many researchers. Fluoropolymer-based additives provide this link. Today, the use of fluoropolymer processing additives has expanded greatly, from an early way of minimizing melt defects, to improving the throughput rates and properties of LLDPE. These additives now provide benefits in a host of polyolefin extrusion applications. 

Fluoropolymer-based processing additives provide a range of benefits beyond melt fracture elimination. Among these benefits are improved production capacities, and a better control of molecular orientation and final physical properties. Owing to their design and low volumetric contributions, no adverse effects have been detected which can be attributed to the PPA s presence. Careful selection of other additives used with the PPA can minimize the PPA requirement. Finally, the use of newer products, such as PPA-2, can overcome additive interferences to further enhance polyethylene properties and productivity. 

Terpolymers oftetrafluoroethylene, hexafluoropro-pylene, and vinylidene fluoride have been found to have unique properties and processing advantages. They usually possess lower melting temperature than other fluoropolymers, flexibility, resistance to a number of chemicals, permeation resistance to fuels, and a number of other desirable attributes. These terpolymers are offered by Dyneon as THV Thermoplastics and are listed in Tables 6.21 and 6.22. 

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