Fluoropolymers properties

ETFE addresses the need for a meehanieally stronger polymer, albeit at a loss of fluoropolymer properties because of the presence of hydrogen in its molecule ... 

Practical application of crystalline perfluoropolymers such as Teflon is often limited due to prohibitive processing costs and / or degradation of thermal and mechanical properties with time and stress. Hybrid fluoropolymers containing hydrogen or other atoms in their structure, however, typically exhibit improved strength and processability over perfluorinated systems. Our interest in polymers with partially fluorinated segments seeks to balance favorable fluoropolymer properties with enhanced processability, thermal resistance, and mechanical properties. 

Carbon, fluorine, and hydrogen are the major elements that form the perfluorinated and partially fluori-nated fluoropolymers. The presence of fluorine is the main reason that these plastics have many special properties, which surpass those of most polymers. The desirable properties span across mechanical, tribological, electrical, and thermal characteristics of these polymers in addition to chemical resistance. Increased fluorine content of the fluoropolymers enhances these properties. Consequently, perfluoropolymers should be sought out when ultimate chemical resistance, electrical properties, etc., are required. This chapter concentrates on presenting the key properties of fluoropolymers. Properties of fluoroplastics films can be found in Ch. 6 and Appendix VI. 

Because of its excekent combination of properties, processibkity, and relatively low price compared to other fluoropolymers, PVDF has become the largest volume fluoropolymer after PTFE consumption in the United States has grown from zero in 1960 to about 6200 metric tons in 1991 (186). About 49% of the consumed volume is PVDF modified by copolymerization with 5—12-wt % HFP to enhance flexibkity. In 1992, Hst price for homopolymer powders was 15.32/kg, and for pekets 15.42/kg the reported market price was 14.09—14.22/kg (187). In the United States, almost ak PVDF is suppHed by Ausimont USA, Inc., Elf Atochem North America, Inc., and Solvay Polymers, Inc. Ausimont and Elf Atochem are producers Solvay is an importer of the resin. Smak amounts of resin are imported from Germany by Huls America, Inc, and from Japan by Kureha Chemical Industry Co., Ltd. PVDE producers and their trademarks are Hsted in Table 4. 

The PVC formulations shown in Table 2 represent typical compounds used by the wine and cable industry. PVC compounders have developed new PVC-based formulations with very good fire and smoke properties (can pass the UL 910 Steiner Tunnel test) that compete with the more expensive fluoropolymers. These can be used in fabricating telecommunication cables usable for plenum area appHcations. 

Commonly used materials for cable insulation are poly(vinyl chloride) (PVC) compounds, polyamides, polyethylenes, polypropylenes, polyurethanes, and fluoropolymers. PVC compounds possess high dielectric and mechanical strength, flexibiUty, and resistance to flame, water, and abrasion. Polyethylene and polypropylene are used for high speed appHcations that require a low dielectric constant and low loss tangent. At low temperatures, these materials are stiff but bendable without breaking. They are also resistant to moisture, chemical attack, heat, and abrasion. Table 14 gives the mechanical and electrical properties of materials used for cable insulation. 

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 ... 

Table 13.3 Typical properties of Teflon AF amorphous fluoropolymers...

A 50 50 mol/mol copolymer of hexafluoroisobutylene (CH2 = C(CF3)2) and vinylidene fluoride was made available by Allied Chemical in the mid-1970s as CM-1 Fluoropolymer. The polymer has the same crystalline melting point as PTFE (327°C) but a mueh lower density (1.88g/cm ). It has excellent chemical resistance, electrical insulation properties and non-stiek characteristics and, unlike PTFE, may be injeetion moulded (at 380°C). It is less tough than PTFE. 

The poly(fluoroalkoxyphosphazene) elastomers offer a unique combination of properties including a wide operating temperature range, excellent fuel and oil resistance and low temperature properties superior to those of the fluoros11leones and fluoropolymer elastomers. 

Since the serendipitous discovery of Teflon at the Dupont Jackson Laboratory in 1938, fluoropolymers have grown steadily in technological and marketplace importance. New synthetic fluorine chemistry, new processes, and new appreciation of the mechanisms by which fluorine imparts exceptional properties all contribute to accelerating growth in fluoropolymers. 

In contrast to past environmental problems associated with fluorocarbon refrigerants, the exceptional properties of fluorine in polymers have great environmental value. Some fluoropolymers are enabling green technologies such as hydrogen fuel cells for automobiles and oxygen-selective membranes for cleaner diesel combustion. 

Curiously, fluorine incorporation can result in property shifts to opposite ends of a performance spectrum. Certainly with reactivity, fluorine compounds occupy two extreme positions, and this is true of some physical properties of fluoropolymers as well. One example depends on the combination of the low electronic polarizability and high dipole moment of the carbon-fluorine bond. At one extreme, some fluoropolymers have the lowest dielectric constants known. At the other, closely related materials are highly capacitive and even piezoelectric. 

Much progress has been made in understanding the sometimes confounding properties of fluoropolymers. Computer simulation is now contributing to this with new fluorine force fields and other parameters, bringing realistic prediction within reach of the practicing physical chemist. 

These two volumes attempt to bring together in one place the chemistry, physics, and engineering properties of fluoropolymers. The collection was intended to provide balance between breadth and depth, with contributions ranging from the introduction of fluoropolymer structure-property relationships, to reviews of subfields, to more focused topical reports. 

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