Polytetrafluoroethylene - PTFE - Chapter

Fluorinated polymers, especially polytetrafluoroethylene (PTFE) and copolymers of tetrafluoroethylene (TFE) with hexafluoropropylene (HFP) and perfluorinated alkyl vinyl ethers (PFAVE) as well as other fluorine-containing polymers are well known as materials with unique inertness. However, fluorinated polymers with functional groups are of much more interest because they combine the merits of pefluorinated materials and functional polymers (the terms functional monomer/ polymer will be used in this chapter to mean monomer/polymer containing functional groups, respectively). Such materials can be used, e.g., as ion exchange membranes for chlorine-alkali and fuel cells, gas separation membranes, solid polymeric superacid catalysts and polymeric reagents for various organic reactions, and chemical sensors. Of course, fully fluorinated materials are exceptionally inert, but at the same time are the most complicated to produce. 

In Chapter 18, we described solvent extraction and solid-phase extraction sample preparation methods, which are applicable to GC analyses as well as others. A convenient way of sampling volatile samples for GC analysis is the technique of head-space analysis. A sample in a sealed vial is equilibrated at a fixed temperature, for example, for 10 min, and the vapor in equilibrium above the sample is sampled and injected into the gas chromatograph. A typical 20-mL glass vial is capped with a silicone rubber septum lined with polytetrafluoroethylene (PTFE). A syringe needle can be inserted to withdraw a 1-mL portion. Or the pressurized vapor is allowed to expand into a 1-mL sample loop at atmospheric pressure, and then an auxiliary carrier gas carries the loop contents to the GC loop injector. Volatile compounds in solid or liquid samples can be determined at parts per million or less. Pharmaceutical tablets can be dissolved in a water-sodium sulfate solution... 

The examples of applications in this chapter focus on operational energy savings to present insights into the vast implementation possibihties of textile materials, such as glass-fibre mesh, polytetrafluoroethylene (PTFE) and ethylene-tetrafluoro-ethylene (ETFE). This chapter provides ... 

In this chapter, we describe a variety of methodologies for applying multidimensional NMR (mostly 2D- and some 3D-NMR) for the characterization of fluoropolymers. Space limitations preclude a comprehensive survey of the literature. Instead, a few of the primary methodologies are described involving combined use of multidimensional NMR methods for structure elucidation. Then, a selected group of papers were reviewed to illustrate the applications of these methodologies to the characterization of some of the most common classes of fluoropolymers, including homo- and copolymers with poly(vinylidene fluoride), fluorinated polyethers, fluori-nated ionomers, poly(vinyl fluoride) and its copolymers, and polytetrafluoroethylene (PTFE) and its copolymers. 

Materials used such as stifFer plastics can reduce hysteresis heating. Crystalline TPs for example (the popularly used acetal and nylon) can be stiffened by 25 to 50% with the addition of fillers and reinforcements. Others used include ABS, polycarbonates, polysulfones, phenylene oxides, polyurethanes, and thermoplastic polyesters. Additives, fillers, and reinforcements are used in plastics gears to meet different performance requirements (Chapter 1), Examples include glass fiber for added strength, and fibers, beads, and powders for reduced thermal expansion and improved dimensional stability. Other materials, such as molybdenum disulfide, polytetrafluoroethylene (PTFE), and silicones, may be added as lubricants to improve wear resistance. 

Chemical methods of analysis are simple and cheap but labour intensive. However, they are essential, coupled with spectroscopic techniques, for deformulation work and in the analysis of additives such as anti-oxidants and stabilisers. Specific examples of the use of these procedures for polypropylene, PVC, polytetrafluoroethylene (PTFE) and polyamides are detailed in chapter 2. 

Polymer electrolyte fuel cells (PEFCs) are unique in that they are the only variety of low-temperature fuel cell to utilize a solid electrolyte. The most common polymer electrolyte used in PEFCs is Nafion , produced by DuPont, a perfluorosulfonic ionomer that is commercially available in films of thicknesses varying from 25 to 175 pm. This material has a fluorocarbon polytetrafluoroethylene (PTFE)-kbone with side chains ending in pendant sulfonic acid moieties. The presence of sulfonic acid promotes water uptake, enabling the membrane to be a good protonic conductor, and thereby facilitating proton transport through the cell. This chapter reviews PEFC development, structure, and properties and presents an overview of PEM technology to date. 

Over the last decade, selected papers1114 have examined the deposition of fluoropolymers, using RF magnetron sputtering. All of these papers have examined the deposition of PTFE, with some of them2314 also studying the deposition of polyimide (PI) films. This chapter extends these studies and will report on the sputter deposition behavior of PTFE (polytetrafluoroethylene), PVDF (polyvinylidenefluoride), and FEP (fluorinated ethylene propylene copolymer) films. 

Hydrogen Fluoride.31 The acid HF is made by the action of concentrated H2S04 on CaF2 and is the principal source of fluorine compounds (Chapter 16). It is commercially available in steel cylinders, with purity approximately 99.5% it can be purified further by distillation. Although liquid HF attacks glass rapidly it can be handled conveniently in apparatus constructed either of copper or Monel metal or of materials such as polytetrafluoroethylene (Teflon or PTFE), Kel-F (a chlorofluoro polymer), etc. 

As discussed in Chapter 10, there are various F-containing polymers that can be used as binders. For example, polytetrafluoroethylene (Pl FF) can be used as a water-based dispersion, and P F can be used after dissolution in organic electrolytes. However, to make a dispersion of PTFE, some surfactants are needed, which will produce some side reactions with electrode materials of lithium-ion batteries. Unfortunately, the dispersion is not stable at elevated temperature and after long-term storage. As a result, PVDF is preferred instead of PTFE since the electrochemical stable window of PVDF is also broader than that of other F-containing polymers, and it is very stable with many positive and negative electrode materials. Its reaction with li metal only starts above 200°C, which is above the normal temperature scope for lithium-ion batteries. As shown in... 

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