Polytetrafluoroethylene Compressibility

Besides the spontaneous, complete wetting for some areas of application, e.g., washing and dishwashing, the rewetting of a hydrophobic component on a solid surface by an aqueous surfactant solution is of great importance. The oil film is thereby compressed to droplets which are released from the surface. Hydrophobic components on low-energy surfaces (e.g., most plastics) are only re wetted under critical conditions. For a complete re wetting of a hydrophobic oil on polytetrafluoroethylene (PTFE) by an aqueous solution, the aqueous solution-oil interface tension must be less than the PTFE-oil interface tension... 

Polytetrafluoroethylene (Teflon) (PTFE) is the most corrosion-resistant thermoplastic polymer. This polymer is resistant to practically every known chemical or solvent combination and has the highest useful temperature of commercially available polymers. It retains its properties up to 500°F (260°C). Because of its exceedingly high molecular weight PTFE is processed by sintering. The PTFE resin is compressed into shapes under high pressure at room temperature and then heated to 700°F (371°C) to complete the sintering process. 

The two compartment trough is schematically shown in Fig. 12. The trough is divided to two large compartment, where monolayer is spread, and a small buffer portion by two fixed barriers with a flexible gate. Compression of monolayers spread on each compartment is controlled independently by two movable polytetrafluoroethylene (PTFE) barriers. A substrate can move from a compartment to the other compartment by passing through the flexible gates... 

Hydrostatic molding is a suitable alternative to compression molding techniques for the production of plastics that do not have the usual melt flow behavior, such as previously reviewed in the Plastic section for polytetrafluoroethylene. 

This property is an important consideration in the design of parts from polytetrafluoroethylene. PTFE deforms substantially overtime when it is subjected to load. Metals similarly deform at elevated temperatures. Creep is defined as the total deformation under stress after a period of time, beyond the instantaneous deformation upon load application. Significant variables that affect creep are load, time under load, and temperature. Creep data under various conditions in tensile, compressive, and torsional modes can be found in Figs. 3.12 through 3.19. 

Wet Bag Isostatic Molding - A method of isostatic molding in which polytetrafluoroethylene (PTFE) powder is compressed between a hard part and an elastic bag. The compaction is achieved by submerging the filled mold in fluid inside a high pressure vessel and pressurizing the vessel. See also Dry Bag Isostatic Molding, Isostatic Molding. 

Figure 13.17 Compressive stress-strain data for two crystalline polymers polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE). (From Kaufman, H.S. and Falcetta, J.J., Eds., Introduction to Polymer Science and Technology, John Wiley Sons, New York, 1977. With permission.)... 

Electrode is processed by spreading a paste containing activated carbon, polytetrafluoroethylene (binder), and carbon black (conducting agent) mixed in a solvent (n-methyl-2-pyroHdone) onto a current collector such as aluminum, then solvent is evaporated and material compressed into an electrode. 

Polytetrafluoroethylene is a white solid with a waxy appearance and feel. It is a tough flexible material of moderate tensile strength with a tendency to creep under compression. Comparative values for some properties of various fluoro-polymers are given in Table 7.1. The electrical insulation properties are outstanding and are nearly as good as those of polyethylene. The coefficient of friction is unusually low and stated to be lower than that of any other solid the non-stick properties are also excellent. 

Lubricants are added to most polymers at low levels to increase the overall rate of processing or to improve surface properties [1-4], They have been used in the past to facilitate extrusion, injection, compression, etc., of many polymers, mainly PVC, acrylonitrile-butadiene-styrene terpolymer (ABS), PS, PMMA, cellulose acetate (CA), polytetrafluoroethylene (PTFE), and so on. Figure 2.1 shows the relative importance of these polymers as far as the use of lubricants is concerned [5]. The most used lubricants and their relative importance in the United States in 1978 were [6] ... 

Saha SP, Muluk S, Schenk 111 W, Davis JW, Ploder B, Grigorian A, et al. A prospective randomized study comparing fibrin sealant to manual compression for the treatment of anastomotic suture-hole bleeding in expanded polytetrafluoroethylene grafts. J Vase Surg 2012 56(1) 134-41. 

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