Polytetrafluoroethylene powder

Polytetrafluoroethylene powders can be extruded but not by the methods applied to conventional thermoplastics. The polymer must not be subjected to excessive mechanical working above the melting point or cracking of the finished piece will result. For this reason, the polymer is worked while it is still cold. The powder is compacted with the aid of a screw or a ram and forced through a hot die in which it is sintered (James). This method is used to fabricate rods or heavy wall tubing or to apply heavy coatings to electrical conductors. 

Data on MCM graft polymerization are extremely limited. A method of preirradiation in air has been used to effect the graft polymerization of Co (II), Ni(II) and Cr(III) acrylate complexes with 2,2 -dipyridyl and 1,10-phenantroline onto a polytetrafluoroethylene powder [Ilf]. 

Violent reactions with ammonium salts, chlorate salts, beryllium fluoride, boron diiodophosphide, carbon tetrachloride + methanol, 1,1,1-trichloroethane, 1,2-dibromoethane, halogens or interhalogens (e.g., fluorine, chlorine, bromine, iodine vapor, chlorine trifluoride, iodine heptafluoride), hydrogen iodide, metal oxides + heat (e.g., beryllium oxide, cadmium oxide, copper oxide, mercury oxide, molybdenum oxide, tin oxide, zinc oxide), nitrogen (when ignited), silicon dioxide powder + heat, polytetrafluoroethylene powder + heat. 

The next few sections describe the characteristics, properties, and methods of production of filled polytetrafluoroethylene powders. 

Reduction Ratio - This factor is the ratio of cross-sectional surface areas of the preform and the extrudate in paste extrusion. Different dispersion polymerized polytetrafluoroethylene powders accommodate different reduction ratio ranges. In general, reduction ratio of the resin decreases as molecular weight increases. Melt fracture and defects appear in the extrudate if it is processed at above its maximum reduction ratio. 

Fig. 4.6.8. (Right) Example of the fixed column end fitting for glass columns, suitable for water and organic solvents (after Ref. 18). 1, inlet capillary 2, thrust screw 3, seal made of soft polytetrafluoroeth-ylene 4, end fitting body made of plastics or metal 5, polyamide or polytetrafluoroethylene filter 6, cap nut 7, seal ring made of polytetrafluoroethylene powder or powdered mixture of graphite and polytetrafluoroethylene 8, rubber rings 9, column.

Various micronized polytetrafluoroethylene powders were compounded with silicone rubber (MQ) and the mechanical properties of the composites were evaluated. At a PTFE level of only 5 wt%, the fractured surface of the composites showed layered structure morphology. This stracture effectively improved the tear strength of the MQ but it also lowered the tensile properties of the composites. The addition of fluorosUicone rubber (FMQ) as a compatibilizer, improved considerably the tensile and tear strength of the composites. Extrusion of the MQ/PTFE/FMQ composites on an electric wire indicated that the spherical PTFE powder was suitable for the extrusion process [55]. 

Grum, F., and Saltzman, M. (1976). A New White Standard of Reflectance. Proceedings of the 18th Session C.I.E., C.I.E. Publication No. 18, p. 91. First description of the use of packed PTFE powder as a tranter and working standard for VV-VIS-NIR diffuse reflectance. Weider, V. R., and Hsia, J. J. (1981). Reflection properties of pressed polytetrafluoroethylene powder. J. Opt. Soc. Am. 71, 856 and Weider, V. R., Hsia, J. J., and Adams, B. (1985). Laboratory intercompaiison study of pressed poly-tetrafluoroethylene powder reflectance standards. Appl. Optics 24, 2225. Along with Grum and Saltzman, the definitive works on PTFE as diffuse reflectance standard. 

Typical reference materials have included freshly formed MgO powder, polytetrafluoroethylene powder, and barium sulfate powder. Much more convenient reference materials that are now available are Spectralon (Labsphere, Inc.) reflectance standards. 

The chromatographic columns for the determination of water in different polymers consist of 10 per cent w/w stationary phase on polytetrafluoroethylene powder (I.C.I. Fluon CD4). 

Dry Bag Isostatic Molding - A method of isostatic molding in which polytetrafluoroethylene powder is compressed between a hard part and an elastic bag. The compaction is achieved by introducing a high-pressure liquid behind the bag as opposed to... 

Fluoroadditives - These are the finely divided low molecular weight polytetrafluoroethylene powders added to other products to impact some of the fluo-ropolymer properties to the host systems. 

Hydrocarbon Lubricant - A hydrocarbon liquid added to dispersion polymerized polytetrafluoroethylene powder (fine powder) to form a paste for extrusion. 

Fluorocarbon soHds are rare in defoamer compositions, presumably on account of their cost. SoHd fluorine-containing fatty alcohols and amides are known. The most familiar fluorocarbon soHd is polytetrafluoroethylene [9002-84-0]. Because it is more hydrophobic than siHcone-treated siHca, it might be expected to perform impressively as a defoamer component (14). However, in conventional hydrocarbon oil formulations it works poorly because the particles aggregate strongly together. In lower surface tension fluids such as siHcone and fluorocarbon oils, the powdered polytetrafluoroethylene particles are much better dispersed and the formulation performs weU as a defoamer. 

The apparatus consists of a 1-1. three-necked flask equipped with a condenser, a dropping funnel, and a stirrer terminating in a stiff, crescent-shaped Teflon polytetrafluoroethylene paddle. The stirrer motor must have good torque (Note 1). The assembled apparatus, which is protected from moisture by means of drying tubes in the condenser and funnel, is preferably predried. About 216-224 g. (1.62-1.68 moles) of powdered anhydrous aluminum chloride is added to the apparatus with as little exposure to the moisture of the air as possible (Note 2). While... 

Powdered Teflon for use in pyrots is covered by US Mil Spec MIL-P-48296IPA) (1 May 1974), Polytetrafluoroethylene (TFE) . Three classes of material are specified (1,2 3). The requirements are purity, 99.4% min infrared spectrum, peaks consistent with figure shown color, TFE shall be opaque and the color shall range from white to gray moisture, 0.05% max ash, 0.1% max mp, 337° 10°C packing density, Class 1 — 1.18 0.13g/cc, Class 2 - 1.25 0.02g/cc, Class 3- 1.14 0.09g/cc particle size by sieve analysis, Class 1 — 95 15 microns, Class 2 — 237 27 microns, Class 3 — 200 30 microns particle size distribution by sieve analysis, as specified in Table 1... 

Compositions whose products of combustion produce energy in the infrared wave band are generally composed of magnesium powder, polytetrafluoroethylene (PTFE) and a binder. For efficient tactical utilization of the energy developed by the combustion process the composition is normally formed into pellets either by press consolidation or by press extrusion. The process being used at Longhorn at the time the electrostatic problem was encountered was press consolidation. The composition was being consolidated into a pellet... 

Sintering machines, 26 565 molybdenum, 17 9-10 of polytetrafluoroethylene, 18 300-301 phosphate ore, 19 7 Sintering process, 10 41, 94, 95 for ceramic membranes, 15 814, 815 sulfur recovery from, 23 772 with tin powder, 24 798-799 Sinter processes... 

Fluorocarbon Resins. This term includes polytetrafluoroethylene, polymers of chloro-trifluoroethylene (fluorothene), vinylidene fluoride (H2C CF2)j hexafluoropropylene (C3Ffl) and similar compds. These polymers are thermoplastic, inert to chemicals and oxidation. They have high heat stability, retain their useful props at both extremely low and high temps, have high electrical resistance to moisture. The materials are available as re sins, powders, and dispersions, and as films, sheets, tubes, rods and tapes. Some of them are rubber-like. Commercially available varieties are Kel-F , Teflon , Fluorel , Aclar and "Halon ... 

Above its melting point of 327° C, polytetrafluoroethylene has some properties more like a rubber than a liquid. The instantaneous Young s modulus is 2—3 X 107 dynes/cm2, and the melt viscosity is about 10u poises at 380° C (Nishioka and Watanabe). Because of this very high melt viscosity, it is not feasible to process the polymer by conventional extrusion or injection molding. Instead, techniques similar to those of powder metallurgy are employed. These involve three basic steps. 

The extrusion of lubricated powders, which has been described by Lontz, Jaffe, Robb, and Happoldt, is a unique method for fabricating polytetrafluoroethylene. An aqueous dispersion is coagulated by mechanical agitation. The powder is then dried and blended with 18—20% of a... 

Plunkett and his assistant decided to cut open the containers. When they did, they found a white, waxy powder inside. Plunkett tested the powder. He found that it was chemically inert and heat resistant. He also found out that it had a very low surface friction. Because of this low surface friction, most things would not stick to the powder. The TFE gas in the container had polymerized to produce this new substance. The new substance s chemical name is polytetrafluoroethylene (PTFE). It was later named Teflon. Teflon is used to protect fabrics and in bakeware to prevent food from sticking to pots and pans. 

As an example, Table 2 compares the results obtained using a smooth Cd cathode and a hydrophobicized Cd electrode prepared from powdered Cd, carbon, acetylene black A-437E, and polytetrafluoroethylene (PTFE) [31]. The current efficiency and current density increased for smooth Cd... 

To prepare a working electrode, carbon powder (PFA-P7-H or PFA-AN8-H) was mixed with polytetrafluoroethylene (PTFE) (5 wt%) to form a pellet and it was sandwiched in Ni mesh as a current collector. The EDL capacitance properties were measured by CV and galvanostatic charge/ discharge in a three-electrode cell vs. Ag/AgCl reference electrode. 1 M-(C2H5)4NBF4 in PC was used as a nonaqueous electrolyte. 

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