Poly tetrafluorethylene

Another commercial membrane prepared by stretching is GoreTex (Fig. 4.6). The polymer here is poly(tetrafluorethylene), which makes the membrane extremely inert and thus convenient for processing even harsh streams. Processing PTFE is only possible by paste extrusion. In paste forming the polymer is mixed with a lubricant such as odorless mineral spirits naphtha or kerosene. The lubricant component is removed by heating to 327 °C. Above this temperature, sintering would lead to a dense PTFE film. 

After lubricant removal, the PTFE film is submitted to an uniaxial or biaxial stretching, giving rise to an interconnected pore structure. The process was proposed by Gore [109] and the resulting porous film is today a successful product in the membrane and textile industry. For uniaxial stretching, the nonsintered film from the paste extrusion is fed to a machine with heating rollers, where 

Dense films of polycarbonate or poly(ethylene terephtalate) can be transformed into porous microfiltration membranes with very narrow pore-size distribution (Fig. 4.7), by exposing them to fission fragments from radioactive decay with subsequent etching in alkaline solutions. The number of pores can be controlled by the length of exposure to the fission segments. The maximum pore 

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All solutions were filtered through a 0.5 ym Fluoropore poly(tetrafluorethylene) filter (FHUP, Millipore Corp.). The solvents trichlorobenzene (TCB), o-dichlorobenzene (ODCB) and a-chloronapthalene (aCN) were used as received without further purification. 

PMMA PNGV PO POx PPMA PrOx PTFE PVD PZT Poly-methylmethacrylate Partnership of New Generation Vehicles Propylene oxide Partial oxidation Poly-methyl methacrylate Preferential carbon monoxide oxidation Poly-tetrafluorethylene Physical vapor deposition Lead-zirconate-titanate... 

Effect of Molecular Weight and Melt Time and Temperature on the Morphology of Poly(tetrafluorethylene)... 

Keywords Bands Morphology Nanofibrils Poly(tetrafluorethylene) Single crystals Shish kebabs... 

Fig. 1 Fracture surface of granular (bulk-polymerized) poly(tetrafluorethylene (PTFE). The sample was held in the melt at 380 °C for an unspecified time followed by slow cooling and fracture after immersion in liquid N2. (Reprinted from Ref. [1] with permission from Wiley-Interscience)...

Teflon (poly(tetrafluorethylene) powder (> 40pm, Aldrich, Saint Louis, Missouri, USA). 

Ishigaki, L, N. Kamiya, T. Sugo, and S. Machi. 1978. Synthesis of an ion-exchange membrane by radiation-induced grafting of acrilyc acid onto poly(tetrafluorethylene). Polym. J.M5) 513-519. 

Tanaka H, Takemura T (19MI) Studies on the high-firessure phases of polyethytene and poly-tetrafluorethylene by Raman spectroscopy. Polymer J., 12 355... 

Figure 2 Adsorption isotherms of four serum proteins to poly-tetrafluorethylene. Proteins dissolved at various bulk concentrations in phosphate buffered saline, pH 7.3 surface tension =72.0 ergs/cm. Proteins as indicated. (Reproduced with permission from Ref. 18. Copyright 1981, Elsevier/North Holland Press).

Polymers with a flexible chain, such as polyethylene (PE), polypropylene, poly(tetrafluorethylene), or poly(methylene oxide), exhibit relaxation processes directly related to the presence of their crystalline Action, For PE, by far the most important system in this context, such processes may be dielectrically active, provided that the sample is "decorated" widi a few C-Cl or C=0 dipoles, by chlorination or oxidation [166]. 

Figure 12-4. Determination of the cosine of the contact angle d on the interfacial surface tension 7/v of the liquid used on different substrates in contact with air (20° C). PE, poly(ethylene) PTFE, poly(tetrafluorethylene) PEP, poly(hexafluoropropylene) FLA, perfluorolauric acid (mono-molecular layer on platinum). (After R. C. Bowers and W. A. Zisman.)...

TEMPERATURE DEPENDENCE OF SURFACE TENSION FOR POLY /TETRAFLUORETHYLENE//SUPERCOOLED LIQUID/ ESTIMATED FROM CONTACT ANGLES. 

At present, heat shield materials consist of poly(tetrafluorethylene), Si02-filled reinforced phenolic resins, or Si02-filled epoxide/polyamide combinations. Development-stage materials are polyimides, silicones, phosphor nitrilic chlorides, and polyboron phosphorus compounds. 

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