Polytetrafluoroethylene beads

Fishtail Guide - A guide used in calendaring polytetrafluoroethylene (fine powder) bead into tape. It allows safe feeding of the bead into the nip point of calendar rolls. It is called fish tail guide because of the similarity of its shape to the tail of a fish. 

Perhaps the best known application of polytetrafluor-oethylene is in kitchen utensils with non-stick coatings, such as pots, pans, and spatulas. Polytetrafluoroethylene is also used to coat fibers to make them water-repellant and stain-resistant. Water will bead up and roll off the surface of clothing and other materials coated with polytetrafluoroethylene instead of penetrating the fabric and possibly... 

Figure 1 contains micrographs of polymethyl methacrylate (PMMA), polycarbonate (PC) and polytetrafluoroethylene (PTFE) surfaces which have undergone erosive wear by the impingement of glass beads. With all three polymers loss from the surface occurs by flake formation as indicated in each of the micrographs. 

Where impurities are present as microparticulate material filtration affords a convenient technique for solvent purification. The mobile phase containing added buffers or reagents may be filtered through a 0.5 pm or smaller filter to remove particulate matter that can damage the analytical system. The equipment for filtration is simple. Usually, it consists of an Elenmayer flask connected to vacuum and a reservoir in which a porous filter disk or membrane is placed. The porous disk is usually made from nonporous spherical glass beads (1-2 pm) and/or polytetrafluoroethylene (PTEE). Membrane materials are usually made from PTEE, cellulose, or nylon. To improve the efficiency of the separation process, the surface of the filter disks or membrane surface are often modified chemically, similar to that used for chemically bonded packing materials in RP-HPLC and/or SPE. In this case, the surface properties (hydrophobic or hydrophilic) of filters and/or membranes determine the extent of purification possible. 

Biomedical Applications. Dillon (114) synthesized IPN membranes from polytetrafluoroethylene (PTFE) and poly(dimethyl siloxane) (PDMS) (see Perfluorinated Polymers, Polytetrafluoroethylene Silicones). These flexible membranes are used for a variety of medical purposes, especially second-degree bum care. These materials are commercially available under the trade name Silon. The PDMS component rapidly transports body fluids away from the bum site, while the PTFE provides mechanical strength. The PTFE is also waterproof, so that when the woimd area is washed, water beads up on the film. An additional valuable feature is that the Aims are highly transparent, so that the doctor can observe the wound area easily, making early treatment of any infection or other problem possible. 

Table 12.1 (7) summarizes the surface tensions of selected polymers. While the surface tension of most polymers varies from about 20 to 50 erg/cm these values are low compared to the surface tension of water, 72.94 erg/cm or mercury, 486.8 erg/cml Thus water beads up on polymers with low surface tensions, not wetting them. For example, low surface tension underlies the utility of the Teflon polytetrafluoroethylene frying pan. 

Selected advancing contact angles are shown in Table 12.4. Confirming common experience, water beads up on polytetrafluoroethylene, while n-octane, a much less polar material, spreads but does not completely wet... 

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. 

Name(s) polytetrafluoroethylene particles, beads, fibers, tridecafluoro-l,l,2,2-tetrahydrooctyltrichlorosilane, perfluoroalkyl group-containing compound CAS 9002-84-0... 

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