Polytetrafluoroethylene foamed

Since many polymeric materials are used as clothing, household items, components of automobiles and aircraft, etc. flammability is an important consideration. Some polymers such as polytetrafluoroethylene and PVC are naturally flame-resistant, but most common polymers such as PE and PP are not. Small-scale horizontal flame tests have been used to estimate the flammability of solid (ASTM D-635), cellular (ASTM D-1692-74), and foamed (ASTM D-1992) polymers, but these tests are useful for comparative purposes only. Large-scale tunnel tests (ASTM E-84) are more accurate, but they are also more expensive to run than ordinary laboratory tests cited before. 

The opacity of plastic foams, and polymers with scratched surfaces, is also governed by Fresnel s law. The n value of the gas which occupies the scratch indentation is much lower than that of the polymer. Light may be directed through rods of transparent polymers, such as PMMA. This effect may be enhanced when the rod or filament is coated with a polymer with a different refractive index, such as polytetrafluoroethylene (ptfe). Optical fibers utilize this principle. 

Various polymeric materials were tested statically with both gaseous and liquefied mixtures of fluorine and oxygen containing from 50 to 100% of the former. The materials which burned or reacted violently were phenol—formaldehyde resins (Bakelite) polyacrylonitrile—butadiene (Buna N) polyamides (Nylon) polychlor-oprene (Neoprene) polyethylene polytrifluoropropylmethylsiloxane (LS63) polyvinyl chloride—vinyl acetate (Tygan) polyvinylidene fluoride—hexafluoropro-pylene (Viton) polyurethane foam. Under dynamic conditions of flow and pressure, the more resistant materials which burned were chlorinated polyethylenes, polymethyl methacrylate (Perspex) polytetrafluoroethylene (Teflon). 

Across the grain, 365, 367 Acrylic foam modifier, 91 Acrylic Metafile series P, 173 Acrylic Metablen series L, 173 Acrylic-modified polytetrafluoroethylene, 163, 173... 

Polytetrafluoroethylene (Teflon) Polyurethane foams Polyvinyl acetate Polyvinyl alcohol Polyvinyl chloride (PVC)... 

Chlorinated polyether Polysulphone Polytetrafluoroethylene Epoxy resin, amine-cured Epoxy resin, anhydride-cured The same filled with 65% of quartz flour The same filled with 65% of Al(OH)8 Epoxy resin, glass-laminated Epoxy resin, cycloaliphatic Expanded polystyrene Expanded polystyrene, flame-retardant Expanded polystyrene, extruded profile The same with flame-retardant Rigid polyurethane foam The same with flame-retardant Polysiocyanurate foam Flexible polyurethane foam Paraffin (candle)... 

Alcel, Syntactic foams, AOC Algoflon, Polytetrafluoroethylene (PTFE), Ausimont USA, Inc. 

An important example of a polymer is that of polyvinylchloride, shown in Figure 9.15. This polymer is synthesized in large quantities for the manufacture of water and sewer pipe, water-repellant liners, and other plastic materials. Other major polymers include polyethylene (plastic bags and milk cartons), polypropylene (impact-resistant plastics and indoor-outdoor carpeting), polyacrylonitrile (Orion and carpets), polystyrene (foam insulation), and polytetrafluoroethylene (Teflon coatings and bearings) the monomers from which these substances are made are shown in Figure 9.16. 

This technique has found the following applications in addition to those discussed in Sections 10.1 (resin cure studies on phenol urethane compositions) [65], 12.2 (photopolymer studies [66-68]), and 13.3 (phase transitions in PE) [66], Chapter 15 (viscoelastic and rheological properties), and Section 16.4 (heat deflection temperatures) epoxy resin-amine system [67], cured acrylate-terminated unsaturated copolymers [68], PE and PP foam [69], ethylene-propylene-diene terpolymers [70], natural rubbers [71, 72], polyester-based clear coat resins [73], polyvinyl esters and unsaturated polyester resins [74], polyimide-clay nanocomposites [75], polyether sulfone-styrene-acrylonitrile, PS-polymethyl methacrylate (PMMA) blends and PS-polytetrafluoroethylene PMMA copolymers [76], cyanate ester resin-carbon fibre composites [77], polycyanate epoxy resins [78], and styrenic copolymers [79]. 

This technique has been used to measure the specific heat of polyamide 6, polypropylene, polymethylene methacrylate, rigid polyvinyl chloride and cellular polyurethane foam, high-density polyethylene, low-density polyethylene and polystyrene [48], epoxy resins [73], polypropylene [74], polymethyl methacrylate [75], high-density polyethylene, low-density polyethylene, polypropylene and polystyrene [77], and polytetrafluoroethylene [76],... 

An example of an application of this concept is described by Ward et al. [79]. This application concerns fuel cell development. The relevant fuel cell cathode employs an aqueous solution of a redox catalyst, which must be regenerated by aerobic oxygenation (see, e.g., reference [80] for a description of this type of fuel cell). Sparging the solution with air produces an unacceptable foam in a situation where contamination with conventional antifoam would damage the integrity of the process. Use of rotary foam devices, on the other hand, consumes an unacceptable proportion of the output of the fuel cell. The resultant foam is, however, readily destroyed by a packed porous bed consisting of a polytetrafluoroethylene (PTFE) mesh. 

Since the pioneering work of Lakes [111], there have been a number of instances of auxetic polymer foams, recent examples mentioned in references [112], [113] and [114], Evans and his collaborators [115] have shown how an anisotropic microstmcture consisting of nodules and fibrils can be produced in polytetrafluoroethylene (PTFE), and give rise to a very large negative Poisson s ratio. Figure 8.35 is a schematic representation of the deformation of microporous PTFE. 

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