Machine Design – May 2019

ePTFE and Athletic Shoes

PTFE, OR POLYTETRAFLUORETHYLENE
((C2F4)n) is a versatile ivory/white and
opaque plastic fluoropolymer. It is also
known as Teflon, the trademarked name
owned by Chemours, a company that was
spun off of DuPont, which originally discov-
ered PTFE in 1938. It has since grown into
an indispensable material used in almost
every industry: from automotive to medical;
aerospace to recreation; in coatings, lin-
ings, mechanical hardware, and fasteners;
and even as a lubricant.
Many of its uses are due to its inert-
ness, a benefit of being constructed out
of carbon-flourine bonds, the strongest
bond known. These bonds make it inert
to all media regardless of its pH, a wide
range of thermal resistance (−450°F to
600°F), weather, UV, and radiation resis-
tant. Its inertness makes it biocompatible
for use inside or outside patients and safe

for use with foods. (Among the only chemi-

cals known to attack PTFE are molten alkali

metals, chlorine trifluoride, and gaseous flu-

orine at high temperatures and pressures.)

It also has a low coefficient of friction,

0.05 to 0.10, the third lowest of any known

solid. This is what makes it such a good

candidate for making nonstick pans and

kitchen utensils. It’s also why so many bear-

ings, gears, seals, gaskets, and bushings

are made from it. Finally, it’s why it is widely

used as a film for making carbon-fiber and

fiberglass composites.

The polymer has good dielectric prop-

erties (electrically insulating), especially at

high radio frequencies. An estimated 50%

of the material is used as insulation in coax-

ial cables and connectors, as well as PC

boards used at microwave frequencies.

It has also found use as a lubricant,

grafting material in biomedical implants,

coatings on catheters, and to coat valves

and seals in uranium enrichment implants.

Adding fillers can increase its strength,

improve its abrasion resistance, add

electrical conductivity, and change other

properties as well. Fillers range from glass

in various percentages, stainless, steel,

molybdenum disulphide, and carbon or

graphite.

ePTFE is expanded Teflon. Manufactur-

ers take PTFE and mechanically expand it,

making it less dense. This makes it an ideal

gasket material. Unlike plain PTFE, ePT-

FE does not creep or cold flow. It is highly

conformable to complex shapes, can seal

damaged flange surfaces, resists blowouts

and higher temperatures better than PTFE,

and is more reliable. One of ePTFE’s more

common or well-known applications is as

a breathable water barrier in athletic shoes

and hiking gear.

PTFE/EPTFE: THEIR UBIQUITOUS USEFULNESS

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