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FLUOROCARBONS (PTFE)
A researcher at the duPont Company Experimental Station one
day in 1938 found a residue at the exit port of a Freon Gas (Fluorinated
Hydrocarbon) container. Upon
further examination he found that the white mass of material has some unique
properties. This was the birth of
Teflon®.
The properties of Teflon® were sought after for military
applications and it soon became an essential material for defence during World
War 11. In the early 40’s all of
the initial production quantities were used for strategic defence applications.
In subsequent years, as the process was developed, Teflon® the first
fluorocarbon, became economical to produce and readily available.
Fluorocarbons are among the more expensive plastics, but
design engineers have found them to be adaptable to a variety of requirements.
They offer a unique combination of heat resistance and low friction
together with good chemical and electrical properties.
Fluorocarbons can be used over a wide temperature range, from as low as
110oF to as high as 5000F.
The most prominent fluorocarbon is TFE.
It is inert to almost all chemicals, cannot be dissolved and exhibits no
moisture absorption. Typical applications would include chemical mixing rod
bearings, gaskets and diaphragms in meters, chemical pump liners, bushings and
bearings, containers for corrosives, valve seats, balls, thrust washers and seal
rings.
In addition TFE has good electrical properties, including
high arc resistance. This gives it
applications in high frequency insulation and stand-off insulators, bus bars in
chemical electro plating, coaxial cable connectors, terminal insulators,
transformers, capacitors, relays and electrical push rods.
The extreme “slipperiness” of fluorocarbon materials
gives them many applications where low friction is required.
In food industries, they can be used to cover work surfaces to avoid
having sticky materials coat the parts. Laboratories
use them to cover surfaces where tacky or corrosive compounds will be used. The anti-friction property of fluorocarbons used in moving
parts may actually improve with time. A
thin layer of material may be deposited on the contacting surface so that you
have the condition of fluorocarbon rubbing against itself.
Some fluorocarbons may be filled or alloyed to enhance
certain properties. The most common
filler is glass, which can greatly increase certain mechanical properties such
as modular and strength. The
desirable fluorocarbon properties of chemical and heat resistance are generally
retained, but the price is, of course, greater for a filled system.
Filled fluorocarbons have been used in journal bearings, piston rings and
bushings.
The fluorocarbon family is made up of several branches.
They are polytetrafluoroethylene (PTFE or TFE), fluorinated ethylene
propylene (FEP), polyvinylidene fluoride (PVDF), Perfluoroalkoxy (PFA),
polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene (ECTFE),
ethylene-tetrafluoroethylene (ETFE) and polyvinylfluoride (PVF).
The most common of the above are PTFE (or TFE) and FEP.
We will give you a brief explanation of the others after giving more
detailed information on PTFE and FEP.
PTFE or TFE – polytetrafluoroethylene is a very dense
material having a density of 2.13-2.19 grams/cc. PTFE is well known for its chemical resistance.
It is insoluble in all organics with the exception of a few exotics.
Electrical properties are excellent. Impact strength is high, but its
resistance to wear, tensile strength and creep resistance are low in comparison
to other engineering materials. Mechanical
properties can be improved by adding fillers such as glass fibers, bronze,
carbon and graphite. PTFE has an
extremely low coefficient of friction. Very
few materials will stick to it.
It has useful properties from cryogenic temperatures up to 2600C
(5500F). PTFE is
produced as TEFLON® by duPont, as HALON® by Allied Chemical Corp., and as
FLUON® by I.C.I. While most of the
fluorocarbons can be processed by conventional methods, PTFE must be processed
by the press and sinter method, or by ram extrusion.
Applications for PTFE are many and varied. Chemical plants use PTFE in process equipment.
Electronics utilize the excellent electrical properties.
Use you imagination to match the properties with applications.
Sheets, rods, tubes and tape and available shapes as standard items.
Other shapes can be produced.
FEP – fluorinated ethylene propylene has all the desirable
properties of PTFE but with a service temperature of 2000C (3920F).
FEP can be extruded by conventional methods into rods or tubes, and
special shapes. It is, like PTFE, a
soft material with lower tensile strength, wear resistance and creep resistance.
It is chemically inert and insoluable in all but a few exotic solvents.
FEP is manufactured by duPont and sold under the trade name TEFLON®.
Applications include electronic items such as wire covering and spaghetti
tubing, linings for pipes in the chemical industry, aircraft wiring and glazing
for solar energy collectors. Availabilities
include film, sheet, rod and tubing.
PVDF – poly-vinylidene fluoride is a high molecular weight
polymer. PVDF exhibits greater
strength and wear and creep resistance than PTFE and FEP. It has good weathering properties and resists most chemicals.
It has a high dielectric constant and a high loss factor. Temperature
range is – 1000 to 1500C. Major markets are in
electrical insulation and chemical processing.
It is marketed under the trade name of
KYNAR® by Pennwalt Co., and is available in sheets, rods, tubes, pipe,
valves and fittings.
PFA – perfluoroalkoxy is a melt processible fluoroplastic.
Properties are similar to PTFE and FEP, although PFA has slightly better
mechanical properties than FEP above 1500C.
It is a duPont product sold under the TEFLON® trade name. Applications include liners for valves, pumps, pipe and
fittings, heat shrinkable tubing for electronics, roll covers and electric wire
insulation. PFA is optically clear
with a refractive index of 1.3.
PCTFE – polychlorotrifluoroethylene is resistant to most
reactive chemicals. However, a few
solvents dissolve PCTFE at temperatures above 1000C.
Others will cause swelling. It
has outstanding barrier properties to gases, especially water vapour.
Electrical properties are excellent.
It is used in chemical process equipment, electrical applications and
cryogenic situations. The product
is produced by the 3M Co., as KEL-F® and as ACLAR® film by Allied Chemical
Corp. KEL-F® is available in rods
and slabs.
ECTFE – ethylene-chlorotrifluoroethylene has greater
strength, creep resistance and wear resistance than PTFE, FEP and PFA.
Mechanical properties are similar to Nylon 6.
It is resistant to most corrosive chemicals and organic solvents.
UL rates ECTFE as 94V-0 in thickness as low as .007”. Temperature ranges from cryogenic to 1800C and for
short periods to 2000C. ECTFE
is sold under the trade name of HALAR® . Applications are in the electrical field, valve parts, watch
parts, lab tubing and containers for corrosive chemicals.
ETFE – ethylene-tetrafluoroethylene has impact resistance,
strength, chemical resistance, electrical properties and weather resistance
which nearly approach those of PTFE and FEP.
It is a duPont product marketed as TEFZEL®. It can be purchased in film, rod and tubing.
It is used for its good electrical properties and in valves and other
chemical process equipment.
PVF – polyvinyl fluoride is a highly crystalline plastic
produced by duPont as a film under the trade name of TEDLAR®.
It has outstanding weathering properties.
It has good abrasion resistance and resistance to staining.
It is often laminated to other materials to make use of its superior
properties. It is also used by
itself as a glazing material for solar collectors.