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Hacker, Robert W. (ed.) / The Wisconsin engineer
Volume 53, Number 5 (February 1949)

Wille, James E.
Teflon,   pp. 22-40 ff.


Page 22


TE FL ON                                  by J E.
                                          by James E. Wille che'50
  For many years, the chemical industry has been search-
ing for a construction material that combines the proper-
ties of chemical inertness and heat resistance. This ma-
terial is required for usc as filters, gaskets, packing and
the like for equipment that must be continuously in con-
tact with high temperatures and corrosive materials. Re-
cently Teflon, a DuPont product, has been placed on the
market; and according to present reports, it is meeting
the demand remarkably well.
  In producing Teflon, chloroform is fluoronated in two
stages  to produce tetraffuoroethylene. This gaseous
chemical is then polymerized to produce a sofid, granular
resin. It is then treated by special process to yield rods,
tubes, sheets and some molded articles.
        Cl-C-y            - F-C-F
             Cl                      Cl
.FC
C-C
FF
            CSC
            I I
            F F
h
               Structural diagram of Teflon.
  One of Polytetrafluoroethylene's most outstanding
properties is its remarkable stability. No known chemical,
hot or cold, will attack it, except molten sodium and po-
tassium, and free fluorine under superatmospheric pres-
sures, and these chemicals are seldom found in industrial
processes. It has served with excellent results in contact
with hot sulfuric and nitric acids, hot concentrated alkalis,
and in many other cases where contact with corrosive ma-
terials is necessary.
  Another of its remarkable properties is its heat resis-
tance. Tensile bars heated to 480f showed a negligible
decrease in tensile strength after several month's exposure,
however, at temperatures above 400f F., care must be
22
taken, for small quantities of fluoronine-containing gases
are liberated. Furthermore, it shows very little tendency
towards embrittlement at low temperatures.
   The non-adhesiveness of the resin has caused problems,
 but it has also been used to advantage in many cases. One
 application made possible by this property is its use as a
 liner for spray towers where buildup of solids on the walls
 has been a problem. It has also been used as a coating for
 the rollers used in the production of some synthetic rub-
 bers. In all cases, it is necessary to fasten Teflon to the
 material being covered by mechanical means.
   Unfortunately, the very advantages which give Poly-
 tetrafluoroethylene its unusual position among plastics
 contribute difficulties in working it.  Since it never be-
 comes molten, even at high temperatures, the ordinary
 techniques of molding and extrusion are not applicable.
 However, it can be extruded into heavy-walled tubes.
 This process is not too efficient, and the rates are meas-
 ured in terms of feet per hour instead of feet per
 minute as is the case of most thermoplastics.
   This plastic has proved very adaptable to ordinary ma-
chining operations, and this enables users to produce ob-
jects of rather complicated structure. However, collants
must be used during the process to guard against the
production of toxic gases. It may also be molded by hy-
draulic pressure. The designs must be simple when pro-
duced by this method, but development of this process is
seen as a solution to the problem.
  The uses of this comparatively new material are many
and varied. Because of its arc-.zitesistance and low elec-
trical loss, it is finding use as the dielectric in coaxial
cable. Even when arcing does occur the surface is merely
scarred, and no conducting carbon coating is formed.
Bound with fiber, it can be Glded into packing rings
that are very suitable for hi*   speed pumps. A recent
development consists of Teflon filled with micro-pulver-
ized glass; preliminary tests indicate that this combina-
tion results in a material having resistance to abrasion
coupled with its other properties.
  Since the material is currcnty bci:v, evaluated by in-
dividuals and concerns representing a wide industrial
range, many new uses for it may be developed in the
future. However, it should be pointed out that this ma-
terial is not recommended for use where substitute pro-
ducts will serve equally as well. It should be considered
only where its service life and consequently low replace-
ment cost will compensate for the relatively high initial
cost.
THE WISCONSIN ENGINEER


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