Physical properties of Fluon® unfilled and filled PTFE

Physical properties of Fluon®
unfilled and filled PTFE
Technical Service Note F12/13
2
Contents
Summary
Page
6
Introduction
6
SECTION 1. THE STRUCTURE OF PTFE
Molecular conformation and crystal structure
Melting behaviour
Crystallinity and texture
Polymer particle structure
Void formation in mouldings
7
7
7
8
9
10
SECTION 2. EFFECTS OF PROCESSING ON
PROPERTIES
Molecular weight
Crystallinity
Orientation
Voids
11
SECTION 3. MECHANICAL PROPERTIES
- UNFILLED PTFE
Compressive stress-strain relationships
Tensile properties
Impact behaviour
SECTION 4. ELECTRICAL PROPERTIES
- UNFILLED PTFE
Permittivity and dielectric loss
Experimental techniques
D.C. conduction behaviour
High voltage uses of PTFE
SECTION 5. THERMAL PROPERTIES
- UNFILLED PTFE
Melting point
Thermal expansion
Thermal conductivity
Specific heat and heat of fusion
Thermal stability
SECTION 6. SURFACE PROPERTIES
- UNFILLED PTFE
Coefficient of friction
Angle of contact
SECTION 7. OTHER PHYSICO-CHEMICAL
PROPERTIES - UNFILLED PTFE
Permeability
Infra-red transmission
11
11
12
12
13
13
18
18
21
21
21
21
24
Refractive index
Melt viscosity
High energy radiation
Chemical resistance
Velocity of sound
Page
28
28
29
29
29
SECTION 8. GENERAL - FILLED PTFE
Function of filler
Choice of filler
Choice of Fluon® grade
The Fluon® range
30
30
30
31
31
SECTION 9. MECHANICAL PROPERTIES
- FILLED PTFE
Compressive deformation
Impact strength
32
SECTION 10. ELECTRICAL PROPERTIES
- FILLED PTFE
Insulating materials
Conducting materials
SECTION 11. THERMAL PROPERTIES
- FILLED PTFE
Thermal expansion
Thermal conductivity
SECTION 12. SURFACE PROPERTIES
- FILLED PTFE
Friction
Wear
32
37
38
38
38
40
40
40
41
41
43
25
25
25
25
26
26
SECTION 13. OTHER PHYSICO-CHEMICAL
PROPERTIES - FILLED PTFE
Permeability
Chemical resistance
45
45
45
SECTION 14. TYPICAL PROPERTIES OF
UNFILLED AND FILLED MOULDED PTFE
46
SECTION 15. SPECIFICATIONS RELATING
TO PTFE
47
SECTION 16. HANDLING PRECAUTIONS
48
SECTION 17. FURTHER INFORMATION
49
SECTION 18. REFERENCES
50
27
27
27
28
28
28
3
4
List of figures
Page
Page
1.
Molecular conformation of PTFE
7
2.
The decay of birefringence in the melt
8
sintered granular PTFE (60 % crystallinity)
3.
Particles of dispersion polymer
9
using evaporated gold electrodes
4.
Aggregates of particles of dispersion
9
polymer
5.
Longitudinal section through
10
Longitudinal section through
10
Internal and external texture of a
10
Variation of relative density
12
13
10. Compressive creep
14
11. Isochronous stress-strain relationship
14
in compression
23
and preconditioning for sintered
22. Variation of specific volume
23. Infra-red transmission spectrum
26
Fluon®
15
G163
13. Creep in compression, at 25°C (77°F),
24. Creep in compression at 20°C (68°F),
16
17
34
Fluon® FC100-25 1000
35
compression at 20°C (68°F), and various
27. Creep in compression at 20°C (68°F):
1
at 25°C (77°F), Fluon® G163
19
36
various Fluon® grades
28. Recovery from creep in compression:
stress-strain curves for PTFE
17. Effect of temperature upon tensile
25. Creep in compression at 20°C (68°F),
strain levels: Fluon® FC100-25 1000
various strain levels, Fluon® G163
16. Effect of temperature upon tensile
33
FC100-25 1000
26. Isometric stress-time curves in
in compression, at 25°C (77°F) and
15. Recovery from creep in compression
G163 and
Fluon®
at various stress levels,
Fluon® G163
14. Isometric stress-strain curves
29
(specimen thickness 0.05 mm (0.002 inch))
Fluon®
12. Isochronous stress-strain curves in
yield stress of PTFE
sintered granular PTFE
with temperature
Basic creep testing equipment
compression, 25°C (77°F),
23
granular PTFE
with crystallinity
9.
20. Plot of log10 apparent volume
21. Effect of different electrode materials
granular polymer
8.
22
resistivity versus log10 time for
sintered extrudate
7.
19. Loss angle versus frequency for
22
PTFE at room temperature
unsintered extrudate
6.
18. Loss angle versus temperature for
Fluon®
36
FC100-25 1000 loaded
at various stress levels
20
29. Loss tangent versus temperature
38
at 1 kHz: glass-filled PTFE
5
Summary
Introduction
This Note describes the physical properties of PTFE.
It should be used in conjunction with other Asahi Glass
Fluoropolymers Technical Service Notes.
Only rarely can the physical properties of PTFE
(polytetrafluoroethylene) be expressed in simple terms.
Because of its high melt viscosity PTFE is not processed
by those techniques associated with most thermoplastic
polymers. The techniques used with PTFE consist
essentially of a cold shaping operation followed by
sintering, during which the polymer particles fuse and
coalesce; finally the fused polymer is cooled. One result
of the fabrication methods used with PTFE is that, in
many respects, the quality of the fabricated polymer is
unusually dependent on the skill with which the
fabrication is carried out. For this reason any table
purporting to express the physical properties of PTFE as
a list of figures - including such tables which appear in
this Note - must be regarded as a very simple summary
of a very complex subject.
Three general surveys of PTFE are:
Fluorine-containing polymers, Part 2:
Polytetrafluoroethylene, C A Sperati and H W
Starkweather, Fortschr. Jochpolym.-Forsch., 2, 1961,
465-495
Polytetrafluoroethylene, S Sherratt, Kirk-Othmer,
Encyclopaedia of Chemical Technology, 9, 2nd edition,
Interscience Publishers Inc., New York, 1966, 805-831.
Fluoroplastics, Vol 1: Non-Melt Processible
Fluoroplastics, S. Ebnesajjad, Published by Plastics
Design library, 2000. ISBN1-884207-84-7
6
Section 1. The structure of PTFE
MOLECULAR CONFORMATION AND CRYSTAL
STRUCTURE
PTFE is a linear chain polymer of great molecular length.
The linearity is indicated by an analysis of the infra-red
spectrum and by the fact that the powder as produced in
the polymerisation reaction is very highly crystalline,
with crystalline weight fractions of 0.90 to 0.95 being
indicated by density, infra-red and X-ray diffraction
measurements. Energy considerations also suggest that
branching by chain transfer is unlikely (ref. 1).
The crystal structure and chain conformation have been
discussed by Bunn and Howells (ref. 2) and later by
others (refs. 3, 4, 5). The crystalline melting point of
sintered PTFE is about 327°C (620°F) and of unsintered
material 332-346°C (630-655°F) but there are two
reversible
first
order
transitions
at
lower
temperatures,19°C and 30°C (66°F and 86°F) (ref. 6),
which together involve a 1% change in density (ref. 7).
Three crystalline phases are observed at atmospheric
pressure: phase I (< 19°C; 66°F), phase ll (19-30°C; 6686°F) and phase lll ( >30°C; 86°F).
Below the 19°C (66°F) transition (phase l), the chain
repeat distance is 16.8 Å and the CF2 groups are equally
spaced along the chain which is twisted to form a helix
on which successive carbon atoms lie, thirteen carbon
atoms being involved in a twist of 180°, (Figure 1).
Between 19 and 30°C (66 and 86°F) (phase ll) the repeat
distance increases to 19.5 Å (refs. 3,8) corresponding to a
twist of 15 carbon atoms in 180°. Above 30°C (86°F),
(phase lll), further disorder sets in and although the
molecular
conformation
prevailing
at
lower
temperatures is maintained, the chains are displaced or
rotated along their long axes by variable amounts which
increase as the temperature is raised further. The reason
for the helical structure is the necessity to accommodate
the large fluorine atoms (van der Waals radius 1.35 Å).
The rotation at each chain bond, with the slight opening
up of the bond angles to 116°, relieves the overcrowding
and permits the shortest F-F distance to be 2.7 Å (ref. 9).
Further studies by various authors (refs.10,11,12,13,14)
have examined the effect of pressure on the room
temperature transitions and the melting point. A study of
pressures above-atmospheric revealed a 2% increase
in density below 19°C (66°F). This fourth crystalline
phase has been labelled phase lll by Weir (ref. 10). A
triple point exists at about 70°C (158°F) and 4.5 kilobars.
The heats of transition were also determined by Yasuda
and Araki (ref. 11); dilatometric and calorimetric studies
have in addition been reported by other workers (refs.
6,15, 16,17).
Figure 1. Molecular conformation of PTFE
MELTING BEHAVIOUR
PTFE has a crystalline melting point at atmospheric
pressure of about 332-346°C (630-655°F) for unsintered
and about 327°C (620°F) for sintered material. The heat of
melting has been estimated by Lupton (ref. 18) as about
685 cal/mole of CF2 groups and leads to an estimate of
the entropy of melting of 1.14 cal/degK mole. This value
is low by comparison with polyethylene (2.29 cal/degK
mole) and arises from the fact that the stiff long
molecules retain a good deal of side-by-side order in the
melt. Indeed, if the depolarisation of light is used to
detect the course of melting, a finite amount of
depolarisation is observed to remain above the melting
point (ref. 19) (Figure 2). The decay of this residual
depolarisation is sensitive to molecular weight, time and
temperature. Bunn (ref. 20) has ascribed the high melting
point to the rigidity of the fluorocarbon chain, small
rotations being hindered by the slightly overcrowded
fluorine atoms.
7
Figure 2. The decay of birefringence in the melt
CRYSTALLINITY AND TEXTURE
The crystallinity and texture of polytetrafluoroethylene
have received a good deal of study. Estimations of the
degree of crystallinity have been made by X-ray (ref. 21),
infra-red (refs. 22, 23) and density methods. For 100%
crystalline PTFE relative densities of 2.347 at 0°C (32°F)
and 2.302 at 25°C (77°F) can be calculated from the X-ray
crystallographic data (ref. 5). The density decrease of
about 2% between these temperatures includes the
decrease of about 1% arising from the transition at 19°C
(66°F). The relative density of amorphous PTFE is not
affected by this transition and values around 2.00 are
obtained by measuring the density at room temperature
(preferably 23°C; 73°F) for a number of samples of
varying crystallinity, and then extrapolating to zero
crystallinity (refs. 8, 24, 25).
If the degree of crystallinity is estimated as a result of Xray or infra-red methods it is then possible to calculate a
theoretical density. Differences between this theoretical
density and the experimentally measured value can be
used to assess the void content of a sample.
Neither the X-ray nor the infra-red method measures an
absolute crystallinity. Each measures ‘disorder’ by a
different criterion and, in addition to this, each is subject
to purely instrumental limitations, so that even for one of
the methods the same value would not necessarily be
determined on two different instruments. Tests show the
degree of crystallinity measured by the infra-red method
is systematically higher than the X-ray crystallinity, the
discrepancy being of the order of 5% at 90% increasing to
10% at 50%.
For instance, the crystallinities estimated by the X-ray
method range from about 90% for unsintered material,
75% for fused and slowly cooled material, to 50% for
8
fused and rapidly quenched samples. The initial high
crystallinity and melting point can never be completely
recovered after fusion because of the complete
reorganisation of the molecular arrangement upon
sintering.
Crystallisation from the melt in bulk produces long bands
which can be seen both in fracture surfaces produced by
breakage at liquid nitrogen temperatures, and in sections
of the material when viewed microscopically in polarised
light (ref. 26). Their dimensions vary from 100µm x 1µm
to 10µm x 0.2µm depending on the crystallisation
conditions and/or molecular weight, the band width
being inversely related to molecular weight (ref. 27).
The bands show fine parallel striations perpendicular to
the band length and it is thought that the bands are the
broken edges of thick lamellar crystals. The
interpretation of the striations is still uncertain and
remains a subject for further investigation (ref.19).
Birefringence measurements show the molecules to lie
perpendicular to the bands and since the average length
of the molecules is greater than the band thickness chain
folding is implied. As the fusion temperature is raised or
a lower molecular weight polymer is used (both of which
tend to reduce the persistence of order in the melt) the
band growths become irregular and tend to agglomerate
into spherulitic structures. The use of very high fusion
temperatures of around 450°C (842°F) results in well
formed spherulites, presumably due to molecular weight
reduction as a consequence of thermal degradation.
Speerschneider and Li have investigated the role of the
large bands in uniaxial deformation and have shown that
distortion of the bands occurs at low temperatures
(ref. 28).
POLYMER PARTICLE STRUCTURE
The particles of polymer produced in the dispersion
polymerisation process are of the order of 0.2µm in size,
whilst those from a granular polymerisation are
hundreds of µm in size, built up from smaller particles.
They are both highly crystalline - about 90 to 95%.
The dispersion particles can be studied directly in a
conventional transmission electron microscope,
providing the electron intensity is kept low (ref. 29). On
raising the electron beam intensity the particles change
rapidly in appearance to become transparent with a
crumpled texture. At this stage the crystallinity has
disappeared and the ‘particles’ probably consist of a
shell of carbon. Electron diffraction patterns and dark
field micrographs suggest that the particles are
composed of a pile of small single crystals (ref. 30) with
the molecular axis along the axis of the brick-shaped
particles (refs. 30, 31). The particles also appear to have
a striated surface structure generally parallel to the long
axis. A replica of some dispersion particles is shown in
Figure 3. During coagulation, the dispersion particles
Figure 3. Particles of dispersion polymer
1µm
aggregate to form a larger particle, made up of a loose
structure of agglomerates of the primary particles
(Figure 4). During cold, lubricated extrusion the
agglomerated particles are highly distorted, with their
primary particles becoming aligned and also drawn into
fibrous material. This effect is illustrated in Figure 5.
If an extrudate such as that depicted in Figure 5 is
sintered and cooled slowly the extrudate will appear as
in Figure 6. In Figure 6 the direction of extrusion was
from left to right.
Granular Polymers
During the early stages of polymerisation granular
particles form as aggregates of smaller particles. This
process continues and large irregular fibrous structures
are produced.
This material is then modified mechanically to reduce it
to the familiar form suitable for processing. For example,
Figure 7 shows the structure of a fine particle granular
powder.
Figure 4. Aggregates of particles of dispersion polymer
100µm
9
Direction of extrusion
1µm
Figure 6. Longitudinal section through sintered
extrudate
0.5µm
Figure 5. Longitudinal section through unsintered
extrudate
VOID FORMATION IN MOULDINGS
When PTFE is moulded the basis of the process is that
the polymer powder is preformed and then sintered. It is
therefore not surprising that mouldings can be produced
which contain microscopic voids and fissures arising
from the porous nature of the unsintered particles and
the molecular re-arrangement caused by sintering.
Correct choice of polymer grade and careful use of
fabrication techniques will help to minimise the
formation of voids. The homogeneity of the final
moulding depends a great deal on the compressibility of
the particles and their surface structure.
In this respect the behaviour of the particles closely
resembles that of powdered metals. Softer particles
(generally more porous ones) compact more easily than
harder ones and will ‘flow’ more easily to fill
interparticulate voids. This leads to a higher ‘green’
strength (of the unsintered preform) and in turn to a
higher sintered strength. As with powdered metals the
strength both of the preform and of the final sintered
moulding depends upon the mean particle size, with
finer particles giving higher strengths. According to
10
10µm
Figure 7. Internal and external texture of a granular
polymer
Rhines as reported by Goetzel (ref. 32) the important
factors affecting powdered metals are the number of
particle-to-particle contacts and their area. Experiments
(ref. 33) suggest that, even where no voids exist,
variations in internal pressure within a preform result in
variations in crystallite size presumably due to the
variations in melting point with pressure, for which
McGeer and Duus (ref. 34) have given the relationship:
Tm = a + bP
Where T = °K, P = atmospheres, a = 597°K and
b = 0.154°C/atm so that 16 MN/m2 (160 kgf/cm2; 1 tonf/in2)
difference in internal pressure can lead to a melting point
difference of the order of 25°C (45°F). Such variations in
internal pressure will result either from poor packing of
the powder in the mould due to poor powder flow
properties or from a lack of compressibility in the
individual particles. The variation in crystallite size
resulting from poor packing leads to variation in
translucency from area to area and lack of
compressibility gives an overall white and opaque
appearance in thin machined sections such as 0.25mm
(0.01 inch) skived tape.
Section 2. Effects of processing on properties
The exact manner in which the fabrication of the
polymer is carried out affects certain intrinsic qualities in
the polymer which, in turn, influence some properties,
notably tensile strength, elongation and dielectric
strength. The intrinsic qualities of PTFE which can be
affected by fabrication conditions are molecular weight,
crystallinity, orientation and the presence or otherwise of
voids and interfaces. These factors will now be
considered in turn.
MOLECULAR WEIGHT
All commercial samples of PTFE (with the exception of
lubricant powders) are of extremely high molecular
weight; granular polymers are of somewhat higher
molecular weight than dispersion polymers. Because of
its insolubility, the molecular weight of PTFE can be
measured only with difficulty.
The best method of assessing the molecular weight of
PTFE is undoubtedly by measuring the viscosity of the
polymer at some temperature above its melting point.
This approach demands, however, some fairly
sophisticated equipment if it is to be successful and less
direct methods of arriving at an idea of molecular weight
are often favoured.
When PTFE is cooled from a temperature above its
melting point at a carefully controlled rate, the extent to
which the polymer crystallises will be inversely
dependent on the molecular weight. Now, assuming the
moulding contains no voids, its crystallinity can be
inferred from its relative density, so the relative density
of a moulding prepared under precisely defined
conditions (this quantity is often called the standard
relative density) can be used as an index of molecular
weight. The relationship:
_
standard relative density = 2.612-0.058 log10 Mn
_
has been given where weight Mn is the number average
molecular weight .
CRYSTALLINITY
As polymerised, PTFE is of 90-95% crystallinity but when
it is heated above its crystalline melting point the
polymer becomes amorphous. In the melt state PTFE
does retain some two-dimensional order but, as the
three dimensional crystal structure has been destroyed,
molten PTFE can properly be thought of as amorphous.
On cooling, the extent to which crystallisation occurs is
dependent both on the molecular weight of the polymer
and on the rate of cooling, particularly at temperatures
just below the melting point. Slow cooling naturally
tends to increase the extent of crystallisation. Almost all
fabricated PTFE displays crystallinities within the range
50 to 75% depending on the rate of cooling.
The crystallinity of PTFE is best measured by X-ray
diffraction or by infra-red absorption methods These
respectively assess ‘order’ and ‘disorder’ within the
specimen. However as the relative density of 100%
crystalline PTFE at 23°C (73°F) is 2.30 while that of 0%
crystalline (100% amorphous) PTFE under the same
conditions is 2.00, the relative density of PTFE can be
used to give a simple index of crystallinity. Clearly it is
essential that the specimens used for relative density
measurements be free from voids and, since such voids
are less likely to occur in specimens produced from
coagulated dispersion polymers, the technique is
probably of greater value in this field than in that of
granular polymers. The relationship between relative
density and crystallinity for void-free specimens of PTFE
is shown in Figure 8.
The level of crystallinity in fabricated PTFE is a matter of
considerable importance. In general, fabricators attempt
to keep the crystallinity to a minimum as the higher the
amorphous content the greater the ultimate tensile
strength and the longer the flex life will be. In some
instances, however, such as where gas permeability
must be reduced, higher crystallinities will be desirable.
The thermal stability of PTFE is so great that, if
processed correctly, the polymer should suffer no
significant degradation and the molecular weight of the
finished product will be determined almost entirely by
that of the raw polymer.
11
Figure 8. Variation of relative density with crystallinity
ORIENTATION
The orientation of PTFE is a measure of the extent to
which the polymer chains are aligned in any particular
direction. This alignment, because of their methods of
processing, is more likely to occur with the coagulated
dispersion polymers than with the granular or aqueous
dispersion materials.
VOIDS
During fabrication, PTFE does not pass through the state
of being a low viscosity liquid and, as a result, articles
made from PTFE may possess voids and interfaces in the
mass of the polymer. These faults are more likely to
occur in large articles made from granular polymers than
in articles of thin cross-section made from either
aqueous or coagulated dispersion polymers.
The problem of voids in granular mouldings can almost
always be overcome by careful choice of the correct
granular polymer for a particular duty and by use of the
appropriate fabrication technique.
For practical purposes the absence of voids in fabricated
PTFE is denoted by good tensile strength, high
elongation at break, low gas permeability, prolonged flex
life and high dielectric strength. It is often possible to
detect voids by examining a thin section - preferably less
than 0.25 mm (0.01 inch) - by transmitted light when a
sample free from voids will be translucent with a faintly
blue colour. On the other hand a sample containing many
voids will be white and opaque with a chalky appearance.
If the sample is first treated with a penetrant dye† then
the detection of voids is made a great deal easier.
† Such as ‘Ardrox’ 996P supplied in the UK by Chemetall plc, 65
Denbigh Road, Bletchley, Milton Keynes, MK1 1PB (UK)
Tel. +44 (0) 1908 649333 Fax +44 (0) 1908 361872
www.aerospace.chemetall.com
in mid-Europe by Chemetall GmbH, Frankfurt a.M. Tel. +49 (0) 697165-0
and in the USA by Chemetall Oakite, 50 Valley Road, N.J. 07922,
Berkeley Heights
Tel. +1 908 508 2214 Fax +1 908 464 7914 Toll-free 800 526 4473
www.oakite.com
12
Section 3. Mechanical properties - unfilled PTFE
Although the classical concept of modulus, which
implies a linear proportionality between stress and
strain, is not strictly applicable to most plastics, the term
is widely used and the resulting implications should be
considered.
The Young’s Modulus of a metal such as steel is the ratio
of stress to strain in the elastic region, and is constant.
For most plastics such a region does not exist and the
ratio of stress to strain will not be constant but will
depend both on the time for which the stress is applied
and the resulting strain. The time-dependence of strain
may be defined as the ‘creep’ behaviour and a study of
creep, together with the equally important phenomenon
of recovery, is essential for a full understanding of the
mechanical properties. An apparatus has been specially
developed for studying the compressive creep of PTFE:
full details of this equipment have been published
elsewhere (ref. 35) but a general impression is given in
Figure 9. With this equipment the stress-strain-time
relationship at a constant temperature may be obtained
by observing either the strain-time relationship at a
constant stress (creep) (Figure 10), or the stress-strain
Alternatively the isochronous curve may be obtained
experimentally on a single specimen by the application
of a series of stresses (σ1 to σ6 Figure 11) in
successively increasing steps and measuring the strain
produced ( 1 to 6 Figure 11) after the section time, t,
has elapsed, allowing a recovery period of 4t by
complete removal of the stress on the specimen between
each successive increase (ref. 36). The isochronous
stress-strain curves presented here have been obtained
in this way. Isometric curves (stress-time relationships at
constant strain) may also be obtained by taking constant
strain sections through a family of creep curves.
∋
COMPRESSIVE STRESS-STRAIN RELATIONSHIPS
relationship at a constant time (isochronous stress-strain
curve) (Figure 11). The isochronous curve is derived by
taking a constant time section through a family of creep
curves and replotting the stress and strain values of the
intersections to give the isochronous curve. The
derivation is shown schematically in Figures 10 and 11.
∋
In some respects PTFE is a typical thermoplastic
polymer; in others it is far from typical. Thus the
mechanical properties of PTFE vary with changes in
time, temperature and crystallinity in the way that one
would expect of a thermoplastic. On the other hand, the
fabrication methods used with PTFE can have a very
large influence on the properties, particularly if
unsatisfactory processing allows a particulate structure
to persist into the fabricated article. PTFE is used only
infrequently in tension so that it is appropriate to make
measurements on samples in compression. The
properties of design interest will be considered in some
detail.
At the termination of a creep experiment the
phenomenon of recovery may be studied by removing
the load on the specimen and observing the decrease of
strain with time. It is convenient to present recovery data
on a ‘fractional recovered strain’ versus ‘reduced time’
graph as an aid to comparison of data obtained on
specimens which have either attained different
maximum strains at the termination of the creep
experiment or for which the times under load have not
been identical. Fractional recovered strain is defined as
the ratio of the strain recovered to the creep strain at the
start of recovery and reduced time as the ratio of the
recovered time to the creep time (ref. 37). Thus a
fractional recovered strain of unity signifies complete
recovery and a reduced time of unity denotes a recovery
time equal to the preceding creep time.
Spherical seating
Figure 9. Basic creep testing equipment
Fixed
platen
Iris diaphragm
device
Specimen
Moving
platen
Pivot
Beam
Load
Automatic
loading
device
13
6
5
6
4
6
3
5
5
6
4
4
5
2
3
4
3
2
3
2
1
2
1
1
Strain
Stress
1
t
Time - (log scale)
Figure 10. Compressive creep
The following information is the result of work done on
behalf of AG Fluoropolymers. A complete picture of the
behaviour of PTFE has not yet been obtained, and in
particular, work on effects of temperature is not
complete. Nevertheless, enough data are now available
to provide some basic information. The data given are for
Fluon® G163 preformed at a pressure of about 16 MN/m2
(160 kgf/cm2; 1 tonf/in2), and sintered at 380°C (716°F).
Isochronous stress-strain behaviour
Figure 12 shows the effect of time on the stress-strain
relationship of Fluon® G163. The non-linearity of the
curves, even at quite low strains, shows how the
apparent modulus decreases with increasing strain.
14
Strain at time (t)
Figure 11. Isochronous stress-strain
relationship in compression
Creep behaviour
Figure 13 shows a family of creep curves at various
stress levels, while Figure 14 shows the same
information plotted as stress against time for various
strain levels. It should be noted that the latter are not true
stress relaxation curves, though the curves should give a
very approximate indication of the decay of stress with
time in a component maintained at a constant strain
level.
Recovery
Figure 15 shows the effect of four different stress levels
on the rate of recovery of strain after removal of the
applied compressive load. It can be seen that the higher
the stress the slower is the recovery.
1100
s
(2
H
ou
rs
10
46
0s
ec
m
in
u
te
on
80 Kgf/cm 2
s)
ds
8
nd
)
rs
4
se
co
7
10
70 Kgf/cm 2
ys
s
nd
1
(1
16
u
ho
1000
da
co
6
10
6
se
900
60 Kgf/cm 2
800
5
700
50 Kgf/cm 2
600
4
40 Kgf/cm 2
500
3
30
400
300
2
20
200
1
100
0
0
0
0.5
Strain - %
1
1.5
2
3
2.5
o
3.5
Stress - Ibf/in 2
Stress - MN/m 2
10
4
o
Figure 12. Isochronous stress-strain relationship in compression, at 25 C (77 F), Fluon® G163
15
:11
60
lbf/
in 2
)
5.0
m
f/c
7M
N/
m
2
(71
.4
kg
8M
4.0
2
N/m 2
:10
15
(81
lbf
.6 k
/in
2
)
gf/c
m2
4.5
lb
f/i
n
2
)
3.5
m
2
(6
1.
2
kg
f/c
m
2
:8
7
0
3.0
6
M
N/
2.5
)
2
/in
25
f
lb
:7
2
m
2.0
f/c
0
1.
(5
2
kg
m
N/
5
M
)
2
/in
1.5
2
.8
(40
2
N/m
cm
gf/
bf
0l
:58
k
4M
2
1.0
2
2
N/m
cm
kgf/
6
(30.
bf/in
l
:435
)
3M
2
f/in )
:290 lb
kgf/cm
2
m
(10.2 kgf/c
1 MN/m
10 2
104
103
1 hour
Time - seconds
o
o
Figure 13. Creep in compression, at 25 C (77 F), Fluon® G163
105
106
:145 lbf/in
107
1 month
10
1 week
0
2
2)
108
1 year
(20.4
2
1
16
2
6 Months
2 MN/m
1 day
Strain - %
0.5
8
80 kgf/cm 2
1100
7
1000
70 kgf/cm 2
900
6
60 kgf/cm 2
800
5
50 kgf/cm 2
700
600
4
40 kgf/cm 2
500
3
30 kgf/cm 2
400
300
2
20 kgf/cm
2
200
1
10
0
Time - seconds
2
10
103
104
105
106
o
107
0
108
Stress - Ibf/in 2
0
100
1 year
6 Months
1 month
1 week
1 day
1 hour
Stress - MN/m2
10 kgf/cm 2
o
Figure 14. Isochronous stress-strain curves in compression, at 25 C (77 F) and various strain
levels, Fluon® G163
17
0.8
2
2
0 lbf/in
cm ; 29
2
2 (20.4 kgf/
f/in
2 ; 580 lb
2 MN/m
2
gf/cm
lbf/in
2 (40.8 k
2 ; 870
m
2
/
N
m
4M
kgf/c
lbf/in
2 (61.2
2 ; 1160
/m
m
6 MN 2 1.6 kgf/c
(8
m
/
8 MN
Fractional recovered strain
0.6
0.4
0.2
0
10-6
10-5
Reduced time
10-4
10-2
10-3
o
10-1
1
10
102
o
Figure 15. Recovery from creep in compression, at 25 C (77 F), Fluon® G163
TENSILE PROPERTIES
The tensile breaking stress and breaking strain are used
extensively for quality control purposes, but they are
unsatisfactory quantities for design purposes for two
reasons: firstly, and most importantly, PTFE should never
be used at strains beyond the yield point (the point at
which the load-deformation curve has a distinct change
of slope) and secondly, the point of fracture is dependent
on specimen shape and is therefore not useful for
predicting behaviour in practice.
The tensile load-extension curves obtained with
specimens of PTFE depend on crystallinity, molecular
weight, the size, shape and perhaps the structure of the
original particles and the severity of faults remaining
after fabrication. Furthermore they depend, as is usual
with thermoplastics, on test temperature and straining
rate. Because of these complications the data here can
only be indicative of general behaviour. Figure 16 shows
the general trends of behaviour in tension for PTFE as a
function of temperature. These are typical curves from
which the yield stress can be derived, though less
precisely than is possible for most other plastics
materials.
The effect of temperature on the yield stress of PTFE is
shown in Figure 17, which is for times to yield of
approximately one minute. If the material is to be under
load for any considerable length of time it should not be
stressed beyond a small fraction of the yield stresses
shown in Figure 17.
IMPACT BEHAVIOUR
The behaviour of plastics under impact conditions
depends both on temperature and on the severity of the
applied stress, as well as on molecular parameters such
as molecular weight and fabrication effects. PTFE is no
exception to these generalisations and with the wide
variation in fabrication procedures available for this
polymer it is impossible to give other than general data.
18
Unnotched specimens of PTFE are resistant to fracture on
impact; even at temperatures as low as -196°C
(320°F) well-fabricated specimens are tough. A test for
judging the quality of a sample from this point of view is
to measure the flexural strength of specimens which
have been immersed for 15 minutes in liquid nitrogen
and then tested within a few seconds of removal. In this
liquid nitrogen dip test which was carried out with three
point loading, a span of 38mm (1.5 inches), a thickness of
3.2mm (0.125 inch) and a rate of test of 457mm/min (18
inches/min) good specimens of PTFE do not break at the
maximum load, the apparent yield stress of such a
specimen being approximately 185 MN/m2 (1900 kgf/cm2;
27 000 lbf/in2). However, less well-fabricated specimens
may be brittle with flexural strengths of approximately
135 MN/m2 (1400 kgf/cm2; 20 000 lbf/in2) in this test.
The behaviour of notched specimens typifies the reaction
of PTFE components with built-in stress concentration
regions. This is shown by measurements of the Charpy
impact strength: the test was carried out with three-point
loading and an impact velocity of 2.44m/second (8
ft/second) at temperatures between -35 and +23°C (-31
and +73°F). One sample was cooled slowly at 25°C/hour
(45°F/hour) and another cooled from the sintering
temperature of 380°C (716°F) to 20°C (68°F) in two hours.
The notch tip radius of the specimens was varied
between 0.25mm (0.01 inch) and 2.03mm (0.08 inch),
spans of 25mm (1 inch) and 38mm (1.5 inch) were used
and the notch depth was held constant at 2.82mm (0.110
inch). There was no consistent difference between the
impact strengths of the samples cooled at different rates.
At temperatures of -20°C (-4°F) and below all notched
specimens broke completely, [impact strength in the
range 6 to 10 kgf/cm2 (3 to 5 ft Ibf/in2), with an 0.25mm
(0.010 inch) notch], whilst at -10°C (+14°F) and above
many specimens did not break completely - that is to say
‘hinge’ breaks occurred.
40
400 kgf/cm 2
-40°C (-40°F)
-20°C (-4°F)
35
5000
-10°C (-14°F)
30
300 kgf/cm 2
4000
0°C (-32°F)
25
10°C (-50°F)
3000
20
200 kgf/cm 2
25°C (77°F)
15
2000
50°C (122°F)
10
100 kgf/cm 2
100°C (212°F)
1000
150°C (302°F)
5
0
0
0
Strain - %
100
200
300
Stress - Ibfin 2
Stress - MNm
2
200°C (392°F)
400
Figure 16. Effect of temperature upon tensile stress-strain curves for PTFE
19
200
2000 kgf/cm 2
25000
150
1500 kgf/cm 2
20000
15000
100
1000 kgf/cm 2
10000
50
500 kgf/cm 2
0
-220
-364
-140
-220
-60
-76
20
68
Temperature
Figure 17. Effect of temperature upon tensile yield stress of PTFE
20
100
212
180
356
0
260°C
500°F
Yield stress - lbf/in 2
Yield stress - MN/m 2
5000
Section 4. Electrical properties - unfilled PTFE
PERMITTIVITY AND DIELECTRIC LOSS
EXPERIMENTAL TECHNIQUES
It has been known since 1946 (ref. 38) that because of its
non-polar nature, the dielectric properties of PTFE were
of an ideal character. In 1953 a careful study by Ehrlich in
the USA (ref. 39) showed that the fall in permittivity from
2.0 to 1.8 in the temperature range 24 to 314°C (75 to
597°F) could be accounted for entirely in terms of density
changes by the Clausius-Mossotti formula. No changes
of permittivity with frequency were detected and
scarcely resolved loss angle† values less than 200µ
radians were recorded.
In 1955 Mikhailov and co-workers in the USSR (ref. 40)
found a loss peak in the -80 to -40°C (-112 to -40°F) range
at audio and radio frequencies which was correlated in
its temperature/frequency location with dynamic
mechanical loss behaviour. From studies of the effect of
changes of crystallinity by quenching and slow cooling
they concluded that the relaxation losses were
attributable to amorphous regions of the polymer. In
1959 Krum and Muller (ref. 41) (of Marburg) reported
higher dielectric loss values than those found by earlier
workers and found more detailed correlation with
mechanical properties and effects of crystallinity
changes. Eby and Sinnott in the USA (ref. 42) have
suggested, however, that these higher loss values must
be due to polar impurities.
The results of measurement done on behalf of AG
Fluoropolymers are presented in Figure 18 where the
variation of the loss angle with temperature is given for
the range -140 to +240°C (-220 to +464°F) and in Figure 19
as loss angle versus frequency at room temperature.
These data, which were obtained using the experimental
techniques described in the next column of this page,
confirm and extend the findings of Ehrlich and Mikhailov
and support Eby and Sinnott’s contention that Krum and
Müller’s higher loss values must be due to polar
impurities.
The dielectric loss of PTFE is sufficiently low to allow the
permittivity to be calculated with an accuracy of better
than 0.5% using the Clausius-Mossotti formula:
-1
+2
= Kd
∋
∋
where
= permittivity
∋
d = relative density
Measurements of permittivity and dielectric loss in the
audio frequency range (178 Hz - 31.6 kHz) were made
using a fully-shielded, three-terminal conjugate Schering
bridge; a resonance substitution method, based on that
published by Hartshorn and Ward (ref. 43) but suitably
modified to give a higher resolution (ref. 44), was used
for the radio frequency region (105-108 Hz). A modified
version of the re-entrant cavity resonator method of
Parry (ref. 45) was used for the 108 - 109 Hz range; an H01
cavity resonator was used at 9 x 109 Hz: this made use of
the Bleaney, Loubser and Penrose (ref. 46) method of
avoiding unwanted modes.
D.C. CONDUCTION BEHAVIOUR
In attempting to study the d.c. conduction behaviour of
PTFE, the current measured was that which occurs after
the application of a d.c. voltage step. In Figure 20 the
results for a typical sintered sample, using evaporated
gold electrodes, are expressed as log (apparent volume
resistivity) as a function of time of polarisation. It will be
seen that steady state conduction was not established
clearly in the time of the experiments (which was 15
minutes). On the diagram are shown lines of constant
loss angle which can be calculated by means of a Fourier
transform assuming a constant permittivity of 2.0. The
short time values are consistent with the low frequency
values (= 20 µ radians) measured by a.c. methods. In fact
it is considered that such d.c. step response results are
equivalent to a low frequency extension of the a.c.
frequency range (refs. 47, 48, 49). The apparent
resistivity is to be thought of as a very low frequency
relaxation loss phenomenon rather than a steady state
charge transport phenomenon, although the onset of
conduction may be apparent above 160°C (320°F).
Figure 21 shows that such currents may be removed by
heat treatment in the presence of electrodes; apparent
resistivity values of > 1018 ohm m have been obtained
from such experiments without showing evidence of
steady state conduction (ref. 47). However, much lower
values are often obtained if unsatisfactory electrodes are
used or if temperature stability or polarising voltage
stability are not good enough to exclude
V
dC
dT
or C
dV
dT
terms for the current.
K = constant, 0.119
From which it can been seen that:
=
1 + 2 Kd
1 - Kd
∋
thus, at a relative density of 2.174 the permittivity is
2.05.
† Loss angle in µ radians is very nearly equal to loss tangent (tan δ) x l06, ie 100µ radians = loss tangent of 0.0001)
21
240
200
31600 Hz
5620 Hz
1000 Hz
178 Hz
32 Hz
160
120
Loss angle - radians
80
40
0
-140 -140
-220 -184
-80
-112
-40
-40
0
32
40
104
80
176
120
248
200
392
160
320
240
464
°C
°F
Temperature
Figure 18. Loss angle versus temperature for sintered granular PTFE (60% crystallinity) using
evaporated gold electrodes
300
Sintered granular polymer, 60% crystallinity
Unsintered coagulated dispersion polymer
93% crystallinity
200
Loss angle - radians
100
0
1
2
log10 Frequency - HZ
3
4
5
6
Figure 19. Loss angle versus frequency for PTFE at room temperature
22
7
8
9
10
18.5
150°C
302°F
160°C
320°F
141°C
286°F
s
18.0
na
id
ar
5
m mho - )j/E( ytivitsiser emulov tnerappA 01gol
=
el g
n
171°C
340°F
as
s
s
a
na
id
sn
17.0
ar
id a
r
00
5
05
=
=
elg
elg
n
n
l
ol
as
s
as
so
16.5
19.6°C
67.3°F
ol
17.5
0
log10 Time - seconds
2
1
3
Figure 20. Plot of log10 apparent volume resistivity versus log10 time for sintered granular PTFE
18
17
16
Evaporated gold electrodes
(Heated 40 hours at 280°C;536°F)
15
m mho - )j/E( ytivitsiser emulov tnerappA 01gol
14
Tinfoil electrodes
(as received)
13
12
11
10
9
-6
-4
log10 Time - seconds
-2
0
2
4
Figure 21. Effect of different electrode materials and preconditioning for sintered granular PTFE
23
HIGH VOLTAGE USES OF PTFE
With regard to high voltage applications it has been
known for a long time that in the presence of surface
discharges failure occurs by erosion, as PTFE is a nontracking material. Parr and Scarisbrick (ref. 50) have
compared the behaviour of a wide range of polymeric
insulators by the IEE tracking test using electrolyte, and
by an ASTM dust-fog test (D21 32-62T). They found that
PTFE was one of the erosion class which showed a long
life, i.e. >1000 hours in the dust-fog test. Thus PTFE has
useful surface characteristics for exploitation in outdoor
applications.
For bulk insulation high quality fabrication will be
required in order to produce structures with the very low
level of porosity and internal voiding demanded by high
voltage applications (ref. 51). Tests by means of
electronic discharge detectors (ref. 52) can be made to
ensure freedom from the damaging discharges which
may occur in voids. Alternatively it is possible to reduce
the discharges by impregnating the PTFE with dielectric
liquids or with a high pressure gas so as to fill, at least
partially, any voids in the polymer. In consequence,
values for dielectric strength obtained from tests
conducted in oil may be misleadingly high for poorly
fabricated PTFE due to impregnation of any voids present
by the oil.
24
Section 5. Thermal properties - unfilled PTFE
MELTING POINT
The melting point of ‘as polymerised’ PTFE increases
with increasing molecular weight and Wunderlich (ref.
52a) has shown that PTFE also superheats, i.e. the
apparent melting point increases with increasing heating
rate.
Melting points determined by Differential Scanning
Calorimetry* on ‘as polymerised’ powders at a heating
rate of 16°C/minute (28.8°F/minute) vary from about
332°C (630°F) for low molecular weight coagulated
dispersion polymer to about 346°C (655°F) for high
molecular weight granular material. Measurements
made at different heating rates indicate that, owing to
the superheating effect, these values may be up to 10°C
(18°F) higher than would be obtained at infinitely slow
heating rates.
The influence of molecular weight on melting point is
much reduced after the polymer has been sintered (once
melted). Most sintered polymers melt in the range 325330°C (617-626°F) when reheated at 16°C/minute
(28.8°F/minute).
The way in which the melting point of sintered PTFE
varies with applied pressure was studied by McGeer and
Duus (ref.34) who reported the following values:
1 atmosphere
69 atmospheres
207 atmospheres
615 atmospheres
324°C
335°C
356°C
419°C
(615°F)
(635°F)
(673°F)
(786°F)
These latter workers used their data to calculate the
latent heat of fusion of PTFE as 14 cal/g at 69
atmospheres and 8.4 cal/g at 207 atmospheres. The
corresponding entropies of fusion are 0.0240 cal/g deg K
and 0.0134 cal/g deg K.
THERMAL EXPANSION
If a graphical representation is made of the specific
volume/temperature relationship for highly crystalline
fabricated PTFE the form of the graph is shown in Figure
22. This graph clearly reveals the presence of the
transition point which occurs at 19°C (66°F) with PTFE
(refs. 7, 53).
Work done on behalf of AG Fluoropolymers showed that
from -60°C to +15°C expansion is approximately linear at
9.5 x 10-5 / °C. Work by Kirby (ref. 53) indicates that this
coefficient is approximately constant down to -190°C.
Above 15°C the coefficient of expansion increases with
temperature. Therefore a more useful way of indicating
thermal expansion is to express it as a percentage
increase in length between two temperatures. Values
obtained parallel to and at right angles to the direction of
the moulding pressure are quoted separately as they
were found to be slightly different.
Temperature
range
°C
15
30
30
30
30
30
°F
to
to
to
to
to
to
30
50
100
150
200
250
59
86
86
86
86
86
to
to
to
to
to
to
86
122
212
302
392
482
Parallel
to direction
of moulding
pressure
%
Perpendicular
to direction
of moulding
pressure
%
0.4
0.3
0.8
1.5
2.4
3.4
0.4
0.3
0.8
1.5
2.3
3.6
THERMAL CONDUCTIVITY
Over the temperature range 20-35°C (68-95°F) the
thermal conductivity of PTFE is 6 x 10-4 cal/cm s °C. This
result may be expressed in a variety of units:
6 x 10-4 cal/cm s °C
2.2 x 10-1 kcal/m h °C
2.6 x 10-3 joule/cm s °C
1.7 Btu in/ft2 h °F
Kline (ref. 54) measured the thermal conductivity of PTFE
at 0, 20, 50 and 70°C (32, 68, 122, 158°F). He reports the
conductivity to be fairly constant, with a slight tendency
to rise at the higher temperatures. His value is about 5.1
x 10-4 cal/cm s °C.
Eiermann and Hellwege (ref. 55) studied this property
over a much wider temperature range of -180 to +90°C (292 to +194°F). All their values fell within the range 5.4 to
6.1 x 10-4 cal/cm s °C. It was confirmed that the
conductivity tends to rise with temperature though a
sharp fall occurred at 20°C (68 F), approximately the
temperature at which it has already been noted that a
lattice transformation of the crystalline component of the
polymer occurs.
* The melting point of a polymer, as measured by DSC, is taken as the temperature at which the peak of the melting endotherm occurs. This peak is
reached when the rate of melting is maximal and indicates the melting point of the bulk of the polymer. The final melting point will be slightly higher
than this.
25
0.66
0.64
0.62
0.60
0.58
0.56
0.54
Specific volume
0.52
0.50
0.48
0.46
0.44
0
-50
-58
32
Temperature
50
122
100
212
150
302
200
392
250
482
300
572
350°C
662°F
Figure 22. Variation of specific volume with temperature
SPECIFIC HEAT AND HEAT OF FUSION
The specific heat of PTFE has been determined by Marx
and Dole (ref. 56). For temperatures above 40°C(104°F)
they give the relationship:
Cp = 0.227 + (2.50 x 10-4) T cal/g °C.
The heat capacity, enthalpy and entropy of PTFE have
been studied and results are reported in two papers (refs.
16, 57).
THERMAL STABILITY
Within its normal range of working temperatures, the
upper limit of which is generally quoted as 260°C (500°F),
PTFE suffers no degradation. Indeed, weight losses
observed between 260 and 360°C (500 and 680°F) will be
exceedingly small and due to the loss of minute amounts
of moisture or gas absorbed in the polymer.
At processing temperatures of about 380°C (716°F) the
rate of decomposition of PTFE is still very low and it is
only at temperatures in excess of 400°C (752°F) that
thermal decomposition of pure PTFE becomes
significant.
Madorsky et al. (ref. 58) studied the pyrolysis of PTFE in
a vacuum at temperatures from 423.5 to 513°C (794 to
955°F) The decomposition rates which they report at
these temperatures are respectively 0.00152% per
minute and 1.264% per minute. They further reported
that tetrafluoroethylene was virtually the only product of
decomposition. This confirmed earlier reports of
26
Lewis and Naylor (ref. 59) that when PTFE was
decomposed at temperatures between 600 and 700°C
(1112 and 1292°F) under pressures of 5 to 760mm Hg the
products were C2F4, C3F6 and C4F8 and that the proportion
of tetrafluoroethylene among the products increased
with decrease in pressure and tetrafluoroethylene was
the sole product at very low pressures.
Cox et al. (refs. 60, 61) have studied the thermal
degradation of PTFE with particular reference to the
differences observed between degradation in a vacuum
and in oxygen. They found that the temperature
necessary to achieve a 25% weight loss in two hours was
494°C (921°F) in a vacuum and 482°C (900°F) in oxygen;
they concluded, therefore, that the thermal degradation
of PTFE was relatively little affected by oxidising
conditions.
Siegle et al. (ref. 62) have evaluated the mechanism of
the depolymerisation reaction from research work done
on heating thin PTFE films in a vacuum and Jellinek (ref.
63) reached similar conclusions. In the case of thicker
sections, which are more likely to be met in practice, the
rate of pyrolysis is controlled by diffusion of monomer as
pointed out by Siegle and Muus (ref. 64).
Paciorek et al. (ref. 65) studied the auto ignition of PTFE
in oxygen and in air. The respective auto-ignition
temperatures were 512°C (954°F) and 575°C (1067°F). In
oxygen only COF2, CO2 and CF4 were formed, while in
air, saturated fluorocarbons, COF2 and CO were the most
abundant species.
Section 6. Surface properties - unfilled PTFE
COEFFICIENT OF FRICTION
Although the low coefficient of friction of PTFE is widely
known, it is interesting to reflect that no reference was
made to this characteristic until about ten years after the
discovery of the polymer. Credit for this first publication
goes to Shooter and Thomas (ref. 66) who measured the
coefficient of friction using a Bowden-Leben machine
with loads of between 1 and 4 kg (2.2 and 8.8 Ib) and
sliding velocities from 0.1 to 10mm/s (0.02 to 2 ft/min).
They reported that the coefficient was 0.04.
Other workers (refs 67, 68, 69) report that while
Amonton’s law is fairly well obeyed at moderate loads
the coefficient of friction rises steeply at very light loads,
say below 100g (31/2 oz). Thompson et al. (ref. 70) who
studied the coefficient at high loads found the extremely
low figure of 0.016 at a load of 1360kg (3000 Ib) .
The coefficient of friction is dependent also on the sliding
velocity, a high speed resulting in a high coefficient. By
combining a low load and a high sliding velocity of
1.89m/s (370 ft/min), Flom and Porile (ref. 71) found the
high value of 0.36 for the coefficient.
In their pioneer paper Shooter and Thomas (ref. 66)
claimed that, at the very low speeds they used, the
coefficient was independent of temperature over the
range 20 to 200°C (68 to 392°F). However, later work has
shown that temperature has some effect. King and Tabor
(ref. 72) report that the coefficient remains steady at
about 0.1 over the range 100 to -45°C (212 to -49°F). On
further cooling the coefficient rises to about 0.2 but does
not alter further even when the polymer is cooled to 80°C (-112°F). For the behaviour at elevated
temperatures the best guide is the work of McLaren and
Tabor (ref. 73) who demonstrated that the coefficient of
friction fell with increase in temperature.
Makinson and Tabor (ref. 74) have also examined the
effect of sliding velocity and substantially agree with the
variation in coefficient of friction with velocity given
above. They have found that whereas at low velocities a
thin continuous film of PTFE is laid down on the other
slide surface (in this case glass), at higher velocities the
PTFE is torn off in discrete fragments.
Of less general importance than the dependence on load,
velocity and temperature, but still of interest is the
observation by Tabor and Williams (ref. 75) that the
coefficient is influenced by the orientation of the
polymer, the coefficient being about 30% higher when
sliding was across the chains than when it was along
them.
ANGLE OF CONTACT
Zisman and his co-workers have studied the contact
angles made with PTFE by a wide range of liquids (refs.
76, 77, 78,79). A few of their results with common liquids
are summarised:
Liquid
Contact angle
Water
n-Hexadecane
Toluene
Benzene
Methylene iodide
Carbon tetrachloride
Mercury
Glycerol
108°
46°
43°
46°
88°, 83°
46°
150°
100°
Fox and Zisman (ref. 76) found that there was a critical
surface tension (ca 17.5 to 20.5 dynes/cm) below which
liquids would wet PTFE (i.e., would spread on a smooth
polymer surface).
27
Section 7. Other physico-chemical properties - unfilled PTFE
investigated the permeation of sulphur dioxide through a
range of polymers including PTFE.
PERMEABILITY
Work using a sample of cast film produced from Fluon®
GP1 led to the following test results for permeability:
Oxygen
Nitrogen
Air
10.5 x 10-10
4.0 x 10-10
5.3 x 10-10
The units are cm3 of gas at NTP x cm (thickness)/cm2 (area).
s. cm Hg measured at 23°C ± 1°C (73°F ± 2°F)
Work published by Barton (ref. 80), who uses the same
units, can be summarised as follows:
Hydrogen
Helium
Nitrogen
Oxygen
Argon
2.4
7.0
3.1
1.0
5.8
x
x
x
x
x
10-9
10-8
10-10
10-9
10-10
Yasuda and Stone (ref, 81) obtained a substantially
higher figure, 23.7 x 10-10 (units as above), for gaseous
oxygen, and an even greater value, 91.0 x 10-10, for
dissolved oxygen, while Pasternak et al. (ref. 82) obtained
a much lower value, 4.2 x 10-10, in experiments with
membranes in the thickness range 0.081-0.145mm
(0.0032-0.0057 inch). The latter authors also give values
for hydrogen (9.8 x 10-10), nitrogen (1.4 x 10-10), and
carbon dioxide (11.7 x 10-10). Casper and Henley (ref. 83),
using PTFE film 0.094mm (0.0037 inch) thick found a
value of 11.6 x 10-10 for hydrogen, and 0.65 x 10-10 for
ethane.
Work on the helium permeability of fabricated PTFE
items has shown that the permeability is very dependent
on crystallinity (as indicated by relative density). For
isostatically-moulded granular PTFE discs the helium
permeability at 25°C (77°F) varied from about 30-40 x 1015 mol m s-1 N-1 at a relative density of 2.08 to about 5-15
x 10-15 moI m s-1 N-1 at a relative density of 2.15: the effect
of crystallinity was much greater than that of varying the
moulding pressure, or the type of PTFE polymer used.
For tubing extruded from coagulated dispersion (CD)
polymers, a similar effect of crystallinity on permeability
was observed. At a relative density of 2.15 the
permeability was about
15-25 x 10-15 mol m s-1 N-1 and this fell to about 5-10 x 1015 mol m s-1 N-1 at a relative density of 2.21. Again, no
effect of CD polymer type could be detected, even though
a considerable number of both homopolymers and
copolymers were examined.
Gerritse (ref. 84) has measured the permeability of PTFE
to oxygen and nitrogen as a function of temperature in
the range 50-125°C (122-257°F); for both gases the
permeation rate at 125°C was about 5-6 times greater
than at 50°C. Felder, Spence and Ferrell (ref. 85)
28
The permeability of PTFE to water vapour has been
studied by Konovalov (ref. 86) and by Korte-Falinski (ref.
87) who both found that PTFE has a lower permeability to
water vapour than almost any other plastics material
examined. For PTFE films in the thickness range 0.050.20mm (0.002-0.008 inch), values were found (ref. 87)
equivalent to about 0.9-1.8 g/m2 per 24 hours, per
0.025mm (0.001 inch), at 20°C (68°F). Toren (ref. 88),
using a special electrolytic measuring technique,
obtained a value equivalent to 2.7 g/m2 per 24 hours per
0.025mm (0.001 inch), for a PTFE film 0.08mm (0.003
inch) thick. A value of 5.4 g/m2 per 24 hours per 0.025mm
(0.001 inch) at 30°C (86°F) has also been quoted (ref. 89).
These somewhat variable results for water vapour
permeability of PTFE may, most probably, be explained
by differences in the film fabrication techniques used, as
well as by different methods of measurement.
INFRA-RED TRANSMISSION
Figure 23 shows the infra-red transmission spectrum for
PTFE.
REFRACTIVE INDEX
Billmeyer (ref. 90), using sodium yellow light and a
sample of PTFE of density 2.12 reported a refractive
index of:
nD= 1.376
Using a far infra-red maser and monochromatic radiation
of wave-length 337µm Chamberlain and Gebbie (ref. 91)
report a figure of 1.391 ± 0.017.
The refractive index of PTFE would be expected to vary
with density, or more strictly with crystallinity, in
accordance with the equation:
n2 - 1
n2 + 2
1
x—=K
d
where
n = refractive index
d = density
K = constant
MELT VISCOSITY
The melt viscosity of PTFE is extremely high by
comparison with other polymers. The observed value
will depend somewhat on the experimental method
used, of which the parallel plate plastometer, the
capillary rheometer and creep methods are the most
important.
100
80
Transmittance - %
60
40
20
0
3
4
5
Wavelength - microns
6
7
8
9
10
11
12
13
14
15
Figure 23. Infra-red transmission spectrum (specimen thickness 0.05mm [0.002 inch])
The melt viscosity of PTFE varies with the shear stress
applied to the polymer and with the temperature of the
polymer but, in general, commercial samples of granular
polymer display viscosities of about 1011 poise in the
temperature range 360 to 380°C (680 to 716°F) and at
shear stresses of about 106 dynes/cm2 (refs. 92, 93, 94).
HIGH ENERGY RADIATION
The effect of high energy radiation on PTFE was first
noted by Liversage (ref. 95) who found that the electrical
resistance of the polymer fell on exposure to X-rays.
Harrington and Giberson (ref. 96), in a study of the
decline in the tensile strength and elongation of PTFE
when exposed to gamma radiation, showed that
irradiation in a vacuum was less damaging than
irradiation in air. This point was confirmed by Wall and
Florin (ref. 97) and a summary of their results is given
below:
1 Megarad has a measurable effect and 2-3 Megarads in
air reduce strength by 40-75%. 4 Megarads reduce
tensile strength to 2% of the original.
A 1975 report from AERE, Harwell (ref. 99a) gives details
of the effects of radiation on the mechanical and
electrical properties of PTFE used in cable for the GEOS
satellite.
CHEMICAL RESISTANCE
As might be expected of a saturated aliphatic
fluorocarbon PTFE is almost completely inert chemically.
Molten or dissolved alkali metals degrade PTFE by
abstracting fluorine from the molecule, while at elevated
temperatures fluorine and compounds capable of
releasing fluorine can break the carbon skeleton and
form low molecular weight fluorocarbons. Apart from
these not very important exceptions, PTFE resists attack
by all the acids, bases and solvents that might be
encountered in industrial practice.
Irradiation in
air
2.4
4.1
2
0
In addition to its remarkable chemical inertness, PTFE is
not dissolved by any solvent within its normal range of
working temperatures. Small quantities of solvents may
be absorbed by PTFE on prolonged exposure especially
at elevated temperatures but this in no way impairs the
usefulness of the polymer.
Irradiation in
a vacuum
0.7
4.1
32.0
73
51
43
Rossa (ref. 100) has given details of the effect of 79
chemicals on PTFE with, in many cases, data on weight
gain.
Radiation dose
eV/g x 10-20
% retention of original
tensile strength
Two general surveys of this subject have been made
(refs. 98, 99).
The more recent work by Monnet and Bensa (ref. 99)
gives further data on the effect of radiation dose on
mechanical properties. They found that as little as 0.01 to
0.1 Megarad dose can affect mechanical properties.
VELOCITY OF SOUND
The velocity of sound in PTFE and the way in which the
velocity changes with changes in temperature has been
studied by Kravtsov (ref. 101). He showed the velocity to
pass through a maximum at 20°C (68°F) in the region of
the first-order transition.
29
Section 8. General-filled PTFE
FUNCTION OF FILLER
CHOICE OF FILLER
The incorporation of fillers has the following general
effects:
It is this choice which presents most problems to the end
user. Unfortunately no simple answer is available, mainly
because the performance of different fillers cannot
always be predicted reliably. Choice frequently depends
upon the results of empirical testing rather than upon
any understanding of the mechanism affecting
properties.
(1)
(2)
(3)
(4)
(5)
Wear resistance is increased to a very marked
extent.
Resistance to ‘creep’ or deformation under load is
increased by a factor of 2 to 5.
Depending upon the filler used, the thermal
conductivity may be increased significantly.
Depending upon the filler used, thermal expansion
may be reduced by a factor approaching 5.
By suitable choice of fillers some control over the
electrical properties of PTFE can be achieved.
In addition to these advantages filled PTFE generally
retains low coefficients of friction, the wide service
temperature range and, depending upon the filler, the
chemical inertness of unfilled PTFE.
Many materials are candidates as fillers for PTFE
provided they can be obtained in the appropriate particle
size and will withstand the processing conditions
necessary to incorporate them and subsequently to
enable the compound to be fabricated. Other
considerations such as availability, cost and
processability further restrict the number of potential
fillers to a relatively small number, as indicated in Table 1.
Table 1. Fillers used with PTFE
Filler
Form
Details
Glass
Usually milled fibres
A minimum aspect ratio
(length: dia) of 10 : 1 is
generally used
Carbon and graphite
Usually in the form of a high purity powdered
coke, or natural or synthetic graphite. Particles
are generally irregular in shape although fibres
are known
Particle size usually
less than about
60µm
Metals
Notably bronze as irregular or spherical particles
Particle size usually
less than about
60µm
Others
Various forms of ‘ceramic’ material including mica are
used both in particulate and fibre form.
Molybdenum disulphide
Thermoplastics
_ 40 x 10-6 inch
Note: 1µm = 10-6m ~
30
CHOICE OF FLUON® GRADE
Having limited the number of potential fillers, the
number of grades of filled PTFE which it is possible to
manufacture is still large, when combinations and
varying percentages of filler are taken into consideration.
However, there are reasons why these too may be
limited:
where lower filler contents of 5% or 15% are justifiable.
There is little case, however, for requiring intermediate
filler contents.
Combinations of filler can give rise to improved wear
properties but this appears to be their only advantage.
THE FLUON® RANGE
(1) The quantity of filler should effectively be limited
to 40% by volume if reasonable mechanical
strengths are to be maintained.
(2) The method of fabricating the filled PTFE powder
can have considerable effect upon its properties
and these can therefore be varied and controlled
during fabrication rather than by a proliferation of
diverse formulations.
The Fluon® filled polymer range consists of moulding
grades denoted by a prefix FC1---
It is considered reasonable therefore to limit the basic
range of filled compounds to filler additions of 25% and
40% by volume although there may be exceptional cases
Typical properties of the Fluon® moulding grades are
given in Table 2 and compared with those of unfilled
PTFE.
Free-flowing moulding grades (agglomerated) are
denoted by a prefix FC8--Development grades are denoted by a prefix XC e.g.
XC1--- for moulding grades.
Table 2. Properties of the Fluon® range
Units
Fillers
FC168-63*
FC100-15 1000
FC100-25 1000
FC160-60
FC150-25
FC140-15
Unfilled
PTFE
Bronze and
graphite
Glass fibre
Glass fibre
Bronze
Powdered
coke
Graphite
None
FiIler by weight
%
63
15
25
60
25
25
-
Filler by volume
%
40
13.3
22.2
27
28
15
-
3.2
2.25
2.25
3.8
2.1
2.2
2.17
Relative density
Maximum tensile
strength: moulded
MN/m2
kgf/cm2
Ibf/in2
4.9-8.3
50-85
700-1200
17.2-240
175-245
2500-3500
12.3-19.6
125-200
1800-2800
10.3-13.7
105-140
1500-2000
11.8-15.2
120-155
1700-2200
13.7-20.6
140-210
2000-3000
20.6-29.9
210-350
3000-5000
Maximum tensile
strength: extruded
MN/m2
kgf/cm2
lbf/in2
-
9.2-12.7
100-130
1400-1900
6.9-10.8
70-110
1000-1600
-
10.3-13.7
105-140
1500-2000
-
13.7-17.2
140-175
2000-2500
Ultimate tensile
elongation: moulded
%
10-15
300-400
200-300
80-160
100-150
200-300
250-400
Ultimate tensile
elongation: extruded
%
-
200-300
100-200
-
75-125
-
250-400
Hardness
Shore D
55-65
55-60
55-70
55-65
60-65
55-65
50-55
Heat stability
The weight loss at 300°C (572°F) should not normally exceed 0.1%
Porosity:
dye immersion
All material can be made non-porous, depending upon the fabrication techniques used
*British Patent No 870117, 926718 and others
31
Section 9. Mechanical properties - filled PTFE
COMPRESSIVE DEFORMATION
The compressive creep behaviour of filled PTFE is one of
the most significant properties to the designer and user.
In comparison with unfilled PTFE the compressive
modulus of filled PTFE is greater and hence, for the same
stress, a lower deformation will occur. This difference
diminishes, however, as temperatures rise and the
compressive performance of unfilled and filled PTFE
draws close together at 200°C (392°F). The reason is
almost certainly that the general reduction in the
compressive modulus of the PTFE matrix overrides the
support given by the random distribution of filler
particles. Table 3 gives approximate values for the stressstrain relationship at different temperatures for Fluon®
FC100-25 1000. These data are based on laboratory tests
and the configuration of the test specimens will have a
significant effect on the results obtained. For this reason
the figures should only be taken as a very approximate
guide.
The room temperature creep behaviour of filled PTFE has
been studied and Figures 24 and 25 show how strain
varies with time and also at various stress levels for
glass-filled Fluon® FC100-25 1000 and, for comparison
purposes, for Fluon® G163. Figure 26 illustrates the
relationship between stress and strain in a way which
indicates the stress relaxation that can occur in PTFE with
time. Figure 27 shows the divergence in creep behaviour
between Fluon® grades containing 25%, 22% and 40% of
filler by volume. Figure 27 used in conjunction with
Figure 24 indicates the relative creep behaviour of Fluon®
filled grades.
Individual design details of specific applications are
bound, however, to significantly modify the data given in
Figures 24 and 27.
Recovery
After being subjected to a compressive load, filled PTFE
will recover some of the resulting strain when the stress
is removed. This recovery is slow and may not be
complete. Figure 28 shows the recovery of Fluon® FC10025 1000 after the removal of applied stress at various
levels.
Table 3. Stress-strain relationship for Fluon® FC100-25 1000 at different temperatures and stresses to produce
stated compression strain after 24 hours.
Stress - kgf/cm2 at T : °C
20
60
100
140
180
220
250
1% strain
63
37
27
17
10
8
6
2% strain
89
60
47
32
20
15
11
3% strain
>
89
75
61
43
28
22
17
4% strain
>
89
86
71
53
36
28
22
32
10
9
8
7
6
Stress = 6.9 MN/m 2 = 70 kgf/cm 2 = 1000 lbf/in 2
5
4
3
®
on
63
G1
Flu
2
00
2
0-
®
1
0
51
0
C1
F
Creep terminated
n
luo
F
0.9
0.8
0.7
0.6
0.5
0.4
0.3
Dotted lines show possible spread
as derived from 100 second isochronous
stress-strain relationship
6 Months
3 weeks
1 week
1 day
1 hour
Strain - %
0.2
0.1
1
10
Time - seconds
10 2
103
104
10 5
106
10 7
10 8
Figure 24. Creep in compression at 20°C (68°F) : Fluon® G163 and Fluon® FC100-25 1000
33
10
9
8
7
6
5
4
3
2
/in
40
17
=
2
f
lb
m
2
/c
gf
k
2
=
2
2
12
n
0
m
N/
M
2
12
=
5
14
/i
bf
l
m
f/c
2
10
=
2
kg
2
/in
/m
N
60
M
10
=
2
1
lbf
11
m
f/c
0.9
.6
0.8
=
2
kg
81
m
N/
2
in
8M
0.7
70
=5
2
0.6
/
lbf
cm
gf/
k
1.2
0.5
=6
2
m
N/
6M
2
0.4
80
/in
lbf
=5
2
m
f/c
0.3
g
8k
0.
2
m
=4
N/
4M
0.2
2
/in
2
/cm
bf
0l
9
=2
6 months
2
1 month
/
MN
1 day
1 hour
Strain - %
2
m
kg
1 week
f
.4
0
=2
0.1
1
10
Time - seconds
10 2
103
104
10 5
106
10 7
Figure 25. Creep in compression at 20°C (68°F) at various stress levels; Fluon® FC100-25 1000
34
10 8
11
1600
1500
10
1400
9
1300
3%
1200
8
1100
2%
7
1000
1.5%
900
6
800
1%
5
700
600
4
0.5%
500
3
400
2
300
0.2%
1
10
Time - seconds
10 2
103
10 5
106
6 months
1 week
1 day
104
10 7
100
0
10 8
Stress - ib/in 2
0
1 month
1
1 hour
Stress - MN/m 2
200
Figure 26. Isometric stress-time curves in compression at 20°C (68°F) , and various strain levels :
Fluon® FC100-25 1000
35
2.6
2.4
Stress: 10 MN/m 2 = 102 kgf/cm 2 = 1450 lbf/in 2
e
m
2.2
lu
vo
y
rb
2.0
0
70
er
-3
2%
fill
0
11
-2
FC
me
00
1.6
m
-2
by
vo
lu
00
1.8
e
5%
le
fil
10
olu
yv
rb
-2
5
1.4
FC
1
00
%
1.2
-63
0
-4
fille
68
1
FC
1.0
0.8
0.6
1 week
0.2
1 day
1 hour
Strain - %
0.4
0
102
1
10
Time - seconds
103
104
105
106
Figure 27. Isometric stress-time curves in compression at 20°C (68°F) , and various strain levels :
Fluon® FC100-25 1000
1.0
6 MN/m 2
61.2 kgf/cm 2
870 lbf/in 2
Fractional recovered strain
0.8
0.6
2
0.4
2 MN/m
2
2 :290 lbf/in
(20.4 kgf/cm
0.2
12 MN/m
0
10-4
10-5
Reduced time
2
)
f/in )
0 lb
2
cm :174
(122 kgf/
10-3
10 MN/m 2
102 kgf/cm 2
1450 lbf/in 2
2
10-2
10
-1
1
Figure 28. Recover from creep in compression : Fluon® FC100-25 1000 loaded at various stress levels
36
10
IMPACT STRENGTH
Table 4 shows the results of Charpy impact tests on
various Fluon® grades, at different temperatures and
different crystallinities. All specimens were sharply
notched (notch tip radius = 0.25mm; 0.01 inch) but even
so none of the specimens broke completely, but gave a
hinge break at + 20°C (68°F). At -20°C (-4°F) all the slowcooled (high crystallinity) samples broke completely, but
two of the six quenched samples (low crystallinity) gave
hinge breaks. In the liquid nitrogen dip test, all
specimens broke completely; strengths were always
lower than at -20°C (-4°F) and again the lower
crystallinity material gave increased resistance to
impact.
There are minor differences between the various Fluon®
grades and, as expected, a low crystallinity gives
maximum impact strength. The conclusion is that
unfilled and filled PTFE are tough in impact, even under
severe test conditions e.g. with sharp notches at -20°C
(-4°F) (see Table 4). They are better than most other
plastics.
Table 4. Charpy impact strength (notch depth 2.80 mm: 0.11 inch; notch tip radius 0.25 mm: 0.01 inch)
Median impact strength (cm kgf/cm2)
+ 20°C
-20°C
(68°F)
(-4°F)
Unfilled PTFE
H*
Fluon®
Fluon®
Fluon®
Fluon®
—
H
—
—
FC100-15 1000
FC100-25 1000
FC160-60
FC150-25
Liquid nitrogen (-180°C approx)
(-290°F approx)
Slow cooled
Quenched
Slow cooled
Quenched
6.8-9.0
8.6-9.6
—
—
12.0
9.4
10.9
7.3
H
H
12.8
7.9
4.5
—
4.1
3.2
5.6
—
4.5
3.2
Notes:
H = hinge break i.e. did not break completely.
H* = specimen almost broke completely.
37
Section 10. Electrical properties - filled PTFE
Although the primary objective in the development of
Fluon® grades has generally been to produce materials
with a range of mechanical properties, the addition of
fillers does have a marked effect on the electrical
properties as well. In particular, graphite - and carbon
filled compounds may have a relatively high
conductivity, which can assist the dissipation of static
charges in applications where these are a problem.
Filled PTFE is a mixture of materials, and voids - no
matter how small - are always present: as with all porous
materials, the properties are dependent on the nature of
the environment and of any inadvertent contamination.
The electrical properties are no exception and are
markedly dependent on the environmental humidity. The
spillage of conducting liquids, electrolytes and greases
on Fluon® grades can affect the properties of the material
even in otherwise dry conditions.
To some extent porosity (and therefore the effects of
humidity and spillage) is dependent upon the method of
fabrication, but even in a relatively non-porous part, the
surface is liable to be absorbent.
for insulation. Tables 5, 6 and 7 give values of loss
tangent, permittivity and volume and surface
resistivities, measured at two levels of humidity, for
Fluon® glass-filled grades.
The effect of temperature on the loss tangent of some
glass-filled grades is shown in Figure 29.
The level of dielectric loss tends to increase as glass
content increases. However, the mechanisms giving rise
to dielectric behaviour of filled materials are complicated,
and in general it must be assumed that these materials
will exhibit Maxwell-Wagner loss processes of relatively
large amplitude at low frequencies (log10 frequency < 0)
in the ‘dry’ state, moving progressively to higher
frequencies with increasing moisture content. Rudner
(ref. 102) reports on, but does not interpret, the
properties of PTFE filled with titanium dioxide using
samples that had been kept at a constant low humidity
with silica gel crystals present to absorb moisture. It is
suspected that these losses are due to a similar
mechanism.
CONDUCTING MATERIALS
INSULATING MATERIALS
Under dry conditions, the glass-filled grades are
excellent electrical insulating materials over a wide range
of temperature. Their insulating properties deteriorate
with increasing humidity, but even at 95% r.h. the
properties are comparable with those of plasticised PVC
and of some thermosetting compounds commonly used
Temperature °F
50
100
200
150
No grade of filled PTFE is a good conductor when
compared with, for example, copper or aluminium.
However, some have sufficiently low volume and surface
resistivities to be considered for use in antistatic
applications: see Table 8.
250
350
300
450
400
0.030
0.028
0.026
0.024
70
00
0.022
030
0.020
FC
11
0.018
0.016
0.014
0.012
0.010
Loss tangent
0.008
000
51
-2
100
0.006
FC
0.004
0.002
0
FC100-05
0
20
40
Temperature °C
60
80
100
120
140
160
180
200
220
240
Figure 29. Loss tangent versus temperature at 1 kHz: glass-filled PTFE
Notes:
Form of specimen: 5 cm (2 inch) diameter disc of skived tape approx.1mm thick (0.04 inch). Electrode system: No electrodes, 3-terminal
fully shielded system. Test apparatus: General Radio Capacitance Measuring Assembly, type 1620A. Electric stress: Up to 120 V/mm (3
V/0.001 inch). Field direction: Perpendicular to the plane of the sample. Relative humidity: Dried for 150 h at 0,1 mm Hg at 116°C (241°F).
Accuracy of test result: Estimated to be ± 5%.
38
Table 5. Loss tangent at room temperature
‘Dry’†
After 9 weeks at 95% r.h.
103 Hz
0.0001
0.00033
0.00065
0 00107
Unfilled PTFE
Fluon® FC100-05
Fluon® FC100-15 1000
Fluon® FC100-25 1000
104 Hz
0.0001
0 00032
0.00063
0 00097
103 Hz
0.0001
0.14
0.32
0.39
104 Hz
0.0001
0.122
0.36
0.28
105 Hz
0.0001
0.058
0.275
0.225
106 Hz
0.0001
0.0126
0.068
0.062
† Dried for 150h at 0.1mm Hg at 116°C (241°F).
Note: Samples were skived from tape 1.0mm thick veneered (0.04 inch) from blocks preformed at 700 kgf/cm2; 10 000 Ibf/in2 freely sintered for 11/2
hours at 380°C (716°F) and cooled at approximately 30°C per hour (54°F per hour).
Table 6. Permittivity at 105 - 107 Hz
Ambient humidity
Unfilled PTFE
Fluon® FC100-15 1000
Fluon® FC100-25 1000
2.02-2.09††
2.2-2.5
2.2-2.5
95% r.h.
2.02-2.09††
2.2-2.5
2.2-2.5
†† Depending on density
Table 7. Volume and surface resistivity
Unfilled PTFE
Fluon® FC100-15 1000
Fluon® FC100-25 1000
Volume
resistivity(1)
(ohm cm)
Surface
resistivity(2)
(ohm)
Dry(3)
Ambient
humidity
95%
r.h.
>1 x 1018
>2 x 1015
>2 x 1015
1017
1015
1015
1015
1015
Notes
(1) Measured on discs of skived tape approx. 50.8mm (2 inch) in diameter and 10mm (0.04 inch) thick, using evaporated
aluminium electrodes. 1 min. value: 120 V/mm (3 V/0.001 inch).
(2) 1 min. value at equilibrium with the environment.
(3) Dried for 150 h at 0.1mm Hg at 116°C (241°F).
Table 8. Volume and surface resistivity of Fluon® grades
FC140-33
FC150-25
FC168-63
FC140-15
FC160-60
Filler(1)
by weight
%
Volume
resistivity(2)
(ohm cm)
Surface
resistivity(3)
(ohm)
33%
25%
63%
15%
60%
102
104
104
106
107
104
107
104
1014
109
Notes
(1 ) Filler % by weight, the remainder being PTFE.
(2) Volume resistivity measured at 23°C (73°F) and 50% r.h. on tape specimens 0.25 to 1.0mm (0.01 to 0.04 inch) thick clamped between disc brass
electrodes. The values given are an indication only and may vary widely with fabrication methods.
(3) Surface resistivity measured at 23°C (73°) and 50% r.h. on tape specimens 0.25 to 1.0mm (0.01 to 0.04 inch) thick using disc and ring brass
electrodes applied by pressure only. No backing guard electrode used. With some materials the measured surface resistivity is very high even when
the volume resistivity is low. This is probably because the veneering method used to prepare tape specimens may have tended to smear a fine PTFE
layer on the surface.
39
Section 11. Thermal properties - filled PTFE
THERMAL EXPANSION
The thermal expansion of most fillers is less than that of
PTFE and since the expansion of the composite will be
somewhere between that of the two constituents, filled
PTFE compounds expand less than unfilled PTFE. During
fabrication certain fillers, notably fibres and platelets,
become preferentially oriented (as do the particles of
PTFE to a much lesser degree). The result is that some
compounds have a markedly different expansion in the
directions parallel and perpendicular to the direction of
moulding.
Measurements on the Fluon® range are shown in Table
9. As thermal expansion is virtually linear below 15°C
(59°F) a coefficient is quoted; but since there is a
transition point at about 19°C (66°F) and the expansion is
far from linear above 30°C (86°F) changes in dimension
are quoted as a percentage for a given temperature
range. Figures for some common metals are also quoted
in Table 9 (Note 2).
It is very important to note that these figures are actual
linear thermal expansions with virtually all stresses
removed from the material. Changes in the dimensions
of a specified part due to changes in temperature will
differ from these figures if stresses are present.
THERMAL CONDUCTIVITY
The thermal conductivity of PTFE is very low, making it a
good thermal insulating material. Many fillers, notably
metals and metal oxides, have high thermal conductivity,
but in general they are effectively encapsulated by PTFE
so that the conductivity of the compounds is still
relatively low.
Typical figures for the Fluon® range are given in Table 10,
together with those of some common metals and
insulating materials.
Table 10. Thermal conductivities
Material
Thermal conductivity
10-4 cal/cm
Btu in/ft2
s deg C
h deg F
Unfilled PTFE
Fluon® FC100-15 1000
Fluon® FC100-25 1000
Fluon® FC140-15
Fluon® FC150-25
Fluon® FC160-60
Fluon® FC140-33
Fluon® FC168-63
Aluminium
Brass
Iron (cast)
Steel (med. carbon)
Glass
Still air
Granulated cork
Kapok
6
8
9
11
13
19
27
30
4950
2300
1520
1100
18.4
0.64
1.10
0.85
1.7
2.3
2.6
3.2
3.8
5.5
7.8
8.7
1400
650
430
310
5.2
0.18
0.31
0.24
Table 9. Linear thermal expansion: Fluon® range (in directions parallel and perpendicular to direction of moulding)
Units
FC100-15 1000
FC100-25 1000
FC150-25
FC160-60
FC140-15
FC168-63
Para Perp
Para Perp
Para Perp
Para Perp
Para Perp
Para Perp
Coefficient of
expansion from
-60 to +15°C
(-76 to +59°F)
x 10-5
per °C
9.2
6.6
9.2
4.4
6.9
6.4
6.6
6.4
8.6
6.4
Change from:
15-30°C (5°-86°F)
%
0.4
0.3
0.4
0.3
0.4
0.2
0.4
0.2
0.3
0.2
0.3
30-50°C (86-122°F) %
0.3
0.2
0.3
0.1
0.2
0.2
0.2
0.1
0.2
0.2
30-100°C (86-212°F) %
0.9
0.6
0.8
0.4
0.6
0.5
0.6
0.5
0.7
30-150°C (86-302°F) %
1.7
1.0
1.5
0.7
1.2
1.0
1.1
0.9
30-200°C (86-392°F) %
2.4
1.5
2.2
1.0
1.9
1.5
1.8
30-250°C (86-482°F) %
3.5
2.2
3.2
1.4
2.7
2.4
2.5
5.4 5.2
Unfilled PTFE
Para Perp
9.9
9.6
0.1
0.4
0.4
0.2
0.2
0.3
0.3
0.6
0.5
0.5
0.8
0.8
1.4
1.0
0.9
0.8
1.5
1.5
1.5
2.1
1.6
1.4
1.3
2.4
2.3
2.2
3.2
2.3
2.1
2.0
3.4
3.6
Notes:
1. All measurements made on samples taken from discs 7.30 cm dia x 1.27 cm thick (2 7/8 inch dia x 1/2 inch), preformed at 700 kgf/cm2 10 000 Ibf/in2 and
sintered at 380°C (716°F).
2. Coefficients of expansion (x 10-5 per °C) of some other materials are: Aluminium 2.4
Brass 1.9
Glass 0.9
Iron (cast) 1.1
Steel (med, carbon) 1.2
40
Section 12. Surface properties - filled PTFE
It is not considered meaningful to tabulate results for
design properties in one large table and so each property
is discussed separately and relevant values included in
their correct context. All values quoted are actual results,
and if applied to design calculation a relevant factor of
safety should be applied.
when mating areas are large, friction is primarily due to
adhesion.
Orientation
It has been shown (see page 27) that the coefficient of
friction can be affected by up to 30% depending upon the
orientation of the PTFE molecules.
FRICTION
Most studies on the friction of PTFE have been carried
out with unfilled PTFE. Whilst the exact mechanisms
involved are still not fully understood (ref.103) a picture
emerges in which the ‘dry’ coefficient of friction is
dependent upon the pressure, the speed, the
temperature, the mating surface, the orientation of the
PTFE, the environment and the time of running.
Coefficients from 0.016 to 0.36 have been quoted and
while this work is discussed in detail on page 27 it may
be summarised (with some additional information) as
follows:
Load and pressure
The classical laws of dry friction state that the friction
force is independent of the apparent area of contact,
making the friction force proportional to load rather than
pressure. Many investigators (eg, refs. 66-70) quote the
coefficient of friction of PTFE as a function of load and
show it to rise steeply at very light loads (below 5 Ib) and
decrease with increasing load. R B Lewis (ref. 104) does
not support this, but suggests the coefficient of friction µ
is proportional to the applied pressure P (Ibf/in2)
according to the formulae:
µ = CP-0,2 where C = 0.12 ± 0.03 at velocities below
10mm/s (2 ft/min)
C = 0.35 ± 0.10 at 50mm/s (10 ft/min)
C = 0.45 ± 0.15 at 500mm/s (100 ft/min)
and above
Speed
The coefficient of friction falls markedly at low speeds
(below 50mm/s; 10 ft/min) and increases with increasing
speed.
Temperature
The coefficient of friction appears to be stable over the
range -45 to 100°C (-49 to 212°F) but to rise at lower
temperatures and fall at higher temperatures (see page
25).
Mating surface
Work by Steijn (ref.105) showed that sliding of PTFE
against steel gave lower coefficients of friction than
sliding bulk PTFE against bulk PTFE. He suggests that
Environment
Steijn (ref.105) showed that prolonged and continuous
running under dry nitrogen (5-10 parts per million of
water) gave rise to intermittently high coefficients of
friction but this was alleviated as soon as normally moist
air (50% r.h.) was admitted. The short term tests at
temperatures from -1 to + 60°C (30 to 140°F) in helium,
oxygen, nitrogen and air showed no such effect and
neither did tests in air at room temperature with relative
humidities in the range 12 to 54%. The friction of PTFE in
vacuum (10-9 mm Hg) was studied by Buckley and
Johnson (ref.106) who obtained coefficients of friction of
0.25 with a load of 1 kg. They also report the coefficient
to be constant over the speed range < 50mm-5 m/s (< 101000 ft/min). This high figure could well be attributed to
the relatively small loads applied, but may be linked with
Steijn’s observations regarding very dry atmospheres.
Several investigators (refs.107, 108) have shown that the
coefficient of friction is decreased dramatically by the
addition of lubricants. This is not surprising since, if a full
film of oil is present, the friction is virtually independent
of the mating surfaces.
Time of running
The work of Steijn (ref. 105) shows that the coefficient of
friction for PTFE on PTFE is influenced by the number of
traverses, the time lapse between runs, the nature
(especially velocity) of the preceding sliding and the
thermal history of the sliding components. Mitchell and
Pratt (ref. 109) demonstrated a similar increase in friction
with time for PTFE on steel, up to a steady level (from
0.05 to 0.20 in 4 hours), and showed this to be due to a
change in the surface of the PTFE rather than a change in
the surface of the steel (i.e. the transfer of PTFE to the
steel).
Filler type and volume
Thompson et al. (ref. 70) suggest that when using
molybdenum disulphide (MoS2), asbestos, carbon,
graphite, and copper as fillers, as the volume of filler
increases the coefficient of friction increases from 0.016
(no filler) to ~ 0.030 (30% of filler), but that there is little
difference in this effect between the various fillers.
41
For a similar range of fillers Milz and Sargent (ref.108)
showed the coefficient to be independent both of the
type of filler and its volume addition. In particular, MoS2
and graphite showed no advantage over glass fibre,
asbestos and copper. Their results for all types ranged
from 0.09 to 0.22 depending on velocity, load, etc. They
concluded that the filler was effectively encapsulated and
the friction was that of PTFE only.
O’Rourke (ref.110) originally came to the same
conclusion but later (ref.111) states that friction is
dependent more upon the volume than the type of filler,
although cadmium oxide is claimed to be an exception.
At the very low temperatures of liquid oxygen and
nitrogen (ref.112) and under conditions of high vacuum
(ref.106) there is considerable variation in the coefficient,
but this does not appear to be correlated with either filler
type or volume. In practical tests with the Wankel engine
(ref.113) using various grades of PTFE as a seal, the
coefficient was again found to be independent of the
filler, whilst in a laboratory test, Ganz and Parkhomenko
(ref.107) state that the type of filler is important; however,
they appear to quote the filler content as % by weight so
that filler type and filler volume are not separable. They
again found MoS2 and graphite fillers to give high
coefficients of 0.26 to 0.34.
The evidence of Mitchell and Pratt (ref.109) is that filler
type has a greater effect than filler volume, with MoS2
giving a lower coefficient than unfilled PTFE. They found
bronze had little effect and kieselguhr increased it by
25%. Work done on behalf of AG Fluoropolymers (see
Table 11) suggests that volume of filler is not directly
related to friction coefficient but fillers in general raise
the coefficient under these particular test conditions by a
factor of about two.
It has also been suggested (refs.110,114) that the addition
of MoS2 and carbon to glass fibre compounds reduces
the coefficient of friction, although figures
quoted show only a marginal decrease. Tests carried out
on behalf of AG Fluoropolymers have not confirmed this
and Buckley et al. (ref.106) found no improvement when
working under vacuum. Similarly, practical tests (ref. 113)
showed no advantages for adding MoS2 to glass
although this combination was suggested (ref.115) as a
possible means of reducing the scoring of shafts, and
(ref.111) for use in very dry gases. It is conceivable that
after prolonged continuous running under dry
conditions, the MoS2 is not subject to the rise in friction
reported for PTFE.
There is therefore conflicting evidence as to the effect of
filler type and volume upon the coefficient of friction of PTFE.
Filler particle size and shape
It is difficult to separate the effects of particle size and
shape from those of filler type, since specific forms of
particle tend to be used with specific types of filler (e.g.
glass fibre, irregular particles of graphite and MoS2,
spherical-bronze, etc.). Moreover, in much of the
published work no details of filler particle are given.
The most explicit work in this field is that of
Speerschneider and Li (ref.116) where, with the very hard
particles of alumina (Al2O3), they found spherical
particles gave coefficients of friction similar to that of
unfilled PTFE (0.05-0.08) whereas irregular particles gave
significantly higher results (0.14-0.15). They attributed
this increase to cleavage of the irregular Al2O3 which
saturates the surface until the coefficient is that of Al2O3
on steel. The abrasive nature of the filler also gives a
‘rough’ surface finish to the steel, thereby giving a
coefficient approximately double that of a ‘smooth’ steel
surface. This effect is less likely to occur with softer
fillers, and this has been found true with bronze, where
no difference in friction has been found between
spherical and irregular particles, although Thompson et
al. (ref. 70) suggest that particle size can have an effect in
extreme cases.
Table 11. Dynamic coefficient of friction for various Fluon® grades
Grade
FC168-63
FC100-15 1000
FC100-25 1000
FC160-60
FC150-25
FC140-15
FC101-20
Coefficient
of friction
0.20
0.10
0.11
0.16
0.17
0.22
0.19
Test conditions
Mating surface: 420 S 37 steel in T condition (BS 970:Part 4:1970)
Surface finish: 0.3µm R (CLA) BS 1134:1972
Pressure: 20 kgf/cm2 (300 Ibf/in2)
Speed: 0.25m/s (50 ft/min)
42
Other parameters (load, speed etc.)
The statements made in the first part of this section for
the effects of load, speed, temperature, etc. upon the
coefficient of friction of unfilled PTFE in general hold
good for filled PTFE, although O’Rourke (ref.111) shows
that the coefficient of glass-filled PTFE does not rise at
low loads, whilst other investigations (refs.108, 112)
suggest that it does.
Environments
Work with filled PTFE at low temperature and in contact
with liquid oxygen and nitrogen (ref.112) shows the
coefficient to rise with the passage of time (e.g. 0.18 to
0.43 in 23 hours), which tends to confirm the work of
Steijn with unfilled PTFE (ref.105).
This same effect at room temperature has been found by
work done on behalf of AG Fluoropolymers and by
Mitchell and Pratt (ref.109) although actual coefficients
are lower (0.07 to 0.20 in 20 hours). There is some
evidence therefore that the coefficient of friction
increases in the presence of liquid oxygen or nitrogen.
High coefficients (0.2 to 0.4) were also found by Buckley
et al. (ref.106) for filled PTFE under high vacuum, but
some of the fillers, notably copper, silver and powdered
coke gave coefficients lower than for unfilled PTFE under
the same conditions. The reasons for these effects are
not known: the effects may be due to temperature or
environment, or the mechanisms may be similar to that
experienced with graphite where the low coefficient of
friction is attributed to the presence of adsorbed gases at
the crystallite interfaces where cleavage occurs (ref. 103).
WEAR
Wear mechanisms
The mechanisms responsible for the wear of PTFE are
not fully understood, but it is generally thought that
adhesion and the freeing of transferred wear fragments,
either in terms of surface energy or by virtue of fatigue,
are of major importance (refs. 103, 104, 109, 117). It is
known that when PTFE is rubbed against other materials
a transfer takes place (refs. 116, 118) and it is believed
that the wear process involves the laying down and
subsequent removal of such transferred layers. An ideal
situation is given (ref. 117) as having a highly oriented
mono-molecular layer of PTFE bonded to the metal
surface which then rubs against as smooth a mating
surface of PTFE as possible.
What is not clear is exactly how and why fillers and
conditions affect both the initial laying down and
subsequent removal of the PTFE particles. It is suggested
that a minimum temperature at the interface is required
to promote adequate bonding and that certain fillers
function by causing frictional heat (ref. 117). It is also
clear that surface finish will affect this transfer, and
whilst there is wide agreement that too rough a mating
surface will cause rapid wear (refs. 111, 117, 119), one
school of thought suggests that too smooth a surface
finish leads to high wear rates, (ref. 111 ) while others
suggest that is not so (refs. 117, 119). The answer may be
that although too fine a finish may well inhibit good
transfer, many filled compounds are sufficiently abrasive
to roughen the mating surface adequately. However, if
the filler or environmental conditions are too abrasive,
rapid wear will occur through ploughing. The
entrapment of wear debris can have a similar affect,
(ref. 109).
It has been suggested that chemical reactions at the
interface may be important. Buckley and Johnson (ref.
106) consider that wear is related to the decomposition
mechanism and hence to the temperature at the
interface, while Hargreaves and Tantam (ref. 112)
suggest lead oxide can be an oxygen carrier to other
metals, giving selective oxidation of roughnesses on the
mating surface. Mitchell and Pratt (ref. 109) have noted
the formation of copper fluoride at the interface of
bronze-filled PTFE, presumably caused by local
degradation of the PTFE and bronze. They do not,
however, attribute the reduction in wear accompanying
the formation of copper fluoride to the chemical action,
but rather to the fact that the area of contact at the
interface increases with time, which reduces the
interface temperature. Vinogradov (ref. 120) did however
attribute a reduction in friction between copper and PTFE
to the formation of the solid lubricant copper fluoride.
Load and speed (Pressure x Velocity)
The most widely quoted formula for the wear of filled
PTFE is that of Archard and Hirst (refs. 121, 122) which
states that the volume wear (W) is proportional to the
relative speed at the interface (V), the load supported
(M) and time run (T), ie,
W
∝ MVT
or using the ‘wear factor’ K
W= KMVT
(Equation 1)
By dividing by an area (A), a linear wear (R) is obtained
such that
W
M
R = — = KVT—;
A
A
M
but — is the pressure applied (P)
A
.
. . R = KTPV
(Equation 2)
Equation 2 suggests that the wear rates of materials can
be classified in at least three ways:
43
(1) By quoting the maximum PV value the material can
withstand (termed limiting PV value). This is found
experimentally either by determining the maximum load
that can be applied at constant velocity while still
maintaining temperature and/or frictional torque
equilibrium, or by determining the PV value at which the
wear rate suddenly increases.
(2) By quoting the PV value which gives a specified wear
rate. This is generally quoted as the PV value to give
0.127mm (0.005 inch) wear in 1000 hours, and is
determined from specific wear tests.
(3) By determining the constant K in Equation 2. This is
known variously as the ‘wear factor’ or ‘K-value’. Work
has been carried out to determine these factors for
various filled PTFE materials (refs. 109, 111). However,
during these and subsequent investigations (ref. 104) it
has been shown that there are two major errors in
accepting results derived from Equation 2:
(a) K is not necessarily a constant for a given material,
but will vary with the load applied, the velocity, the
length of time run, the temperature and other factors
such as clearance and conditions at the interface.
(b) The method of determining the factors is
invariably to test specimens. The conditions of test
have a considerable effect upon the results and
universal values cannot be obtained from one series
of tests.
Temperature
R B Lewis (ref. 104) suggests that each material has two
_ 7) and severe wear (K >
wear rates (metric), mild wear (K ~
35) which is attributed to a rise in temperature at the
interface. The actual temperature at which the transition
occurs is reported to depend upon the load. He concludes
that the PV value at which transition begins depends upon
the application geometry, ambient temperature, and
manner and amount of cooling, whilst the slope of the
transition depends upon the application parameters and
properties of the compositions. The mild wear is reported
to be characterised by wear of the surface layers whilst
severe wear is characterised by bulk removal of material.
Similar conclusions were drawn by Summers.
Smith (ref.123) who considered the composite to be hard
granules in a ‘cement’ of softer materials suggests that
the mild wear region corresponds to a gradual attrition of
the hard granules whilst the change to severe wear occurs
when the ‘cement’ becomes softened by heat and the
granules are plucked bodily out of the matrix. From work
carried out by Mitchell and Pratt (ref.109) and work done
on behalf of AG Fluoropolymers, it is concluded that the
entrapment of wear debris as well as surface temperature
is a very important factor in determining whether severe
wear occurs or not.
44
For example, although the difference in running
conditions between a thrust washer and a piston ring is
mainly considered to be one of interface temperature, it
is also true that wear debris is far less likely to become
entrapped in the piston ring. It is also true that
differences in wear rate can be attributed to differences
in behaviour (abrasive or otherwise) when trapped wear
debris is present. Nevertheless, whatever the
mechanisms, it is generally accepted (refs.104, 106, 113,
117) that an increase in interface temperature increases
the wear rate.
Mating surface and material
At room temperatures and above it is generally agreed
that a hard, approximately 900 VPN (Vickers Pyramid
Number), mating surface is beneficial. Softer materials
can be used providing the filler will not abrade them. The
materials with good dry bearing properties of their own
(e.g. bronze) are preferred to the softer more easily
damaged materials (e.g. aluminium). There is some
divergence of opinion as to the suitability of chromium
plating. Pratt (ref.117) shows chromium plating to be
advantageous whereas O’Rourke et al. (refs.111,124)
show it to give poor results. The answer might well be
that the fillers used by Pratt were less abrasive than those
used by O’Rourke
The surface finish of a material is generally quoted as a
mean centre line average - CLA - or Ra (BS1134-2: 1990) of
the ‘peaks and valleys’ of its surface as detected by
traversing a diamond stylus across it. This does not fully
specify a surface however, since a turned and a ground
surface of the same Ra value will be different. It is now
generally accepted that a ground surface is superior to a
turned surface and that above 0.75µm the wear rate of the
filled PTFE will increase. The existence of a lower limit is
still in dispute and so the best compromise is to use a
ground surface finish of 0.2-0.4µm.
Lubrication
‘Lubricant’ is a very general term and it used to be stated
that any liquid will act as a lubricant and be beneficial to
PTFE. To some extent this is true in that, if hydrodynamic
conditions are established, no wear will take place, but
filled PTFE may run under conditions of boundary
lubrication. Hydrocarbon oils are generally advantageous,
with a significant reduction in wear rates. This is not so
with water. O’Rourke (ref.111) confirmed that the wear
factor increased for unfilled and various filled PTFE
compounds when running against steel with water
boundary lubrication.
Work done on behalf of AG Fluoropolymers has shown
that boundary lubrication with water gave a reduction of
wear life of 50% when filled PTFE ran against steel.
Section 13. Other physico-chemical properties
- filled PTFE
PERMEABILITY
CHEMICAL RESISTANCE
The permeability of filled PTFE is very dependent upon
methods of fabrication. Since there is no chemical
bonding between PTFE and the fillers used, the
permeability is generally greater than that of unfilled
PTFE. As the filler content increases, particularly above
10% by volume, special care, or special techniques, have
to be adopted to ensure minimum permeability. Specific
measurements have not been made, but from porosity
tests it is concluded that permeabilities can be made
close to that of unfilled PTFE if the correct method of
fabrication is used.
PTFE is one of the most chemically resistant materials
known, and fillers can only worsen this position. Table 12
gives a list of the probable suitability of the Fluon® range
for use with various common chemicals. As noted below
this table, some of the information was obtained from
direct experimentation whilst other data were predicted
from a knowledge of the chemistry of the individual
constituents. As with unfilled PTFE, chemical attack on
the filled PTFE should not be confused with chemical
attack on adjacent parts resulting from permeability of
the filled PTFE.
Table 12. Suitability of Fluon® range for use with various chemicals at 50°C (122°F)
NB. This table is intended solely as a general guide to material selection. Because exposure conditions can vary considerably in different
applications, the user is strongly advised to undertake tests under conditions relevant to the specific application.
Chemical
Fluon® Grade
FC168-63
FC100-15 1000
FC100-25 1000
FC150-25†
FC140- 15†
FC160-60
50% H2SO4
U
S*
PS
U
Conc. HCl
U
PU*
PS
U
Conc. HNO3
U
PU*
PS
U
40% NaOH
PS
PU*
PS
PS
0.880 NH4OH
U
S*
PS
U
Benzene
PS
S*
PS
PS
Phenol
PS
S*
PS
PS
Trichloroethylene
PS
S*
PS
PS
Ethanol
PS
S*
PS
PS
Fluorine
-
PU
PS
-
Chlorine
PS(dry)
PS
PS
PS (dry)
Bromine
-
PS
PS
-
HF
PS∆
U
PS
PS∆
SO2
-
PS
PS
-
Mercury
U
PS
PS
U
Notes
S= Satisfactory
U = Unsatisfactory
PS = Not tested, but probably satisfactory
PU = Possibly unsatisfactory
† FC150-25 and FC140-15 will be attacked only by oxidation, although there may be a slight reduction in weight when in contact with other
chemicals, due to attack on the very small quantities of impurities (less than 2%) inherently present in the filler.
* The results of tests in which samples of tape 50.8mm (2 inches) square and 0.38mm (0.015 inch) thick were used in order to give the maximum
surface area to weight ratio. The samples were dried, weighed and then immersed in the various liquids at 50°C (122°F). After a period of four weeks
the samples were removed from the liquids, washed, dried and re-weighed to determine whether attack had occurred. Materials listed as
‘satisfactory’ showed no change in weight over the four week period and those showing some change are listed as ‘possibly unsatisfactory. Over the
four week period the average change in weight of the ‘possibly unsatisfactory’ materials was 7%. The tensile properties were measured before and
after the chemical resistance tests: no statistically significant changes in tensile properties were recorded in any of the tests, including those in which
weight losses occurred.
∆ Up to 70°C (160°F).
45
Section 14. Typical properties of Fluon® unfilled and filled
moulded PTFE
Property
Units
Unfilled
†FC100-25 1000
†FC160-60
Relative density
-
2.1-2.2
2.25
3.8
Filler by weight and type
-
-
25% glass fibre
60% bronze
Maximum tensile strength
MN/m2
kgf /cm2
Ibf/in2
20.6-34.3
210-350
3000-5000
12.3-19.6
125-200
1800-2800
10.3-13.7
105-140
1500-2000
Elongation at break
%
250-400
200-300
80-160
Compressive modulus for
1% deformation (20°C,1 day)
MN/m2
kgf/cm2
1 bf /in2
392
4000
55,000
588
6000
85,000
736
7500
105,000
Impact strength at -20°C
(Charpy, notched)
cm kg/cm2
ft Ib/in2
8
4
9
45
11
55
Hardness
Shore D
60-65
70-75
70-75
Volume resistivity
ohm cm
> 1018
1015
107
Surface resistivity
ohms
1017
1015
109
Permittivity at 23°C, lO5-107 Hz:
dry
95% r.h.
-
2.05
2.05
2.35
2.35
Conducting filler
Conducting filler
0.0001
0.0001
0.001
0.3-0.4
Conducting filler
Conducting filler
1.8
1.0
1.5
1.1
Loss tangent at 23°C and 103 -104 Hz:
dry
95% r.h.
Linear thermal expansion 20-150°C:
parallel to direction of moulding
perpendicular to direction of
moulding
%
%
1.9
1.8
Thermal conductivity
10-4 cal/cm s °C
Btu in/ft2 h °F
6
1.7
9
2.6
19
5.5
Continuous service temperature
°C
°F
-250 to +260
-420 to +500
-250 to +260
-420 to +500
-250 to +260
-420 to +500
Coefficient of friction (dynamic)
-
0.06
0.12
0.13
Resistance to weathering
-
Excellent
Excellent
Excellent
Chemical resistance
-
Fluon® is chemically inert and unaffected by all
known chemicals except alkali metals, fluorine under
certain conditions, and some fluorine compounds at
elevated temperatures. Filled Fluon® has inferior chemical
resistance because of the presence of fillers.
The data presented are based on experiments which are believed to be accurate and reliable. Additional data are available on request.
† The Fluon® range contains compositions of PTFE with fillers such as glass-fibre, bronze, powdered coke and graphite.
46
Section 15. Specifications relating to PTFE
Fluoropolymer raw materials can be designated and
specified using ISO 12086-1 and -2:1995.
Virgin PTFE semi-finished products can be designated
and specified using ISO 13000-1 and -2:1997.
In addition there are numerous national specifications
covering raw materials, semi-finished and finished
articles which change continually.
Please contact Asahi Glass Fluoropolymers UK Ltd for
details.
47
Section 16. Handling precautions
Within its working temperature range PTFE is a
completely inert material, but when heated to its
sintering temperature it gives rise to gaseous
decomposition products or fumes which can produce
unpleasant effects if inhaled. Fumes can be produced
during processing: for example, when the material is
heated to sinter it, or when brazed connections are being
made to cable insulated with PTFE. The inhalation of
these fumes is easily prevented by applying local exhaust
ventilation to atmosphere as near to their source as
possible.
Smoking should be prohibited in workshops where PTFE
is handled because tobacco contaminated with PTFE will
during burning give rise to polymer fumes. It is therefore
important to avoid contamination of clothing, especially
the pockets, with PTFE and to maintain a reasonable
standard of personal cleanliness by washing hands and
removing any PTFE particles lodged under the
fingernails.
48
Section 17. Further information
The following is a comprehensive list of Technical
Service literature for Fluon® PTFE available from the
AG Fluoropolymers sales office.
F1
The Moulding of PTFE granular powders
F2
The Extrusion of PTFE granular powders
F3/4/5 The Processing of PTFE coagulated
dispersion powders
F6
Impregnation with PTFE aqueous
dispersions
F8
Processing of filled PTFE powders
F9
Finishing processes for
polytetrafluoroethylene
F11
Colouring of polytetrafluoroethylene
F12/13 Physical properties of unfilled and filled
polytetrafluoroethylene
F14
Isostatic compaction of PTFE powders
F15
Cast Film from Fluon® PTFE dispersion GP1
FTI500 Fluon® - A Guide to Applications, Properties
& Processing
FTI800 Potential Material & Equipment Suppliers
Information contained in this publication (and otherwise
supplied to users) is based on our general experience
and is given in good faith, but we are unable to accept
responsibility in respect of factors which are outside our
knowledge or control. All conditions, warranties and
liabilities of any kind relating to such information,
expressed or implied, whether arising under statute, tort
or otherwise are excluded to the fullest extent
permissible in law. The user is reminded that his legal
responsibility may extend beyond compliance with the
information provided. Freedom under patents, copyright
and registered designs cannot be assumed.
Fluon® grades are general industrial grades. It is the
responsibility of the purchaser to check that the
specification is appropriate for any individual application.
Particular care is required for special applications such as
pharmaceutical, medical devices or food. Not all grades
are suitable for making finished materials and articles for
use in contact when foodstuffs. It is advisable to contact
the AG Fluoropolymers sales office for the latest position.
Users of Fluon® are advised to consult the relevant
Health and Safety literature which is available from the
AG Fluoropolymers sales office.
Users of any other materials mentioned in this
publication are advised to obtain Health and Safety
information from the suppliers.
This edition ©AGFP September 2002
49
Section 18. References
1
Free energies of formation of fluorocarbons and
their radicals. Thermodynamics of formation and
depolymerisation of polytetrafluoroethylene, W M D
Bryant, J.Poly. Sci., 56, 1962, 277-296
2
Structures of molecules and crystals of
fluorocarbons, C W Bunn and E R Howells, Nature,
174, 4429, 18th September, 1954, 549-551
3
Crystal structure of polytetrafluoroethylene, R H H
Pierce, E S Clark, J F Whitney and W M D Bryant,
Abstracts of 130th Amer. Chem. Soc. meeting,
Atlantic City, September, 1956, 9S
4
Unusual features in the crystal structure of
polytetrafluoroethylene, E S Clark and L T Muus,
Abstracts of 132nd Amer. Chem. Soc. meeting, New
York, September, 1957, 5T
5
Partial disordering and crystal transitions in
polytetrafluoroethylene, E S Clark and L T Muus,
Zeit. Krist.,117, 1962, 119-127
6
Volume-temperature relationships for the room
temperature transition in ‘Teflon’*, F A Quinn, D E
Roberts and R N Work, J. App. Phys., 22, 8, August
1951, 1085-1086
7
A
room-temperature
transition
in
polytetrafluoroethylene, H A Rigby and C W Bunn,
Nature, 164, 4170, 1st October 1949, 583
8
Fluorine-containing
polymers,
Part
2:
Polytetrafluoroethylene, C A Sperati and H W
Starkweather, Fortschr. Hochpolym. - Forsch., 2,
1961, 465-495
12 Transitions and melting of polytetrafluoroethylene
(‘Teflon’) under pressure, C W F T Pistorius, Polymer,
5, 1964, 315-317
13 The pressures of some solid-solid transitions, G C
Kennedy and P N La Mori, J. Geophys. Res., 67, 1962,
851-856, Chem. Abstr., 57, 1962, 4119 a
14 Behaviour of polytetrafluoroethylene (‘Teflon’) under
high pressures, R I Beecroft and C A Swenson, J.
App. Physics, 30, 11, November 1959, 1793-1798
15 Thermal expansion of Ftoroplast IV (fluoroplast,
‘Teflon’) between 190 and 325°, l E Leksina and S I
Novikova, Soviet Phys. Solid State, 1, 1959, 453-459,
Chem. Abstr., 54, 1960, 16914 f
16 Calorimetric properties of polytetrafluoroethylene
(‘Teflon’) from 0 to 365°K, G T Furukawa, R E
McCoskey and G J King, J. Res. Nat. Bur. Stand., 49,
4, October 1952, 273-278
17 Specific heat of synthetic high polymer, Part 5: A
study of the order-disorder transition In
polytetrafluoroethylene, P Marx and M Dole, J.
Amer. Chem. Soc., 77, 1955, 4771 -4774
18 Effect of pressure on the specific volume of polymer
melts, J M Lupton, Abstracts of 134th Amer. Chem.
Soc. meeting, Chicago, September, 1958, 37T-38T
19 R P Palmer, lCI Plastics Division, unpublished work
20 The melting points of chain polymers, C W Bunn, J.
Poly. Sci., 16, 1955, 323-343
21 E R Howells, ICI Plastics Division, unpublished work
9
Chain configurations in crystals of simple linear
polymers, C W Bunn and D R Holmes, Disc. Faraday
Soc., 25, 1958, 95-103
10 Transitions and phases of polytetrafluoroethylene
(‘Teflon’). C E Weir, J. Res. Nat. Bur. Stand., 50, 2,
February 1953, 95-97
11 Effect of pressure on the room-temperature
transition of polytetrafluoroethylene and its heat of
transition, T Yasuda and Y Araki, J App. Poly. Sci.,
5,15,1961, 331-336
*Trade mark of E I du Pont de Nemours and Company (Inc)
50
22 An independent measurement of the amorphous
content of polymers, R G J Miller and H A Willis, J.
Poly. Sci., 19, 1956, 485-494
23 The molecular structure of perfluorocarbon
polymers.
Infra-red
studies
on
polytetrafluoroethylene, R E Moynihan, J. Amer.
Chem. Soc., 81, 1959, 1045-1050
24 Physical properties of fluorocarbon plastics, Part 2:
Relations
between
crystallinity
and
room
temperature transition effects in PTFE, Toshihiko
Kuroda and Hiroshi Sakami - Nagoya Kogyo Gijutsu
Shikensho Hokoku 7,1-8 (1958), Chem. Abstr., 57,
4828h
25 Structure of polytetrafluoroethylene, G Butenuth,
Verhandlungsber. Kolloid - Ges., 18, 1958,168-179,
Chem. Abstr., 52, 14213 i
306
38 Polytetrafluoroethylene,W E Hanford and R M Joyce,
J. Amer. Chem. Soc., 68, 1946, 2082-2085
39 Dielectric properties of ‘Teflon’ from room
temperature to 314°C and from frequencies of 102 to
105 c/s, P Ehrlich, J. Res. Nat. Bur. Stand., 51, 4,
October 1953, 185-188
26 The fine structure of polytetrafluoroethylene, C W
Bunn A J Cobbold and R P Palmer, J. Poly. Sci., 28,
1958, 365-376
40 Dielectric losses of polytetrafluoroethylene, G P
Mikhailov, S P Kabin and A L Smolyanskii, Zhur. Tekh.
Fiz., 25, 1955, 2179-2182, Chem. Abstr., 50, 1956,
3026f
27 Some
observations
on
the
structure
of
polytetrafluoroethylene, C J Speerschneider and C H
Li, J. App. Physics, 33, 5, May 1962, 1871-1875
41 Vorbehandlung and dielektrisches Verhalten
Hochpolymere, F Krum and F H Muller, Koll. Zeits.
164, 1959, 81-107
28 A correlation of mechanical properties and
microstructure of polytetrafluoroethylene at various
temperatures, C J Speerschneider and C H Li, J. App.
Physics, 34,10, October 1963, 3004-3007
42 Transitions
and
relaxations
in
polytetrafluoroethylene, R K Eby and K M Sinnott, J.
App. Physics, 32, 9, September 1961, 1765-1771
43 Hartshorn and Ward, J. Inst. Elec. Engrs, 1936, 79, 597
29 Dispersions de polytetrafluorethylène, E Grimaud, J.
Sanlaville and M Troussier, J. Poly. Sci., 31, 1958,
525-527
30 A J Cobbold and R P Palmer, ICI Plastics Division,
unpublished work
31 Polymer single crystals, P H Geil, Interscience
Publishers, New York, 1963, 483
32 Treatise on powder metallurgy, 2, S. Goetzel
33 W G Rodway, ICI Plastics Division, unpublished work
34 Effect of pressure on the melting point of ‘Teflon’
polytetrafluoroethylene resin. P L McGeer and H C
Duus, J. Chem. Phys., 20, 1952, 1813-1814
35 Uniaxial
compressive
creep
of
polytetrafluoroethylene, D A Thomas, Polymer
Engineering and Science, 9, 1969, 415-422
36 Experimental technique in uniaxial creep testing, D A
Thomas and S Turner, Interscience Publishers Inc,
New York, Testing of polymers, Vol 4
37 S Turner, Polymer Engineering and Science, 6, 1966,
44 Barrie, Proc. Inst. Elec. Engrs, 112, 2, February 1965
45 Parry, Proc. Inst. Elec. Engrs, 98, Part 3, 54, July 1951,
303
46 Bleaney, Loubser and Penrose, Proc. Phys. Soc., 59,
Part 2, March 1947, 185
47 Reddish, l U P A C Symposium, Montreal, August
1961
48 Reddish, Society of Chemical Industry Symposium,
April 1958, published proceedings
49 Reddish and Barrie, l U P A C Symposium,
Wiesbaden, 1958
50 D J Parr and R M Scarisbrick, Proc. Inst. Elec. Engrs,
112, August 1965, 1625
51 Effects of fabrication on the properties of ‘Teflon’
resins, P E Thomas. J F Lontz, C A Sperati and J L
McPherson, S P E Journal, 12, June 1956, 89-96
52 G Mole, E R A reports V/T115,1952 and V/T149, 1962
52a Superheating of linear high polymers: PTFE, E
51
Helmuth, B Wunderlich and J H Rankin, Appl.
Polymer Symposium No 2,1966, 101-109
53 Thermal expansion of polytetrafluoroethylene
(‘Teflon’) from -190°C to +300°C, R K Kirby, J. Res.
Nat. Bur. Stand., 57, 2, 1956, 91-94
54 Thermal conductivity studies of polymers, D E Kline,
J. Poly. Sci., 50, 1961, 441-450
55 Thermal conductivity of high polymers from -180 to
+90°C K.Eiermann and K H Hellwege J Poly Sci., 57,
1962, 99-106
56 Specific heat of synthetic high polymers, Part 5: A
study of the order-disorder transition in
polytetrafluoroethylene, P Marx and M Dole, J.
Amer. Chem. Soc., 77, 1955, 4771-4774
57 Relative enthalpy of polytetrafluoroethylene from 0
to 440°C, T B Douglas and A W Harman, J. Res. Nat.
Bur. Stand., 69A, 2, 1965, 149-157
58 Thermal degradation of tetrafluoroethylene and
hydrofluoroethylene polymers, S L Madorsky, V E
Hart, S Straus and V A Sedlak, J. Res Nat. Bur.
Stand., 51, 1953, 327-333
59 PyroIysis of polytetrafluoroethylene, E E Lewis and
M A Naylor, J. Amer. Chem. Soc., 69, 1947, l968-l970
60 Thermal degradation of fluorine containing
polymers, Part 1: Degradation in vacuum, J M Cox, B
A Wright and W W Wright, J. App. Poly. Sci., 8, 1964,
2935-2950
61 Thermal degradation of fluorine containing polymers,
Part 2: Degradation in oxygen, J M Cox, B A Wright
and W W Wright, J. App. Poly. Sci., 8, 1964, 29512961
62 The molecular structure of perfluorocarbon
polymers,
Part
2:
Pyrolysis
of
polytetrafluoroethylene, J C Siegle, L T Muus, TungPo Lin and H A Larsen, J. Poly. Sci., A, 2, 1964, 391404
63 H G Jellinek, Paper No 16 of the 12th Canadian High
Polymer Forum, Candy Alpine Inn, Ste. Marguerite,
Quebec
52
64 Pyrolysis of polytetrafluoroethylene, J C Siegle and L
T Muus, Abstracts of 130th Meeting of Amer. Chem.
Soc., Atlantic City, 1956, 8S
65 Oxidative thermal degradation of PTFE, K L Paciorek,
R H Kratzer: J Kaufman, J. Poly. Sci., 1973, 1465-1473
66 The frictional properties of some plastics, K V
Shooter and P H Thomas, Research, 2, 1949, 533-535
67 The friction and deformation of polymers, M W
Pascoe and D Tabor, Proc. Roy. Soc., 235A, 1956, 210224
68 The frictional properties of plastics, K V Shooter and
D Tabor, Proc. Phys. Soc., 65B, 1952, 661-671
69 Frictional properties of plastics, K V Shooter, Proc.
Roy. Soc., 212A, 1952, 488-491
70 The sliding friction of ‘Teflon’, J B Thompson, G C
Turrell and B W Sandt, S P E Journal, 11, 4, April
1955, 13-14, 38
71 Friction of ‘Teflon’ sliding on ‘Teflon’, D G Flom and
N T Porile, J. App. Physics, 26, 1955, 1088-1092
72 The effect of temperature on the mechanical
properties and the friction of plastics, R K King and D
Tabor, Proc. Phys. Soc., 66B, 1953, 728-736
73 Visco-elastic properties and the friction of solids, K G
McLaren and D Tabor, Nature, 197, 4870, 1963, 856859
74 Friction and transfer of polytetrafluoroethylene, K R
Makinson and D Tabor, Nature, 201, 4918, 1964, 464466
75 Effect of orientation on the friction of PTFE, D Tabor
and D E W Williams, Wear, 4, 5, 1961, 391-400,
Rubber Abs. 40, 258
76 The spreading of liquids on low energy surfaces, Part
1: Polytetrafluoroethylene, H W Fox and W A Zisman,
J. Colloid Science, 5, 1950, 514-531
77 Wetting of fluorinated solids by hydrogen bonding
liquids, A H Ellison, H W Fox and W A Zisman, J
Phys. Chem., 57, 1953, 622-627
78 Wettability of halogenated organic solid surfaces, A
H Ellison and W A Zisman, J. Phys. Chem., 58, 1954,
260-265
92 Viscosity and plasticity of polytetrafluoroethylene
resin above the melting point, A Nishioka and M
Watanabe, J. Poly. Sci., 24,106, 1957, 298-300
79 Wetting of low energy solids by aqueous solutions
of highly fluorinated acids and salts, M K Bernett and
W A Zisman, J. Phys. Chem., 63 1959, 1911-1916
93 Molecular weight of polytetrafluoroethylene, R C
Doban, A C Knight, J H Peterson and C A Sperati,
Abstracts of 130th Amer. Chem. Soc. Meeting,
Atlantic City, September 1956, 9S
80 The permeability of some plastic materials to H2, He,
N2, O2 and A, R S Barton, U K A E A Report M599,
1960. Chem. Abstr., 54, 14750h
81 H Yasuda and W Stone, J. Poly. Sci., Al, 4, 1966,
1314-1316
82 R A Pasternak, M V Christensen and J Heller,
Macromolecules, 3, 1970, 366-371
83 G V Casper and E J Henley, Polymer Letters, 4, 1966,
417-421
84 Gas chromatographic measurement of the
permeability of PTFE, PVC, polyethylene and nylon
tubing towards oxygen and nitrogen. R G Gerritse.
Journal of Chromatography, 77, 1973, 406-409
85 Permeation of sulphur dioxide through polymers. R
M Felder, R D Spence, and J K Ferrell, Journal of
Chemical and Engineering Data 20, 3, 1975
86 Structure of polymers and properties of films, P G
Konovalov, Sbornik Stateu Vsesoyuz, Zaochnogo
Politekh. Inst., Moscow, 23, 1960, 92-102, Chem.
Abstr., 55, 1961, 20488b
87 Perméabilité des matières plastiques à la vapeur
d’eau, M Korte-Falinski, J de Chimie Physique, 59,
1962, 27-35
94 Reactions of irradiated polytetrafluoroethylene
resin, M I Bro, E R Lovejoy and G R McKay, J. App.
Poly. Sci., 7, 1963, 2121-2133
95 The effects of X-rays on the insulation properties of
polytetrafluoroethylene, W E Liversage, Brit. J.
Radiol., 25, 1952, 434-436, Chem. Abstr., 46, 1952,
10679g
96 Chemical and physical changes in gamma-irradiated
plastics, R Harrington and R Giberson, Modern
Plastics, 36, November 1958, 199-221, 314, 317
97 Polytetrafluoroethylene - a radiation resistant
polymer, L A Wall and R E Florin, J. App Poly. Sci.,
2, 5, 1959, 251
98 The effect of radiation on PTFE, Fluon® Engineering
News, ICI Plastics Division, May 1964, 4
99 A Monnet and R Bensa, Energie Nucleaire, 13, 2,
March/April 1971, 123-132
99a The effects of radiation on the mechanical and
electrical properties of the GEOS satellite long
boom cable materials, D Verdin and P R Goggin,
AERE, Harwell, July 1975
100 Fluorocarbon polymers in the Chemical Industry, B
B Rossa, Praktische Chemie, 15, 2, 1964, 64-73
88 P E Toren, Anal. Chem., 37, 7, 1965, 922-923
89 Journal of ‘Teflon’, (E I du Pont de Nemours &
Company Inc), European edition, 8, March/April
1970; US edition, December, 7, 1964
90 Measurements of the refractive index of films, F W
Billmeyer, J. App. Physics, 18, 5, 1947, 431-434
91 Determination of the refractive index of a solid using
a far infra-red maser, J E Chamberlain and H A
Gebbie, Nature, 206, 4984, 1965, 602
101 Temperature dependence of sound velocity in
PTFE, V M Kravtsov, Akust. Zh., 11, 3, 1965, 400
401, Chem. Abstr., 64, 3707b
102 Filled fluorocarbons - new component materials-,
M A Rudner, Elec. Manuf. February 1955-80
103 Friction, lubrication and wear: a survey of work
during the last decade-, F P Bowden and D Tabor,
Brit. J. Appl. Phys. 17, 1966, 1521-1544
53
104 Predicting bearing performance of filled ‘Teflon’ TFE
resins, R B Lewis, ASME Paper 66-WA/RP-1
105 The effect of time, temperature, and environment
on the sliding behaviour of polytetrafluoroethylene,
R P Steijn, ASLE Trans. 9, 1966, 149-159
106 Friction, wear and decomposition mechanisms for
various polymer compositions in vacuum to 10-9
millimetre of mercury, D H Buckley and R L
Johnson, NASA Tech. Note D-2073, December 1963
107 Anti-friction properties of PTFE filled with ground
coke, S N Ganz and V D Parkhomenko, Soviet
Plastics, January 1966, 42-43
115 A comparison of materials for use as unlubricated
journal bearings, F F Simpson, Proc. l. Mech. E. 175,
No.10 1961, 528-536
116 The role of filler geometrical shape in wear and
friction of filled PTFE, C J Speerschneider and C H
Li, Wear, 5, 1962, 392-399
117 Plastics as bearing materials, with particular
reference to PTFE, G C Pratt, Plast. Inst. Trans. and
Journal, 32, August 1964, 255-260
118 The friction and transfer of PTFE, K Makinson E D
Tabor, Proc. Roy. Soc. 281A, 1964, 49-61
108 Frictional characteristics of plastics, W C Milz and L
B Sargent, Lubrication Engng.1955
119 The wear of PTFE impregnated metal bearing
materials, D C Mitchell, l. Mech. E. Conference on
Lubrication and Wear, London, 1-3 October 1957
109 Friction, wear and physical properties of some filled
PTFE bearing materials, D C Mitchell and G Pratt, I.
Mech. E. Conference on Lubrication and Wear,
London, 1-3 October 1957
120 A study of heavy metal to plastic friction duties and
of the wear of hardened steel in the presence of
polymer, G V Vinogradov, V A Mustafaev and Yu Ya
Podolsky, Wear, 8, 1965, 358-373
110 Design properties of filled-TFE plastics
J T
O’Rourke, Machine Design, 13 September 1962
121 Contact and rubbing of flat surfaces, J F Archard, J.
Appl. Phys. 24,1953, 981-988
111 Fundamentals of friction PV, and wear of
fluorocarbon resins, J T O’Rourke, Modern Plastics,
43, September 1965, 161-169
122 The wear of metals under unlubricated conditions,
J F Archard and W Hirst, Proc. Roy. Soc. 236A, 1956,
397-410
112 Performance of some plain bearing materials under
boundary conditions at low temperatures, R
Hargreaves and D H Tantam, Proc. l. Mech. E. 175,
No. 20 1961, 941-954
123 Performances of unlubricated piston rings, D
Summers-Smith, Lubrication and Wear Convention,
I. Mech. E.1963, 280
113 Friction and wear tests at high rubbing speeds, VDI
Zeitschrift, 109, No.16 1967, 722-727
114 Non-lubricated bearings and piston rings of
tetrafluoroethylene, R B Fehr, SPE Journal, August
1960, 943-948
54
124 Internal report on DECHEMA
Colloquium 17, November 1967
(Germany),
55
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Downington, PA 19335
United States of America
Telephone: +1 610-423-4300
Toll Free Telephone (US only) 800-424-7833
Fax: +1 610-423-4305
email: [email protected]
web: www.agcchem.com
SINGAPORE
ASAHI GLASS SINGAPORE CHEMICALS
PTE., LTD.
460 Alexandra Road
#17-03 PSA Building
Singapore 119963
Telephone: +65 6273 5656
Fax: +65 6276 8783
email: [email protected]
CHINA
AGC CHEMICALS TRADING
(SHANGHAI) CO., LTD.
Room 6405, Rui Jin Business Center
118 Rui Jin (2) Road, Shanghai
China
Postcode: 200020
Telephone: +86 21 6415 165
Fax: +86 21 6415 9506
email: [email protected]