Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

PCTFE vs PTFE - A Comparison of Two Very Similar Polymers

Even though PTFE remains a niche polymer among more generic materials such as PP (Polypropylene), PVC, PE (Polyethylenes, such as HDPE and LDPE), and even Nylons, within the engineering space it is now quite common. Most applications involving high temperature, corrosive chemicals, high voltages, or high wear/friction now look to PTFE automatically as a solution. 

Despite this, there do exist applications where PTFE does not fit the bill and a compromise must be made. For example, applications where high dimensional stability is needed across a wide temperature range, PTFE tends to fall short. The high linear thermal expansion coefficient of PTFE means that it cannot hold its dimensions as temperatures vary. In such a situation, we have seen PEEK being adopted. While PEEK does do the trick, it is also 10X the cost of PTFE.

Similarly, certain applications where cost is a constraint need to make do with POM (Delrin), or even PVC, where PTFE cannot be used. In such a scenario, we possibly forego some of PTFE’s key properties.

Over the years a variety of new polymers that have been developed to fill the performance and commercial gaps between PEEK and PTFE. These include PFA, FEP, PEK, PPS (Ryton), and PCTFE.

Although not well known, PCTFE forms an ideal substitute for PTFE in certain applications where PTFE is unable to perform adequately. The table below is meant to offer a snapshot comparison of the two, such that any application engineer can evaluate the key differences.

 

 

Unit

PTFE

PCTFE

Remarks

Properties

Tensile Strength

Mpa

20-30

30-35

With a marginally higher tensile strength, PCTFE rates higher than PTFE on this metric

Elongation

%

200-350

100-250

PCTFE is stiffer than PTFE, which means it lacks some of the softness of PTFE when it comes to sealing, but that it also holds its dimensions more easily

Melting Point

Deg. C

350-380

200-220

PTFE is still preferred on outright high-temperature applications

Dielectric Breakdown Voltage

KV/mm

50-100

20-40

PTFE rates higher on outright dielectric strength

Coefficient of Friction

 

 0.03-0.05

0.25-0.35 

PTFE rates higher as a non-stick material 

 

 

 

 

 

 

Processing

Injection Moulding

 

No

Yes

PCTFE has more versatility when processing, allowing for more complex parts

Compression Moulding

 

Yes

Yes

 

 

 

 

 

 

Characteristics

Chemical Resistance

 

Extreme

Very Good

PTFE is still unmatched in chemical resistance

Thermal Stability

 

OK

Very Good

PCTFE rates higher than PTFE when it is a question of stability over a wide range of temperatures

Price

 

Med

High

PCTFE is more expensive than PTFE, and is therefore used in specific applications only

As you can see from the above chart, PCTFE and PTFE each have unique advantages and disadvantages when compared with one another. Like all polymers, the application needs to be properly understood and the commercials need to be weighed in before any decision can be made.

However, it is fair to say that when dimensional stability across a temperature range is a must, PCTFE is growing to become the most effective substitute for PTFE.

Datasheet for PCTFE:

Property

Value

Units

Method

MECHANICAL PROPERTIES

Tensile Strength

4860 - 5710
34 - 39

psi
MPa

D 638

Elongation

100 - 250

%

D 638

Flexural Strength, 73°F

9570 - 10300
66 - 71

psi
MPa

 

Flex Modulus

200 – 243 x 103
1.4 – 1.7

psi
MPa

 

Impact Strength, Izod, 23 deg C

2.5 – 3.5

ft-lb/in

D 256

Compressive Stress at 1% deformation,

1570 – 1860
11 - 13

psi
MPa

D 695

Density

2.10 to 2.17

gm/cu.cm

 

THERMAL PROPERTIES

Coefficient of Linear Expansion

7 x 10-5

K-1

 

Melting Point

410 -414
210 - 212

deg F
deg C

 

Thermal Conductivity

1.45
0.84

Btu·in/h·ft2·°F
W/m·K

ASTM C 177

Specific Heat

0.22
0.92

Btu/lb/deg F
kJ/Kg/deg K

 

Heat Distortion Temperature, 66 lb/sq.in (0.455 MPa)

259
126

deg F
deg C

D 648

Processing Temperature

620
327

deg F
deg C

 

ELECTRICAL PROPERTIES

Dielectric Strength, short time, 0.004”

3000

Volt/mil

D 149

Arc-Resistance

360

sec

D 495

Volume Resistivity, @ 50% RH

2 x 1017

ohm-cm

D 257

Surface Resistivity, @ 100% RH

1 x 1015

Ohm sq-1

D 257

Dielectric Constant, 1 kHz

2.6

ε

D150-81

Dissipation Factor, @ 1 kHz

0.02

 

D150-81

OTHER PROPERTIES

Water Absorption

0.00

% increase in weight

D570-81

Flame Rating+

Non-flammable

 

D 635

Coefficient of friction (Dynamic)

 

0.25-0.35

D 1894

Specific Gravity

2.10 to 2.17

 

D792

Moisture Permeability Constant

0.2

g/m, 24 hours

 

O2 Permeability

1.5 x 10-10

Cc, cm/sq.cm, sec, atm

 

N2 Permeability

0.18 x 10-10

Cc, cm/sq.cm, sec, atm

 

CO2 Permeability

2.9 x 10-10

Cc, cm/sq.cm, sec, atm

 

H2 Permeability

56.4 x 10-10

Cc, cm/sq.cm, sec, atm

 



 

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