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Permeability ofTeflon™ FEP Resins
(gm/100in2/24 hrs-1mil)1 TABLE 1
GASES2 23 ° C/73 ° F 35°C/95°F 50°C/122°F
Carbon Dioxide
Helium
Hydrogen Chloride
Nitrogen 0.18
Oxygen 0.39
VAPORS3
Acetic Acid 0.42
Acetone 0.13 0.95 3.29
Acetophenone 0.47
Benzene 0.15 0.64
N-Butyl Ether 0.08 0.65
Carbon Tetrachloride 0.11 0.31
Decane 0.72 1.03
Dipentene 0.17 0.35
Ethyl Acetate 0.06 0.77 2.90
Ethyl Alcohol 0.11 0.69
Hexane 0.57
Hydrochloric Acid (20%) <0.01
Methanol 5.61
Piperdine 0.04
Skydrol Hydraulic Fluid 0.05
Sodium Hydroxide (50%) 4x10-5
Sulfuric Acid (98%) 8x10-6
Toluene 0.37 2.93
Water 0.09 0.45 0.89
1. Note that the permeation data listed in Table 1 is based on
0.001” thickness of Teflon™ FEP encapsulation. The
transmission rate significantly decreases when the
thickness of encapsulation is increased. See water vapor
transmission rate chart.
2. Test method: ASTM D-790-59 (at 1atm).
3. Test method: ASTM E-96-53T (vapor Pressure).
WaterVaporTransmission Rate of
Teflon™FEP Resins @ 40°C/104°F
Transmission Rate = gm/100in 2/24hrs
0.40
0.35
0.30
0.25
0.20
0.15
0.10
<.05
3 6 9 10 12
Thickness/mils
Please note that the vapor transmission rate significantly decreases when
the thickness of encapsulation is increased
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Gas Permeability
All plastics have some permeability to gases. In the case
of Teflon™ FEP Encapsulated O-Rings, however, gases
and vapors will permeate at a considerably lower rate than
for most other plastics. The primary permeation
mechanism is intermolecular migration. This migration
rate depends on the type of gas, pressure, temperature,
size of contact areas, and thickness of encapsulation.
While highly corrosive gases do not attack the
Teflon™FEP Encapsulation of the o-ring, they may
eventually permeate through and damage the elastomer
core and hence affect the mechanical properties. Thus, in
addition to chemical resistance, these permeability effects
must be considered in gas sealing systems.
Absorption
Teflon™ FEP Encapsulated O-Rings absorb practically no
common acids or bases at temperatures as high as
200°C/329°F with exposures up to one year. Even the
absorption of solvents is surprisingly small; weight
increases are generally less than 1% at elevated
temperatures and exposure times. Due to the Teflon™
FEP encapsulation, the effects of volume swell (one of the
principal causes of seal failure) can be virtually ignored.
Thickness of Encapsulation
As discussed earlier, the thickness of encapsulation must
be considered in determining migration rates. The
thickness of the encapsulation varies with the cross
section of the o-ring.
Final selection of applications must be based on functional
evaluations or experience under actual end use
conditions. This has become industry practice dictated by
the many complex aspects of performance in severe
conditions. The end user should thoroughly test any
application, and independently conclude satisfactory
performance of the product for his intended use, and shall
assume all risk and liability whatsoever in connection
therewith.
Cross Wall Cross Wall
Section Section Section Section
(mm/inches) (mm/inches) (mm/inches) (mm/inches)
1.50mm/.059 0.203mm/.008 7.50mm/.295 0.508mm/.020
1.60mm/.063 0.203mm/.008 8.00mm/.312 0.508mm/.020
1.78mm/.070 0.254mm/.010 8.40mm/.330 0.508mm/.020
2.00mm/.079 0.254mm/.010 9.00mm/.354 0.508mm/.020
2.40mm/.094 0.254mm/.010 9.50mm/.374 0.508mm/.020
2.62mm/.103 0.279mm/.011 10.00mm/.393 0.508mm/.020
3.00mm/.118 0.279mm/.011 11.00mm/.433 0.762mm/.030
3.53mm/.139 0.305mm/.012 12.00mm/.472 0.762mm/.030
4.00mm/.157 0.305mm/.012 12.70mm/.500 0.762mm/.030
4.50mm/.177 0.381mm/.015 14.00mm/.551 0.762mm/.030
5.00mm/.196 0.381mm/.015 15.00mm/.591 0.762mm/.030
5.33mm/.210 0.381mm/.015 16.00mm/.625 0.762mm/.030
5.70mm/.225 0.381mm/.015 18.00mm/.708 0.762mm/.030
6.00mm/.236 0.381mm/.015 19.00mm/.750 0.762mm/.030
7.00mm/.275 0.508mm/.020 20.00mm/.787 0.762mm/.030