A Comparison with PTFE
Why Does Permeation Matter in Beverage Filling?
Bottled beverages, especially beer, should reach consumers with minimal loss of quality. If oxygen enters the product during the filling process, chemical reactions may occur that can alter the composition of the beverage, affect its flavor, and even reduce its shelf life. Both outcomes are undesirable and should therefore be avoided whenever possible.
Until now, EPDM and FKM, as well as PTFE and modified PTFE grades (e.g., TFM®), have been the primary materials used for seals and flexible tubing (commonly referred to as Teflon® tubing). Particularly during equipment shutdowns, atmospheric gases could diffuse into the system due to osmotic pressure, demonstrably increasing, for example, the oxygen concentration in beverages.
Why Is Teflon® Not Diffusion-Tight?
Although PTFE is considered more diffusion-resistant than the elastomer materials commonly used in these applications, this fluoropolymer, despite its outstanding properties, still exhibits certain shortcomings. One reason is that PTFE is a compression-molded and sintered material containing micropores that are inherently created during the manufacturing process. In addition, its macromolecules have only a limited ability to conform closely to one another, resulting in a less dense molecular structure. Finally, the intermolecular (Van der Waals) forces are extremely weak due to the strong carbon-fluorine (C-F) bond. In thermoplastics, these cohesive forces normally help individual molecules adhere to one another, thereby creating an effective barrier against gas permeation.
Is There a Material Comparable to PTFE That Offers Better Resistance to Gas Permeation Without Introducing Significant Drawbacks?
UHMW-PE (ORGANOR® P1) has a molecular structure that is very similar to that of PTFE. Like PTFE, UHMW-PE consists of very long-chain, linear polymers with carbon-based backbone chains, whose macromolecules are not cross-linked. In UHMW-PE, however, the carbon backbone is surrounded by hydrogen atoms (H) instead of fluorine atoms (F). As a result, the material is PFAS-free (free of per- and polyfluoroalkyl substances).
The Van der Waals forces in UHMW-PE are significantly stronger, resulting in a substantially denser molecular structure. This has now been demonstrated as part of a bachelor’s thesis conducted in cooperation with Münster University of Applied Sciences, initiated by bock machining gmbh.
How Is Gas Permeation / Diffusion Tightness Measured?
Gas permeation
“The permeation coefficient is a material constant; therefore, its determination is not tied to a specific test method or specimen geometry.” [DIN 53536, October 1992]. The test concept is based on DIN 53380-2. To reduce measurement time and increase detection sensitivity, certain modifications were made to the test setup.
The test system consists of two chambers separated by the test specimen. One chamber is pressurized with the test gas, while the opposite chamber is evacuated. The resulting concentration gradient creates a defined diffusion flow through the specimen in one direction.
After a material-specific conditioning period, a steady-state diffusion flow is established. This constant diffusion flow serves as the basis for determining the permeation rate.
Figure 1 below shows a schematic illustration of the test system.
The measurement is primarily based on the increase in partial pressure within the measuring chamber. The evacuated volume of the measuring chamber is continuously monitored using mass spectrometry, thereby determining the concentration of the test gas.
Permeation measurements are carried out at three pressure levels: 2 bar, 4 bar, and 6 bar. By pressurizing Chamber 1 and evacuating Chamber 2, pressure differentials of 3 bar, 5 bar, and 7 bar, respectively, are established across the test specimen.
The measurements are conducted at an ambient temperature of 23°C (73.4°F).
The test gas used is helium.
Permeation measurement
Figure 2 below shows the permeation measurement for M4b, illustrating the measurement procedure and the selected measurement points. Table 1 presents the corresponding measurement points and the recorded values in detail.
The measurement points are recorded approximately 10 minutes after a constant mass flow has been established. The 6-bar pressure level was maintained for an extended period to determine how the mass flow changes over longer test durations.
After a time interval of 135.8 minutes between measurement point 3 and the reference point, the difference in the leakage rate was found to be 3.9%. This indicates that, within the first 10 minutes after a steady-state mass flow has been established, a constant volumetric flow is achieved and 95% of the measurement signal is captured.
| Time [min] | Leakage [mbar⋅𝑙/𝑠] | |
| Measurement point 1 | 20,3 | 1,39E-04 |
| Measurement point 2 | 29,4 | 2,52E-04 |
| Measurement point 3 | 43,5 | 3,68E-04 |
| Reference point | 179,3 | 3,83E-04 |
Can the Thermal Operating Range of UHMW-PE Be Extended?
In beverage filling systems, two temperature levels must generally be considered:
CIP (Clean-in-Place) processes at temperatures up to 95°C (203°F), steam sterilization at temperatures up to 121°C (250°F). Until now, UHMW-PE (ORGANOR® P1) has been suitable only for applications up to approximately 80°C (176°F), even under moderate mechanical loads.
With ORGANOR® P25, bock machining gmbh has developed a modified UHMW-PE grade that is also suitable for these operating conditions while providing even greater resistance to gas permeation than conventional PE 1000. In addition, the material’s already outstanding mechanical properties have been further enhanced.
See also:
➥ PFAS-Free, Heat-Resistant Plastics: State of the Art
What Components Can Be Manufactured from Modified UHMW-PE?
ORGANOR® P25 is likewise a compression-molded and sintered material that is processed by machining. This makes it the material of choice for applications in the food industry, where physiological safety, flexural fatigue resistance, and cleanability (up to approximately 125°C / 257°F) are critical requirements.
Whether used for diaphragms, bellows, static seals, or flexible product transfer lines, virtually all machined PTFE components are prime candidates for replacement. This not only provides a material structure that is up to ten times more resistant to gas permeation, but also offers the additional advantage of being PFAS-free.
- P25 = ORGANOR® P25 = modficated UHMW-PE
- P1 = ORGANOR® P1 =UHMW-PE
- M4b = ENDUFLON® M4b = modificated PTFE
- V1 = ENDUFLON® V1 = PTFE
Teflon® is a registered trademark of The Chemours Company.
Stefan Bock
