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Q3 Permeation Products & Services Newsletter

Friday, November 10, 2023

 
 

Quarter 3 | October 2023

 
 

Determining Equilibrium in Permeation Testing

Since permeation deals with gas diffusion through some medium driven by concentration differences, equilibrium occurs when there is a steady state flux of permeant molecules from a higher to lower concentration.

What does equilibrium look like? If we graph permeant transmission rate versus time, there are three basic types of trends:


 

  • Low barrier materials permeate readily and quickly reach a steady state
  • High barrier behavior depicts initial out gassing of atmospheric permeant molecules from the surface of the structure. This is displayed by a large continuous decrease in transmission rate until equilibrium
  • Complex barriers display both decreases (out gassing) and increases in permeant flux

There is no universal time to reach equilibrium. Test duration depends on multiple factors, such as temperature, barrier structure, barrier thickness, and solubility. The only way to decrease time to equilibrium is by increasing thermal energy (i.e., temperature.) Selecting consistent equilibrium criteria equates to increased reproducibility.


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Interchangeable Test Cartridges Improve Results

Accurate permeation testing for PPM (parts-per-million) or PPB (parts-per-billion) of gas molecules through barriers depends on precise testing methods. It requires not only a high precision gas sensor but leak-free mounting and precise test conditions.

Since not all barriers are thin, smooth and homogenous, a growing majority of permeation testing samples need specialized preparation and mounting to achieve accurate and repeatable results.

To simplify this challenge, AMETEK MOCON’s permeation instruments feature removable and interchangeable test cartridges. We offer a range of different cartridges designs, each specialized for different sample types to provide accurate and repeatable test results with minimal effort. Some cartridges extend the testing range on an instrument without sacrificing precision or accuracy. Others are designed for paper-based barriers that often leak through the edge, interfering with data accuracy.

Additionally, testing formed packages has historically been time consuming and challenging. Our specialized test cartridges enable simpler, more accurate testing for a wide range of package types.





For expanded instrument testing without giving up accuracy or repeatability, check out the range of cartridges offerings for AMETEK MOCON permeation instruments.

 

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What temperature should I use for transmission rate testing?

This is a common question received by our permeation testing laboratory experts. It's difficult to answer, as temperature directly relates to the measured transmission rate value. Higher temperatures mean more energy is released for faster equilibrium times and higher transmission rate values.

While many labs start by testing at real-life storage conditions, it’s often necessary to determine how a material or package performs at higher or lower temperatures. This is where predictive modeling prove useful. Below is a graph of polymer film tested for OTR at various temperatures. Note the curved line, which makes it difficult to make accurate transmission rate predictions at higher temperatures.





As a “rule of thumb,” transmission rates double for every 10°C increase in temperature. This increase is referred to as an Arrhenius relationship; graphing the data with an Arrhenius plot (lnTR vs 1/Temp K) produces a much more linear relationship, and can be a powerful predictive tool for estimating transmission rates at other temperatures.


Read the full article to learn the full details of this case study, our best practices for predictive modeling with Arrhenius plot data, and the most common recommendations we make to customers regarding temperature.

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Resources

New application notes available (click images below).

Questions about our lab testing services? Visit the updated webpage, now with comprehensive documentation of transmission rate test methods.

Events

There are no more events currently scheduled for 2023. Stay tuned for our upcoming lists of shows in 2024!

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