Permeation testing and the barriers – what can be measured…and why?

There are different ways to work with permeation rate calculations, depending on what you are testing for and the type of testing you need to carry out.

If you want to find out how much oxygen will permeate through your package, or if you need to analyze the throughput of water vapor through packaging films and barriers, there is a permeation test instrument to match.

So, what are the popular types of permeation test instruments? Well, our customers typically call on us to help them with different types of tests: oxygen permeation testing and water vapor permeation testing. And now we’ll take a little time to explore both.

Oxygen permeation testing and the water vapor permeation test

Most commonly found in the food and beverage industries, these testing methods are great for quality control of your package or packaging materials – a key consideration for food producers whose goods are packaged under a modified atmosphere; when it’s essential to limit oxygen in order to inhibit the growth of microorganisms. This will prolong shelf life and keep your customers healthy!

It may well be the life-giving gas, but oxygen has the potential to destroy aroma and vitamin C, and affect the taste of your products. Want to check the barrier properties of the films you have selected for your finished packaging and determine their oxygen permeability? It’s important to pick a high-quality oxygen permeation test.

The oxygen barrier properties of packaging materials have improved tremendously in recent years. Take polyethylene terephthalate (PET) for example. It’s a form of polyester that’s extruded – or molded – into plastic bottles and containers for packaging foods and beverages, personal care products, and many other consumer products. These days a PET bottle can achieve impressive results like 0.015 cm³/one liter bottle, per day.

Predominantly, people in industry measure the oxygen permeability of a film before it has been incorporated into the package – where the process of heating, stretching, and forming can affect its properties.

Our permeation testing guidebook allows you to access insights into the ways our affordable and accurate instruments allow you to accurately determine your oxygen transmission rate (OTR).

Water vapor permeation testing

It goes without saying that you don’t want water vapor to get through your packaging films and barriers. It’s obvious why you wouldn’t want this in the food sector – nobody likes soggy potato chips! But it’s also a vital and more demanding consideration for our customers who work with highly sensitive electronics in the automotive or aerospace sectors, for example.

 In order to measure water vapor permeability through a material, you’ll need to know the water vapor transmission rate (WVTR) or moisture vapor transmission rate (MVTR). Simply put, this permeation rate calculation shows you the mass of water vapor that is transmitted through a measured area in a specific unit of time under specified conditions of temperature and humidity.

 Water vapor analyzers enable you to achieve this. Today, most available instruments offer a wide measurement range of 0.002-1000 g/m²/day and precision temperature, humidity, and flow control. This enables you to achieve accurate and repeatable results. Whether you need them for research and development testing of the water transmission rate (wvtr) in both current and newly formulated packaging film materials, or for speedy quality control testing.

When undertaking a permeation rate calculation, it’s also really important to consider temperature and its impact on permeation rates. Even just a one-degree rise or fall in temperature can alter the results considerably. Our customers in the packaging industry are susceptible to this. So, correct temperature control during your experiments is vital in order to obtain accurate and repeatable results.

We can help with all of this. Industrial Physics has been helping clients with permeation testing, across multiple sectors, for over 30 years. Our versatile and easy-to-operate permeation instruments contain the highest-quality sensors on the market. They give you rapid results and accurate readings…even at the lowest levels.

Whether you need a permeation test to support your research and development or to enable effective quality control testing processes, we have the oxygen, gas, and water vapor permeation test devices to do the job – we can even help you with product development, third party analysis, or academic research services.

For more information, get in touch today!

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Techniques for water vapor permeation measurement

Traditionally a WVTR testing, and permeation rate calculation measurement system consists of a wet and adjacent dry chamber, separated by a sheet of barrier material. Observing ‘Fick’s Law’, strict control of the wet and dry environments can be used to calculate the water vapor transmission rate through a barrier. The law states that diffusion through a barrier is a linear function of the concentration gradient across the barrier and its thickness.

The most common sensing method for water vapor permeation measurement is the infrared (IR) light spectral absorption method.

NDIR (Non-Dispersive Infrared) is well established and is popular for permeation testing. It’s typically based on the absorption of a single optically filtered peak.

Further, the coulometric sensor option, the latest technology, the P₂0₅, with a new ASTMF3299-18 standard. It’s based on the electrolysis current of the water vapor absorbed in a hygroscopic material.

The calibration standards for water vapor measurement instruments

Most IR sensor-based permeation testing instruments have a characteristic response to water vapor concentration. This is down to the design of the instrument detector, which can be subject to drift over time. Consequently, such devices need regular calibration.

In contrast, the P₂0₅ coulometric sensors follow ‘Faraday’s Law’, which relates to the electrochemical dissociation of a water molecule to precisely two electrons; thereby providing a current which is absolutely related to water consumption levels.

Calibration standards are available in the form of traceable gas bottles, producing standards over the range of 5-2000 ppbv.

The differences in commercial water vapor measurement instruments

There are two classes of commercial permeation testing instruments for measuring water vapor transmission rate commonly available. These are the NDIR spectroscopic absorption designs and the coulometric instruments.

NDIR spectroscopic permeation testing instruments are not absolute, so periodic calibration against a standard will be necessary to combat any drift and to maintain accuracy.

Coulometric water vapor transmission rate measurement typically requires a little more housekeeping in the form of sensor maintenance, but beyond that, modern digital instruments are straightforward and user-friendly. Benefits include absolute measurements, directly related to the precise amount of water vapor transmitted, which don’t require the use of a standard. The latest instruments have already exceeded the sensitivity of the NDIR types, with further improvements within reach.