Measuring the oxygen transmission rate on PET bottle caps

Oxygen is a life-giving gas in the atmosphere, but when too much gets through a PET bottle, it can ruin the taste, aroma, vitamin C content, and carbonation of the beverage contained (footnotes 1,2,4). 

PET bottle testing is important. Once inside, oxygen causes chemical processes that decrease shelf life. If you encounter an oxygen permeation problem with your PET bottles it can lead to product recalls, expense, wasted time, and reputational damage.  

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To combat this, soft drinks manufacturers need precise knowledge about the composition of packaging materials, oxygen permeation and the interaction between oxygen, the packaging and the beverage. 

When it comes to controlling oxygen permeation, proactivity is key. Perform the right PET bottle quality checks and analyze your raw materials properly now, and you’ll avoid problems later. 

The importance of oxygen transmission rate testing

Packaging is there to ensure adequate protection and stability for a beverage throughout its shelf life. Oxygen transmission rate testing helps you understand how different PET bottle samples and finished products perform.  

The molecular structure of PET only offers a sufficient barrier against oxygen ingress and loss of CO2 for a given amount of time. So, it’s important to match the permeability of the PET bottles you want to use (material, seals, closures) with the sensitivity and shelf life of your beverages. 

Oxygen transmission rate testing is a well-established method to test the barrier properties of PET bottles and caps. We can supply all of the PET bottle testing equipment you need. 

Systech PET bottle testing

Systech is our oxygen, gas, and moisture analysis specialist brand. Through Systech, we manufacture high sensitivity, trace oxygen and moisture sensors and systems for use in measuring gas transfer rates in packaging materials, modified atmosphere gas detection and analysis and process gas applications.  

Our PET bottle testing equipment provides high sensitivity and repeatable test systems to meet the requirements of international testing standards and the needs of our plastic, food, pharmaceutical, medical device and industrial customers.

Through Systech we make industry leading oxygen transmission rate testing devices such as the Systech OxySense® 8101e and the Systech OxySense 8107 oxygen transmission rate analyzers. If you want to ensure the highest quality in your PET bottles, check out our full range of Systech plastic bottle testing equipment.
  

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The progression of PET bottle performance

In recent years, packaging materials have improved tremendously with respect to their oxygen barrier properties. The oxygen permeation barrier of a one-liter PET bottle is now down to 0,015 cm³/bottle per day (footnote 3). 

But despite the fact that the packaging material is being down graded with less material used, the oxygen permeation barrier properties are being improved to extend product shelf life. As the packages become more sophisticated, it’s wise to analyze each area of the package separately in order to understand where the oxygen permeation occurs. 

Testing bottle caps and closures

Although caps and closures equate to only 0.5% to 6% of the total package, it’s worthwhile to check their contribution to any oxygen permeation. The rest of this article covers ideas and guidelines regarding the testing of caps and closures with respect to their oxygen transmission rate contribution of the package. 

There are several challenging tasks that bottle caps need to perform: 

• It should be easy to open 

• It must be tamper proof 

• It must be tight under all conditions for transportation and storage 

• Its integration into the complete package 

Oxygen permeation testing is a well-established method to test the barrier properties of films and packages. Systech test and measurement equipment enables you to focus on the PET bottle cap itself as well as the other package components. 

When inspecting the cap during PET bottle testing, it’s important to understand that the closure must be tested under the same or very similar conditions to where it fulfills its task. That means a cap should be tested on the thread of the bottle and the closure of  a carton package should be tested when connected to the package material. Therefore, a bottle closure is tested with a bottle neck cut off from a preform. 

It’s also important when PET bottle testing to measure a preform neck together with an aluminum top. The results will be used to determine the oxygen permeation rate of the cap independently from the permeation rate of the threaded region of the preform.  

In most cases, a preform with a suitable thread from any supplier can be used as a standard for testing cap modifications. However, for a final permeation result, it’s better to test with a preform that’s later blown into the bottle – together with the correct cap selected for the finished product. This eliminates variations in the selection of the PET masterbatch. However, the interface between the closure and a carton package is highly sophisticated, and it’s best to include this area in the oxygen transmission rate. 

Permeation testing carton packages

The closure of a carton package is prepared for an oxygen transmission rate procedure by cutting out the closure from the package, without opening or breaking the seal. This is important because most closures have a double seal and/or a tamper proof feature that enhances the barrier.  

Once opened, the barrier performance will be altered from the sealed condition. The cut-out will include the cardboard, as the integration of the closure into the carton material is part of the sophisticated technology. Therefore, it makes sense to test it in this condition. The cut out is glued (using a two-part epoxy resin) into a mask made from  aluminum foil, for a perfect oxygen barrier. 

Permeation rate detection threshold of 4E-05 cm³/pack a day.

Systechs’ state of the art oxygen permeation rate analyzers are capable of testing the oxygen barrier properties of packages with a detection threshold of 4E-05 cm³/pack a day. Several different packages from various supermarket shelves have been used for permeation testing. The oxygen transmission rates for the closures have been measured in the range between 0,25 and 0,01 cm³/cap day. It does not cover all available systems – this is simply a demonstration of how the test principle works. 

In the case of bottle caps, the bottlenecks with the caps and the preform threads with the aluminum shims are glued directly on the platen of the permeation analyser. Using a rapid setting epoxy resin, sealing the caps and preforms onto the platen is a quick and simple procedure. 

All the cap samples and preforms used in our plastic bottle testing were collected from recent packaging industry shows and exhibitions. The pairing of the caps to the preforms was done arbitrarily. In this case study, it’s the test principle and the description of the procedure that  is of interest. The variety of available cap systems in the market cannot be measured in the frame of an application report.  

Oxygen transmission rates for this random selection of caps have been measured between 8,3 E-02 and 1,47E-02 cm³/cap and day, including a contribution from the preform neck in the range of 2,6 and 2,16 E-03 cm³/neck day. 

Testing beer packaging

When focusing on beer packaging, the PET/glass discussion is always accompanied by the crown cork as the preferred closure for glass bottles. Oxygen permeation rates are detectable, although the metal of the crown cork and the glass bottle are perfect barriers. A detailed measurement showed values of typical 1 x10E-03 cm³/cap/day (footnote 5). 

Footnotes 

1. Modeling of Oxygen Diffusion through a Model Permeable Package and Simultaneous Degradation of Vitamin C in Apple Juice. F. H. Barront, 6. Hart#*, J. GiacinS and R. Hernandez* 

Food Science and Packaging Department. Clemson University, Clemson, SC 29634, USA; SSch 

PACKAGING TECHNOLOGY AND SCIENCE VOL 6 301-309 (1993)] 

1.  The role of oxygen in brewing. The BREWER International • www.igb.org.uk • March 2002, p45 

1. Courtesy of KHS Plasmax Hamburg 

1. Vitamin C contents of citrus fruit and their products: a review. Nagy, Steven, Florida Dep. of Citrus, Agric. Res. & Education Cent., Lake Alfred, Florida 33850, USA. 1980 Journal-of-Agricultural-and-Food-Chemistry; 28 (1) 8-18, many ref. 

1. 5. Untersuchung der Permeation von Sauerstoff durch EPT Flaschen Bachelorarbeit. Thomas Meier, Verpackungstechnick/Packaging Technology der Technischen Fachhockschule Berlin, University of Applied Sciences. 

February 2014 

By Peter Heumeller, Business Friends Market Entry Consultants, Wachtberg, Germany and Graham Jennings, Systech, Thame, UK. 

Experts in plastic bottle testing

We’ve learnt a thing or two about oxygen transmission rate testing over the decades.  Industrial Physics is now recognized as a brand that likes to bring new, innovative PET bottle testing equipment to market. 

Ensure accuracy and productivity at lower costs with our oxygen permeation testing options. Find out more by downloading our guidebook: ‘How our permeation equipment works for you’.  

Then, you could check out this blog on permeation testing and the barriers – what can be measured…and why? Or, read about this innovative method for analyzing oxygen permeation of packaging film. 

If you’re interested in learning more about our range of oxygen transmission rate testing equipment, then just get in touch! 

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