Substrate Secrets

Question: What would you suggest as a method to measure the barriers of the final closed package?

Answer: This is a great question as ultimately the protection provided by the package will be the package barrier as opposed to simply the flat sheet film barrier.  There are several was to measure total package barrier and they are generally related to the rate of leaking or gas exchange from or to the sealed bag.  There are several companies which supply package leak detection and they are generally based on pressurizing the package (positive pressure or vacuum) to detect leaks.  Another method is to measure head space inside the bag as a function of time.  You can find such instrument systems at www.mocon.com and a presentation titled “Shelf-Life Evaluation: Combining Barrier And Package Integrity Measurement To Successfully Achieve A Viable System” can be downloaded from  http://www.meatandpoultryonline.com/article.mvc/Shelf-Life-Evaluation-Combining-Barrier-And-P-0002?VNETCOOKIE=NO 

Ignoring for a moment the presence of pin holes in the face of the bag, in order to start with a package barrier test it is important to determine if the package seals are air tight (Hermetic).  A simple way to look for leaks is to submerge the sealed package under water, place a weight on the package and examines the seals for leaks as bubbles will be visible (much like finding a hole in a bicycle tire).   For a small bag (20cmx12cm) it was customary to use a 5 kg weight to pressurize the package.  In general leaks will be present at the center seal (lap of fin) and the corner seals.  The rate and number of leaks is dependent on the film design (Morgan & Mount, US Patent 5,049,436) and the set up of the packaging machine seal bars.

The package barrier measurements above measure the presence of leaks and can determine the rate of leaking.  This information has to be correlated with shelf life testing to determine the correlation to the test and the package performance for a given product.  A more direct way to measure package barrier is to measure head space concentration of the gas of interest (for example water, oxygen or Carbon dioxide) in the bag as a function of time when placed in a particular environment.  I will describe these measurements in a separate posting as well as how to compare these results with the flat film barriers against a sealed bag.  This can give insights to the quality of the seals or the impact of the package formation on the final package barrier.