Barrier properties of packaging materials are important requirements to consider when selecting and developing optimal packaging systems. Packaging materials could prevent ingress of oxygen and/or moisture, they could keep desired balance of oxygen and carbon dioxide (CO2) and they could prevent loss or ingress of flavours and solvents.

Our web based calculator for barrier properties was developed by a team of Norner experts and is a tool for making simulations in the packaging design phase. By using this calculator, the developer can investigate changes in design and layer structures without expensive testing in a screening phase. 

It will also be possible to reduce instrumented testing of permeability and actual testing of shelf life in the development phase. 

The simulation model estimates the oxygen transmission rate (OTR) and water vapour transmission rate (WVTR) of packages by most plastic materials like PE, PP, PET, PA and EVOH. Barrier properties of co-injection or co-extruded multilayer and in-mould-label solutions can be studied and evaluated for cups, bottles, films and square containers.

The flexibility of geometrical options, permeability properties and environmental conditions provides a useful tool for design, development and application of plastic packaging.

The shelf life of a food product is the period between the manufacture and the retail purchase, during which time the product is of satisfactory quality in terms of nutritional value, flavour, texture, appearance and safety.

The shelf life of a food product is depending on the “activity” of the product, the environment in the value chain and distribution, especially the temperature as well as the properties of the packaging system, especially the permeability.

New barrier features - constant CO2 concentration and declining CO2 concentration (as in MAP)

Norner has now upgraded this web based calculator with CO2 transmission rate calculators. Two new models have been developed for calculation; one is for a constant CO2 concentration on one side and the other is for a declining CO2 concentration (as in MAP). 

A second upgrade is the possibility to calculate the permeability for a sequence of different conditions, i.e. a dynamic simulation of the packaging. This allows the user to simulate the variations in conditions in the value chain. 

The dashboard and web interphase is also redesigned and the calculators are available both in a full version, which is payable, and a free simplified version. 

A wider selection of materials, unlimited number of layers for extruded films and blown articles, unlimited number of layers for cup and square boxes as well as IML and an unlimited number of conditions calculated in a sequence is available in the payable version.

Fig 1: Example 1 - Loss of CO2 pressure in a MAP tray made from 100µm plain PP with initial concetration of 80% CO2. 

Examples 

1 - Modified atmosphere packaging

Modified atmosphere is the practice of modifying the gas composition of the internal atmosphere of a package (MAP) to improve shelf life. For instance, the use of gas mixtures with relatively high levels of CO2 can double the shelf life of raw poultry.

In this example, poultry is MAP-packed with 80% CO2 in a thermoformed tray (20x10x5 cm) with a lidding film consisting of decorated aluminium foil. Since the logistics is cold and low permeation can be expected, a plain 100 µm PP tray was tested versus a barrier tray consisting of 40µmPE/4µmTIE/5µmPA6/3µmEVOH32/5µmPA6/4µmTIE/40µmPE. Loss of CO2 pressure in the plain PP tray as a function of time is illustrated in the figure on previous page. 

The figure show only a minor loss of CO2 in the plain PP tray. For the barrier tray the loss of CO2 is insignificant and the MAP atmosphere is constant during the 20 days we selected for these calculations. At the same time, the barrier towards oxygen was calculated using the OTR calculator. The results show that the plain PP tray has total transmission of 30 ml versus 0,13 ml for the barrier tray. 

The balance of MAP gases and oxygen transmission is the key to keep the food fresh and it can be expected that the plain PP in this example is sufficient to retain the CO2/MAP gas, but insufficient to keep the oxygen transmission sufficiently low. 

2 - Packed meat

The quality of meat is affected by the presence of oxygen. This effect is further influenced by temperature and temperature is known to vary through the logistic chain from producer via retailer to consumer.

This example describes a logistic chain comprising storage at producer, transportation to retailer, storage at retailer, transportation to consumer and storage at consumer. We have  assumed that temperatures alter between 4 and 20°C. An oxygen limit of 1 ml is further defined. It is interesting to compare the barrier performance of a multilayer and a monolayer film.  

We have defined a costly a but common 7-layer PE/PA/EVOH film structure with the following composition; [40µmPE/4µmTIE/5µmPA6/3µmEVOH32/5µmPA6/4µmTIE/40µmPE].

As a cheaper alternative solution, a thermoformed monolayer PET tray, 200 microns, is defined. The oxygen transmissions during the logistic chain over a period of 22 days is calculated and given in the figures below.

These examples illustrate that an acceptable shelf life for the defined oxygen limit is achieved for the 7-layer PE/PA/EVOH film structure, while for the monolayer thermoformed PET is insufficient since the oxygen limit is reached already at the producer.