Study on the Relation between Gas Composition in Nitrogen-Filled Packaging and Packaging Materials Barrier Properties

Abstract: Nitrogen-filled packaging is an important measure to prevent oxidative deterioration of food and medicine. In this paper, the effects of the packaging materials barrier properties on the quality of nitrogen-filled packaging are analyzed by testing the gas composition in nitrogen-filled packaging and the packaging materials barrier properties. The test principle, parameters, application and test procedure, the used headspace analyzer and differential pressure gas permeability tester are introduced, so as to provide reference for monitoring the quality of nitrogen-filled packaging.

Keywords: nitrogen-filled packaging, packaging materials, barrier properties, headspace analyzer, differential pressure gas permeability tester, gas composition, oxygen permeability, nitrogen permeability

Nitrogen is an inert gas, it is not prone to react with other substances, and can inhibit the growth and reproduction of most microorganisms. Nitrogen is often filled into product packaging to prevent oxidative deterioration and mildew. The quality-keeping effect of nitrogen-filled packaging is related to the content of nitrogen in the packaging. High concentration nitrogen can keep the product quality for a long time, when the content of nitrogen is reduced to a certain level, the quality-keeping effect will be lost. Nitrogen content in packaging is not only related to the purity of filled nitrogen, but also to the barrier and sealing properties of packaging materials. The deterioration and mildew of products packed in nitrogen-filled packages is possibly due to the poor barrier of packaging.

Test Sample

This study took a cake nitrogen-filled package as the sample. The gas composition in the package after storage for a certain time, and the nitrogen and oxygen permeability of the packaging material were tested.

Standard

Differential pressure method is used to measure the permeability of different gases. The test process is based on ASTM D1434 Standard Test Method for Determining Gas Permeability Characteristics of Plastic Film and Sheeting.

Test instrument

In this paper, HGA-02 headspace gas analyzer is used to analyze the gas composition in the sample package, and VAC-V2 pressure differential gas permeability tester to test the gas permeability of the packaging material. These two equipments are independently developed and manufactured by Jinan Labthink Instruments Co., Ltd.

Test principle

Oxygen, carbon dioxide and nitrogen are the common filling gases in the packaging of food and pharmaceutical products. Oxygen sensor and carbon dioxide sensor are equipped in the headspace analyzer. The oxygen and carbon dioxide content in packaging can be accurately measured and the nitrogen content can be calculated accordingly.

The principle of differential pressure method assumes that when the volume and temperature are constant, the gas pressure is proportional to the gas volume. The test chamber is divided into upper and lower parts by the clamped sample. The upper chamber is filled with test gas under certain pressure. The volume of the lower chamber is fixed and known, and a low pressure environment is formed by vacuum pumping. During the test, the gas in upper chamber permeates into the lower chamber through the sample, results in the increase of the pressure in the lower chamber. The pressure sensor in the lower chamber monitors the increase of pressure in real time, and calculates the amount of gas permeated through the certain area of the sample in certain time.

Figure1  HGA-02 Headspace gas analyzer

Figure2  VAC-V2 Different pressure gas permeability tester

Test procedure

gas composition test

(1) Turn on the equipment and set the test parameters such as sampling time and analysis time.

(2) Randomly pick six nitrogen-filled packages sample. Paste a gasket in the middle of the sample. Insert the sampling needle through the gasket into the sample package. Watch for the sampling needle not touch the cake packed inside the sample.

(3) Press the test button and start the test. The gas in the sample enters the equipment through the sampling needle and is analyzed by gas analyzer. The equipment automatically displays the content of oxygen and carbon dioxide in the tested samples when the test is completed.

Gas permeability test

(1) Cut three samples with a diameter of 97 mm from the surface of the package sample. Apply a layer of vacuum grease around the test area of the test chamber, pay attention to the vacuum grease not to touch the test area, then place filter paper and sample in turn, and seal tight the upper chamber.

(2) Connect the equipment with oxygen source. Set test temperature, test humidity, sample thickness and other parameters, click the test button to start the test and turn on the vacuum pump. The equipment automatically calculates and displays the test results.

(3) After the oxygen permeability test is completed, reconnect the equipment with the nitrogen gas source, set parameters, turn the vacuum pump and carries on the test.

Test results

The arithmetic average of the test results of each sample is obtained. After storage for a period of time, the oxygen content and carbon dioxide content in the sample packaging were 16.4% and 0%, respectively, and the nitrogen content was 83.6%. The oxygen permeability of the packaging materials was 716.534 cm³/(m²·24h·0.1MPa) and the nitrogen permeability was 168.247 cm³/(m²·24h·0.1MPa).

Conclusion

The operation of the two equipments is simple; the test is efficient, stable and accurate. The test results reflect the gas composition in the tested samples package and the nitrogen and oxygen barrier properties of the packaging materials. The test result shows that the gas permeability of the packaging materials is high; the barrier ability of nitrogen and oxygen is low. It could be assumed that the gas composition in the packaging would gradually change. This assumption is verified by the test result of the gas composition in the package verified. After storage for a period of time, the gas composition in packaging changed greatly, oxygen content increased significantly, while nitrogen content decreased, which greatly reduced the expected quality assurance effect of nitrogen-filled packaging. In conclusion, nitrogen-filled packaging materials should have high barrier properties.

Labthink Instruments Co., Ltd, is dedicated to providing customers with packaging testing solutions and helping the manufacturers to reach their goals of quality and safety assurance through improvement of packaging testing techniques and development of high-end packaging testing instruments. With 30 years of experience in R&D, production and test, under the guidance of advanced sensor technology and design concept, Labthink developed a new generation of C-series barrier testing equipment. C- Series testing equipment adopts self-determination sensor technology, achieves a revolutionary upgrading in accuracy, efficiency and automation, and realized the paradigm shift of packaging barrier testing instruments. For more information please visit www.labthink.com