Oxygen Permeability Comparison of Different Packaging Films for fresh fruits and vegetables

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Abstract: oxygen permeability is an important reference index for the application of fresh fruits and vegetables packaging film materials. In this study, the oxygen permeability of three kinds of cling film samples are tested, and the factors affecting the oxygen permeability of the samples are compared and analyzed. This paper includes the introduction of the test principle, equipment parameters, application scope and test process, provides a reference for further studies on the oxygen permeability of cling films.

Keywords: oxygen permeability, cling film, differential pressure method, differential pressure gas permeability tester, fresh fruit and vegetable packaging

Fresh fruits and vegetables maintain a certain metabolism such as respiration after picking. Respiration is the process of decomposing the substrate of fruits and vegetables to produce small molecular substances. When aerobic respiration occurs, carbon dioxide, water and heat are produced. When anaerobic respiration occurs, alcohol, carbon dioxide and heat are produced. Alcohol accumulating in fruits and vegetables will affect its appearance and damage its nutritional value. In order to ensure the freshness of fruits and vegetables, it is necessary to inhibit the respiration, especially anaerobic respiration, to retain its high nutrition. The fresh-keeping technology of fresh fruits and vegetables includes physical, chemical and biological methods. Packaging technology is an important part of them, and plastic film is the main material of fresh fruits and vegetables packaging. In order to maintain the texture, flavor and nutrition of fresh fruits and vegetables, the packaging materials of fresh fruits and vegetables should have appropriate oxygen permeability and high carbon dioxide permeability, so as to inhibit anaerobic respiration, control aerobic respiration and timely discharge carbon dioxide generated by respiration.

In this experiment, three kinds of fresh fruits and vegetables packaging cling films were selected as test samples numbered as 1#, 2# and 3# respectively, of which 2# and 3# were modified materials. The purpose of this test is to compare the oxygen permeability of the three samples. Because the permeability is relatively high, the principle of differential pressure method is adopted. The test process is conducted in accordance with ISO 15105-1:2007 Plastics — Film and sheeting — Determination of gas-transmission rate — Part 1: Differential-pressure methods.

In order to improve the efficiency of the test, this paper uses the VAC-V2 Differential Pressure Gas Permeability Tester, which can test three kinds of samples at the same time. The isntrument is independently developed and produced by Jinan Labthink Instruments Co., Ltd.

The principle of differential pressure method determines the gas transmission rate of a film under a differential pressure by using a pressure sensor. The pressure difference is the drive for the gas permeation, and the pressure sensor measures the change of the gas pressure. When the volume and temperature are fixed, the gas pressure is directly proportional to the gas quantity. Therefore, according to the change of gas pressure, the change of gas quantity can be obtained. When the specimen is mounted in the gas diffusion cell to form a sealed barrier between two chambers, the lower-pressure chamber is firstly evacuated, followed by the evacuation of the entire cell. A flow of gas is thereafter introduced into the evacuated higher-pressure chamber and a constant pressure difference is generated between two chambers. The gas permeates through the specimen from the higher pressure side into the lower side. The gas permeability and other barrier properties of the specimen can be obtained by monitoring the pressure changes in the lower chamber, the gas permeability of the sample can then be obtained by the test.

Figure 1 VAC-V2 Differential Pressure Gas Permeability Tester

(1) Cut one specimen with a diameter of 97mm from each surface of the three samples.

(2) Apply the vacuum grease around the three test chambers of the equipment, place filter paper and sample on each test chamber, gently press the contact part between the sample and the test chamber, remove the air bubble and then tighten the test chamber cover.

(3) Connect the oxygen source. Set parameter information such as sample name, thickness, test temperature, humidity and test mode, open the vacuum pump, click test button to start the test. The instrument is run according to the set parameters, and the test results are displayed after the test.

The oxygen permeability samples 1#, 2# and 3# were 712.8cm³/(m²·24h·0.1MPa),5947.3 cm³/(m²·24h·0.1MPa) and 4637.3 cm³/(m²·24h·0.1MPa) respectively.

The test is operable and efficient; the test result is accurate and reliable. The result shows that  the oxygen permeability of the three samples from high to low 2#, 3# and 1#. The oxygen permeability of samples 2# and 3# is significantly higher than that of sample 1#, could be related to the addition of the modified materials in samples 2# and 3#, because the presence of the modified materials increases the oxygen permeance channel in the materials. The type and amount of the modified materials will affect the permeability of the he materials, so the oxygen permeability of 2# and 3# samples are different.

In addition to oxygen transmission, the instrument used in this paper can also be used to test the carbon dioxide transmission of fresh fruit and vegetable packaging film.