Influence of Test Temperature on Nitrogen Permeability of Materials

Abstract: Nitrogen permeability is an important factor affecting the preservation ability of packaging materials filled with nitrogen. This paper evaluates the influence of temperature on the nitrogen preservation ability of packaging materials by testing the nitrogen permeability at different temperatures, and introduces the test principle, the parameters and application scope of VAC-V2 Gas Permeability Tester, and the test process, provides enterprises with a reference to control the packaging materials nitrogen permeability.

Keywords: nitrogen permeability, temperature, differential pressure, differential pressure gas permeability tester, packaging materials

Nitrogen is an inert gas, which hardly reacts with other substances at room temperature. Therefore, it is often used as a protective gas to fill packaging, such as infusion bags, milk powder bags, potatochips bags, snicks bags, etc. The packaging of this kind of products is usually filled with nitrogen to prevent oxidation deterioration of products, and inhibit the growth and reproduction of microorganisms and prevent mildew. In addition, nitrogen in packaging also has a certain cushioning effect, which can prevent the product from deforming or breaking when it is crushed or dropped by external force.

To ensure the nitrogen-filled packaging can fully carry out the protective functions, packaging materials should have good nitrogen preservation ability so as to effectively prevent the loss of nitrogen in the packaging. Influencing factors of nitrogen permeability in packaging materials include packaging material structure, thickness, environmental temperature, humidity and so on. This paper studies the influence of temperature on nitrogen permeability of packaging materials by testing nitrogen permeability of the same materials at different temperatures.

Test sample

This study tests the nitrogen permeability of KPA / CPP packaging materials at different temperatures.

Test standard

The present methods for measuring gas permeability of flexible plastic packaging materials include isobaric method (Coulometric method) and differential pressure method. The principle of isobaric method is limited by the types of sensors and can only be used to measure oxygen permeability. Therefore, this experiment adopts the principle of differential pressure method. The test process is based on GB/T 1038-2000 ” Plastics–Film and sheeting–Determination of gas transmission–Differential-pressure method”.

Test instrument

This paper uses VAC-V2 gas permeability tester to measure the nitrogen permeability of samples. The instrument is independently developed and manufactured by Jinan Labthink Instruments Co., Ltd.

Test principle

The principle of differential pressure method is that the gas permeability of the sample is obtained by monitoring the change of gas pressure over time. Therefore, the type of the test gas is not limited by the sensor, and can be applied to the measurement of oxygen, nitrogen, carbon dioxide, air, helium, sulfur hexafluoride and other gases. During the test, the test chamber is divided into two chambers by clamped the specimen: the upper chamber and the lower chamber. The upper chamber is filled with a certain pressure of test gas, and the lower chamber is vacuumed to form a low-pressure environment. The test gas permeates through the specimen from the upper chamber to the lower chamber, which causes the change of the pressure in the lower chamber. The pressure sensor monitors the change of the pressure in the lower chamber in real time, and then obtains the gas permeability and other parameters of the sample.

图1 VAC-V2压差法气体渗透仪

Figure 1 VAC-V2 Gas Permeability Tester

Test procedure

(1) Three specimens with a diameter of 97 mm were cut from the surface of the sample.

(2) Apply a layer of vacuum grease evenly around the test area of the test chambers, and place a piece of filter paper in each test area. Three specimens were pasted on the test chamber respectively, and gently pressed to remove the bubbles in the contact area, clamping the cover of the test chamber.

(3) Connect the instrument with the nitrogen gas source. Set the sample name, thickness, test temperature and humidity. Click on the test button to start the test. The equipment carries out the test according to the set parameters, and shows the nitrogen permeability and other results when the test is finished.

(4) Repeat to the above steps, measure the nitrogen permeability of the samples at 23℃、40℃ respectively.

Test results

Nitrogen permeability of the sample was 0.974 cm³/(m²·24h·0.1MPa) at the temperature of 23℃,  and 2.162 cm³/(m²·24h·0.1MPa) at the temperature of 40℃.

Conclusion

In conclusion, the test results are accurate and reliable. Compared with the test results at 23℃, the nitrogen permeability of KPA/CPP samples at 40℃ is obviously higher, which indicates that the material’s nitrogen permeability increases and nitrogen barrier ability decreases with the increase of temperature. In terms of the test process, the instrument is easy to operate. Three identical or different samples can be tested simultaneously, the test efficiency is hugely improved.