Common food sterilization processes include high-temperature sterilization, low-temperature sterilization, high-pressure sterilization, irradiation sterilization, microwave sterilization, UV sterilization and etc. Generally, the sterilization is carried out after the completion of food packaging, which means the materials used for packaging is also sterilized. This requires that when choosing sterilization process or selecting packaging materials, not only the influence of sterilization on food, but also the adaptability of packaging materials to sterilization process. The influence of packaging materials on sterilization and the influence of sterilization process on the properties of packaging materials should be taken into account to prevent the performance of materials from deterioration after sterilization. In this paper, the barrier properties of packaging materials after a certain sterilization process were studied.

Test Sample

In this test, a composite film containing PVDC material was used as the test sample to test the oxygen permeability of the sample before and after sterilization.

Standard

This test is based on the principle of coulometer method, and the test process is in accordance with ASTM D3985 – 17 “Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Sensor”.

Test Instrument

In this paper, C230H Oxygen Transmission Rate Test System is used. The equipment is independently developed and produced by Jinan Labthink Instruments Co., Ltd.

Test Principle

The coulometric method, also known as the equal-pressure method, is to monitor the electrical signal of oxygen participating in the electrochemical reaction to obtain the oxygen permeability and other parameters of the material. The upper and lower test chambers of the equipment are separated by the clamped sample. The upper chamber is filled with high-purity oxygen of a certain pressure, and the lower chamber is filled with high-purity nitrogen of the equal pressure to the upper chamber. Under the effect of concentration difference, the oxygen penetrates into the lower chamber from the upper chamber through the sample, and the nitrogen in the lower chamber carries the penetrated oxygen to the coulometric sensor for test and analysis. According to the correlation between the measured electric signal, the unit of oxygen and the electric signal generated by the electrochemical reaction, the amount of oxygen permeating through the sample per unit area in a certain time can be calculated, thus the oxygen transmission rate is obtained.

Figure 1 C230H Oxygen Transmission Rate Test System

Test process

(1) Use a sampler to cut three specimens from the sample before sterilization, and clamp the specimens in the three test chambers of the instrument.

(2) Set the parameter such as sample name, sample thickness, test temperature, humidity and test mode in the operating software. Click “test” to start the test. The equipment runs the test according to the set parameters, and displays the test results after the test.

(3) Follow the above steps to test the oxygen permeation of the sterilized sample.

Test result

Take the arithmetic mean of the test results of three samples as the oxygen permeability of each sample. In this test, the oxygen transmission of the sample before sterilization is16.432 cm³/ (m²·day), and that of the sample after sterilization is 11.934 cm³/ (m²·day).

Conclusion

In this experiment, the influence of sterilization process on the oxygen barrier properties of the material was obtained by comparing the oxygen transmission rate of the sample before and after sterilization. From the test results, the oxygen transmission rate of the sterilized sample is lower than that of the pre-sterilized sample, which indicates that the barrier performance of the sterilized sample to oxygen is improved, and that the temperature, pressure, radiation and other factors in the sterilization process may affect the molecular structure of the packaging material, and thus affect the barrier performance of the packaging material. The test process is simple and highly intelligent, the control of parameter in the test process is stable, and the test results accurate, which can truly reflect the oxygen barrier properties of the sample.

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