For packaging materials with the same material structure, the thickness of materials is an important factor affecting their barrier performance. With the increase of material thickness, the gas permeation path in packaging material is prolonged, and the time of gas permeating from one side to the other side of the sample is increased, the amount of gas permeated through the material reduces and the material gas barrier performance improves. However, the increase of material thickness comes with higher packaging cost and less environmental friendliness. Therefore, study on relationship between material thickness and barrier performance is necessary for balancing cost, environmental friendliness and barrier properties when choosing packaging materials. In this paper, the oxygen permeability of the same film with different thickness was measured, and the correlation diagram of thickness and oxygen permeability was made to evaluate the effect of thickness on the oxygen permeability of materials.

Test samples

In this study, the oxygen permeability of a single layer material with thickness of 10μm, 12μm, 15μm and 25μm was measured.

Test Standards

At present, the testing methods of oxygen permeability of flexible plastic packaging materials include differential pressure method and equal pressure method (coulometric method). 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 study VAC-V2 differential pressure method gas permeability tester is used, which is designed and produced by Jinan Labthink Instruments.

The principle of differential pressure method is to measure the change of pressure in tester chambers and calculate the material gas permeability. Clamp the sample in the test chamber to divide it into upper and lower chamber. 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 VAC-V2 Differential pressure gas permeability tester

Test Procedure

(1) Cut three specimens with a diameter of 97 mm from the sample with a thickness of 10 μm. Apply vacuum grease around the three test chambers of the equipment; place a piece of supporting filter paper in each chamber. Then clamp the three specimens in three test chambers respectively, and tighten the test chamber cover.

(2) The equipment is connected with oxygen source. Se the test parameters such as sample name, sample thickness, test temperature, humidity and test mode in the operation software. Turn on the vacuum pump and click start button to start a test. The equipment runs the test according to the set parameters, and the test results are displayed after the test.

(3) Follow the steps in (1) and (2) to test the oxygen permeability of the samples with thickness of 12 μm、15 μm、25 μm

Test results

The arithmetic average of the test results of the three specimens from each sample is the oxygen permeability of the sample. The oxygen permeability of samples with thickness of 10 μm, 12 μm, 15 μm and 25 μm were 84.608 cm³/(m²·24h·0.1MPa)、67.069 cm³/(m²·24h·0.1MPa)、56.483 cm³/(m²·24h·0.1MPa)、29.164 cm³/(m²·24h·0.1MPa) respectively. The correlation of sample thickness and its oxygen permeability is shown in figure 2.

Conclusion

The oxygen permeability of the same material with four different thickness was tested by VAC-V2 pressure differential gas permeability tester. The equipment is easy to operate, the test efficiency is high, and the test results is accurate. As shown in Figure 2, the oxygen permeability decreases with the increase of sample thickness, which indicates that the oxygen barrier performance of the sample increases with the increase of sample thickness. In addition, with the increase of sample thickness, the correlation of thickness and oxygen permeability reduces. When the sample is thin, the oxygen barrier performance of the sample increases with the increase of sample thickness. The improvement in oxygen barrier performance become smaller as the thickness increases

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