The basic principle of warm paste’s mechanism is to convert chemical energy into heat through the oxidation-reduction reaction participated by oxygen. The amount of oxygen is an important factor affecting the rate of the reaction. A large amount of oxygen will result in strong reactions and release a large amount of heat in a short time, while a small amount of oxygen will release less heat. Therefore, the outer package of warm paste should have high oxygen blocking performance, which can effectively barrier the oxygen contacted with warm paste during storage. The inner package should have appropriate oxygen permeability, which can not only prevent the skin from scalding due to a large amount of heat released in a short time, but also avoid low temperature due to slow heat release. The purpose of this paper is to test the oxygen permeability of the inner packaging used for warm paste.

Test sample

In this experiment, a brand of non-woven fabric for inner packaging of warm paste was selected as the test sample to test its oxygen transmission rate.

The test method of oxygen permeability of materials includes two principle: differential pressure method and coulometric method (isobaric method). Because the oxygen permeability of the tested sample is relatively high, the principle of differential pressure method is adopted to test the sample. The test process is designed base on ISO 2556 – Plastics — Determination of the gas transmission rate of films and thin sheets under atmospheric pressure — Manometric method.

Test instrument

In this paper, VAC-V1 Differential Pressure Gas Permeability Tester is used as the test instrument, which is independently developed and produced by Jinan Labthink Instruments Co., Ltd.

The principle of pressure difference method is to control the pressure on both sides of the sample to form a certain pressure difference, then monitor the pressure rise on the low-pressure side, and calculate the gas transmission of the material. The test chamber of the instrument is divided into upper and lower chambers by the clamped sample. The upper chamber is filled with test gas of certain pressure. The lower chamber forms a low-pressure environment by vacuumizing. The test gas penetrates into the lower chamber from the upper chamber through the sample, causing the gas pressure in the lower chamber to rise. The gas transmission of the sample is obtained by monitoring the gas pressure in the lower chamber as the penetration time increases.

Figure 1 VAC-V1 Differential Pressure Gas Permeability Tester

Test process

Because the permeability of the tested sample is high and the transmission is beyond the standard test range of the instrument, this test adopts small transmission area and lower chamber expansion volume.

(1) Cut a 40 mm diameter sample from the sample surface, evenly apply a layer of vacuum grease around the test area, clamp the sample on the test chamber of the instrument, and tighten the upper cover of the test chamber.

(2) Set the sample name, test area, test temperature and other parameter information in the control software of the instrument, click the test option, start the test, and turn on the vacuum pump. The instrument is tested according to the set parameters, and the test results are displayed after the test.

Test result

In the oxygen transmission rate of the inner packaging material for the tested warm paste is 7.634×10⁷ cm³/(m²·24h·0.1MPa).

Conclusion

It is an important factor to use packaging materials with the appropriate oxygen permeability as the inner package of warm paste to ensure the proper temperature and effective time of warm paste. This paper introduced the test method of measuring the gas permeability of high permeability materials by testing the oxygen transmission rate of the inner packaging bag samples of a brand of warm paste. The test process is simple, the instrument is easy to operate, the test range is high, the accuracy of the test results is good, and it can reflect the oxygen permeability into the inner packaging in unit time.