How to test the breathability of food packaging bags? These are what you need to know

As we all know, oxygen has a great impact on the quality of food. Some food packaging (such as carbonated drinks and coffee) also have strict requirements on the permeability of carbon dioxide. Therefore, controlling the permeability of food packaging materials and the content of organic gases inside the packaging has become one of the main tasks of food packaging.

Below, Shunxingyuan Packaging, a professional flexible packaging manufacturer, will analyze the impact of the permeability of food packaging bags on food based on its experience, and briefly introduce how to test the permeability of food packaging bags.

I. The impact of gas permeability on the quality of food contents

1. Cause the oil in the food to oxidize. This oxidation can occur even at low temperatures. The peroxides produced by oil oxidation not only make the food lose its edible value, but also cause strange smells and produce toxic substances.

2. Most bacteria in food multiply and grow due to the presence of oxygen, causing food spoilage.

3. If necessary protective measures are not taken during the storage and transportation of fresh fruits and vegetables, the fruits and vegetables will absorb oxygen and release carbon dioxide and water due to respiration, and consume some nutrients, resulting in overripe, softening, and changes in flavor of vegetables and fruits.

4. At room temperature, the reaction rate of oxidative browning is much faster than that of heat browning. For flavor foods, such as concentrated broth and foods that are easily oxidized and browned, even a small amount of residual oxygen can cause browning, causing the food to lose its flavor or deteriorate.

5. In addition to being sensitive to oxygen, carbonated drinks, beer, coffee, juice and other products are also greatly affected by carbon dioxide.

II. Introduction to the main methods of permeability testing

In order to prevent the above situations, it is necessary to conduct permeability tests on food packaging to ensure the gas barrier performance of the packaging materials. According to the testing principle, the permeability testing methods can be divided into two categories: pressure difference method and coulometric sensor method.

1. Pressure difference method testing principle

The test chamber is divided into two independent spaces by the film to be tested. The test gas is filled into one side (high-pressure chamber), and a certain pressure difference is formed on both sides of the sample. The gas in the high-pressure chamber permeates through the film into the low-pressure chamber. By measuring the pressure or volume change in the low-pressure chamber, the permeability of the gas can be obtained.

2. Coulometric sensor method testing principle

The test chamber is divided into two independent gas flow systems by the film to be tested. One side is the flowing test gas (pure oxygen or oxygen-containing mixed gas can be used, and the relative humidity of the gas can be set), and the other side is the flowing nitrogen. The pressure difference on both sides of the sample is equal, but the oxygen partial pressure is different. Under the action of the concentration difference, the oxygen passing through the film is sent to the coulometric sensor by the nitrogen flow, so that the oxygen permeability of the material can be calculated.

The testing principles of the pressure difference method and the isobaric method are different, the testing conditions are different, and the units of the test results are also different (the unit of the pressure difference method is cm3/m2• 24h • 0.1MPa ，and the unit of the isobaric method is cm3/m2 • d ), so the uncorrected original data obtained from these two testing methods are theoretically not comparable. However, after using the standard membrane to calibrate the isobaric method equipment and applying the correction factor to the formal test, the test results of the pressure difference method and the isobaric method can be compared.

Due to the support of membrane technology theory, the pressure difference method has been used as a basic method in permeability testing. Scientific research and testing institutions mostly use this method. Its outstanding advantage is that it has no selectivity for the test gas, and it has very good versatility for different test gases. With the advancement of vacuum gauge detection technology and the application of vacuum technology in equipment design, the detection accuracy and repeatability of test data have been greatly improved.

The sensor method emerged with the continuous maturity of oxygen detector technology. Because the sensor used is a consumable component, the correction factor obtained from equipment calibration is not valid for a long time, and periodic equipment calibration needs to be performed according to requirements. Moreover, the sensor must be replaced when the consumption reaches a certain level.