Oxygen permeability test of packaging containers based on ASTM F1307

With the rapid development of the packaging industry, lightweight and easily transportable packaging containers, such as PET plastic bottles, paper-plastic aluminum composite flexible packaging, and other new materials gradually replaced bulky, fragile glass bottle packaging. However, the performance of these new packaging materials, especially Is the barrier performance meeting the quality requirements of the product packaging? This is a topic of common concern for consumers, users and manufacturers of packaging products, and quality inspection agencies at all levels, and it is also an urgent problem to be solved. At present, there is no clear standard for oxygen permeability testing of packaging materials. Therefore, ASTM F 1307 standard is generally followed when related tests are performed.

In this paper, the ASTM F 1307 standard is introduced to briefly introduce the oxygen permeability test of packaging containers.

First, the scope of application

ASTM F 1307 discusses a test method for determining the steady permeation rate of oxygen permeation into a package. More specifically, this test method is applicable to all packages that can seal up a dry space during normal use.

Second, the test method summary

ASTM F 1307 uses a Coulomb oxygen sensor and related equipment in a manner similar to ASTM D 3985. Oxygen transmission rate (O2GTR) is measured after the package is mounted on the test device and equilibrated in the test environment. Oxygen was used as the test gas and nitrogen as the carrier gas. After the package is clamped, the following test environment can be established: the inside of the package is slowly purged with a nitrogen stream and the outside is exposed to an environment where the oxygen concentration is known (eg in an atmosphere with a known oxygen concentration, or at 100% In an oxygen environment). The inside and outside of the package form a certain oxygen concentration difference, the outside is the side with high oxygen concentration, and the inside is the side with low oxygen concentration. During the whole infiltration process, oxygen penetrates through the wall of the packaging from the outside of the packaging to the inside, and then it It will be carried by the carrier gas flow to the Coulomb sensor. The Coulomb sensor detects that oxygen will output current, and the current is proportional to the total amount of oxygen flowing into the sensor per unit time.

Third, packaging oxygen permeability test data representation

The oxygen permeability of the package (O2GTR) is the total amount of oxygen that permeates through the surface of the package per unit time. Its SI unit is mol/pkg.s. The testing state must be stated, including temperature, oxygen partial pressure difference, and Humidity on both sides of the package. The common unit of O2GTR is cm3(STP)/pkg.d, where 1 cm3(STP) is equal to 44.62 x 10-6 mol. Since the number of moles of oxygen permeated and its volume can be interchanged under certain environmental conditions, the meaning is the same regardless of whether it is expressed in terms of moles or using gas volume.

If the unit of test result of the package is compared with the unit of test result of the film, it is not difficult to find that the test area is absent, which means that it is no longer involved in the calculation and replaced by a pkg unit.

1. Definition of pkg

For those who have not been exposed to the package barrier test, this unit will feel very strange, in fact, it is a unit of quantity applicable to any package, equivalent to pieces, packages, is a shorthand for the package. For example, a 2.25L PET bottle or a 1L PET bottle is 1pkg, which does not change due to differences in volume and area.

2. The use of pkg units

As the name implies, the oxygen permeability test of the package is performed to obtain the true oxygen permeability data of the package. Previously, in order to obtain the oxygen permeability data of the package, the oxygen permeability of the container sheet was first examined, and then the overall air permeability of the container was estimated according to the surface area of ​​the container and the thickness of the container. However, the wall thickness of the container is very uneven and the shape is very irregular, making it difficult to accurately determine the surface area of ​​the container, and the material properties have undergone certain changes in the production process of the blow molding and injection molding of the package. Therefore, the estimated air permeability of the container is related to There is indeed a certain gap in the actual test results, so it is more important to directly test the oxygen permeability of the package. Regardless of the shape of the package and its thickness, pkg units can be used to express the oxygen barrier properties of the package as a whole, which is very advantageous for analyzing the overall barrier properties of the package.

Fourth, equipment calibration

The oxygen sensor used in ASTM F 1307 is a Coulomb device that produces a linear output in accordance with Faraday's law. Experience has shown that in some cases, the loss of the sensor and the damage to a certain degree will weaken the response efficiency of the sensor, so the test system needs periodic calibration. The calibration process is the same as the test process. The calibration data is used to calculate the correction factor Q. Q will directly participate in the calculation of the results of the formal test. Therefore, the accuracy of the calibration coefficient Q directly affects the accuracy of future test results.

Fifth, the test process

1. Packaging clips

The method of clamping the package onto the device depends on the shape, type, and test object of the package. For most tests, the package can be exposed to the ambient atmosphere (constant oxygen concentration). However, if the barrier property of the package is good, the package can be immersed in a 100% oxygen environment to increase the test concentration gradient. This is more conducive to testing. It can be covered with a plastic bag or other container outside the package. Which inject oxygen to achieve.

Labthink TOY-C1 provides a method to achieve 100% oxygen concentration in a test environment (Figure 1) with simple operation and good reusability. The biggest advantage of this kind of clamping structure is that it can easily realize the circulation of air circulation on both sides of the package by using a special design, and it does not need piping to support circulation. The number of pipe connections is small, which reduces the possibility of equipment leakage. Compared to the glue seal structure given in the standard, it does not need to seal the air inlet pipe and the air outlet pipe, thus simplifying the installation and disassembly of the entire set of clamping attachments.

2. ASTM F 1307 Test Procedure

Prepare the equipment and then slowly dry the system overnight (bypassing the sensor) with a dry carrier gas stream. The entire system is purged after completing the installation of the packaging attachment. The air inside the package is cleaned with a high flow rate of nitrogen, and the purification time depends on the volume of the package. After that, reduce the nitrogen flow rate to 5-15 mL/min and hold it for 30 min (bypassing the sensor), then introduce the nitrogen flow into the sensor. When the sensor's continuous output value begins to stabilize, the operator can record this value, which is Ee (packaging). Again bypass the sensor. Remove the packaging and insert a stainless steel “perfect package” circuit between the carrier devices. After 10 to 15 minutes, the carrier gas flow is introduced into the sensor. Keep this configuration for 30 minutes, or record the value as Eo (wrapper) after the sensor's output current is reduced and stabilized at a lower value.

The suitability of the flow rate of the carrier gas flow during the entire test is critical and must be accurately adjusted to the standard.

3. Other considerations

First, the oxygen sensor used is a consumable sensor. When the sensor's output signal shows significant attenuation and cannot be compensated by the calibration system, the sensor needs to be replaced. Do not allow reverse air infiltration into the system, because about 21% of the oxygen concentration in the air will make the loss of the sensor larger, so when not using the sensor, it is best to always keep a low flow of nitrogen gas inside.

Second, when testing low-barrier packaging, the oxygen content in the mixed test gas can be appropriately reduced. When testing barriers with poor barrier properties, the oxygen content in the carrier gas flow is high, which can easily lead to sensor saturation. An effective way to solve this problem is to place the package in a mixed test gas, in which the oxygen concentration is lower than the oxygen concentration in the air, and the test result can be converted using the oxygen partial pressure value in the test gas. . This requires a plastic bag outside the package to ensure the oxygen content of the bag, and the barrier property of the plastic bag is very good, otherwise there is oxygen concentration on both sides of the plastic bag (one side is air and the other side is mixed gas). Poorly, it also increases the oxygen content in the bag, which is unfavorable for controlling the oxygen content in the test gas, and is not conducive to the objective and accurate test results.

Again, you need to control the ambient temperature. The oxygen permeability of most plastics can vary from 3% to 9% per degree Celsius. Since the packaging test attachment does not provide temperature control function, from the perspective of test data, placing the device in a constant temperature environment is more conducive to data reproducibility.

Sixth, summary

ASTM F 1307 is the current standard method for detecting the oxygen permeability of a package. It uses the sensor method test principle; the test results are packaged as a unit to facilitate the overall evaluation of the package; the Reference Package (reference packaging) calibration system has a correction factor Q, which is one of the important steps of the test; the sample mounting process It is complicated, but the effect of clamping directly affects the test results. The sample clamping method provided by Labthink TOY-C1 is one of the effective methods to solve this problem.

Languang Lab Zhao Jiang Guangdong Packaging 2005 4th