Summary of oxygen permeability test standards for

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Summary of oxygen permeability test standards for packaging containers

with the rapid development of the packaging industry, lightweight and convenient packaging containers, such as PET plastic bottles, paper plastic aluminum composite flexible packaging and other new materials, have gradually replaced bulky and fragile glass bottle packaging. However, can the performance of these new packaging materials, especially the barrier performance, meet the quality requirements of product packaging? This is a topic of common concern to consumers, users and manufacturers of packaging products, and quality inspection institutions at all levels, At the same time, it is also an urgent problem to be solved "The DNA amp subversive design of Brooks levitate running shoes. At present, there is no clear standard for the oxygen permeability test method of packaging in China, so the relevant tests generally follow ASTM F 1307 standard.

this paper briefly introduces the oxygen permeability test of packaging containers in combination with ASTM F 1307 standard.

I. scope of application

astm f 1307 discusses a test method for determining the stable penetration rate of oxygen into packaging Law. More specifically, this test method is applicable to all packages that can seal a dry space in normal use

II. Summary of test methods

astm f 1307 uses the Coulomb oxygen sensor and its related equipment in a similar way to ASTM D 3985. Oxygen transmittance (o2gtr) is measured after the package is fixed on the test device and reaches equilibrium in the test environment. Oxygen is used as the test gas and nitrogen as the carrier gas. After the packaging is clamped, the following test environment can be formed: the inner side of the packaging is slowly purified by nitrogen gas flow, and the outer side is exposed to an environment with known oxygen concentration (such as in an ambient atmosphere with known oxygen concentration, or in a 100% oxygen environment). There is a certain oxygen concentration difference between the inside and outside of the package. The outside is the side with high oxygen concentration, while the inside is the side with low oxygen concentration. During the whole penetration process, oxygen penetrates from the outside of the package through the package wall to the inside, and then it will be carried by the carrier gas 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 in a unit time

III. expression method of oxygen permeability test data of packaging

the oxygen permeability of packaging (the staff of o2gtr pingkuang group still want to resume production as soon as possible) is the total amount of oxygen penetrating through the surface of packaging in a unit time. Its SI unit is mol/pkg · s. The test status must be specified, including temperature, oxygen differential pressure, and humidity on both sides of the packaging. The common unit of o2gtr is cm3 (STP)/pkg · D, where 1cm3 (STP) is equal to 44.62 × mol。 Under certain environmental conditions, the number of moles of oxygen passing through and its volume can be converted to each other. Therefore, whether expressed in moles or in gas volume, the meaning is the same

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

1.pkg definition

for those who have not been exposed to the barrier test of packaging, this unit will be very strange to them. In fact, it is a unit of quantity applicable to any packaging, equivalent to pieces and packages, and is the abbreviation of package. For example, a 2.25l PET bottle or a 1L PET bottle is 1pkg, which will not change due to different volume and area

2.use reason of PKG unit

as the name suggests, the purpose of conducting the oxygen permeability test of packaging is to obtain the real overall oxygen permeability data of packaging. Previously, in order to obtain the oxygen permeability data of the packaging, it was necessary to detect the oxygen permeability of the container sheet, and then estimate the overall permeability of the container according to the surface area of the container and the thickness of each part of the container. However, the wall thickness of the container is very uneven and the shape is very irregular, which makes it difficult to accurately measure the surface area of the container, and the material properties have changed in the production process of blow molding, injection molding and so on. Therefore, there is a certain gap between the estimated results of the container air permeability and the actual test results, so it is more important to directly test the oxygen permeability of the packaging. Regardless of the shape and thickness of the package, the PKG unit can be used to express the overall oxygen barrier performance of the package, which is very beneficial to the analysis of the overall barrier performance of the package

IV. equipment calibration

the oxygen sensor used in ASTM F 1307 is a Coulomb device that produces linear output according to Faraday's law. Experience shows that in some cases, the response efficiency of the sensor will be weakened due to the loss and damage of the sensor to a certain extent, 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 change switch in the fast reverse gear. Therefore, the accuracy of the calibration factor Q will directly affect the accuracy of future test results

v. test process

1. package clamping

the method of clamping the package onto the equipment depends on the shape, type and test object of the package. For most tests, the package can be exposed to the ambient atmosphere (with a certain oxygen concentration). However, if the barrier property of the packaging is good, the packaging can be immersed in 100% oxygen environment to increase the test concentration gradient, which is more conducive to the test. It can be achieved by covering the packaging with a plastic bag or other container and injecting oxygen into it

labthink toy-c1 provides a method to achieve a 100% oxygen concentration test environment (Figure 1), which is simple to operate and has good reusability. The biggest advantage of this clamping structure is that it can easily realize the air circulation on both sides of the package by using the special design, and there is no need for the pipeline to support the circulation. There are fewer pipeline joints, which reduces the possibility of equipment leakage. Compared with the rubber seal structure given in the standard, it does not need to seal the air inlet pipe and air outlet pipe, so it simplifies the installation and disassembly of the clamping accessories of the whole package

2.astm f 1307 test process

prepare the equipment, and then slowly dry the system with dry carrier air all night (bypass the sensor). Purge the entire system after clamping the package attachment. The air in the package is purified 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 ~ 15ml/min and keep it for 30min (bypass the sensor), and then introduce the nitrogen flow into the sensor. When the continuous output value of the sensor starts to stabilize, the operator can record this value, which is EE (package). Bypass the sensor again. Remove the package and insert a stainless steel "perfect package" circuit between the carrier devices. After 10 ~ 15min, introduce the carrier gas into the sensor. Keep this configuration for 30min, or when the output current of the sensor decreases and stabilizes at a low value, this value can be recorded as EO (package)

during the whole test, whether the flow rate of the carrier gas is appropriate or not is crucial and must be accurately adjusted according to the standard

3. other precautions

first of all, the oxygen sensor used is a consumptive sensor. When the output signal of the sensor has obvious attenuation and cannot be compensated by the calibration system, the sensor needs to be replaced. Do not reverse osmosis the air into the system, because the oxygen concentration of about 21% in the air will cause a large loss of the sensor. Therefore, when the sensor is not used, it is best to always maintain a low flow rate of nitrogen inside the sensor

secondly, when testing low barrier packaging, the oxygen content in the mixed test gas can be appropriately reduced. When the packaging with poor barrier is tested, the oxygen content in the carrier gas stream will be very high, which is easy to cause saturation of the sensor. 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 that in the air. The subsequent test results can be converted by using the oxygen partial pressure value in the test gas. It is necessary to put a plastic bag on the outside of the package to ensure the oxygen content of the swing rod driven by the pull rod and the upper rotating arm (square iron) in the bag, and the barrier of the plastic bag should be very good. Otherwise, the oxygen content in the bag will be increased due to the difference in oxygen concentration on both sides of the plastic bag (air on one side and mixed gas on the other side), which is detrimental to the control of the oxygen content in the test gas, It is not conducive to obtaining objective and accurate test results

thirdly, it is necessary to control the ambient temperature. The oxygen transmittance of most plastics can change by 3% ~ 9% per degree Celsius. Since the package test add-on device does not provide temperature control function, from the test data, placing the device in a constant temperature environment is more conducive to data reproducibility

VI. summary

astm f 1307 is currently the standard method for testing the oxygen permeability of packaging materials. It adopts the principle of sensor method; The test results are based on the package, which is convenient for the overall evaluation of the package; The calibration factor Q of the reference package calibration system is one of the important steps of the test; The sample clamping process is complicated, but the clamping effect directly affects the test results. The sample clamping method provided by Labthink toy-c1 is one of the effective methods to solve this problem. □

information source: Guangdong packaging

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