The main factors affecting the barrier properties of packaging materials and the latest testing techniques

Packaging as the first line of defense for product safety, barrier properties of packaging materials is an important means to ensure product safety, it can guarantee product quality and preservation, to ensure the expected shelf life, reduce the risk of public disease caused by product deterioration.

In the production and use of packaging materials, there are many factors that affect the barrier properties of the material. Therefore, we first look at what factors affect the barrier properties of the material.

I. The main factors affecting barrier properties:

1. Influence of the material itself:

Polymer's three-dimensional structure, degree of crystallinity, chain orientation, hydrophilicity, surface properties, additives, thickness, and multilayer structure and other factors will affect the barrier property of the material in varying degrees.

2. The influence of external factors:

Impact of ambient temperature: Per temperature increase 1 °C, the permeability of the material will increase by 5 to 7%

The influence of environmental humidity: Relative humidity affects polar polymers containing hydrogen bonds. In the case of high humidity, the air permeability of materials such as NYLOR, EVOH, etc. will rise suddenly.

Therefore, when we study the barrier properties of packaging materials, we must consider the characteristics of the materials, as well as the internal and external environment in which the materials are ultimately used.

The latest technology of barrier test:

1. Oxygen permeability test:

Isobaric Coulomb power sensor method, this is the patent technology of American MOCON company, MOCON company has 40 years of professional experience in penetration testing, has the world's most advanced permeability testing technology, and a variety of patents and international standards recognized, ASTM and ISO related standards are based on MOCON products. At present, there are more than 3000 MOCON devices in the world, and the US market share has reached 98%.

1) Isobaric Coulomb power sensor technology introduction:

Coulomb power sensor is an internationally recognized absolute value sensor. Each oxygen molecule in the sensor releases four electrons. The relationship between the number of oxygen molecules and the number of electrons is linearly proportional to the accuracy of the sensor. Penetration concentration and sensor environmental changes. Therefore, instruments using this sensor do not require calibration and calibration.

ISO 15105-2 and ASTM D3985, the international standards for isobaric oxygen permeability testing, all require the use of a Coulomb power sensor to detect 100% of the infiltrated oxygen. At present, only the MOCON company's oxygen permeability meter uses a true Coulomb battery absolute value sensor, which truly conforms to the ISO 10105-2 and ASTM D3985 standards. Its accuracy and reliability are recognized globally.

Some equipment manufacturers use a common electrochemical sensor. In order to extend the service life of the sensor, the outer layer of their sensor is covered with a soft film. Only part of the oxygen that penetrates from the sample can penetrate this layer. The soft membrane finally enters the sensor and generates electrical signals. This secondary infiltration violates the 100% oxygen detection required by international standards. The presence of this soft membrane makes this sensor a relative value sensor and requires different concentrations of oxygen. Perform calibration. According to the laboratory comparison test data organized by the ASTM Committee, the accuracy of these non-Coulomb sensors cannot meet the requirements of the ASTM standards. In particular, when measuring low-transmissivity materials, the test results will show significant deviations.

2) Test chamber temperature and humidity control technology:

The permeability of the material changes with the temperature and humidity of the test. The MOCON isobarically-coulomb-power sensor method oxygen permeation tester allows precise temperature and humidity control of the test sample.

The accuracy of the temperature and humidity sensor detection is the premise of the control. The temperature and humidity sensor position in the MOCON oxygen permeability meter is very close to the test sample, can truly reflect the temperature and humidity environment of the sample, and the temperature and humidity sensor can be easily removed. Use a desiccant and saturated salt solution for a two-point calibration to avoid aging drift in the sensor circuit.

The humidity generation method adopted by MOCON is the double pressure method recommended by the American National Institute of Standards and Research (NIST). The control is simple and stable. Some devices use the dual flow method, which is similar to the dual valve adjustment of hot and cold water, and is difficult to control stably. They did not reach the humidity range they stated, and their humidity sensors were not installed next to the sample and the customer was not aware of the sensor's accuracy.

3) Test stability in ambient temperature:

Since the Coulomb quantity sensor used by MOCON is an absolute value sensor, its linear relationship is independent of changes in oxygen concentration and ambient temperature.

The ordinary electrochemical sensor (non-coulomb coulometric) oxygen permeability instrument uses a relative value sensor, and the outer layer of the sensor is covered with a soft film. Since the sensor is located in the chassis of the instrument, the temperature of the sensor will change with the ambient temperature, and the oxygen permeability of the soft film itself will change, so that the accuracy of the sensor test is easily affected by changes in the ambient temperature. The standard laboratory's ambient temperature varies between 4°C (±2°C). This tiny temperature change will cause these relative-value sensors to fluctuate by more than 0.5cc/m2day. This fluctuation will generate test data for high-barrier materials. Great influence.

4) Traceability of test equipment:

Absolute sensors used by MOCON do not require calibration, but MOCON still provides standard films that are traceable to NIST, giving customers an alternative means of verification. Users only need to use them when verifying the instrument. MOCON offers a variety of standard traceability membranes of different orders of magnitude. As long as the measurement values ​​of these several standard membranes are within the allowable error range, the instrument can be kept in an optimal state according to a linear relationship, achieving full-scale test accuracy.

Ordinary electrochemical sensors (non-Coulomb coulometric) oxygen permeability instruments use relative value sensors, so they must be calibrated and compensated using standard films. Using three standard films, only three oxygen concentration gradients can be calibrated. Because of the non-linear relationship, the accuracy of these three calibration points does not represent the accuracy of other points, and therefore cannot guarantee the accuracy of the full scale.

5) Comparison with traditional differential pressure method:

The traditional differential pressure method has a relatively simple test principle, requiring only accurate measurement of the gas pressure and the ability to test the barrier properties of a variety of gases. However, the pressure difference method has its own limitations in its accuracy and application.

The lower limit of the differential pressure test can only reach 0.5 cc/m2day, and the smaller transmittance data cannot guarantee the accuracy. Therefore, the differential pressure method can no longer be applied to the detection of high barrier materials.

The presence of this pressure difference can destroy the performance structure of the material itself.

The differential pressure method cannot test a complete package.

The repeatability of the test is poor. There is no supply of traceable standard membranes at home and abroad. Only the original reference membrane can be used for verification. There is no uniform reference value between devices of different manufacturers.

Vacuum pumping technology directly affects the test accuracy and test efficiency.

In the high-permeation test range, the differential pressure method can be mutually confirmed by the equal pressure method. The equal pressure—Coulomb power sensor method is used as a more accurate and advanced test method. The linear relationship of the sensor is used to ensure the Low penetration test accuracy in the test range.

The isobaric testing range can be as low as 0.005 cc/m2day, which is sufficient to accurately detect these high barrier materials.

The same pressure on both sides of the sample will not destroy the performance structure of the material itself.

Can test the complete package or bottle, only need to add a small attachment.

The repeatability of the test is very good, and the equipment can be verified by using the standard film traced back to the NIST's NIST, so that the test results of different laboratories can be well compared.

2. Breathability test:

The isobaric-infrared sensor method is currently the most recognized method for measuring the moisture vapor transmission rate. The MOCON moisture vapor meter adopts the isobaric-infrared sensor method and conforms to various international standards such as ASTM F1249 and ISO 15106-2. .

1) Isobaric Infrared Sensor Technology Introduction:

It only discriminates the linear ratio of certain wavelengths in infrared spectrum absorbed by water vapor to distinguish the concentration of water vapor. Water vapor only flows in the pipeline with the carrier gas, without any treatment, and there are no other interference factors. Infrared sensors are relative-value sensors that require calibration.

2) The same test chamber temperature and humidity control technology as the oxygen permeability tester is used to ensure the accuracy of the test.

3) Traceability of test equipment:

MOCON offers a variety of standard films that are traceable to NIST to calibrate and calibrate the device.

4) Comparison with some traditional methods:

The traditional cup method has poor testing accuracy and has a great influence on human factors. At present, ISO has eliminated this test method. And it takes a long time to test, sometimes it takes days or even months to test.

Traditional electrolytic methods require the use of a hygroscopic agent to absorb water vapor, electrolysis of water vapor through the electrodes, and judgment based on the electrolytic current. In this way, the secondary treatment process of the water vapor, the efficiency of the moisture absorbent, and the loss of the electrode all affect the accuracy of the test, and the cumulative error is large. Moreover, the electrolyzer needs to be regenerated regularly, which takes time and effort.

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