Determination of Oxygen Permeability of Special Films for Modified Atmosphere Packaging

Foreword

As the pace of life accelerates, people are increasingly aware of the importance of packaging for food insurance. In order to improve the shelf life of products, people actually invented a variety of special packaging materials and packaging systems. Gas-modified packaging for fresh vegetables is one of them. We know that keeping moisture is the key to keeping vegetables fresh. Polyolefin film is usually a good water barrier material. Using polyolefin film as the basic material should be a good choice. However, another problem with keeping vegetables fresh is that they require oxygen and emit carbon dioxide, ie they have a respiration effect, which requires the use of a film with a high oxygen transmission rate. Although the polyolefin film itself has a high oxygen transmission rate (Oxygen Transmission Rate, OTR for short), it is still insufficient for vegetables. By increasing the oxygen transmission rate through laser drilling on the film, the environment needed for the respiration of vegetables can be satisfied.

This article uses MOCON (Fang Kang) to help a vegetable company select a suitable film for use as a vegetable packaging bag as an example. It describes how to use the MOCON Ox-Tran Oxygen Permeability Tester to measure oxygen permeability of normal and laser-perforated films. rate.

Experimental apparatus and method

The entire project is divided into two steps. Initially, the vegetable company provided five primary film samples that required MOCON to test their oxygen transmission rates and then selected three of them for laser drilling. The second step is to measure the oxygen permeability of the punched film.

Oxygen permeability experiments of five primary film samples were performed on the OX-TRAN® Model 2/21 oxygen permeability tester from MOCON USA. OX-TRAN? Model 2/21 conforms to ASTM D3985. The experimental procedure follows the principle of equal pressure. The sample is divided into two independent gas flow systems in a gas permeable chamber. The gas to be tested flows on one side (either pure oxygen or oxygen-containing gas). The mixed gas can be set to relative humidity), and the other side is flowing nitrogen to keep the oxygen content at zero. The total pressure on both sides of the sample is equal, but the partial pressure of oxygen is different. Under the effect of oxygen concentration difference, oxygen passes through the membrane. Oxygen molecules passing through the membrane are transported under nitrogen flow to a coulometric analysis sensor (special Coulomb sensor). The coulometric sensor can accurately measure the amount of oxygen contained in the nitrogen stream and calculate the oxygen permeability of the material. . The instrument accurately controls the temperature, relative humidity, and pressure throughout the test.

The OX-TRAN® Model 2/21 instrument has three sub-models and is tested on the same principle. The difference lies in the test range. For example, MOCON Ox-Tran Model 2/21-L is suitable for testing high-barrier and low-oxygen film materials. MOCON Ox-Tran Model 2/21-T is suitable for testing high-barrier low-oxygen film materials. Table 1.

Table 1. Testing ranges of MOCON Ox-Tran 2/21 sub-models
MOCON Ox -Tran 2/21 Test area cc/(m2*day) cc/(package*day) L-type mask is not used, 50cm2 0.005-200 0.000025 -1.0
Use a mask, 5 cm2 0.05-2,000

Type H does not use a mask, 50 cm2 0.05-200 0.00025-1.0
Use a mask, 5 cm2 0.5-2,000

Type T does not use face mask, 100 cm2 775-155,000 3.875-1,550

Figure 1. OX-TRAN? Model 2/21 schematic

Figure 2. Appearance of the OX-TRAN® Model 2/21

After the Oxygen Permeability tests were performed on the above-mentioned H-type and T-type instruments for five primary film samples, the vegetable company selected three samples with higher oxygen permeability, and sent them to the MOCON after laser drilling. Determination. Testing microporous films is a challenge to common test methods. Here we must use a special test method to test the punched film material on the MOCON Ox-Tran 2/21-T instrument. A sample containing 4 micropores in a test area of ​​100 cm2 was selected. The basic method is to add a piece of non-perforated film and a microporous film together to obtain the OTR sum. Using the non-perforated film OTR that has been obtained before has no hole, the OTR containing hole is calculated by the following mathematical formula:
1/OTR Sum = 1/OTR No Hole + 1/ OTR Holes After OTR contains holes, the difference between the value and the OTR non-hole value is the oxygen permeability contributed by 4 micropores.

Experimental results and discussion:

During the experiment, control the test temperature at 10oC and use 100% pure oxygen. Table 2 shows the oxygen permeation rates of the five samples. From Table 2 it can be seen that the oxygen transmission rates of Film D and Film E are too low to be suitable for vegetable storage bags. The oxygen permeation rates of the three materials perforated after screening are listed in Table 3.

Table 2. Oxygen Permeability Rate of Five Primary Film Samples Oxygen Permeability cc / (m2*day)
Film A 1070
Film B 1010
Film C 1130
Film D 10.31
Film E 8.77

Table 3. Oxygen Permeability of Microporous Films and Contribution of Microwells to Oxygen Permeability Oxygen Permeability Rate cc / (m2 *day) Oxygen Permeability cc / (4 Holes *day)
(4 micro-holes in the test area 100 m2) Estimated contribution of 4 micro-holes to OTR Film A 6150 5080
Film B 6230 5220
Film C 6300 5170

With the estimated contribution of the 4 microwells to OTR from Table 3, and the oxygen permeability of the previously obtained membrane, the vegetable company can now begin designing the packaging. According to the demand of different vegetables for oxygen, manufacturers can meet the environment needed for the respiration of various vegetables by increasing or decreasing the number of micropores on the bags.

Friends who are interested in the instruments mentioned in this article can be represented to MOCON China by Beijing Danbell Instrument Co., Ltd.