Determination of oxygen permeability of the specia

Determination of oxygen permeability of special film for modified atmosphere packaging

preface

with the acceleration of the pace of life, people increasingly realize the importance of packaging for food insurance. In order to improve the shelf life of products, people have invented various special packaging materials and packaging systems. The modified atmosphere 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 of vegetable preservation is that they need oxygen and emit carbon dioxide, that is, they have respiration, which requires the use of high oxygen permeability films. Although polyolefin film itself has high oxygen transmission rate (OTR), it is still not enough for vegetables. Through laser drilling on the film to increase the oxygen permeability, it can meet the needs of the environment for vegetable respiration

taking MOCON as an example, this paper introduces how to use MOCON ox tran oxygen permeability tester to measure the oxygen permeability of ordinary films and laser perforated films

experimental instruments and methods

the whole subject is carried out in two steps. At the beginning, the vegetable company provided five primary film samples, asked MOCON to test their oxygen permeability, and then selected three of them for laser drilling. The second step is to measure the oxygen permeability of the perforated film

the oxygen permeability experiment of five primary membrane samples was carried out in the oxygen permeability tester ox-tran of MOCON company in the United States? Completed on the model 2/21 system. OX-TRAN? Model 2/21 complies with ASTM d3985. The experimental process follows the principle of isobaric method. The sample is separated into two independent air flow systems in the ventilation chamber. One side is the flowing gas to be tested (which can be pure oxygen or mixed gas containing oxygen, and the relative humidity can be set), and the other side is the 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 the concentration difference of oxygen, oxygen penetrates the film. The oxygen molecules through the film are carried by the nitrogen gas flow and sent to the electric quantity analysis sensor (the specially designed Coulomb sensor increased by 1% compared with the same period in 2012). The electric quantity analysis sensor can accurately measure the amount of oxygen contained in the nitrogen gas flow, so as to calculate the oxygen transmittance of the material. The instrument accurately controls the temperature, relative humidity and pressure in the whole test process

OX-TRAN? Model 2/21 instrument has three sub models, which are tested with the same principle, and the difference lies in the test range. For example, MOCON ox - hydraulic servo UTM experimental machine can carry out dynamic test and fatigue test. Tran model 2/21-l is suitable for the test of high barrier and low oxygen permeability film materials, and MOCON ox -tran model 2/21-t is suitable for the test of high barrier and low oxygen permeability film materials. See Table 1 for the scope

table 1 MOCON ox tran 2/21 test range of each sub model

mocon ox tran 2/21 test area cc/(M2 * day) cc/(package * day) L-type without mask, 50cm2 0 0.000025 -1.0

use mask, 5 cm2 0, 000

type H does not use a mask, 50 cm2 0 0 0

use mask, 5 cm2 0, 000

according to the British independent station on April 22, the T-type does not use a mask, 100 cm2, 000 3, 550

figure 1 OX-TRAN? Schematic diagram of model 2/21

Figure 2 OX-TRAN? Model 2/21 appearance

after testing the oxygen permeability of five primary membrane samples on the above-mentioned H-type and T-type instruments, the vegetable company selected three samples with higher oxygen permeability, and then sent them to MOCON for further determination after laser drilling. Testing thin films containing micropores is a challenge to the usual testing methods. Here we must adopt a special test method to test the perforated film material on the MOCON ox -tran 2/21-t instrument. A sample with 4 micropores in the test area of 100 cm2 was selected. The basic method is to stack an unperforated film with a microporous film to test the total OTR. Using the unperforated film obtained before, the OTR porosity is calculated by the following mathematical formula:

1/otr total = 1/otr nonporous + 1/otr porous. After the OTR porosity is obtained, the difference between its value and the OTR nonporous value is the oxygen permeability contributed by 4 micropores

experimental results and discussion:

during the experiment, control the test temperature at 10? C. Use 100% pure oxygen. Table 2 shows the oxygen permeability of five samples. It can be seen from table 2 that the oxygen permeability of film D and film e is too low to be used as fresh-keeping bags for vegetables. The oxygen permeability of the three perforated materials after screening is listed in Table 3

Table 2 Oxygen permeability of five primary film samples

oxygen permeability of samples CC/(M2 * day)

film a 1070

film B 1010

film C 1130

film D 10.31

film e 8.77

table 3 The oxygen permeability of microporous films and the contribution of micropores to oxygen permeability

sample oxygen permeability CC/(M2 * day) oxygen permeability CC/(4 holes * day)

(the test area is 100 m2, including 4 micropores) estimate the contribution of 4 micropores to OTR

film a 61505080

film B 62305220

film C 63005170

with the estimated contribution of 4 micropores to OTR obtained from table 3, as well as the oxygen permeability of the film itself previously obtained, Now the vegetable company can start designing packaging bags. According to the oxygen demand of different vegetables, manufacturers can increase or reduce the number of pores on the bag to meet the environment required by the respiration of various vegetables

friends who are interested in the instruments mentioned in this article that bring better comfort to drivers and passengers can contact MOCON's China agent Beijing danbell Instruments Co., Ltd