To determine if aluminizing substrate films impacts the films barrier properties the C230G Oxygen Transmission Rate Test System was used to test the oxygen transmission rate (OTR) of different coated films, such as BOPP and PET, using a coulometric method.
This article explores the testing method used and the range of the applications it can be used for. This research will help materials scientists test and select aluminized films with the barrier properties that they require.
As aluminum foil has very high barrier properties it is a desirable material for use in protective packaging. However, aluminum is also expensive; meaning using pure aluminum in packaging is costly. For this reason, aluminum coated film is often used as this still behaves as an effective barrier whilst being significantly cheaper.
Aluminum coated films are used frequently as packaging for pharmaceuticals, household cleaning products and food.
Common substrates that are coated with aluminum include CPP, PET and POPP and more. Coating is carried out using a vapor deposition method to form coated films such as VMCPP, VMPET and VMPOPP. The barrier properties vary between materials and, due to differences in the evaporation process used, can vary between manufacturers and batches.
Differences in the deposition method used result in differences in the density and width of the aluminum layer, and in the COF between the substrate and the deposited metal.
This article explores how to test the relationship between the barrier properties of a aluminized film and the material used.
This test used two different aluminum-coated film samples – VMPET and VMBOPP. The films were selected with similar thicknesses to make the OTR comparison more valid.
The OTR can be tested using one of two methods – the coulometric (equal pressure) method or the differential pressure method. The tests are carried out in adherence to ASTM D3985, Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Sensor.
Testing was carried out using Labthink Instrument’s C230G Oxygen Transmission Rate Test System.
The coulometric testing method is also called the equal pressure method. The pre-conditioned sample is positioned as a barrier between upper and lower test cells, which are then purged with nitrogen.
The chambers are purged with nitrogen at the same flow rate and O2 is switched into the upper chamber. Due to the concentration difference between the two chambers, oxygen molecules permeate through the specimen into the lower chamber and are carried to the coulometric sensor.
The sensor then generates proportional electrical signals. Through the analysis of these signals, the OTR is obtained.
Figure 1. C230G Oxygen Transmission Rate Test System
The instrument can test films of OTRs between 0.005 ~ 200 cm3/(m2·day). The test range is 0.000025 ~ 1 cm3/(pkg·day), with a resolution of 0.0001 cm3/(m2·day) and a repeatability of 0.005 cm3/(m2·day) or 2%.
The instruments humidity and temperature are controlled automatically via internal sensors which maintain a constant testing environment. Testing can take place at humidities between 0%RH, (5±1) %RH ~ (90±1) %RH and 100 %RH, and temperatures between (10±0.2) ℃ ~ (55±0.2) ℃.
The instrument can simultaneously test three different samples of size 108 mm × 108 mm.
Data collection can be centralized using the optional DataShieldTM system, which can output data in several different formats. Communication can take place via LAN or a private network and all data is protected using security algorithms. This platform can be used alongside third party software.
The C230H conforms to the following international and Chinese standards: GB/T 31354, GB/T 19789, DIN 53380-3, JIS K7126-2-B, ASTM D3985, ASTM F1307, ASTM F1927, DIN 53380-3, JIS K7126-2-B and YBB 00082003.
Using the C230H Oxygen Transmission Rate Test System it is possible to measure the OTR of lots of different materials including: plastic films and plastic composites, sheets of PP, PVC and PVDC, paper, metal-based films, toothpaste tubes, yogurt cups, vacuum seal packaging, rubber, peanut oil buckets, tetra pak, silicon wafers, glass bottles and three-piece metal cans.
In addition, it is also possible to use the C230H to test the OTR of solar panel sheets, sealing lids, blister packs, battery shells, automotive fuel tanks and pipes.
- Three sample sections, of size 108 mm x 108 mm, should be cut from the VMBOPP sample using a cutter.
- The three sample sections should be clamped between the chambers in the test cell and secured.
- The name of the sample, the testing conditions (temperature and humidity) and other parameters should be set.
- Run the test, once completed the results will be automatically displayed by the system
The coulometric test provided the following results:
VMPET samples – the three films had OTRs of 1.0973 cm3/(m2·day), 1.0287 cm3/(m2·day), and 0.9347 cm3/(m2·day) and 1.0973 cm3/(m2·day); with a mean of 1.0202 cm3/(m2·day).
VMBOPP samples – the three films had OTRs of 58.8713 cm3/(m2·day), 51.4492 cm3/(m2·day) and 50.0341 cm3/(m2·day); with a mean of 53.4515 cm3/(m2·day).
Testing the OTR of the two different aluminized films showed that VMPET was a more effective barrier than VMBOPP; this may be related to the fact that PET is a better barrier than BOPP.
The testing method used is easy to carry out with easy-to-use equipment. The results collected are of high accuracy and repeatability.
This information has been sourced, reviewed and adapted from materials provided by Labthink International, Inc.
For more information on this source, please visit Labthink International, Inc.