The standard "ASTM D1434-23 Standard test method for determining gas permeability properties of plastic films and sheets" developed by the American Society for Testing and Materials (ASTM) describes a manometric method for determining the steady-state transmission rate of a gas through plastics in the form of films, sheets, laminates, and plastic-coated papers or fabrics. This test method allows the determination of:
For the purposes of this standard, the following terms and definitions apply:
In testing, the sample is mounted in a gas conduction chamber, forming a closed semi-barrier between two chambers. One chamber contains the test gas at a given high pressure, and the other chamber receives the permeate gas at a lower pressure. The low-pressure chamber is initially evacuated. After evacuation, the low-pressure chamber is allowed to accumulate the permeate test gas. The conduction of the gas through the test specimen is determined by monitoring the gradient of increasing pressure over time.
These measurements give semi-quantitative estimates of gas transmission of single pure gases through films and sheets. The correlation of the measured values to any use, such as packaged content protection, must be determined by experience. The gas transmission rate is affected by conditions not specifically mentioned in these tests, such as moisture content, plasticizer content, and inhomogeneity. These tests do not include any provision for testing seals that may be included in packaging applications. The tests are performed using gas with 0 percent moisture change.
To reduce material off-gassing concerns (such as absorbed water vapor or solvents), all test specimens are conditioned in a desiccator at 618 degrees plus/minus 21 degrees in accordance with ASTM D48-23 for tests where conditioning is required, at least 2 hours prior to testing, over calcium chloride or other suitable desiccant.
Alternative methods of conditioning samples may be used if these conditions are described in the report. For example, an alternative conditioning may be to place the sample in a cleaning box to remove absorbed moisture or solvents.
For ambient testing, the cell temperature should be controlled at 23 degrees plus/minus 2 degrees. For devices that can control cell temperature, a tolerance of plus/minus 1 degree should be used.
The techniques used to sample a lot of material to be tested by the test methods described will depend on the type of information sought. Care should be taken to ensure that the samples are representative of conditions across the width and length of the film rolls. The standard “ASTM D1898-68(1989) Standard Practice for Sampling Plastics” states that in sampling a lot of material, a sufficient number of samples should be tested to ensure that the information is representative of the lot or other lot size being tested.
When performing the test, the appropriate volume filling is placed in the low-pressure chamber. A filter paper is placed in the low-pressure chamber. A thin and uniform layer of vacuum grease is applied to the sealing surface of the low-pressure chamber in contact with the sample. Excessive grease should be avoided as it may overflow into the filter paper and reduce the transmission rate exposure area.
The conditioned sample is placed in the low pressure chamber and checked for wrinkles or looseness. Wrinkling of the sample can cause leakage from the chamber and a loosely mounted sample will have a greater surface area. Both of these can lead to inaccurate test results.
The O-ring and sealing surface in the high-pressure chamber are lightly greased and then carefully placed over the sample and secured in place with uniform pressure to ensure a vacuum-tight seal.
The vacuum pump is started and the ambient air is evacuated from the low-pressure chamber system, then the high-pressure chamber is evacuated. When the air is evacuated to 26 Pa or less, the relevant valve is closed and the vacuum pump is stopped. The time required to evacuate the system depends on the system volume and the sample gas output.
If the pressure in the low-pressure chamber rises immediately, this may be an indication of a leak or that a large amount of sample gas has been vented and the sample assembly or initial evacuation, or both, must be repeated.
The test gas is introduced into the high pressure chamber. When the pressure reaches the desired test pressure level, the gas supply is shut off. The high pressure value is recorded. When the test gas is added, the increase in pressure on the low pressure side confirms that the gas has passed through the sample.
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