ASTM D1434 standard is for the estimation of the steady-state rate of transmission of a gas through plastics in the form of film, sheeting, laminates, and plastic-coated papers or fabrics. To tell ASTM D1434, it is fundamental to introduce the following terms:
Gas Transmission Rate
1. Gas Transmission Rate (GTR) is the measurement of the amount of gas that passes through a substance over a given period. The SI unit of GTR is 1 mol / (m2·s).
The gas transmission rate is affected by conditions not provided specifically for in these tests, such as moisture content (the test method requires gas with 0% moisture changes), plasticizer content, and nonhomogeneities.
Permeance
2. Permeance (P) is in general the degree to which a material admits a flow of matter or energy. The SI unit of permeance is 1 mol / (m2·s·Pa)
More specifically, permeance is the ratio of the gas transmission to the differential pressure of the gas on the two sides of the material.
Permeance measured exhibits a strong dependence on the procedure being used, as well as on the laboratory performing the testing.
Gas Permeability Coefficient/ Gas Permeability
3. Gas Permeability Coefficient (P), also known as Gas Permeability, is the volume of gas passed through unit thickness and area of the sample in unit time under constant temperature and unit pressure. In ASTM D1434, Gas Permeability Coefficient involves conversion of the gas transmission rate to a unit thickness basis.
Gas permeability coefficient is not recommended unless the relationship of the thickness and gas transmission rate is known from previous studies.
ASTM D1434 Test Method
Procedures of test method for determining gas permeability characteristics need to pay attention to the details. GPT-201B Gas permeability tester is is professionally applicable to the determination of gas transmission rate and permeability coefficient:
1. Semiquantitative principle estimates for the gas transmission of single pure gases.
2. The test does not include any provision for testing seals that may be involved in packaging applications.
3. Consistence with other methods is sometimes poor and may be material-dependent. The using material often affect the between-laboratory precision. It is suggested that this method not be used for referee purposes unless both of user and seller can reach that they are measuring the same quantity or a mutually agreed upon level of precision.
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