Plastics — Film and Sheeting — Determination of Gas-transmission Rate — Part 1: Differential-pressure Methods
1 Scope
This document specifies two methods (method using a pressure sensor and method using a gas chromatograph) for determining the gas transmission rate of single-layer plastic film or sheet and multi-layer structures under a differential pressure.
This document is applicable to the determination of gas transmission rate of plastic film and sheeting. The determination of gas transmission rate of other materials can be used as reference.
Note: Differential-pressure method also commonly known as pressure difference method.
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 6672 Plastics film and sheeting — Determination of thickness by mechanical scanning (GB/T 6672-2001, ISO 4593:1993, IDT)
3 Terms and Definitions
For the purposes of this document, the following terms and definitions apply.
3.1
gas transmission rate; GTR
volume of gas passing through a plastic material, per unit area and unit time, under unit partial-pressure difference between the two sides of the material
Note: When expressed in mass fraction, in moles per meter second pascal [mol/(m2·s·Pa)]; when expressed in volume fraction, in cubic centimeters per square meter per day per Pascal [cm3/(m2·d·Pa)].
3.2
gas permeability; coefficient of gas permeability
P
volume of gas passing through a plastic material of unit thickness, per unit area and unit time, under unit partial-pressure difference between the two sides of the material
Note 1: When expressed in mass fraction, in mole meters per square meter second pascal [mol·m/(m2·s·Pa)]; when expressed in volume fraction, in cubic centimeter centimeters per square meter day pascal [cm3·cm/(m2·d·Pa)].
Note 2: Although P is a physical property of a polymeric material, differences in film preparation affecting polymer orientation and crystal structure will have an effect on the permeation properties.
Note 3: P is only used for measuring single-layer plastic film and sheeting of a single material.
4 Principle
A test specimen is mounted in a gas transmission cell (see Figures A.1 and B.1) so as to form a sealed barrier between two chambers. The lower-pressure chamber is evacuated, followed by evacuation of the higher-pressure chamber. A gas is introduced into the evacuated higher-pressure chamber and permeates into the lower-pressure chamber. The amount of gas which permeates through the specimen is determined by the increase in pressure on the lower-pressure side or by gas chromatography.
5 Test Specimens
5.1 Test specimens shall be representative of the material under investigation, free from shrivelling, folds and pinholes, and of uniform thickness. They shall be larger than the gas transmission area of the measurement cell and be capable of being mounted airtight.
5.2 Use three specimens unless otherwise specified or agreed upon among the interested parties.
5.3 Mark the side of the material facing the permeating gas.
Note: In principle, the test should replicate the actual conditions of use, with the gas passing from the inside to the outside of e.g. packaging material, or vice versa.
5.4 Measure the thickness of each specimen in accordance with GB/T 6672, to the nearest 1 micron (μm). At least five points distributed over the entire test area, and record the minimum, maximum and average values.
6 Apparatus, Test Procedure and Calculation of Results
Two test methods for gas transmission rate are described in the annexes of this document:
— Annex A: Method using a pressure sensor;
— Annex B: Method using a gas chromatograph.
7 Expression of Results
Express the test result as the arithmetic mean of the results obtained for all the specimens, rounding to three significant figures.
8 Precision
The precision of these test methods is not known because interlaboratory data are not available. When interlaboratory data are obtained, a precision statement will be added at the following revision.
9 Test Report
The test report shall include the following information:
a) No. of this document;
b) the method of measurement used (pressure sensor or gas chromatography);
c) all details necessary for identification of the test apparatus used (make, manufacturer, etc.), including, when a pressure sensor is used, the type of pressure sensor;
d) all details necessary for identification of the sample tested;
Foreword II
Introduction V
1 Scope
2 Normative References
3 Terms and Definitions
4 Principle
5 Test Specimens
6 Apparatus, Test Procedure and Calculation of Results
7 Expression of Results
8 Precision
9 Test Report
Annex A (Normative) Method Using a Pressure Sensor
Annex B (Normative) Method Using a Gas Chromatograph
