ASTM D3985-17

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Designation: D3985 − 05 (Reapproved 2010) D3985 − 17
Standard Test Method for
Oxygen Gas Transmission Rate Through Plastic Film and
Sheeting Using a Coulometric Sensor
This standard is issued under the fixed designation D3985; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial changes were made throughout in November 2010.
1. Scope
1.1 This test method covers a procedure for determination of the steady-state rate of transmission of oxygen gas through plastics
in the form of film, sheeting, laminates, coextrusions, or plastic-coated papers or fabrics. It provides for the determination of (1)
oxygen gas transmission rate (OTR), (2) the permeance of the film to oxygen gas (PO ), and (3) oxygen permeability coefficient
(P'O ) in the case of homogeneous materials.
1.2 This test method does not purport to be the only method for measurement of OTR. There may be other methods of OTR
determination that use other oxygen sensors and procedures.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1434 Test Method for Determining Gas Permeability Characteristics of Plastic Film and Sheeting
D1898 Practice for Sampling of Plastics (Withdrawn 1998)
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
F1927 Test Method for Determination of Oxygen Gas Transmission Rate, Permeability and Permeance at Controlled Relative
Humidity Through Barrier Materials Using a Coulometric Detector
3. Terminology
3.1 Definitions:
3.1.1 oxygen permeability coeffıcient (P'O )—the product of the permeance and the thickness of film. The permeability is
meaningful only for homogeneous materials, in which case it is a property characteristic of the bulk material. This quantity should
not be used, unless the relationship between thickness and permeance has been verified on tests using several different thicknesses
of the material. The SI unit of oxygen permeability is the mol/(m·s·Pa). The test conditions (see 3.1.3) must be stated.
3.1.2 oxygen permeance (PO )—the ratio of the OTR to the difference between the partial pressure of O on the two sides of
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the film. The SI unit of permeance is the mol/(m ·s·Pa). The test conditions (see 5.1) must be stated.
3.1.3 oxygen transmission rate (OTR)—the quantity of oxygen gas passing through a unit area of the parallel surfaces of a
plastic film per unit time under the conditions of test. The SI unit of transmission rate is the mol/(m ·s). The test conditions,
including temperature and oxygen partial pressure on both sides of the film must be stated.
This test method is under the jurisdiction of ASTM Committee F02 on FlexiblePrimary Barrier Packaging and is the direct responsibility of Subcommittee F02.10 on
Permeation.
Current edition approved Oct. 1, 2010Nov. 15, 2017. Published November 2010December 2017. Originally approved in 1981. Last previous edition approved in 20052010
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as D3985 – 05 (2010) . DOI: 10.1520/D3985-05R10E01.10.1520/D3985-17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
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D3985 − 17
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3.1.3.1 A commonly used unit of OTR is the cm (STP)/(m ·d) at one atmosphere pressure difference where 1 cm (STP) is
44.62 μmol, 1 atm is 0.1013 MPa, and one day is 86.4 × 10 s. The OTR in SI units is obtained by multiplying the value in
−10
inch-pound units by 5.160 × 105.163 × 10 .
4. Summary of Test Method
4.1 The oxygen gas transmission rate is determined after the sample has equilibrated in a dry test environment. In this context,
a “dry” environment is considered to be one in which the relative humidity is less than 1 %.
4.2 The specimen is mounted as a sealed semi-barrier between two chambers at ambient atmospheric pressure. One chamber
is slowly purged by a stream of nitrogen and the other chamber contains oxygen. As oxygen gas permeates through the film into
the nitrogen carrier gas, it is transported to the coulometric detector where it produces an electrical current, the magnitude of which
is proportional to the amount of oxygen flowing into the detector per unit time.
5. Significance and Use
5.1 The OTR is an important determinant of the packaging protection afforded by barrier materials. It is not, however, the sole
determinant, and additional tests, based on experience, must be used to correlate packaging performance with OTR. It is suitable
as a referee method of testing, provided that the purchaser and the seller have agreed on sampling procedures, standardization
procedures, test conditions, and acceptance criteria.
5.2 Limited statistical data on correlations with Test Method D1434 methods are available ; however, the oxygen transmission
rate of a standard reference material (see 12.1) as determined manometrically by NIST, is in good agreement with the values
obtained in the coulometric interlaboratory test using material from the same manufacturing lot. Thus, this test method may be used
as a referee method.
6. Interferences
6.1 The presence of certain interfering substances in the carrier gas stream may give rise to unwanted electrical outputs and error
factors. Interfering substances include free chlorine and some strong oxidizing agents. Exposure to carbon dioxide should also be
minimized to avoid damage to the sensor through reaction with the potassium hydroxide electrolyte.
7. Apparatus
7.1 Oxygen Gas Transmission Apparatus, as diagrammed in Fig. 1 with the following:
7.1.1 Diffusion Cell shall consist of two metal halves, which, when closed upon the test specimen, will accurately define a
circular area. The volume enclosed by each cell half, when clamped, is not critical; it should be small enough to allow for rapid
gas exchange, but not so small that an unsupported film which happens to sag or bulge will contact the top or bottom of the cell.
The diffusion cell shall be provided with a thermometer well for measuring temperature.
7.1.1.1 O-Ring—An appropriately sized groove, machined into the oxygen (or test gas) side of the diffusion cell, retains a
neoprene O-ring. The test area is considered to be that area established by the inside contact diameter of the compressed O-ring
when the diffusion cell is clamped shut against the test specimen. The area, A, can be obtained by measuring the inside diameter
of the imprint left by the O-ring on the specimen after it has been removed from the diffusion cell.
7.1.1.2 The nitrogen (or carrier gas) side of the diffusion cell shall have a flat raised rim. Since this rim is a critical sealing
surface against which the test specimen is pressed, it shall be smooth and flat, without radial scratches.
7.1.1.3 Diffusion Cell Pneumatic Fittings—The diffusion cell shall incorporate suitable fittings for the introduction and exhaust
of gases without significant loss or leakage.
7.1.1.4 It is desirable to thermostatically control the diffusion cell. A simple heating or heating/cooling system regulated to
60.5°C, is adequate for this purpose. A thermistor sensor and an appropriate control circuit will serve to regulate the cell
temperature unless measurements are being made close to ambient temperature. In this case, it is desirable to provide cooling
capability to remove some of the heat.
7.1.1.5 Experience has shown that arrangements using multiple diffusion cells are a practical way to increase the number of
measurements which can be obtained from a coulometric sensor. Valving connects the carrier gas side of each individual diffusion
cell to the sensor in a predetermined pattern. Carrier gas is continually purging the carrier gas sides of those cells that are not
connected to the sensor. Either test gas or carrier gas, as is appropriate, purges the test gas chamber of any individual cell.
7.1.2 Catalyst Bed—A small metal tube with fittings for attachment to the inlet on the nitrogen side of the diffusion cell shall
contain 3 to 5 g of 0.5 % platinum or palladium catalysts on alumina to provide an essentially oxygen-free carrier gas.
7.1.3 Flowmeter—A flowmeter having an operating range from 5 to 100 mL/min is required to monitor the flow rate of the
nitrogen carrier gas.
7.1.4 Flow Switching Valves—Valves for the switching of the nitrogen and test gas flow streams.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D20-1085. Contact ASTM Customer
Service at service@astm.org.
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FIG. 1 A Practical Arrangement of Components for the Measurement of Oxygen Transmission Rate Using the Coulometric Method
7.1.5 Coulometric Sensor—An oxygen-sensitive coulometric sensor (see Note 1) operating at an essentially constant efficiency
shall be used to monitor the quantity of oxygen transmitted.
NOTE 1—It is deemed advisable upon initial setup of the voltage recorder and periodically thereafter to check the response of the recorder on all ranges
to a suitable voltage input.
7.1.6 Load Resistor—The current generated by the coulometric cell shall pass through a resistive load across which the output
voltage is measured. Typical values for the load resistor are such that the values yield a convenient relationship between the output
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voltage and the oxygen transmission rate in standard units cm (STP)/(m ·d).
7.1.7 Voltage Recorder—A multirange, potentiometer strip chart recorder may be used for measuring the voltage developed
across the load resistor. The recorder should be capable of measuring a full-scale voltage of 50 mV. It should be capable of
measuring voltages as low as 0.100 mV and have a resolution of at least 10 μV. An input impedance of 1 megohm or higher is
acceptable.
8. Reagents and Materials
8.1 Nitrogen Carrier Gas shall consist of a nitrogen and hydrogen mixture in which the percentage of hydrogen shall fall
between 0.5 and 3.0 volume %. The carrier gas shall be dry and contain not more than 100 ppm of oxygen. A commercially
available mixture known as “forming gas” is suitable.
8.2 Oxygen Test Gas shall be dry and contain not less than 99.5 % oxygen (except as provided in 14.11).
8.3 Sealing Grease—A high-viscosity silicone stopcock grease or a high-vacuum grease is required for sealing the specimen
film in the diffusion cell.
9. Precautions
9.1 Extended use of the test unit, with no moisture in the gas stream, may in some older systems result in a noticeable decrease
in output and response time from the sensor (equivalent to an increase in the calibration factor, Q). This condition is due to drying
out of the sensor.
9.2 Temperature is a critical parameter affecting the measurement of OTR. Careful temperature control can help to minimize
variations due to temperature fluctuations. During testing, the temperature shall be monitored to the nearest 0.5°C. The average
temperature and the range of temperatures found during a test shall both be reported.
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9.3 The sensor will require a relatively long time to stabilize to a low reading characteristic of a good barrier after it has been
used to test a barrier such as low-density polyethylene. For this reason, materials of comparable gas transmission qualities should
be tested together.
9.4 Back diffusion of air into the unit is undesirable. Care should therefore be taken to ensure that there is a flow of nitrogen
through the system at all times. This flow can be low when the instrument is not being used.
9.5 Elevated temperatures can be used to hasten specimen outgassing, provided that the treatment does not alter the basic
structure of the specimen (crystallinity, density, and so forth). This can be accomplished by the use of the heaters in the diffusion
cells.
10. Sampling
10.1 The sampling units used for the determination of OTR shall be representative of the quantity of product for which the data
are required, in accordance with Practice D1898. Care shall be taken to ensure that samples are representative of conditions across
the width and along the length of a roll of film.
11. Test Specimens
11.1 Test specimens shall be representative of the material being tested and shall be free of defects, including wrinkles, creases,
and pinholes, unless these are a characteristic of the material being tested.
11.2 Average thickness shall be determined to the nearest 2.5 μm (0.0001 in.), using a calibrated dial gage (or equivalent) at
a minimum of five points distributed over the entire test area. Maximum, minimum, and average values shall be recorded.
11.3 If the test specimen is of an asymmetrical construction, the two surfaces shall be marked by appropriate distinguishing
marks and the orientation of the test specimen in the diffusion cell shall be reported (for example, “side II was mounted facing
the oxygen side of the diffusion cell”).
12. Calibration
12.1 General Approach—The oxygen sensor used in this test method is a coulometric device that yields a linear output as
predicted by Faraday’s Law. In principle, four electrons are produced by the sensor for each molecule of oxygen that passes into
it. Considering that the sensor is known to have a basic efficiency of 95 to 98 %, it may be considered an “intrinsic” standard that
does not require calibration, and can thus be used as a reference method.
12.2 Experience has shown, however, that under some circumstances the sensor may become depleted or damaged to the extent
that efficiency and response are impaired. For that reason, this test method incorporates means for a periodic sensor evaluation.
This evaluation is derived from measurements of a known-value “reference package.” Experience indicates however, that a
specimen-to-specimen variability of the reference material is such that a change should never be made in the calibration factor,
as the result of a measurement using a single sheet of the reference material.
12.3 Es
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