1、Designation: D 3985 05Standard Test Method forOxygen Gas Transmission Rate Through Plastic Film andSheeting Using a Coulometric Sensor1This standard is issued under the fixed designation D 3985; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a procedure for determinationof the steady-state rate of transmission
3、 of oxygen gas throughplastics in the form of film, sheeting, laminates, coextrusions,or plastic-coated papers or fabrics. It provides for the determi-nation of (1) oxygen gas transmission rate (O2GTR), (2) thepermeance of the film to oxygen gas (PO2), and (3) oxygenpermeability coefficient (PO2) in
4、 the case of homogeneousmaterials.1.2 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limita
5、tions prior to use.1.3 This test method does not purport to be the only methodfor measurement of O2GTR. There may be other methods ofO2GTR determination that use other oxygen sensors andprocedures.2. Referenced Documents2.1 ASTM Standards:2D 1434 Test Method for Determining Gas PermeabilityCharacter
6、istics of Plastic Film and SheetingD 1898 Practice for Sampling of Plastics3E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodF 1927 Test Method for Determination of Oxygen GasTransmission Rate, Permeability and Permeance at Con-trolled Relative Humidit
7、y Through Barrier Materials Usinga Coulometric Detector3. Terminology3.1 Definitions:3.1.1 oxygen permeability coeffcient (PO2)the productof the permeance and the thickness of film. The permeability ismeaningful only for homogeneous materials, in which case it isa property characteristic of the bulk
8、 material. This quantityshould not be used, unless the relationship between thicknessand permeance has been verified on tests using several differentthicknesses of the material. The SI unit of oxygen permeabilityis the mol/msPa. The test conditions (see 3.1.3) must bestated.3.1.2 oxygen permeance (P
9、O2)the ratio of the O2GTR tothe difference between the partial pressure of O2on the twosides of the film.The SI unit of permeance is the mol/(m2sPa).The test conditions (see 5.1) must be stated.3.1.3 oxygen transmission rate (O2GTR)the quantity ofoxygen gas passing through a unit area of the paralle
10、l surfacesof a plastic film per unit time under the conditions of test. TheSI unit of transmission rate is the mol/(m2s). The test condi-tions, including temperature and oxygen partial pressure onboth sides of the film must be stated.3.1.3.1 A commonly used unit of O2GTR is the cm3(STP)/m2d) at one
11、atmosphere pressure difference where 1 cm3(STP)is 44.62 mol, 1 atm is 0.1013 MPa, and one day is86.4 3 103s. The O2GTR in SI units is obtained by multiplyingthe value in inch-pound units by 5.160 3 1010.4. Summary of Test Method4.1 The oxygen gas transmission rate is determined after thesample has e
12、quilibrated in a dry test environment. In thiscontext, a “dry” environment is considered to be one in whichthe relative humidity is less than 1 %.4.2 The specimen is mounted as a sealed semi-barrierbetween two chambers at ambient atmospheric pressure. Onechamber is slowly purged by a stream of nitro
13、gen and the otherchamber contains oxygen. As oxygen gas permeates throughthe film into the nitrogen carrier gas, it is transported to thecoulometric detector where it produces an electrical current,the magnitude of which is proportional to the amount ofoxygen flowing into the detector per unit time.
14、5. Significance and Use5.1 The O2GTR is an important determinant of the packag-ing protection afforded by barrier materials. It is not, however,the sole determinant, and additional tests, based on experience,1This test method is under the jurisdiction ofASTM Committee F02 on FlexibleBarrier Packagin
15、g and is the direct responsibility of Subcommittee F02.10 onPermeation.Current edition approved June 1, 2005. Published July 2005. Originally approvedin 1981. Last previous edition approved in 2002 as D 3985 02e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cu
16、stomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.must be used to correl
17、ate packaging performance with O2GTR.It is suitable as a referee method of testing, provided that thepurchaser and the seller have agreed on sampling procedures,standardization procedures, test conditions, and acceptancecriteria.5.2 Limited statistical data on correlations with Test MethodD 1434 met
18、hods are available4; however, the oxygen transmis-sion rate of a standard reference material (see 12.1)asdetermined manometrically by NIST, is in good agreementwith the values obtained in the coulometric interlaboratory testusing material from the same manufacturing lot. Thus, this testmethod may be
19、 used as a referee method.6. Interferences6.1 The presence of certain interfering substances in thecarrier gas stream may give rise to unwanted electrical outputsand error factors. Interfering substances include free chlorineand some strong oxidizing agents. Exposure to carbon dioxideshould also be
20、minimized to avoid damage to the sensorthrough reaction with the potassium hydroxide electrolyte.7. Apparatus7.1 Oxygen Gas Transmission Apparatus, as diagrammed inFig. 1 with the following:7.1.1 Diffusion Cell shall consist of two metal halves,which, when closed upon the test specimen, will accurat
21、elydefine a circular area. The volume enclosed by each cell half,when clamped, is not critical; it should be small enough toallow for rapid gas exchange, but not so small that anunsupported film which happens to sag or bulge will contactthe top or bottom of the cell. The diffusion cell shall beprovi
22、ded with a thermometer well for measuring temperature.7.1.1.1 O-RingAn appropriately sized groove, machinedinto the oxygen (or test gas) side of the diffusion cell, retains aneoprene O-ring. The test area is considered to be that areaestablished by the inside contact diameter of the compressedO-ring
23、 when the diffusion cell is clamped shut against the testspecimen. The area, A, can be obtained by measuring the insidediameter of the imprint left by the O-ring on the specimen afterit has been removed from the diffusion cell.7.1.1.2 The nitrogen (or carrier gas) side of the diffusion cellshall hav
24、e a flat raised rim. Since this rim is a critical sealingsurface against which the test specimen is pressed, it shall besmooth and flat, without radial scratches.7.1.1.3 Diffusion Cell Pneumatic FittingsThe diffusioncell shall incorporate suitable fittings for the introduction andexhaust of gases wi
25、thout significant loss or leakage.7.1.1.4 It is desirable to thermostatically control the diffu-sion cell.Asimple heating or heating/cooling system regulatedto 60.5C, is adequate for this purpose. A thermistor sensorand an appropriate control circuit will serve to regulate the celltemperature unless
26、 measurements are being made close toambient temperature. In this case, it is desirable to providecooling capability to remove some of the heat.7.1.1.5 Experience has shown that arrangements using mul-tiple diffusion cells are a practical way to increase the numberof measurements which can be obtain
27、ed from a coulometricsensor. Valving connects the carrier gas side of each individualdiffusion cell to the sensor in a predetermined pattern. Carrier4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: D201085.FIG. 1 A Practical Arr
28、angement of Components for the Measurement of Oxygen Transmission Rate Using the Coulometric MethodD3985052gas is continually purging the carrier gas sides of those cellsthat are not connected to the sensor. Either test gas or carriergas, as is appropriate, purges the test gas chamber of anyindividu
29、al cell.7.1.2 Catalyst BedA small metal tube with fittings forattachment to the inlet on the nitrogen side of the diffusion cellshall contain 3 to5gof0.5%platinum or palladium catalystson alumina5to provide an essentially oxygen-free carrier gas.7.1.3 FlowmeterA flowmeter having an operating rangefr
30、om 5 to 100 mL/min is required to monitor the flow rate ofthe nitrogen carrier gas.7.1.4 Flow Switching ValvesValves for the switching ofthe nitrogen and test gas flow streams.7.1.5 Coulometric SensorAn oxygen-sensitive coulomet-ric sensor6operating at an essentially constant efficiency shallbe used
31、 to monitor the quantity of oxygen transmitted.7.1.6 Load ResistorThe current generated by the coulo-metric cell shall pass through a resistive load across which theoutput voltage is measured. Typical values for the load resistorare such that the values yield a convenient relationship betweenthe out
32、put voltage and the oxygen transmission rate in standardunits (cm3(STP)/m2d).7.1.7 Voltage RecorderA multirange, potentiometer stripchart recorder may be used for measuring the voltage devel-oped across the load resistor. The recorder should be capable ofmeasuring a full-scale voltage of 50 mV. It s
33、hould be capableof measuring voltages as low as 0.100 mV and have aresolution of at least 10 V. An input impedance of 1 megohmor higher is acceptable.8. Reagents and Materials8.1 Nitrogen Carrier Gas shall consist of a nitrogen andhydrogen mixture in which the percentage of hydrogen shallfall betwee
34、n 0.5 and 3.0 volume %. The carrier gas shall be dryand contain not more than 100 ppm of oxygen.Acommerciallyavailable mixture known as “forming gas” is suitable.8.2 Oxygen Test Gas shall be dry and contain not less than99.5 % oxygen (except as provided in 14.11).8.3 Sealing GreaseA high-viscosity s
35、ilicone stopcockgrease or a high-vacuum grease is required for sealing thespecimen film in the diffusion cell.9. Precautions9.1 Extended use of the test unit, with no moisture in the gasstream, may in some older systems result in a noticeabledecrease in output and response time from the sensor (equi
36、va-lent to an increase in the calibration factor, Q). This conditionis due to drying out of the sensor.9.2 Temperature is a critical parameter affecting the mea-surement of O2GTR. Careful temperature control can help tominimize variations due to temperature fluctuations. Duringtesting, the temperatu
37、re shall be monitored to the nearest0.5C. The average temperature and the range of temperaturesfound during a test shall both be reported.9.3 The sensor will require a relatively long time to stabilizeto a low reading characteristic of a good barrier after it hasbeen used to test a barrier such as l
38、ow-density polyethylene.For this reason, materials of comparable gas transmissionqualities should be tested together.9.4 Back diffusion of air into the unit is undesirable. Careshould therefore be taken to ensure that there is a flow ofnitrogen through the system at all times. This flow can be lowwh
39、en the instrument is not being used.9.5 Elevated temperatures can be used to hasten specimenoutgassing, provided that the treatment does not alter the basicstructure of the specimen (crystallinity, density, and so forth).This can be accomplished by the use of the heaters in thediffusion cells.10. Sa
40、mpling10.1 The sampling units used for the determination ofO2GTR shall be representative of the quantity of product forwhich the data are required, in accordance with PracticeD 1898. Care shall be taken to ensure that samples arerepresentative of conditions across the width and along thelength of a
41、roll of film.11. Test Specimens11.1 Test specimens shall be representative of the materialbeing tested and shall be free of defects, including wrinkles,creases, and pinholes, unless these are a characteristic of thematerial being tested.11.2 Average thickness shall be determined to the nearest2.5 m
42、(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 distinguishi
43、ngmarks and the orientation of the test specimen in the diffusioncell shall be reported (for example, “side II was mountedfacing the oxygen side of the diffusion cell”).12. Calibration12.1 General ApproachThe oxygen sensor used in thistest method is a coulometric device that yields a linear outputas
44、 predicted by Faradays Law. In principle, four electrons areproduced by the sensor for each molecule of oxygen that passesinto it. Considering that the sensor is known to have a basicefficiency of 95 to 98 %, it may be considered an “intrinsic”standard7that does not require calibration, and can thus
45、 beused as a reference method.12.2 Experience has shown, however, that under somecircumstances the sensor may become depleted or damaged tothe extent that efficiency and response are impaired. For thatreason, this test method incorporates means for a periodic5The sole source of supply of the catalys
46、t known to the committee at this timeis Englehard Industries Division, Chemical Dept., 429 Delancey Street, Newark, NJ07105. If you are aware of alternative suppliers, please provide this information toASTM International Headquarters. Your comments will receive careful consider-ation at a meeting of
47、 the responsible technical committee,1which you may attend.6It is deemed advisable upon initial setup of the voltage recorder and periodi-cally thereafter to check the response of the recorder on all ranges to a suitablevoltage input.7Garner, E. L., and Raspberry, S. D., “Whats new in Traceability,”
48、 Journal ofTesting and Evaluation, Vol 21, No. 6, November 1993, pp. 505509.D3985053sensor evaluation. This evaluation is derived from measure-ments of a known-value “reference package”. Experienceindicates however, that a specimen-to-specimen variability ofthe reference material8is such that a chan
49、ge should never bemade in the calibration factor, as the result of a measurementusing a single sheet of the reference material.12.3 Establishing a System Calibration Constant (Used onlyon systems using a chart recorder to determine O2GTR)Determine the exposed area, A, of the calibrating reference film(see 7.1.1.1). Using the permeance value furnished with thereference film, determine the O2GTR through that film of thatarea (A). Use this value to determine the calibration constant,Q:Q 5O2GTR 3 RLEe2 Eo(1)where:O2GTR = Oxygen transmission rate through
