Designation:F1249–06
Standard Test Method for
Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor1
This standard is issued under thefixed designation F1249;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(e)indicates an editorial change since the last revision or reapproval.
Note—Paragraph13.1.1was editorially corrected and the year date was changed on June22,2006.
1.Scope
1.1This test method covers a procedure for determining the rate of water vapor transmission throughflexible barrier materials.The method is applicable to sheets andfilms up to3 mm(0.1in.)in thickness,consisting of single or multilayer synthetic or natural polymers and foils,including coated materials.It provides for the determination of(1)water vapor transmission rate(WVTR),(2)the permeance of thefilm to water vapor,and(3)for homogeneous materials,water vapor permeability coefficient.
N OTE1—Values for water vapor permeance and water vapor perme-ability must be used with caution.The inverse relationship of WVTR to thickness and the direct relationship of WVTR to the partial pressure differential of water vapor may not always apply.
1.2This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.
2.Referenced Documents
2.1ASTM Standards:2
D374Test Methods for Thickness of Solid Electrical Insu-lation
D1898Practice for Sampling of Plastics3
E96/E96M Test Methods for Water Vapor Transmission of Materials
E104Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions
E178Practice for Dealing With Outlying Observations
E691Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3.Terminology
3.1Definitions:
3.1.1water vapor permeability coeffıcient—the product of the permeance and the thickness of thefilm.The permeability is meaningful only for homogeneous materials,in which case it is a property characteristic of bulk material.
3.1.1.1Discussion—This quantity should not be used unless the relationship between thickness and pe
rmeance has been verified in tests using several thicknesses of the material.An accepted unit of permeability is the metric perm centimeter,or 1g/m2per day per mm Hg·cm of thickness.The SI unit is the mol/m2·s·Pa·mm.The test conditions(see3.1)must be stated.
3.1.2water vapor permeance—the ratio of a barrier’s WVTR to the vapor pressure difference between the two surfaces.
3.1.2.1Discussion—An accepted unit of permeance is the metric perm,or1g/m2per day per mm Hg.The SI unit is the mol/m2·s·Pa.Since the permeance of a specimen is generally a function of relative humidity and temperature,the test condi-tions must be stated.
3.1.3water vapor transmission rate(WVTR)—the time rate of water vaporflow normal to the surfaces,under steady-state conditions,per unit area.
3.1.3.1Discussion—An accepted unit of WVTR is g/m2per day.The test conditions of relative humidity and temperature where the humidity is the difference in relative humidity across the specimens,must be stated.
4.Summary of Test Method
4.1A dry chamber is separated from a wet chamber of known temperature and humidity by the barrier material to be tested.The dry chamber and the wet chamber make up a
1This test method is under the jurisdiction of ASTM Committee F02on Flexible
Barrier Materials and is the direct responsibility of Subcommittee F02.10on
Permeation.
Current edition approved June22,2006.Published June2006.Originally
approved in1989.Last previous edition approved in2005as F1249–05.
2For referenced ASTM standards,visit the ASTM website,,or
contact ASTM Customer Service at For Annual Book of ASTM
Standards volume information,refer to the standard’s Document Summary page on
the ASTM website.
3Withdrawn.
Copyright©ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA19428-2959,United States.
diffusion cell in which the test film is sealed.Water vapor diffusing through the film mixes with the gas in the dry chamber and is carried to a pressure-modulated infrared sensor.This sensor measures the fraction of infrared energy absorbed by the water vapor and produces an electrical signal,the amplitude of which is proportional to water vapor concentra-tion.The amplitude of the electrical signal produced by the test film is then compared to the signal produced by measurement of a calibration film of known water vapor transmission rate.This information is then used to calculate the rate at which moisture is transmitted through the material being tested.5.Significance and Use
5.1The purpose of this test method is to obtain reliable values for the WVTR of plastic film and sheeting.
5.2WVTR is an important property of packaging materials and can be directly related to shelf life and packaged product stability.
5.3Data from this test method is suitable as a referee method of testing,provided that the purchaser and seller have agreed on sampling procedures,standardization procedures,test conditions,and accept
ance criteria.
6.Apparatus
6.1This method utilizes water vapor transmission appara-tus 4(Fig.1)comprised of the following:
6.1.1Diffusion Cell —An assembly consisting of two metal halves which,when closed upon the test specimen,will accurately define a circular area.A typical acceptable diffusion cell area is 50cm 2.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 that happens to sag or buckle will contact the
top or bottom of the cell.A depth of approximately 6mm (0.250in.)has been found to be satisfactory for 50-cm 2cells.6.1.1.1Diffusion Cell O–Ring —An appropriately sized groove machined into the humid chamber side of the diffusion cell retains a neoprene O–ring.The test area is considered to be the area established by the inside contact diameter of the compressed O–ring when the diffusion cell is clamped shut against the test specimen.
6.1.1.2Diffusion Cell Sealing Surface —A flat rim around the dry side of the diffusion cell.This is a critic
al sealing surface against which the test specimen is pressed;it shall be smooth and without radial scratches.
6.1.1.3Diffusion Cell Air Passages —Two holes in the dry half of the diffusion cell.This is necessary only in the earlier model WVTR instruments that have a separate conditioning rack and testing chamber.These shall incorporate O–rings suitable for sealing the diffusion cell to the test chamber pneumatic fittings for the introduction and exhaust of air without significant loss or leakage.
N OTE 2—Use of Multiple Diffusion Cells —Experience has shown that arrangements using multiple diffusion cells are a practical way to increase the number of measurements that can be obtained in a given time.A separate conditioning rack (Fig.2)may be used that contains a manifold which connects the dry-chamber side of each individual diffusion cell to a dry-air source.Dry air is continually purging the dry chamber of those cells that are connected to the conditioning rack while the humid chamber side is held at a specific relative humidity by distilled water or a saturated-salt solution.It is desirable to thermostatically control the temperature of the conditioning rack as described in 6.1.3.
6.1.2Test Chamber —A cavity into which the diffusion cell is inserted.Again,this is necessary only in the earlier model WVTR instruments that have a separate conditioning rack and testing chamber.The t
est chamber shall incorporate means for clamping the diffusion cell in accurate registration with pneu-matic system openings to the dry-air source and the infrared detector.The chamber shall also provide a thermometer well for the measurement of temperature.
6.1.3Diffusion Cell Temperature Control —It is desirable to thermostatically control the temperature of the diffusion cell to within 61°F.A simple resistive heater attached to the station in such a manner as to ensure good thermal contact is adequate
4
The sole source of supply of the apparatus known to the committee at this time is Mocon/Modern Controls,Inc.,7500Boone Avenue North,Minneapolis,MN 55428.If you are aware of alternative suppliers,please provide this information to ASTM International Headquarters.Your comments will receive careful consider-ation at a meeting of the responsible technical committee,1which you may
attend.
FIG.1Measuring
System
FIG.2Conditioning
System
for this purpose.A thermistor sensor and an appropriate control circuit will serve to regulate the temperature unless measure-ments are being made close to ambient temperature.In that case it may be necessary to provide cooling coils to remove some of the heat.editorially
6.1.4Flowmeter—A means for regulating theflow of dry air within an operating range of5to100cc/min is required.
6.1.5Flow-Switching Valves,for the switching of dry-gas flow streams of the water vapor transmission apparatus.
6.1.6Infrared Sensor—A water vapor detector capable of sensing1µg/L of water,or,in other terms,1ppm
by volume, or0.002%relative humidity at3
7.8°C.
6.1.7Recording Device—A multirange strip chart recorder
or other appropriate instrument for measuring the voltage developed by the signal amplifier.
6.1.8Desiccant Drying System,shall be capable of reducing the concentration of water vapor in the gas source down to less than0.5ppm by volume or0.001%relative humidity at 3
7.8°C.In earlier model WVTR equipment,a separate desic-cant drying system is needed for the conditioning rack and test chamber.
6.1.9Flow-Metering Valve—Afine-metering valve capable of controlling the dry-gasflow rate to the test cell when the apparatus is in the“measure’’mode of operation.
7.Reagents and Materials
7.1Desiccant,4,5for drying gas stream.
7.2Absorbent Pads(not critical),such asfilter pads of30 to75mm in diameter.Necessary only in earlier model WVTR equipment that utilizes distilled water or saturated salt solu-tions to generate the desired relative humidity.
7.3Distilled Water,for producing100%relative humidity, or various saturated salt solutions to produce other relative humidities as described in Practice E104.Newer WVTR equipment does not require saturated salt solutions.Refer to the manufacturer’s instructions for generating relative humid-ity.
7.4Reference Film,known WVTR material for system calibration.
7.5Sealing Grease,a high-viscosity,silicone stopcock grease or other suitable high-vacuum grease is required for lubrication of O–rings and to seal the specimenfilm in the diffusion cell.
7.6Nitrogen Gas,shall be dry and contain not less than 99.5%nitrogen.Needed only with certain WVTR instruments.
8.Sampling
8.1Select material for testing in accordance with standard methods of sampling applicable to the material under test. Sampling may be done in accordance with Practice D1898. Select samples consid
ered representative of the material to be tested.If the material is of nonsymmetrical construction,the orientation should be noted.9.System Calibration With Reference Film
9.1Follow the manufacturer’s instructions for calibrating the WVTR instrument with a referencefilm.
10.Test Procedure
10.1Preparation of Apparatus(Fig.1)—If preceding tests have exposed the apparatus to high moisture levels,outgas the system to desorb residual moisture.
10.2Number of Specimens Tested—Test enough specimens to characterize package permeation rates but never less than three per sample.
10.3Preparation of Test Samples:
10.3.1Cut the test specimen to approximately10cm by10 cm(4in.by4in.).
10.3.2Measure specimen thickness at four equally spaced points within the test area and at the center in accordance with guidelines described in Test Method D374.
10.3.3Lightly grease the cell sealing surface and the cell O–ring.
10.3.4For earlier model WVTR systems that require the use of distilled water or saturated salt solutions,insert one to three absorbent pads into the lower half-cell and dampen with distilled water or a desired salt solution.Otherwise,for newer WVTR instruments,follow the manufacturer’s instructions for generating the desired relative humidity.
10.3.5Affix the testfilm to the diffusion cell following the manufacturer’s instructions.Fig.3shows the type of diffusion cell used in earlier model WVTR equipment that consisted of a separate conditioning rack and testing chamber.Diffusion cells in newer WVTR equipment are similar to the lower half of the cell displayed in Fig.3.
10.3.6If using a separate conditioning rack,clamp the assembled cell in the conditioning rack.Allow thefilm to condition in the diffusion cell until steady state has been attained.If unfamiliar with the material being tested,the operator should investigate the effect of conditioning time to be certain that sufficient time has been allowed for the material to equilibrate under the test conditions(see Note3).
10.4Measure the WVTR of thefilm specimen following the manufacturer’s instructions.
N OTE3—When testing materials for which the operator has no previous history,additional time must be allowed to assure that true equilibrium has been reached.When in doubt,retest after an additional c
onditioning interval of several hours.
5Linde Molecular Sieve,Type4A or Type5A,in the form of1⁄8in.pellets as may be obtained from the Union Carbide Co.,Linde Division,Danbury,CT
06817-0001.FIG.3Film Diffusion
Cell
10.5Record temperature of each test with reference to a thermometer or thermocouple installed in the test chamber thermometer well.Temperature is a critical parameter affecting the measurement of WVTR.During testing,monitor the temperature,periodically,to the nearest0.5°C.Report the average temperature and the range of temperatures observed during the test.
10.6Standby and Shutoff Procedures:
10.6.1Follow the manufacturer’s instructions for putting the instrument in standby when not being used.
10.6.2When the system is not to be used for an extended period and there are nofilms that require conditioning,the electrical power may be turned off.
11.Calculation
11.1WVTR—If using a recorder,calculate water vapor transmission rate using the formula:
WVTR5C~ES2EO!
where:
C=a calibration factor expressing rate as a function of voltage(or mV).The value of C is derived from tests
of a known referencefilm(Section9),
EO=permeation system zero level voltage,and
ES=equilibrium voltage obtained with the test specimen.
Newer computer-controlled systems will automatically cal-culate the WVTR.
11.2Permeance—Calculate sample permeance(if required) using the following relationship:
Metric Perms5WVTR
P w5g/m
2·day·mm Hg
where:
WVTR=Specimen water vapor transmission rate,g/m2·d, and
P w=Water vapor partial pressure gradient across the test specimen,mmHg.
11.3Permeability Coeffıcient—Calculate the water vapor permeability coefficient(if required)using the following rela-tionship:
Permeability5metric perms·t
where:
t=the average thickness of the specimen,mm.Note: Permeability calculations are meaningful only in cases
where materials have been determined to be homoge-
neous.
12.Report
12.1Report the following information:
12.1.1A description of the test specimen.If the material is nonsymmetrical(two sides different),include a statement as to which side was facing the high humidity,
12.1.2The humidity environment on each side of the test film and means by which it was obtained,
12.1.3The test temperature(to nearest0.5°C),
12.1.4The values of WVTR and,if desired,values of permeance and permeability.These entries should be rounded off to three significantfigures or less,as may be consistent with the operator’s estimate of precision or bias,
12.1.5A statement of the means used to obtain the calibra-tion factor,
12.1.6The effective area exposed to permeation and a description of how it was defined,
12.1.7The time to reach steady-state after introduction of the diffusion cell into the test chamber,and
12.1.8A description of the conditioning procedure.
13.Precision and Bias
13.1Precision:
13.1.1Four differentfilm materials cut and distributed in accordance with Practice E691were evaluated by eight laboratories.The number of laboratories and materials in this study does not meet the minimum requirements for determin-ing precision prescribed in Practice E691.Of the total eight laboratories that participated in this round robin,one did not report results for the PET sample.Due to equipment limita-tions,onlyfive laboratories were able to measure the water vapor transmission rate of the EVOH material.Of thesefive labs,the data from two laboratories were determined to be outliers in accordance with Practice E178.In addition,due to the type of equipment used,two of the laboratories participat-ing in the round robin actually measured all of the samples at 90%RH and converted the results to100%RH driving force by multiplying by1.11.
Precision,characterized by repeatability S r and r,and repro-ducibility S R and R,has been determined for the following materials to be:
Materials No.of Labs Average†S r S R r R
PET714.00.3  2.00.8  5.7
PE829.8  2.3  4.6  6.312.9 EVOH3239.626.7177.674.7497.3 PP8  4.10.20.60.5  1.7
†Editorially corrected.
13.2Bias—Measured values are derived from comparisons with known-value referencefilms.The accuracy of this method is therefore dependent upon the validity of the values assigned to these referencefilms.This information should be available from the manufacturer of the reference
films.
APPENDIX
(Nonmandatory Information)
X1.TESTING POOR BARRIERS
X1.1Normal procedures as described for the modulated infrared permeation system are considered suitable for testing barrier materials having rates up to100g/m2–day.Above that level,a different approach may be required in order to keep the sensor output within design limits.
X1.2In general,the testing of a“high transmitter’’requires that means be employed to reduce the concentration of water vapor in the sensor.This may be accomplished in two ways: X1.2.1By increasing theflow of dry gas(possible in earlier model WVTR equipment),or
X1.2.2By reducing the area of the testfilm.
X1.3Alternatively,apply foil masks with die-cut apertures. These may be applied to both sides of a barrier to reduce the sample area.Metal masks utilizing a neoprene O-ring are yet another alternative.
X1.4Each of these methods,when used alone or in combination,serves to reduce the vapor concentration of the air stream.
N OTE X1.1—The precision and bias of results obtained with reduced-area masked samples has not been established.
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