ASTM_F_372_-_99_2003.pdf

Designation:F 372 99(Reapproved 2003)Standard Test Method forWater Vapor Transmission Rate of Flexible Barrier MaterialsUsing an Infrared Detection Technique1This standard is issued under the fixed designation F 372;the number immediately following the designation indicates the year oforiginal adoption or,in the case of 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 rapid procedure for determin-ing the rate of water vapor transmission of flexible barriermaterials in film or sheet form.This test method is applicableto sheets and films up to 3 mm in thickness,consisting ofsingle-layer or multilayer synthetic or natural polymers andmetal foils including coated materials.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 limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D 374 Test Methods for Thickness of Solid Electrical Insu-lationD 1898 Practice for Sampling of PlasticsE 96 Test Methods for Water Vapor Transmission of Mate-rialsE 104 Practice for Maintaining Constant Relative Humidityby Means of Aqueous SolutionsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 Definitions:3.1.1 water vapor transmission rate(WVTR)(of a bodybetween two specified parallel surfaces)the time rate ofwater vapor flow normal to the surfaces,under steady condi-tions,through unit area,under the conditions of test(forexample,temperature and relative humidity).An accepted unitof WVTR is g/daym2.The test conditions must be stated.3.1.2 water vapor permeance(of a body between twospecified parallel surfaces)the ratio of its WVTR to the vaporpressure difference between the two surfaces.An accepted unitof permeance is a metric perm,or 1 g/daym2mm Hg.Sincethe permeance of a specimen is generally a function of relativehumidity and temperature,the test conditions must be stated.4.Summary of Test Method4.1 A dry chamber is separated from a wet chamber ofknown temperature and humidity by the barrier material to betested.The time for a given increase in water vapor concen-tration of the dry chamber is measured by monitoring thedifferential between two bands in the infrared spectral region,one in which water molecules absorb and the other where theydo not.This information is then used to calculate the watervapor movement through a known area of barrier material.5.Significance and Use5.1 The purpose of this test method is to rapidly obtainreliable values for the WVTR of barrier materials.5.2 The WVTR is an important property of packagingmaterials,which can be related to shelf life and productstability.5.3 In any application,the WVTR of a barrier material isdetermined by its permeance under the given conditions.Inmost cases,the WVTR will increase when the absolutehumidity is increased on the wet side of the barrier and whenthe temperature of the environment increases,particularly if apolymeric material is the primary water vapor barrier in theconstruction.5.4 Values for water vapor permeance and water vaporpermeability must be used with caution.The inverse relation-ship of WVTR to thickness and the direct relationship ofWVTR to the partial pressure differential of the water vapor arenot always linear.6.Apparatus6.1 Water Vapor Transmission Apparatus,3(Fig.1)with thefollowing:1This test method is under the jurisdiction ofASTM Committee F02 on FlexibleBarrier Materials and is the direct responsibility of Subcommittee F02.30 on TestMethods.Current edition approved May 10,1999.Published July 1999.Originallypublished as F 372 73.Last previous edition F 372 94.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3Modern Controls,Inc.no longer supplies the IRD-2,but some are still in use.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.6.1.1 Temperature Control,capable of maintaining humidchambers and test material at 37.8 6 0.1C(100 6 0.2F).6.1.2 Infrared Detection System,capable of detectingchanges of 1 g of water vapor per litre or in other terms 1 ppmby volume or 0.002%relative humidity at 37.8C.6.2 Micrometer,graduated to 0.0025 mm(0.10 mil)orbetter,and accurate to 0.00125 mm(0.05 mil)to measurespecimen thickness.6.3 Analytical Balance,accurate to 0.0001 g.6.4 Clock or Watch.6.5 Schwartz U-Shaped Drying Tube.6.6 Calcium Chloride Drying Tube.6.7 Sponges.7.Reagent and Materials7.1 Desiccant for Drying Air Stream.47.2 Desiccant for Drying Tubes.57.3 Distilled W