ASTM_D_6701_-_01.pdf

Designation:D 6701 01Standard Test Method forDetermining Water Vapor Transmission Rates ThroughNonwoven and Plastic Barriers1This standard is issued under the fixed designation D 6701;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 procedure for determining therate of water vapor transmission ranging between 500 to100,000 g/m2day through nonwoven and plastic barrier mate-rials.The method is applicable to films,barriers consisting ofsingle or multilayer synthetic or natural polymers,nonwovenfabric,and nonwoven fabrics coated with films up to 3 mm(0.1in.)in thickness.1.2 This test method provides for the determination of(1)water vapor transmission rate(WVTR),and(2)the permeanceto water vapor.1.3 The values stated in metric units are to be regarded asthe standard.The acceptable units for water vapor transmissionrate are usually g/m2day.1.4 This standard does not purport to address all of thesafety concerns,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:D 123 Terminology Relating to Textiles2D 1898 Practice for Sampling of Plastics3D 4204 Practice for Preparing Plastic Film Specimens for aRound-Robin Study4D 5729 Test Methods for Thickness of Nonwoven fabrics5E 691 Practice for Conducting an Interlaboratory Test Pro-gram to Determine the Precision of Test Methods6F 1249 Test Method for Water Vapor Transmission RateThrough Plastic Film and Sheeting Using a ModulatedInfrared Sensor73.Terminology3.1 Definitions:3.1.1 water vapor permeability coeffcient,nthe ratio ofthe permeance and the thickness.3.1.1.1 DiscussionThis quantity should not be used unlessthe relationship between thickness and permeance has beenverified in tests using several thickness of the material.Thewater vapor permeability is meaningful only for homogeneousmaterials,in which case it is a property characteristic of bulkmaterial.An accepted unit of water vapor permeability is themetric perm centimeter,or 1g per m2per day per mm Hg-cm ofthickness.The SI unit is the mol/m2-s-Pa-mm.3.1.2 water vapor permeance,nthe ratio of a barrierswater vapor transmission rate to the vapor pressure differencebetween the two surfaces.3.1.2.1 DiscussionAn accepted unit of water vapor per-meance is the metric perm,or 1 g/m2per day per mm Hg.TheSI unit is the mol/m2-s-Pa.Since the water vapor permeance ofa specimen is generally a function of relative humidity andtemperature,therefore those conditions must be stated.3.1.3 water vapor transmission rate(WVTR),nthesteady-state time rate of water vapor flow through unit area ofa specimen,normal to the surfaces under specific conditions oftemperature and humidity at each surface.3.1.3.1 DiscussionA common practice accepted unit ofwater vapor transmission rate is metric g/m2per day.The testconditions of relative humidity and temperature where thedriving force is the difference in relative humidity across thespecimen must be stated.4.Summary of Test Method4.1 A dry chamber,guard film,and a wet chamber make upa diffusion cell in which the test film is sealed.A first test ismade of the water vapor transmission rate of the guard film andair gap between an evaporator assembly that generates 100%relative humidity.A sensor produces an electrical signal,theamplitude of which is proportional to water vapor concentra-tion.The electrical signal is routed to a computer for process-ing.The computer calculates the transmission rate of the airgap and guard film and stores the value for further use.Thebarrier is then sealed in the test cell and the apparatus started1This test method is under the jurisdiction ofASTM Committee D13 on Textilesand is the direct responsibility of Subcommittee D13.64 on Nonwoven Fabrics.Current edition approved August 10,2001.Published October 2001.2Annual Book of ASTM Standards,Vol 10.01.3Annual Book of ASTM Standards,Vol 08.03.4Annual Book of ASTM Standards,Vol 04.06.5Annual Book of ASTM Standards,Vol 07.02.6Annual Book of ASTM Standards,Vol 11.03.7Annual Book of ASTM Standards,Vol 15.09.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.in the test mode.As before,the electrical signal representingthe water vapor is sent to the computer which then calculatesthe transmission rate of the combination of the air gap,theguard film,and the test barrier.The computer then uses thisinformation to calculate the water vapor transmission rate ofthe material being tested.The computer determines when themeasured results indicate that the specimens have reachedequilibrium values and the tes