ASTM_D_7191_-_18.pdf

Designation:D719118Standard Test Method forDetermination of Moisture in Plastics by Relative HumiditySensor1This standard is issued under the fixed designation D7191;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()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the quantitative determinationof water down to 20 ppm in plastics using a relative humiditysensor.1.2 Values stated in SI units are to be regarded as standard.1.3 Specimens tested in this test method can reach or exceed250C,use caution when handling them after testing hascompleted.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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.NOTE1There is no known ISO equivalent to this standard.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD883 Terminology Relating to PlasticsD1600 Terminology forAbbreviated Terms Relating to Plas-ticsD6869 Test Method for Coulometric and Volumetric Deter-mination of Moisture in Plastics Using the Karl FischerReaction(the Reaction of Iodine with Water)E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 DefinitionsThe definitions used in this test method arein accordance with Terminology D883.4.Summary of Test Method4.1 A sample is loaded into a septum-capped glass vial thatis moved into a heater to evolve the volatiles from the sampleinto the headspace.A coaxial needle,or two needle set,piercesthe septum of the vial as it enters the heater.A dry carrier gasthen flows into the vial and carries the evolved volatiles in theheadspace into the sensor manifold.In the sensor manifold,thecarrier gas is cooled to allow high-boiling volatiles to condenseon a hydrophobic filter.The filters hydrophobic propertiesallow the moisture in the carrier gas to pass through and thenbe measured as an increase in potential at the relative humiditysensor.This sensor signal is integrated over time to provide ameasurement of the total mass of water in the sample.The totalmoisture is then divided by sample mass to yield moisturecontent.4.2 This test method utilizes a sealed,airtight flow systemthat prevents contamination of the analyzer from water presentin the atmosphere.5.Significance and Use5.1 This test method is intended for use as a control,acceptance,and assessment test.5.2 Moisture can seriously affect the processability of plas-tics.It is possible that high moisture content will cause surfaceimperfections(that is,splay or bubbling)or degradation byhydrolysis.Low moisture(with high temperature)has beenknown to cause solid phase polymerization.5.3 The physical properties of some plastics are greatlyaffected by the moisture content.6.Interferences6.1 Elevated concentrations of some common solvents suchas methanol,ethanol and acetone will give biased high read-ings due to their polar characteristics and ability to permeatethe thermoset polymer layers of the relative humidity sensor.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved Dec.1,2018.Published December 2018.Originallyapproved in 2005.Last previous edition approved in 2010 as D7191-10.DOI:10.1520/D7191-18.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.1 7.Apparatus7.1 Moisture Analyzer3,an apparatus that consists of:7.1.1 Flow Regulator,capable of maintaining the carrier gasflow rate within the manufacturers specified conditions.7.1.2 Flow Meter,capable of measuring the carrier gas flowrate in accordance with the manufact