1、Designation:D467212Standard Test Method forPolyurethane Raw Materials:Determination of WaterContent of Polyols1This standard is issued under the fixed designation D4672;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last
2、 revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This test method measures water content of polyols andmany other organic compounds.1.2 The values stated in SI units are to be
3、 regarded as thestandard.The values given in parentheses are for informationonly.1.3 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 deter
4、mine the applica-bility of regulatory limitations prior to use.NOTE1This test method is equivalent to ISO 14897.2.Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD883 Terminology Relating to PlasticsE180 Practice for Determining the Precision of ASTMMethods for Analysis
5、and Testing of Industrial and Spe-cialty Chemicals(Withdrawn 2009)33.Terminology3.1 Definitions:3.1.1 polyurethane,na polymer prepared by the reactionof an organic diisocyanate with compounds containing hy-droxyl groups.3.1.1.1 DiscussionPolyurethanes,or urethanes,as they aresometimes called,may be
6、thermosetting,thermoplastic,rigidor soft and flexible,cellular or solid.(See Terminology D883.)4.Summary of Test Methods4.1 This method is based essentially on volumetric orcoulometric titrations that follow the reduction of iodine bysulfur dioxide in the presence of water.This reaction proceedsquan
7、titatively when methanol or another alcohol(ROH)andpyridine(C5H5N)or a similar amine(RN)are present to reactwith the sulfur trioxide(SO3)and hydriodic acid(HI)producedaccording to the following reactions:ROH+SO2+RN RNHSO3RH2O+I2+RNHSO3R+2RN RNHSO4R+2RNHI4.2 To determine water,Karl Fischer reagent(a
8、solution ofiodine,sulfur dioxide,imidazole,and pyridine or a pyridinesubstitute)is added to a solution of the sample in methanol orother alcohol until all the water present has been consumed.The titrant is either added by buret(volumetry)or generatedelectrochemically in the titration cell(coulometry
9、).Coulomet-ric titrations eliminate the need for standardizing the reagent.5.Significance and Use5.1 This test method is suitable for quality control,as aspecification test,and for research.The water content of apolyol is important since isocyanates react with water.6.Apparatus6.1 Several commercial
10、 Karl Fischer autotitrators are avail-able4that employ volumetric or coulometric titrations.Theseinstruments consist of an automated buret assembly,a sealedtitration vessel with appropriate electrodes and sensingcircuitry,and a vacuum system for removal of solution afteranalysis.These automated syst
11、ems provide several advantagesand conveniences.Atmospheric moisture contamination can bemore closely controlled;calibration is simplified;and thepreneutralization step is automatic.Titrations are rapid,andreagent consumption is low.Autotitrators automatically calcu-late and display or print the wate
12、r concentration.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand are the direct responsibility of Subcommittee D20.22 on Cellular Materials-Plastics and Elastomers.Current edition approved Aug.1,2012.Published August 2012.Originallyapproved in 1991.Last previous editi
13、on approved in 2000 as D4672-00(2006)1.DOI:10.1520/D4672-12.2For 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.3The l
14、ast approved version of this historical standard is referenced onwww.astm.org.4Instruments similar to and including the following types have been foundsuitable for determining water content of polyols,based on round-robin studies:Metrohm models 633,652,658,665,684,701,720,737,and 758(available fromB
15、rinkmann Instruments,Inc.at )and Mettler Toledo modelsDL 18,31,37,and 38().*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 7.Reagents7.1 Commercial reagents and reagent syst
16、ems of varioustypes are available5for use with autotitrators for water deter-mination.Pyridine-free reagents have improved stability andless objectionable odor than the conventional Karl Fischerreagent.Reagents can be purchased in split or composite formsin different concentrations to fit various ranges of watercontent.A composite reagent contains all the componentsrequired for a Karl Fischer titration in a single solution.Splitimplies separate solutions of the solvent and titrant.8.Sampling8.1
