ASTM_D_7253_-_22.pdf

Designation:D725322Standard Test Method forPolyurethane Raw Materials:Determination of Acidity asAcid Number for Polyether Polyols1This standard is issued under the fixed designation D7253;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.Scope*1.1 This test method measures the acidic constituents inpolyether polyols and reports the results as acid number.Thetypical acid number range is 0-0.1 mg KOH/g sample.(SeeNote 1.)1.2 The values stated in SI units are to be regarded asstandard.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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.NOTE1There is no known ISO equivalent to this standard.1.4 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:2D883 Terminology Relating to PlasticsE456 Terminology Relating to Quality and StatisticsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE2935 Practice for Evaluating Equivalence of Two TestingProcesses3.Terminology3.1 DefinitionsFor definitions of terms used in this testmethod see Terminology D883,unless otherwise specified.Forterms relating to precision and bias and associated issues,theterm used in this standard are defined in accordance withTerminology E456.3.2 Definitions of Terms Specific to This Standard:3.2.1 acid numberthe quantity of base,expressed in mil-ligrams of potassium hydroxide,that is required to titrate acidicconstituents in 1 g of sample.4.Summary of Test Method4.1 The sample is dissolved in 2-propanol.The resultingsingle-phase solution is titrated at room temperature with 0.02N methanolic potassium hydroxide solution to an end pointindicated by the color change(pink endpoint)of the addedphenolphthalein.NOTE2It is permissible to use automatic titrators using a potentio-metric endpoint for the titration portion of this test provided the automatictitration method is tested to obtain at least equivalent results to the manualtitration.NOTE3Phenolphthalein is the indicator of choice based on publishedhydroxyl number methods that include an acid number correction.Otherindicators are chosen if specific acids are of interest.Bromothymol blue(green endpoint)is used for stronger acids(pKas 7).5.Significance and Use5.1 This test method is suitable for quality control,as aspecification test,and for research.Acid numbers indicate theextent of any neutralization reaction of the polyol with acids.The results of this method measure batch-to-batch uniformityand are used as correction factors in calculating true hydroxylnumbers.6.Interferences6.1 Samples or constituents that are highly-colored willinterfere with or prevent the use of this test method.In thiscase,a potentiometric titration using an autotitrator isrecommended,see Note 2.7.Apparatus7.1 Buret,10 mL,manual or automatic.7.2 Graduated cylinder,10 mL,maximum.7.3 Balance,analytical with sensitivity of at least 60.0001g.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.22 on Cellular Materials-Plastics and Elastomers.Current edition approved March 15,2022.Published March 2022.Originallyapproved in 2006.Last previous edition approved in 2016 as D7253-16.DOI:10.1520/D7253-22.2For 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.*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 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.17.4 Erlenmeyer flask,at least 250 mL capacity.7.5 Stirring bars or stirring rods.8.Reagents and Materials8.1 Purity of ReagentsUse reagent-grade chemicals in alltests.Unless otherwise indicated,it is intended that all reagentsconform to the specifications of the Committee on AnalyticalReagents of the American Chemical Society wh