ASTM_D_7253_-_06_2011e1.pdf

Designation:D725306(Reapproved 2011)1Standard 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.1NOTEReapproved with editorial changes in September 2011.1.Scope1.1 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.No other units of measurement are included in thisstandard.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 determine the applica-bility of regulatory limitations prior to use.NOTE1There is no known ISO equivalent to this standard.2.Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 Definitions:For definitions of terms used in this testmethod see Terminology D883.3.2 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.NOTE2Phenolphthalein is the indicator of choice based on publishedhydroxyl number methods that include an acid number correction.Otherindicators can be chosen if specific acids are of interest.Bromothymolblue(green endpoint)can be 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.7.Apparatus7.1 Buret,10 mL,can be manual or automatic.7.2 Graduated cylinder,10 mL,maximum.7.3 Balance,analytical with sensitivity of at least 60.0001g.7.4 Erlenmeyer flask,at least 250 mL.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 where such1This 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 Sept.1,2011.Published October 2011.Originallyapproved in 2006.Last previous edition approved in 2006 as D7253-06.DOI:10.1520/D7253-06R11E01.2For 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 States1 specifications are available.3Other grades can be used pro-vided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.8.2 Phenolphthalein,Indicator Grade.8.3 Phenolphthalein Indicator SolutionDissolve 1 g ofphenolphthalein in 100 mL of methanol.8.4 Potassium Hydroxide Standard Solution(0.02 N)Prepare and standardize a 0.02 N methanolic potassium hy-droxide solution.(1.32 g KOH pellets(85%KOH)per 1000mL methanol,standardized with potassium hydrogen phtha-late.)9.Procedure9.1 Add 100 6 20 mL of 2-propanol and 1 mL of phenol-phthalein indicator solution to an Erlenmeyer flask.9.2 Titrate the stirred solution with 0.02 N KOH solution tothe first faint pink endpoint that persists for 30 seconds.9.3 Weigh 50-60 g of sample into the same Erlenmeyer flaskand record the weight of the sample to the nearest 0.1 g.9.4 Stir or swirl the solution in the flask until the sample iscompletely dissolved.9.5 Titrate the clear sample solution with standardized 0.02N KOH solution to the first faint pink endpoint that persists for30 seconds.10.Calculation or Interpretation of Res