1、Designation: D7253 16Standard 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
2、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 a
3、s 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 stan
4、dard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE 1There is no known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsE691 Practice for Conducting an I
5、nterlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 DefinitionsFor 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,
6、 that is required to titrate acidicconstituents in1gofsample.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 en
7、dpoint) of the addedphenolphthalein.NOTE 2It 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.NOTE 3Phenolphthalein is the in
8、dicator 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 qu
9、ality 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 Samp
10、les 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, can be manual or automatic.7.2 Graduated cylinder, 10 mL, maximum.7.3 Balance,
11、analytical with sensitivity of at least 60.0001g.7.4 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 specif
12、ications 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
13、. 1, 2016. Published September 2016. Originallyapproved in 2006. Last previous edition approved in 2011 as D7253 - 11(2011)1.DOI:10.1520/D7253-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards
14、 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 States1specifications are available.3Other
15、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 SolutionDissolve1gofphenolphthalein in 100 mL of methanol.8.4 Po
16、tassium 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.) The KOH solution is to remain capped to avoid theformation of carbonates due to
17、 the reaction with atmosphericCO2.9. 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 in
18、to 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 sec
19、onds.10. Calculation or Interpretation of Results10.1 Calculate the acid number, in milligrams of KOH/gram of sample as follows:Acid Number 5 A 3N 356.1#/W (1)where:A = volume of KOH solution for the titration of the samplein mL,N = the normality of the KOH solution, andW = the weight of the sample
20、used in g.11. Report11.1 Report results to the nearest 0.001 mg KOH/g.12. Precision and Bias412.1 Table 1 is based on a round robin involving sevenlaboratories and conducted in 2005 in accordance with PracticeE691. All labs used a colorimetric endpoint titration for thegeneration of the data used in
21、 this study. All the samples wereprepared at one source, but the individual specimens wereprepared at the laboratories that tested them. Each test resultwas the average of two individual determinations. Each labo-ratory made duplicate determinations on each material on eachof two days. (WarningThe f
22、ollowing explanations of r andR (12.2 12.2.3) are intended only to present a meaningfulway of considering the approximate precision of this testmethod. The data in Table 1 is not to be rigorously applied tothe acceptance or rejection of material, as those data arespecific to the round robin and are
23、not representative of otherlots, conditions, materials, or laboratories. Users of this testmethod are to apply the principles outlined in Practice E691 togenerate data specific to their laboratory and materials orbetween specific laboratories. The principles of 12.2 12.2.3are then valid for such dat
24、a.)12.2 Precision12.2.1 Repeatability, (r)Comparing two replicates for thesame material, obtained by the same operator, using the sameequipment on the same day. The two replicate results are to bejudged not equivalent if they differ by more than the r value forthat material.12.2.2 Reproducibility, (
25、R)Comparing two results, eachthe mean of replicates, for the same material, obtained bydifferent operators, using different equipment in differentlaboratories on different days. The two test results are to bejudged not equivalent if they differ by more than the R valuefor that material.12.2.3 Any ju
26、dgment in accordance with 12.2.1 and 12.2.2has an approximate 95 % (0.95) probability of being correct.12.3 There are no recognized standards by which to esti-mate the bias of this test method.13. Keywords13.1 acidity; acid number; hydroxyl number; polyetherpolyols3Reagent Chemicals, American Chemic
27、al Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K. and the United States Phamacopeia andNational Formulary, U.S. Pharma
28、ceutical Convention, Inc. (USPC), Rockville,MD.4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D20-1244.TABLE 1 Round Robin Data for Acid Number (mg KOH/g) inAccordance with Practice E691Material Average SrASRBrCRDnE1 0.026 0.00
29、1 0.005 0.003 0.013 72 0.015 0.001 0.005 0.004 0.014 73 0.016 0.002 0.005 0.005 0.013 74 0.105 0.001 0.008 0.004 0.022 6ASr= within-laboratory standard deviation of the replicates.BSR= between-laboratory standard deviation of the averages.Cr = within-laboratory repeatability limit = 2.8*Sr.DR = betw
30、een-laboratory reproducibility limit = 2.8*SR.En = number of laboratories contributing valid data for this material.D7253 162SUMMARY OF CHANGESCommittee D20 has identified the location of selected changes to this standard since the last issue(D7253 - 11(2011)1) that may impact the use of this standa
31、rd. (September 1, 2016)(1) Subsection 1.2 ScopeChanged to comply with the BlueBook.(2) Subsection 4.1 Summary of Test MethodAdded note toindicate use of automatic titrators is permissible.(3) Subsection 6.1 InterferencesAdded recommendation foruse of an autotitrator.(4) Subsection 8.4 Reagents and M
32、aterialsAdded to protectreagent from atmospheric CO2.(5) Minor editorial changes throughout the method.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that d
33、etermination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved
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