1、Designation: D4672 00 (Reapproved 2006)1 D4672 12Standard Test MethodsMethod forPolyurethane Raw Materials: Determination of WaterContent of Polyols 1This standard is issued under the fixed designation D4672; the number immediately following the designation indicates the year oforiginal adoption or,
2、 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 NOTERemoved non-mandatory language throughout in March 2006.1. Scope*1.1 TheseThis test me
3、thods measuremethod measures water content of polyols and many other organic compounds.1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.1.3 This standard does not purport to address all of the safety concerns, if any, asso
4、ciated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.NOTE 1TheseThis test methods aremethod is equivalent to ISO 14897.2. Referenced Documents2.1 ASTM Stand
5、ards:2D1193 Specification for Reagent WaterD883 Terminology Relating to PlasticsE180 Practice for Determining the Precision of ASTM Methods for Analysis and Testing of Industrial and Specialty Chemicals(Withdrawn 2009)33. Terminology3.1 Definitions:3.1.1 polyurethane, na polymer prepared by the reac
6、tion of an organic diisocyanate with compounds containing hydroxylgroups.3.1.1.1 DiscussionPolyurethanes, or urethanes, as they are sometimes called, may be thermosetting, thermoplastic, rigid or soft and flexible, cellularor solid. (See Terminology D883.)4. Summary of Test Methods4.1 Test Methods A
7、 and B are This method is based essentially on volumetric or coulometric titrations that follow the reductionof iodine by sulfur dioxide in the presence of water. This reaction proceeds quantitatively when methanol or another alcohol (ROH)and pyridine (C5H5N) or a similar amine (R8N) are present to
8、react with the sulfur trioxide (SO3) and hydriodic acid (HI) producedaccording to the following reactions:ROH + SO2 + R8N R8NHSO3RH2O + I2 + R8NHSO3R + 2R8N R8NHSO4R + 2R8NHI1 These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and are the direct responsibility of Subcomm
9、ittee D20.22 on Cellular Materials -Plastics and Elastomers.Current edition approved March 15, 2006. Published June 2006. Originally approved in 1991. Last previous edition approved in 2000 as D4672 - 00. DOI:10.1520/D4672-00R06E01.2 For referenced ASTM standards, visit the ASTM website, www.astm.or
10、g, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved version of this historical standard is referenced on www.astm.org.This document is not an ASTM standard an
11、d is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only
12、the current versionof the standard as published by ASTM is to be considered the official document.*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 States14.2 To determine water,
13、 Karl Fischer reagent (a solution of iodine, sulfur dioxide, imidazole, and pyridine or a pyridinesubstitute) is added to a solution of the sample in methanol or other alcohol until all the water present has been consumed. Thetitrant is either added by buret (volumetry) or generated electrochemicall
14、y in the titration cell (coulometry). Coulometric titrationseliminate the need for standardizing the reagent.5. Significance and Use5.1 TheseThis test methods aremethod is suitable for quality control, as a specification test, and for research. The water contentof a polyol is important since isocyan
15、ates react with water.TEST METHOD A: MANUAL PROCEDURENOTE 2Commercially available automated Karl Fischer titrators are used extensively.5.2 The description of the manual systems presented below is for reference purposes and has been included in order to betterdefine the principles of the Karl Fische
16、r measurement.6. Apparatus6.1 Titration VesselA vessel of approximately 300-mL capacity, such as a tall-form, lipless beaker, provided with a tight-fittingclosure to protect the reaction mixture from atmospheric moisture. The vessel shall also be fitted with a nitrogen inlet tube, a 10-mLburet, a st
17、irrer (preferably magnetic), and a port that may be opened momentarily for sample and solvent addition or removal ofelectrodes. It is convenient to provide a vacuum line leading to a 1-L trap bottle for drawing off the titrated solution. Pass thenitrogen through a drying tube containing anhydrous ca
18、lcium sulfate before it enters the titration vessel.6.2 Instrument ElectrodesPlatinum with a surface equivalent of two No. 26 wires, 4.762 mm (0.19 in.) long. The wires areto be 3 to 8 mm apart and inserted in the vessel so that 75 mL of solution will cover them.6.3 Instrument Depolarization Indicat
19、orHaving an internal resistance of less than 5000 V and consisting of a means ofimpressing and showing a voltage of 20 to 50 mV across the electrodes and capable of indicating a current flow of 10 to 20 Aby means of a galvanometer or ratio tuning circuit.6.4 Buret AssemblyFor Karl Fischer reagent, c
20、onsisting of a 10-mL buret with 0.05-mL subdivisions connected by means ofglass or polyethylene (not rubber) connectors to a source of reagent. Several types of automatic dispensing burets may be used.Since the reagent loses strength when exposed to moist air, all vents must be protected against atm
21、ospheric moisture by adequatedrying tubes containing anhydrous calcium sulfate. All stopcocks and joints are to be lubricated with an inert lubricant.7. Reagents7.1 Purity of ReagentsUse reagent-grade chemicals in all tests. Unless otherwise indicated, it is intended that all reagents shallconform t
22、o the specifications of the Committee on Analytical Reagents of the American Chemical Society where suchspecifications are available.4 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without lessening the accuracy of the det
23、ermination.7.2 Purity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent water as defined byType I of Specification D1193.7.3 Karl Fischer ReagentEquivalent to 2.5 to 3.0 mg of water/mL. Dilute commercially available stabilized Karl Fischerreagent (6 mg of wa
24、ter/mL) with an equal volume of anhydrous ethylene glycol monomethyl ether (containing less than 0.1 %water). (See Note 3.)NOTE 3Improved, pyridine-free Karl Fischer reagents have been made available and are now highly recommended as a replacement for the previousreagents. See Section 14, under Test
25、 Method B, Automated Procedure.7.4 Titration Solvent, Anhydrous MethanolUnless the methanol is extremely dry it will require a large amount of dilute KarlFischer solution to react with its residual water. For this reason the solvent shall be further dried by adding undiluted Karl Fischerreagent (6 m
26、g of water/mL) to a bottle of methanol until a light red-brown color persists. Add methanol until the solution is a paleyellow. A 100-mL portion of the treated solvent requires 1 to 10 mL of dilute Karl Fischer reagent.8. Sampling8.1 It is essential to avoid changes in the water content of the mater
27、ial during sampling operations. Many polyols are quitehygroscopic and errors from this source are particularly significant in the determination of the small amount of water usuallypresent. Use almost-filled, tightly capped containers and limit as much as possible contact of the sample with air when
28、transferringthe sample to the titration vessel. Avoid intermediate sample containers, if possible. If several different analyses are to be performedon the same sample, determine the water first and do not open the sample prior to the actual analysis.9. Standardization of Reagent9.1 Standardize the K
29、arl Fischer reagent daily using the same procedures as used for titrating the sample.D4672 1229.1.1 Add 100 mL of titration solvent to the flask and titrate the residual moisture as described in Section 10. To this titratedsolvent, immediately add 1 drop of water from a weighing pipet. Weigh the pip
30、et to 60.1 mg. Complete the titration with KarlFischer reagent as described in Section 10. It may be necessary to refill the buret during the titration.9.1.2 Calculate the equivalence factor, F, in terms of milligrams of water per millilitre of reagent as follows:equivalency factor, F 5A/B (1)where:
31、A = water added, mg, andB = Karl Fischer reagent required, mL.10. Procedure10.1 Adjust the nitrogen valve so that dry nitrogen flows into the titration vessel at a slow rate (20 to 50 mL/min). Introduceapproximately 100 mL of titration solvent into the titration vessel, making sure that the electrod
32、es are covered with solvent. Adjustthe stirrer to give adequate mixing without splashing. Titrate the mixture with Karl Fischer reagent to the end point. (See Note 4.)10.2 To the prepared titration mixture, add the amount of sample as indicated in Table 1. Exercise care when the sample istransferred
33、 so that water is not absorbed from the air, particularly under conditions of high humidity. Allow the solution to stir 1or 2 minutes until dissolution is complete.10.3 Titrate the mixture again with Karl Fischer reagent to the same end point previously employed. Record the amount ofreagent used to
34、titrate the water in the sample.NOTE 4The end point is that point in the titration when two small platinum electrodes upon which a potential of 20 to 50 mV has been impressedare depolarized by the addition of 0.05 mL of Karl Fischer reagent (equivalent to 2.5 to 3.0 mg water/mL) causing a change of
35、current flow of 10 to 30V that persists for at least 30 s.11. Calculation11.1 Calculate the water content of the sample as follows:water, %5VF/10W (2)where:V = Karl Fischer reagent required by the sample, mLF = equivalency factor for Karl Fischer reagent, mgwater/mL reagent, andW = sample used, g.12
36、. Precision and Bias12.1 Attempts to develop a precision and bias statement for this test method have not been successful. For this reason, data onprecision and bias cannot be given. Anyone wishing to participate in the development of precision and bias data needs to contactthe Chairman, Subcommitte
37、e D20.22 (Section 20.22.01), ASTM, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA194282959.TEST METHOD B: AUTOMATED PROCEDURE6. Apparatus6.1 Several commercial Karl Fischer autotitrators are available4 that employ volumetric or coulometric titrations and provideresults superior to those o
38、f the manual procedure, described above. titrations. These instruments consist of an automated buretassembly, a sealed titration vessel with appropriate electrodes and sensing circuitry, and a vacuum system for removal of solutionafter analysis. These automated systems provide several advantages and
39、 conveniences. Atmospheric moisture contamination canbe more closely controlled; calibration is simplified; and the preneutralization step is automatic. Titrations are rapid, and reagentconsumption is low. Autotitrators automatically calculate and display or print the water concentration.7. Reagents
40、7.1 Commercial reagents and reagent systems of various types are available5 for use with autotitrators for water determination.Pyridine-free reagents have improved stability and less objectionable odor than the conventional Karl Fischer reagent. Reagents4 Instruments similar to and including the fol
41、lowing types have been found suitable for determining water content of polyols, based on round-robin studies: Metrohmmodels 633, 652, 658, 665, 684, 701, 720, 737, and 758 (available from Brinkmann Instruments, Inc. at ) and Mettler Toledo models DL 18, 31, 37,and 38 ().5 Reagents for Karl Fischer t
42、itrations include Hydranal products from Riedel-deHan (www.rdhlab.de), which are available through Sigma-Aldrich (www.sigma-) and AquaStar products which are sold by EMScience ().D4672 123can be purchased in split or composite forms in different concentrations to fit various ranges of water content.
43、 A composite reagentcontains all the components required for a Karl Fischer titration in a single solution. Split implies separate solutions of the solventand titrant.8. Sampling8.1 Sampling is conveniently accomplished by use of a tared syringe. The material is drawn into the syringe, weighed, andd
44、elivered through the sample port of the autotitrator vessel. The syringe is then reweighed to obtain the sample weight bydifference.8.1.1 Take note of the sample handling warnings inIt is essential to avoid changes in the water content of the material duringsampling operations. Many polyols are quit
45、e hygroscopic and errors from this source are particularly significant in thedetermination of the small amount of water usually present. Use almost-filled, tightly capped containers and limit as much aspossible contact of the sample with air when 8.1.transferring the sample to the titration vessel.
46、Avoid intermediate samplecontainers, if possible. If several different analyses are to be performed on the same sample, determine the water first and do notopen the sample prior to the actual analysis.9. Standardization of Reagent9.1 Since different autotitrators may vary in standardization procedur
47、es, consult the operating manual for the autotitrator in use.Water is an excellent primary standard. In addition, stable, prepackaged, primary standards are also available for establishing thestandardization factor.10. Procedure10.1 Refer to the operating manual for the autotitrator in use. Basicall
48、y, after preneutralization of the reagent in the titratorvessel, the sample is introduced, and the volumetric titration (or coulometric generation of titrant) proceeds automatically to theend point.NOTE 2In choosing the appropriate sample size for use with specific autotitrators, use the manufacture
49、rs recommendations. If no instructions areavailable, use the guidelines listed in Table 21 and Table 32.TABLE 2 Volumetric TitrationA% Water Expected Suggested Sample Size, gBelow 0.5 5100.51.0 1Above 1.0 0.5A For titrant concentration equivalent to 5 mg H2 O per mL.TABLE 3 Coulometric Titration% Water Expected Suggested Sample Size, gBelow 0.1 50.10.5 10.51.0 0.111. Calculation11.1 Following each titration, autotitrator automatically calculates and displays the water content, based on th
