1、Designation: D 4672 00 (Reapproved 2006)e1Standard Test Methods forPolyurethane Raw Materials: Determination of WaterContent of Polyols1This standard is issued under the fixed designation D 4672; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTERemoved non-mandatory language throughout in March 2006.1. Scope*1.1 These test methods measure wa
3、ter content of polyolsand many other organic compounds.1.2 The values stated in SI units are to be 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 therespo
4、nsibility 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.NOTE 1These test methods are equivalent to ISO 14897.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterD
5、 883 Terminology Relating to PlasticsE 180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals3. Terminology3.1 Definition:3.1.1 polyurethane, na polymer prepared by the reactionof an organic diisocyanate with compounds containing hy-
6、droxyl groups.3.1.1.1 DiscussionPolyurethanes, or urethanes, as theyare sometimes called, may be thermosetting, thermoplastic,rigid or soft and flexible, cellular or solid. (See TerminologyD 883.)4. Summary of Test Methods4.1 Test Methods A and B are based essentially on volumet-ric or coulometric t
7、itrations that follow the reduction of iodineby sulfur dioxide in the presence of water. This reactionproceeds quantitatively when methanol or another alcohol(ROH) and pyridine (C5H5N) or a similar amine (R8N) arepresent to react with the sulfur trioxide (SO3) and hydriodicacid (HI) produced accordi
8、ng to the following reactions:ROH+SO2+R8N R8NHSO3RH2O+I2+R8NHSO3R+2R8NR8NHSO4R + 2R8NHI4.2 To determine water, Karl Fischer reagent (a 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 wa
9、ter present has been consumed.The titrant is either added by buret (volumetry) or generatedelectrochemically in the titration cell (coulometry). Coulomet-ric titrations eliminate the need for standardizing the reagent.5. Significance and Use5.1 These test methods are suitable for quality control, as
10、 aspecification test, and for research. The water content of apolyol is important since isocyanates react with water.TEST METHOD A: MANUAL PROCEDURENOTE 2Commercially available automated Karl Fischer titrators areused extensively.5.2 The description of the manual systems presented belowis for refere
11、nce purposes and has been included in order tobetter define the principles of the Karl Fischer measurement.6. Apparatus6.1 Titration VesselA vessel of approximately 300-mLcapacity, such as a tall-form, lipless beaker, provided with atight-fitting closure to protect the reaction mixture from atmo-sph
12、eric moisture. The vessel shall also be fitted with a nitrogeninlet tube, a 10-mL buret, a stirrer (preferably magnetic), and aport that may be opened momentarily for sample and solventaddition or removal of electrodes. It is convenient to provide avacuum line leading to a 1-L trap bottle for drawin
13、g off the1These test methods are under the jurisdiction of ASTM Committee D20 onPlastics and are the direct responsibility of Subcommittee D20.22 on CellularMaterials - Plastics and Elastomers.Current edition approved March 15, 2006. Published June 2006. Originallyapproved in 1991. Last previous edi
14、tion approved in 2000 as D 4672 - 00.2For 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.1*A Summary of Changes s
15、ection appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.titrated solution. Pass the nitrogen through a drying tubecontaining anhydrous calcium sulfate before it enters thetitration vessel.6.2 Instrum
16、ent ElectrodesPlatinum with a surface equiva-lent of two No. 26 wires, 4.762 mm (0.19 in.) long. The wiresare to be 3 to 8 mm apart and inserted in the vessel so that 75mL of solution will cover them.6.3 Instrument Depolarization IndicatorHaving an inter-nal resistance of less than 5000 V and consis
17、ting of a means ofimpressing and showing a voltage of 20 to 50 mV across theelectrodes and capable of indicating a current flow of 10 to 20A by means of a galvanometer or ratio tuning circuit.6.4 Buret AssemblyFor Karl Fischer reagent, consisting ofa 10-mL buret with 0.05-mL subdivisions connected b
18、y meansof glass or polyethylene (not rubber) connectors to a source ofreagent. Several types of automatic dispensing burets may beused. Since the reagent loses strength when exposed to moistair, all vents must be protected against atmospheric moisture byadequate drying tubes containing anhydrous cal
19、cium sulfate.All stopcocks and joints are to be lubricated with an inertlubricant.7. Reagents7.1 Purity of ReagentsUse reagent-grade chemicals in alltests. Unless otherwise indicated, it is intended that all reagentsshall conform to the specifications of the Committee onAnalytical Reagents of the Am
20、erican Chemical Society wheresuch specifications are available.3Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.7.2 Purity of WaterUnless otherwise indicated, referencesto wa
21、ter shall be understood to mean reagent water as definedby Type I of Specification D 1193.7.3 Karl Fischer ReagentEquivalent to 2.5 to 3.0 mg ofwater/mL. Dilute commercially available stabilized Karl Fis-cher reagent (6 mg of water/mL) with an equal volume ofanhydrous ethylene glycol monomethyl ethe
22、r (containing lessthan 0.1 % water). (See Note 3.)NOTE 3Improved, pyridine-free Karl Fischer reagents have beenmade available and are now highly recommended as a replacement for theprevious reagents. See Section 14, under Test Method B, AutomatedProcedure.7.4 Titration Solvent, Anhydrous MethanolUnl
23、ess themethanol is extremely dry it will require a large amount ofdilute Karl Fischer solution to react with its residual water. Forthis reason the solvent shall be further dried by addingundiluted Karl Fischer reagent (6 mg of water/mL) to a bottleof methanol until a light red-brown color persists.
24、 Add metha-nol until the solution is a pale yellow. A 100-mL portion of thetreated solvent requires 1 to 10 mL of dilute Karl Fischerreagent.8. Sampling8.1 It is essential to avoid changes in the water content ofthe material during sampling operations. Many polyols arequite hygroscopic and errors fr
25、om this source are particularlysignificant in the determination of the small amount of waterusually present. Use almost-filled, tightly capped containersand limit as much as possible contact of the sample with airwhen transferring the sample to the titration vessel. Avoidintermediate sample containe
26、rs, if possible. If several differentanalyses are to be performed on the same sample, determinethe water first and do not open the sample prior to the actualanalysis.9. Standardization of Reagent9.1 Standardize the Karl Fischer reagent daily using thesame procedures as used for titrating the sample.
27、9.1.1 Add 100 mL of titration solvent to the flask and titratethe residual moisture as described in Section 10. To this titratedsolvent, immediately add 1 drop of water from a weighingpipet. Weigh the pipet to 60.1 mg. Complete the titration withKarl Fischer reagent as described in Section 10. It ma
28、y benecessary to refill the buret during the titration.9.1.2 Calculate the equivalence factor, F, in terms of milli-grams of water per millilitre of reagent as follows:equivalency factor, F 5 A/B (1)where:A = water added, mg, andB = Karl Fischer reagent required, mL.10. Procedure10.1 Adjust the nitr
29、ogen valve so that dry nitrogen flowsinto the titration vessel at a slow rate (20 to 50 mL/min).Introduce approximately 100 mL of titration solvent into thetitration vessel, making sure that the electrodes are coveredwith solvent.Adjust the stirrer to give adequate mixing withoutsplashing. Titrate t
30、he mixture with Karl Fischer reagent to theend point. (See Note 4.)10.2 To the prepared titration mixture, add the amount ofsample as indicated in Table 1. Exercise care when the sampleis transferred so that water is not absorbed from the air,particularly under conditions of high humidity. Allow the
31、solution to stir 1 or 2 minutes until dissolution is complete.10.3 Titrate the mixture again with Karl Fischer reagent tothe same end point previously employed. Record the amount ofreagent used to titrate the water in the sample.NOTE 4The end point is that point in the titration when two smallplatin
32、um electrodes upon which a potential of 20 to 50 mV has beenimpressed are depolarized by the addition of 0.05 mL of Karl Fischerreagent (equivalent to 2.5 to 3.0 mg water/mL) causing a change of currentflow of 10 to 30 V that persists for at least 30 s.3Reagent Chemicals, American Chemical Society S
33、pecifications , 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 Pharmacopeiaand National Formulary, U.S. Pharmacopeial C
34、onvention, Inc. (USPC), Rockville,MD.TABLE 1 Recommended Sample SizeWater Content, % Sample Size, gBelow 0.5 weight containing approximately 25 mg of waterAOver 0.5 5AThis weight should not exceed 30 g.D 4672 00 (2006)e1211. Calculation11.1 Calculate the water content of the sample as follows:water,
35、 % 5 VF/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. Precision and Bias12.1 Attempts to develop a precision and bias statement forthis test method have not been successful. For this reas
36、on, dataon precision and bias cannot be given. Anyone wishing toparticipate in the development of precision and bias data needsto contact the Chairman, Subcommittee D20.22 (Section20.22.01),ASTM, 100 Barr Harbor Drive, PO Box C700, WestConshohocken, PA 194282959.TEST METHOD B: AUTOMATED PROCEDURE13.
37、 Apparatus13.1 Several commercial autotitrators are available4thatemploy volumetric or coulometric titrations and provide resultssuperior to those of the manual procedure, described above.These instruments consist of an automated buret assembly, asealed titration vessel with appropriate electrodes a
38、nd sensingcircuitry, and a vacuum system for removal of solution afteranalysis. These automated systems provide several advantagesand conveniences.Atmospheric moisture contamination can bemore closely controlled; calibration is simplified; and thepreneutralization step is automatic. Titrations are r
39、apid, andreagent consumption is low. Autotitrators automatically calcu-late and display or print the water concentration.14. Reagents14.1 Commercial reagents and reagent systems of varioustypes are available5for use with autotitrators for water deter-mination. Pyridine-free reagents have improved st
40、ability 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 solut
41、ion. Splitimplies separate solutions of the solvent and titrant.15. Sampling15.1 Sampling is conveniently accomplished by use of atared syringe. The material is drawn into the syringe, weighed,and delivered through the sample port of the autotitrator vessel.The syringe is then reweighed to obtain th
42、e sample weight bydifference.15.1.1 Take note of the sample handling warnings in 8.1.16. Standardization of Reagent16.1 Since different autotitrators may vary in standardiza-tion procedures, consult the operating manual for the autoti-trator in use. Water is an excellent primary standard. Inaddition
43、, stable, prepackaged, primary standards are also avail-able for establishing the standardization factor.17. Procedure17.1 Refer to the operating manual for the autotitrator inuse. Basically, after preneutralization of the reagent in thetitrator vessel, the sample is introduced, and the volumetricti
44、tration (or coulometric generation of titrant) proceeds auto-matically to the end point.NOTE 5In choosing the appropriate sample size for use with specificautotitrators, use the manufacturers recommendations. If no instructionsare available, use the guidelines listed in Table 2 and Table 3.TABLE 2 V
45、olumetric TitrationA% Water Expected Suggested Sample Size, gBelow 0.5 5100.51.0 1Above 1.0 0.5AFor titrant concentration equivalent to 5 mg H2O per mL.TABLE 3 Coulometric Titration% Water Expected Suggested Sample Size, gBelow 0.1 50.10.5 10.51.0 0.118. Calculation18.1 Following each titration, aut
46、otitrator automatically cal-culates and displays the water content, based on the storedvalues of sample weight, standardization factor, and titrantvolume consumed. (See 11.1 for the manual calculation.)19. Precision and Bias6,719.1 PrecisionThe following data should be used forjudging the acceptabil
47、ity of results (95 % confidence limits):19.1.1 RepeatabilityDuplicate results obtained by thesame analyst are to be considered suspect if they differ by morethan the percent relative listed in Table 4 for the water levelwhich most closely matches the sample being analyzed.TABLE 4 Repeatability Stati
48、sticsWater Level Volumetric Coulometric0.03 8.2 2.80.42 1.6 3.11.6 1.1 3.14Instruments 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
49、 fromBrinkmann Instruments, Inc. at ) and Mettler Toledo modelsDL 18, 31, 37, and 38 ().5Reagents for Karl Fischer titrations 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 (www.em-).6Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: D20-1068.7Supporting data have been filed at ASTM International Headquarters and m
