1、Designation: D5523 10Standard Test Method forPolyurethane Raw Materials: Acidity by ArgentometricDetermination of Hydrolyzable Chlorine in Monomeric,Aromatic Isocyanates1This standard is issued under the fixed designation D5523; the number immediately following the designation indicates the year ofo
2、riginal 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. Scope1.1 This test method measures the hydrolyzable chlorinecontent o
3、f monomeric, aromatic isocyanates used as polyure-thane raw materials and expresses it as HCl acidity. The testmethod is applicable to toluene diisocyanate (TDI) and mono-meric methylene di(phenylisocyanate), known as MDI. Themain sources of hydrolyzable chlorine and, therefore, acidity inmonomeric
4、aromatic isocyanates are carbamyl chlorides, acidchlorides, and dissolved phosgene. All of these compoundsreact with alcohols and water to form hydrochloric acid.1.2 This test method applies only to monomeric isocyanatesin which all of the acidity is derived from species that generateHCl on solvolys
5、is.1.3 The values stated in SI units are to be regarded as thestandard.1.4 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 th
6、e 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 Plastics3. Terminology3.1 Definitions: For definitions of terms used in this testmethod, see Terminology D883.3.2 De
7、finitions of Terms Specific to This Standard:3.2.1 aciditythe acid strength of a sample expressed asparts per million hydrochloric acid (HCl) present.3.2.2 hydrolyzable chlorinethe amount of chlorine re-leased as chloride ion under the conditions of the test,expressed as parts per million chlorine.4
8、. Summary of Test Method4.1 The sample reacts with 2-propanol to form urethanesand hydrochloric acid, which is liberated from the labilecarbamyl chlorides, acid chlorides, and dissolved phosgene.The chlorides of the liberated acid are then determinedpotentiometrically using standard methanolic silve
9、r nitratesolution and calculated as parts per million HCl.5. Significance and Use5.1 This test method is suitable for research or for qualitycontrol to characterize TDI and MDI.5.2 This test method was developed to overcome problemswith low-level acidity determinations that use glass electrodesin th
10、e presence of reagent alcohol solvents. Reagent alcoholscontain acidic and basic species, which complicate the glasselectrode methods at low levels of acidity.6. Interferences6.1 Acidic species that do not generate chloride ions underthe conditions of this test method will not be determinedbecause a
11、cidity is determined indirectly from the chloride ionconcentration.6.2 Acidic species that do not produce chloride ions areexpected to be negligible at low levels of acidity and for themonomeric isocyanates in this test method.6.3 Care must be taken to avoid chloride contamination ofglassware and sa
12、mple containers.7. Apparatus7.1 Potentiometric Titrator.7.2 Combination Silver Billet Electrode (Note 2).7.3 Oven, 70C (Note 3).7.4 Magnetic Stirrer.NOTE 2The combination silver billet electrode is to be stored in 0.01N methanolic silver nitrate solution in order to keep the electrode1This test meth
13、od 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 Aug. 1, 2010. Published September 2010. Originallyapproved in 1994. Last previous edition approved in 2004 as
14、D5523 - 041. DOI:10.1520/D5523-10.2For 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.1Copyright ASTM Internation
15、al, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.conditioned properly. The use of chloride containing solutions must beavoided during storage and maintenance of the apparatus.NOTE 3Monomeric MDI samples can be solid when received in thelaboratory. An oven is to
16、 be used to melt the sample prior to beginning thetest procedure.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the A
17、merican Chemical Society wheresuch specifications are available.3Other grades can be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.8.2 Methanol.8.3 2-Propanol.8.4 Nitric Acid, concentrated, 70
18、 %.8.5 Silver Nitrate.8.6 Methanolic Silver Nitrate Solution (0.01 N)Prepareby dissolving 1.70 g AgNO3/L of solution. Potentiometricallystandardize with titration-grade sodium chloride frequentlyenough to detect changes of 0.00005 N.8.7 Methanolic Silver Nitrate Solution (0.001 N)Prepareby dissolvin
19、g 0.170 g AgNO3/L of solution. Potentiometricallystandardize with titration-grade sodium chloride frequentlyenough to detect changes of 0.000005 N.9. Sampling9.1 Since organic isocyanates react with atmospheric mois-ture, take special precautions in sampling. Usual samplingmethods, even when conduct
20、ed rapidly, can cause contamina-tion of the sample with insoluble urea. Therefore, blanket thesample with dry air or nitrogen at all times. (WarningManydiisocyanates are known or suspected sensitizers. Over-exposure to diisocyanates can lead to adverse health effectswhich include the development of
21、occupational asthma andother respiratory, skin and eye effects. Engineering controlsand/or personal protective equipment, including respiratory,skin and eye protection, are to be used when there is a potentialfor over-exposure to diisocyanates. The product suppliersMaterial Data Safety Sheet (MSDS)
22、provides more detailedinformation about potential adverse health effects and otherimportant safety and handling information. Always follow thespecific instructions provided on the MSDS.)10. Test Conditions10.1 Samples are to remain sealed against moisture untilimmediately before testing.11. Procedur
23、e11.1 Weigh 10.0 g of the sample into a beaker and record theweight to the nearest 0.0001 g (Note 4).11.2 Add 100 mLof 2-propanol to the beaker, cover, and stirthe sample for 10 min.11.3 Add 100 mL of methanol, cover, and continue stirringthe sample solution for an additional 20 min (Note 5).11.4 Ad
24、d ten drops of concentrated nitric acid solution tothe sample solution.11.5 Cool the sample solution to room temperature in an icebath if necessary.11.6 Titrate the sample solution potentiometrically with theappropriate methanolic silver nitrate solution (Note 6).11.7 Record the volume of titrant us
25、ed to reach the end pointto at least the nearest 0.001 mL.11.8 If the chloride content of the reagents is in question,run a blank (steps 11.1 to 11.7 with no isocyanate sampleadded) to ensure that the reagents are free of chloride interfer-ences. If chloride is detected, subtract the volume (mL) ofA
26、gNO3required to titrate the blank from the volume (mL) ofAgNO3required to titrate the sample.NOTE 4The beaker must be of such size to accommodate approxi-mately 300 mL of solution, and it must be of a shape to allow the propercoverage for the electrode. For monomeric MDI, it is acceptable to gentlyw
27、arm the beaker on a hot plate to keep the sample molten prior to theaddition of 2-propanol. This will assist in dissolution of the sample. Once2-propanol has been added, remove the beaker from the hot plate.NOTE 5The stirring times were chosen to ensure an adequate reactiontime for material that has
28、 been adjusted with an acid chloride. Inmonomeric, unadjusted material, it is acceptable to reduce the stirringtimes to those required to obtain uniform solutions and stable electroderesponses (approximately 2 min).NOTE 6For expected acidities or hydrolyzable chlorines below 20ppm, use the 0.001 N m
29、ethanolic silver nitrate solution as the titrant. Forexpected acidities or hydrolyzable chlorines above 20 ppm, use the 0.01N methanolic silver nitrate solution as the titrant.12. Calculation12.1 Calculate the acidity, as ppm HCl, as follows:acidity 5S 3 N 3 36.465 3 106W 3 1000(1)where:S = AgNO3req
30、uired for titration of the sample, mL,N = normality of AgNO3solution, meq/mL,W = sample weight, g,36.465 = equivalent weight of HCl, mg/meq,1000 = factor for converting milligrams to grams, and106= factor for converting to parts per million.12.2 Because hydrolyzable chlorine is measured, the ppmhydr
31、olyzable chlorine can be calculated as follows:hydrolyzable chlorine 5S 3 N 3 35.465 3 106W 3 1000(2)where:S = AgNO3required for titration of the sample, mL,N = normality of AgNO3solution, meq/mL,W = sample weight, g,35.465 = equivalent weight of Cl, mg/meq,1000 = factor for converting milligrams to
32、 grams, and106= factor for converting to parts per million.3Reagent Chemicals, American Chemical 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
33、 Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.D5523 10213. Precision and Bias413.1 Attempts to develop a precision and bias statement forthis test method have not been successful due to the limitednumbe
34、r of laboratories participating in round-robin tests. Dataon precision and bias cannot be given for this reason. Contactthe Chairman, Subcommittee D20.22 (Section D20.22.01),ASTM, 100 Barr Harbor Drive, PO Box C700, West Consho-hocken, PA 194282959, if you are interested in participatingin the devel
35、opment of precision and bias data for this testmethod.13.2 A limited round robin was conducted with nine labo-ratories.13.2.1 It has been estimated that duplicate results for eitheracidity or hydrolyzable chlorine by the same analyst are to beconsidered suspect if they differ by 63.9 ppm for results
36、greater than 10 ppm and 60.6 ppm for results less than 10ppm.13.2.2 It has been estimated that results reported by differentlaboratories for either acidity or hydrolyzable chlorine are to beconsidered suspect if they differ by 615.5 ppm for resultsgreater than 10 ppm and 63.5 ppm for results less th
37、an 10ppm.14. Keywords14.1 acidity; HC; hydrolyzable chlorine; isocyanates; isocy-anates aromatic; MDI; methylene-bis-(4-phenylisocyanate);methylene di(phenylisocyanate); polyurethane; raw materials;TDI; test method; titration; toluene diisocyanateASTM International takes no position respecting the v
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40、uarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This stan
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42、rviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D20-1181.D5523 103
