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Designation: D5523 − 15Standard Test Method forPolyurethane Raw Materials: Acidity by ArgentometricDetermination of Hydrolyzable Chlorine in Monomeric,Aromatic Isocyanates 1This standard is issued under the f i xed designation D5523; 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.1. Scope*1.1 This test method measures the hydrolyzable chlorinecontent of 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 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 solvolysis.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 the applica-bility of regulatory limitations prior to use.N OTE 1—There is no known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM Standards: 2D883 Terminology Relating to Plastics3. Terminology3.1 Def i nitions—For def i nitions of terms used in this testmethod, see Terminology D883.3.2 Def i nitions of Terms Specif i c to This Standard:3.2.1 acidity—the acid strength of a sample expressed asparts per million hydrochloric acid (HCl) present.3.2.2 hydrolyzable chlorine—the amount of chlorine re-leased as chloride ion under the conditions of the test,expressed as parts per million chlorine.4. 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 silver nitratesolution and calculated as parts per million HCl.5. Signif i cance 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 the 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 acidity 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 sample containers.7. Apparatus7.1 Potentiometric Titrator.7.2 Combination Silver Billet Electrode (Note 2).7.3 Oven, 70°C (Note 3).7.4 Magnetic Stirrer.1 This 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 April 1, 2015. Published May 2015. Originallyapproved in 1994. Last previous edition approved in 2010 as D5523 - 10. DOI:10.1520/D5523-15.2 For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s 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 States1