ASTM_D_5523_-_21.pdf

Designation:D552321Standard 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 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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.NOTE1There is no known ISO equivalent to this standard.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsE456 Terminology Relating to Quality and StatisticsE2935 Practice for Conducting Equivalence Tests for Com-paring Testing Processes3.Terminology3.1 DefinitionsTerms used in this standard are defined inaccordance with Terminology D883,unless otherwise speci-fied.For terms relating to precision and bias and associatedissues,the terms used in this standard are defined in accordancewith Terminology E456.3.2 Definitions 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.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.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 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.1This 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 Jan.15,2021.Published January 2021.Originallyapproved in 1994.Last previous edition approved in 2015 as D5523-15.DOI:10.1520/D5523-21.2For 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.*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 StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.16.2 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 Potentiome