ASTM_D_2572_-_97_2010.pdf

Designation:D257297(Reapproved 2010)Standard Test Method forIsocyanate Groups in Urethane Materials or Prepolymers1This standard is issued under the fixed designation D2572;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.This standard has been approved for use by agencies of the Department of Defense.1.Scope1.1 This test method covers the determination of the isocya-nate group(NCO)content of a urethane intermediate orprepolymer.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 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.For specific hazardstatements,see Section 8.2.Referenced Documents2.1 ASTM Standards:2D841 Specification for Nitration Grade Toluene3.Summary of Test Method3.1 The urethane prepolymer is allowed to react with anexcess of di-n-butylamine in toluene(Note 1).After thereaction is complete,the excess of di-n-butylamine is deter-mined by back titration with standard hydrochloric acid.NOTE1Solvents other than toluene may be needed in some cases,forexample,anhydrous dimethylformamide(DMF),but the procedure hasnot been evaluated using them.4.Significance and Use4.1 The percent NCO is used to establish unit ratios forstoichiometric reactions with co-reactants.5.Interferences5.1 Phosgene,the carbamyl chloride of isocyanate,hydro-gen chloride,or any other acidic or basic impurities ofsufficient strength will interfere.The concentration of thesecompounds is usually sufficiently low that their effect on thedetermination is negligible.6.Apparatus6.1 Polyethylene Stoppers(or corks)covered with alumi-num foil to fit 250-mL Erlenmeyer flasks.6.2 Magnetic Stirrer with PTFE-fluorocarbon-covered stir-ring bar.6.3 Pipet,325-mL.6.4 Buret,350-or 100-mL.6.5 Analytical Balance.7.Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests unless otherwise specified.Unless otherwiseindicated,it is intended that all reagents shall conform to thespecifications of the Committee on Analytical Reagents of theAmerican Chemical Society,where such specifications areavailable.4Other grades may be used,provided that it is firstascertained that the reagent is of sufficiently high purity topermit its use without lessening the accuracy of the determi-nation.7.2 Bromphenol Blue Indicator,Prepare 0.1%solution bymixing 0.10 g of acid,nonwater soluble bromphenol blue with1.5 mL of 0.1 N sodium hydroxide solution and diluting to 100mL with distilled water.7.3 Di-n-butylamine Solution,0.1 N in dry toluene.Notstandardized.1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings,Materials,and Applications and is the direct responsibility ofSubcommittee D01.33 on Polymers and Resins.Current edition approved Dec.1,2010.Published December 2010.Originallyapproved in 1967.Last previous edition approved in 2003 as D2572 97(2003)1.DOI:10.1520/D2572-97R10.2For 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.3Burets and pipets shall conform to National Institute of Standards andTechnology tolerances.4Reagent 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 Ltd.,Poole,Dorset,U.K.,and the United States Pharmacopeiaand National Formulary,U.S.Pharmacopeial Convention,Inc.(USPC),Rockville,MD.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 7.4 Hydrochloric Acid Solution,0.1 N standardized usingbromphenol blue indicator solution.7.5 Isopropyl Alcohol.7.6 Toluene,anhydrous,conforming to Specification D841or equivalent dried with molecular sieve pellets.8.Hazards8.1 Diisocyanates are strong skin irritants and sensitizers.They are also hazardous to the lungs.(TLV for toluene 2,4-diisocyanate is 0.005 ppm.)Avoid contact with skin,eyes,andclothing,and avoid breathing these substances.Use withadequate ventilation.In case of contact,wash with plenty ofwater and flush eyes for 15 min.Call a physician before reuse.See Suppliers Material Safety Data Sheet for additionalinformation.9.Procedure9.1 Weigh to 0.1 g a specimen containing approximately 1.1milliequivalents of NCO(for example,1.0 g of prepolymercontaining approximately 5%NCO)in a 250-mL Erlenme