ASTM_D_4876_-_98.pdf

Designation:D 4876 98Standard Test Method forPolyurethane Raw Materials:Determination of Acidity ofCrude or Modified Isocyanates1This standard is issued under the fixed designation D 4876;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(e)indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This test method determines the total acidity,expressedas HCl,of crude or modified isocyanates.The test method isapplicable to products derived from toluene diisocyanate,methylene-bis-(4-phenylisocyanate),and polymethylenepolyphenylisocyanates.(See Note 1.)1.2 The values stated in SI units are to be regarded as thestandard.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 specifichazards statements see 7.1 and Note 2.NOTE1There is no equivalent ISO standard.2.Referenced Documents2.1 ASTM Standards:D 841 Specification for Nitration Grade Toluene2D 883 Terminology Relating to Plastics3D 1193 Specification for Reagent Water4E 180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial Chemicals5E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method63.Terminology3.1 DefinitionsFor definitions of terms used in this testmethod see Terminology D 883.4.Summary of Test Method4.1 Labile chlorine compounds react with methanol toliberate hydrogen chloride.The hydrogen chloride is titratedpotentiometrically with alcoholic potassium hydroxide.5.Significance and Use5.1 These test methods can be used for research or forquality control to characterize isocyanates used in polyurethaneproducts.6.Apparatus6.1 Potentiometric Titrator or pH Meter.6.2 Calomel Electrode.6.3 Glass Electrode.6.4 Lunge Pipet,or any weighing device suitable for weigh-ing a liquid sample by difference to the nearest 0.001 g.6.5 Magnetic Stirrer.6.6 Thermometer,10 to 100C range.7.Reagents7.1 Purity of ReagentsUse reagent-grade chemicals in alltests.Unless otherwise indicated,it is intended that all reagentsconform to the specifications of the Committee on AnalyticalReagents of the American Chemical Society where suchspecifications are available.7Other grades may be used,pro-vided 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 water shall be understood to mean reagent water as definedby Type 1 of Specification D 1193.7.3 Methanol-Anhydrous reagent grade with a water contentof 0.10%maximum.7.4 Potassium Hydroxide,Methanolic Solution(0.02 N)Prepare a 0.02 N methanolic potassium hydroxide(KOH)solution and standardize frequently enough to detect changesof 0.001.7.5 TolueneDry,conforming to Specification D 841 anddried by a drying agent.1This test method is under the jurisdiction ofASTM Committee D-20 on Plasticsand is the direct responsibility of Subcommittee D 20.22 on Cellular Plastics.Current edition approved Nov.10,1998.Published January 1999.Originallypublished as D 4876 88.Last previous edition D 4876 88.2Annual Book of ASTM Standards,Vol 06.04.3Annual Book of ASTM Standards,Vol 08.01.4Annual Book of ASTM Standards,Vol 11.01.5Annual Book of ASTM Standards,Vol 15.05.6Annual Book of ASTM Standards,Vol 14.02.7Reagent 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.Pharmaceutical Convention,Inc.(USPC),Rockville,MD.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.8.Sampling8.1 Since organic isocyanates react with atmospheric mois-ture,special precautions must be taken in sampling(Caution:Note 2).Usual sampling methods(for example,sampling anopen drum with a thief),even when carried out rapidly,cancause contamination of the sample with insoluble urea.There-fore,the sample must be blanketed with dry air or nitrogen atall times.NOTE2Organic isocyanates are toxic when they are absorbed throughthe skin,or when the vapors are breathed.Adequate ventilation should beprovided and protective gloves and eyeglasses should be worn.9.Test Conditions9.1 Since isocyanates react with moisture,laboratory hu-midity should be kept low,preferably around 50%relativehumidity.10.Procedure10.1 Weigh to the nearest 1 mg 1.0 to 1.5 g of crudeisocyanate into ea