ASTM_D_5629_-_16.pdf

Designation:D562916Standard Test Method forPolyurethane Raw Materials:Determination of Acidity inLow-Acidity Aromatic Isocyanates and PolyurethanePrepolymers1This standard is issued under the fixed designation D5629;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 acidity,expressed as ppmof hydrochloric acid(HCl),in aromatic isocyanate or polyure-thane prepolymer samples of below 100 ppm acidity.The testmethod is applicable to products derived from toluene diiso-cyanate and methylene di(phenylisocyanate)(see Note 1).Refer to Test Method D6099 for determination of acidity inmoderate-to high-acidity aromatic isocyanates.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.NOTE1This standard is equivalent to ISO 14898,Method B.2.Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD6099 Test Method for Polyurethane Raw Materials:Deter-mination ofAcidity in Moderate to HighAcidityAromaticIsocyanatesE180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals(Withdrawn 2009)3E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 ISO Standards:4ISO 14898 PlasticsAromatic Isocyanates for Use in theProduction of PolyurethaneDetermination of Acidity3.Terminology3.1 DefinitionsThe terminology in this test method fol-lows the standard terminology defined in Terminology D883.3.2 Definitions of Terms Specific to This Standard:3.2.1 acidity,nthe acid strength of a sample expressed inppm HCl.4.Summary of Test Method4.1 The isocyanate is mixed with an excess of n-propanol,acosolvent and a known amount of HCl.Additional acid isreleased into the solvent system during urethane formation.The acid is then titrated potentiometrically with methanolicKOH.The same procedure is performed with a blank solutionand the difference in titer is used to calculate the acidity presentin the isocyanate sample.5.Significance and Use5.1 This test method is suitable for research or for qualitycontrol to characterize aromatic isocyanates and low-acidityprepolymers.Acidity correlates with performance in somepolyurethane systems.6.Apparatus6.1 Disposable Beakers,250 mL.6.2 Repipet,pipet or buret,50 mL.6.3 Pipet,100 mL,class A volumetric;or a 100-mL buretwith a dosing unit;or a 100-mL repipet,class A volumetric.6.4 Potentiometric Titrator:6.4.1 Reference Electrode,bridge-type electrolyte(doublejunction),sleeve-type diaphragm,having saturated LiCl/ethanol solution in both chambers,or equivalent.6.4.2 pH Glass Electrode(see Note 2).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 April 1,2016.Published April 2016.Originallyapproved in 1994.Last previous edition approved in 2011 as D5629-11.DOI:10.1520/D5629-16.2For 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.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from American National Standards Institute(ANSI),25 W.43rd St.,4th Floor,New York,NY 10036,http:/www.ansi.org.*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 NOTE2A combination pH electrode with internal reference isacceptable.6.5 Magnetic Stirrer.6.6 Polytetrafluoroethylene-Coated Stir Bars.6.7 Watch Glasses.6.8 Analytical Balance,capable of weighing to the nearest0.1 mg.7.Reagents and Materials7.1 0.01 N KOH in Methanol,for example,0.66 g 87.7%KOH/1000 mL methanol,standardized with potassium hydro-gen phthalate(KHP).7.2 Toluene or THF(dried for 24 h over 5 A molecularsieves).7.3 n-Propanol,acidified with 120 L concentrated hydro-chloric acid per 4-L bottle.Allow this solution to stand for atleast 24 h before use to allow equilibration.The solution is tobe mixed well before dispensing.8.Sampling8.1 Since organic isocyanates react with atmosphericmoisture,take special precautions in sampling.Usual samplingmethods,even when conducted rapidly,can cause contamina-tion of the sample with insoluble urea.Therefore,blanket thesample with dry air or nitr