ASTM_D_6474_-_12.pdf

Designation:D647412Standard Test Method forDetermining Molecular Weight Distribution and MolecularWeight Averages of Polyolefins by High Temperature GelPermeation Chromatography1This standard is issued under the fixed designation D6474;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 covers the determination of molecularweight distributions and molecular weight averages of linearpolyolefins by high temperature gel permeation chromatogra-phy(GPC).This test method uses commercially availablepolystyrene standards and equipment and is applicable topolyethylenes(excluding high pressure low density polyethyl-eneLDPE)andpolypropylenessolublein1,2,4-trichlorobenzene(TCB)at 140C.This test method is notabsolute and requires calibration.NOTE1Size exclusion chromatography(SEC)often is used as analternative name for gel permeation chromatography(GPC).NOTE2Specific methods and capabilities of users may vary withdifferences in columns,instrumentation,applications software,and prac-tices between laboratories.NOTE3One general method is outlined herein;alternative analyticalpractices can be followed and are attached in notes where appropriate.NOTE4There is no known ISO equivalent to this standard.1.2 The values stated in SI units,based on IEEE/ASTMS1-10,are to be regarded as the standard.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.2.Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD3016 Practice for Use of Liquid Exclusion Chromatogra-phy Terms and RelationshipsD5296 Test Method for Molecular Weight Averages andMolecular Weight Distribution of Polystyrene by HighPerformance Size-Exclusion ChromatographyE685 Practice for Testing Fixed-Wavelength PhotometricDetectors Used in Liquid ChromatographyE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodIEEE/ASTM S1-10 Standard for Use of the InternationalSystem of Units(SI):The Modern System(replacesASTM E 380 and ANSI/IEEE Standard 268-1992)3.Terminology3.1 DefinitionsDefinitions of terms applying to plasticsappear in Terminology D883.3.2 Definitions of Terms Specific to This Standard:3.2.1 polyolefin,nused in this context,refers to PE(exceptLDPE)and PP thermoplastics.4.Summary of Test Method4.1 In this test method,a polyolefin sample is dissolved in asolvent and injected onto a chromatographic column(s)packedwith a solid substrate,which separates the molecules accordingto their size in solution.The separated molecules are detectedand recorded as they elute from the column according toconcentration.Through calibration,retention times are con-verted to molecular weights.Average molecular weight param-eters and molecular weight distribution are determined fromthe molecular weight concentration data.5.Significance and Use5.1 This test method measures the molecular weight distri-bution and molecular weight averages of polyethylene(exceptLDPE)and polypropylene resins.Differences in molecularweight and molecular weight distribution significantly affectphysical properties,such as morphology,strength,melt flowetc.,and as a result,the final properties of products made fromthese resins.6.Interferences6.1 Amajor interference is the presence of insoluble,highlyentangled,high molecular weight material that may be linear orcross-linked.A successful outcome of the test requires that the1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommitttee D20.70 on Analytical Methods.Current edition approved Dec.15,2012.Published December 2012.Originallyapproved in 1999.Last previous edition approved in 2006 as D647499(2006).DOI:10.1520/D6474-XX.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 States1 sample be dissolved completely prior to the chromatographicseparation.The presence of the above-described material oftenprecludes the necessary dissolution step.6.2 A mismatch in the antioxidant level in the dissolvedsample and that of the TCB eluent(see 8.1).6.3 The accuracy of the molecular weight results decreases,that is,they become increasingly underestimated,as the-olefin comonomer content increases in linear low densityp