ASTM_D_6645_-_01_2010.pdf

Designation:D664501(Reapproved 2010)Standard Test Method forMethyl(Comonomer)Content in Polyethylene by InfraredSpectrophotometry1This standard is issued under the fixed designation D6645;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.Scope1.1 This test method covers the determination of methylgroups(that is,comonomer content)in polyethylenes byinfrared spectrophotometry.The test method is applicable tocopolymers of ethylene with 1-butene,1-hexene,or 1-octenehaving densities above 900 kg/m3.High-pressure low-densitypolyethylenes(LDPE)and terpolymers are excluded.1.2 The values stated in SI units,based on IEEE/ASTM SI-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.NOTE1There is no known ISO equivalent to this standard.2.Referenced Documents2.1 ASTM Standards:2D792 Test Methods for Density and Specific Gravity(Rela-tive Density)of Plastics by DisplacementD1505 Test Method for Density of Plastics by the Density-Gradient TechniqueD1898 Practice for Sampling of Plastics(Withdrawn 1998)3D2238 Test Methods forAbsorbance of Polyethylene Due toMethyl Groups at 1378 cm1D3124 Test Method for Vinylidene Unsaturation in Polyeth-ylene by Infrared SpectrophotometryD5576 Practice for Determination of Structural Features inPolyolefins and Polyolefin Copolymers by Infrared Spec-trophotometry(FT-IR)E131 Terminology Relating to Molecular SpectroscopyE168 Practices for General Techniques of Infrared Quanti-tative AnalysisE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE932 Practice for Describing and Measuring Performance ofDispersive Infrared SpectrometersE1421 Practice for Describing and Measuring Performanceof Fourier Transform Mid-Infrared(FT-MIR)Spectrom-eters:Level Zero and Level One TestsIEEE/ASTM SI-10 Standard for Use of the InternationalSystem of Units(SI):The Modern System3.Terminology3.1 TerminologyThe units,symbols,and abbreviationsused in this test method appear in Terminology E131 orIEEE/ASTM SI-10.3.2 comonomer-olefin monomer.In this test method,comonomer refers to 1-butene,1-hexene,and 1-octene only.4.Summary of Test Method4.1 The band located between 1377 cm-1and 1379 cm-1isdue to a deformation vibration of the CH3group.Bands atapproximately 772 cm-1(branch methylene rocking mode),895cm-1(methyl rocking mode),and 785 cm-1(branch methylenerocking mode)are characteristic of ethyl(that is,butenecopolymer),butyl(that is,hexene copolymer),and hexyl(thatis,octene copolymer)branches,respectively.44.2 This test method determines the methyl(that is,comonomer)content of a polyethylene copolymer based on theIR absorbance at 1378 cm-1from a pressed plaque.Thecomonomer type has to be known and a calibration curve hasto be available prior to the analysis.If the comonomer is notknown a priori,the presence of bands at 772 cm-1,895 cm-1,and 785 cm-1can be used to identify ethyl(minimum of 1branch per 1000 carbons),butyl(minimum of about 5 branchesper 1000 carbons),and hexyl(minimum of about 5 branchesper 1000 carbons)branches,respectively.A more sensitive and1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved Jan.1,2010.Published January 2010.Originallyapproved in 2001.Last previous edition approved in 2001 as D6645-01.DOI:10.1520/D6645-01R10.2For 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.4Blitz,J.P.,and McFadden,D.C.,“The Characterization of Short ChainBranching in Polyethylene Using Fourier Transform Infrared Spectroscopy,”J.Appl.Pol.Sci.,51,13(1994).Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 less ambiguous identification is obtained by C13 NMR spec-troscopy.The latter technique is also used as a referencetechnique to provide polymer standards for the generation ofcalibration curves.NOTE2For comonomer identification,it is recommended,for maxi-mum sensitivity,to view the second derivative of the IR spectrum.4.3 The method is calibrated by plotting absorbance at 1378cm-1per unit area of the methylene combination band at 2019cm-1(that is,internal thickness correction approach)or per unitof spectral cross-section(that is,the reciprocal