ASTM_D_3124_-_98_2011.pdf

Designation:D312498(Reapproved 2011)Standard Test Method forVinylidene Unsaturation in Polyethylene by InfraredSpectrophotometry1This standard is issued under the fixed designation D3124;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 is applicable to all types ofpolyethylenes,those ethylene plastics consisting of ethyleneand a-olefin copolymers longer than propylene,and blends ofthe above in any ratio.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.Specific hazardsstatements are given in Section 8.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Test Method for Density of Plastics by the Density-Gradient TechniqueD1898 Practice for Sampling of Plastics(Withdrawn 1998)3E131 Terminology Relating to Molecular SpectroscopyE168 Practices for General Techniques of Infrared Quanti-tative AnalysisE177 Practice for Use of the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 MethodsE275 Practice for Describing and Measuring Performance ofUltraviolet and Visible SpectrophotometersIEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units(the Modernized Metric System)Proposed Methods for Evaluation of Spectrophotometers43.Terminology3.1 GeneralThe units,symbols,and abbreviations used inthis test method appear in Terminology E131 or StandardIEEE/ASTM SI 10.4.Summary of Test Method4.1 The band at 888 cm-1(11.26 m)is characteristic ofvinylidene groups(1,2).5It is the strongest vinylidene bandand is due to the deformation vibrations of the C-H bonds inthe CH2group.4.2 This band is overlapped by absorption at 11.25 to 11.07m(889 to 903 cm-1)from vibrations of terminal methylgroups on alkyl groups longer than ethyl.By using a bromi-nated sample in the reference beam of a double-beam spectro-photometer along with an untreated sample in the samplebeam,the methyl absorption is cancelled out.For spectrom-eters with computerized spectral manipulation capabilities,thesame effect may be accomplished by subtraction of thebrominated spectra from the untreated spectra.The bromina-tion destroys the vinylidene unsaturation in the sample(1)inthe reference beam but leaves the methyl absorption intact.Thus,the methyl absorption is eliminated because it appears inboth the sample and reference beams.The vinylidene absorp-tion is then seen without interference in the difference spec-trum.4.3 Integrated absorbance,instead of the usual absorbanceat the band peak,is used in this test method.Integratedabsorbance is found by integrating the spectrum over theabsorbance band when the spectrum is plotted as absorbanceversus frequency,in cm-1.A very good approximation tointegrated absorbance is obtained by multiplying the absor-bance at the band peak by the band half-width,the width of theband in cm-1at an absorbance equal to 50%of the peakabsorbance.This approximation may be used for this testmethod if integrated absorbance is not available.Most spectral1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods(Section D20.70.08).Current edition approved Feb.1,2011.Published March 2011.Originallyapproved in 1972.Last previous edition approved in 2003 as D3124 98(2003).DOI:10.1520/D3124-98R11.2For 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.4Proceedings.Am.Soc.Testing Mats.,ASTEA,Vol 58,1958,pp.472494.5The boldface numbers in parentheses refer to the list of references at the end ofthis test method.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 manipulation software contains algorithms for adequately de-termining baseline corrected integrated absorbances.Integratedabsorbance is used because it is more nearly constant for aseries of materials containing the same absorbing group indifferent environments,or in different states of aggregation.Itis independent of changes in line shape.Peak absorbances arequite dependent on line shape factors,especially line width,which depends on the state of aggregation.Calibration with aliqu