ASTM_D_6248_-_21.pdf

Designation:D624821Standard Test Method forVinyl and Trans Unsaturation in Polyethylene by InfraredSpectrophotometry1This standard is issued under the fixed designation D6248;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 most types of polyethylene,those ethylene plastics consisting of ethylene and-olefincomonomers longer than propylene,and blends of the above inany 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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.Specific hazards statements are given in Section 8.NOTE1There is no known ISO equivalent for this standard.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.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 TechniqueD3124 Test Method for Vinylidene Unsaturation in Polyeth-ylene by Infrared SpectrophotometryE131 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 Spectrophotometers3.Terminology3.1 GeneralThe units,symbols,and abbreviations used inthis test method appear in Terminology E131.4.Summary of Test Method4.1 The band at 965 cm1is characteristic of the trans-vinylene substituted group.The band at 908 cm1is character-istic of the terminal vinyl group.4.2 These bands are not seriously overlapped by interferinggroups from the polymer.The vinyl absorbance at 908 cm1isclose to the absorbance band from terminal methyl groups onchains longer than ethyl,at 895 cm1.This interference isminimal for most products.Inclusion of the bromination andspectral subtraction step from Test Method D3124 has beenfound to improve the results for some very low densityproducts.4.3 Integrated absorbance is used in this test method.Integrated absorbance is found by integrating the spectrumover the absorbance band when the spectrum is plotted asabsorbance versus frequency,in cm1.Most spectral manipu-lation software contains algorithms for adequately determiningbaseline corrected integrated absorbencies.4.4 Calibration is performed using a solution of 1-octene fornormal vinyl groups,and trans-3-hexene for trans-vinylenegroups.5.Significance and Use5.1 There are three types of olefinic groups present insufficient concentrations to warrant consideration,one or moreof that can normally be found in any polyethylene.The threetypes are trans-vinylene,R-CH=CH-R,sometimes referred toastrans-internalunsaturation;vinylideneorpendentmethylene,RRC-CH2;and vinyl unsaturation,R-CH=CH2,also referred to as terminal unsaturation.5.2 The type and quantity of these groups can influence thechemical and physical properties of the resin.Information1This 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 Nov.15,2021.Published December 2021.Originallyapproved in 1998.Last previous edition approved in 2012 as D6248-98(2012)1,which was withdrawn January 2021 and reinstated in November 2021.DOI:10.1520/D6248-21.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.1?concerning their presence can also be used to characterize oridentify unknown resins or blends of resins.5.3 Additives can interfere with unsaturation measurements.The use is cautioned to determine which additives are presentand if there any absorbance