1、Designation: D6645 18Standard 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 yea
2、r 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 methylgroups (that is, comonomer content) in polyethylenes byinfrar
3、ed 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 regarde
4、d 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, health, and environmental practices and deter-mine the applicability of regulatory limita
5、tions prior to use.NOTE 1There is no known ISO equivalent to 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 R
6、ecom-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-Grad
7、ient TechniqueD2238 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-t
8、rophotometry (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 Spectro
9、metersE1421 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 abbre
10、viationsused 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, or 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
11、 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 an ethyl branch (that is,butene copolymer), a butyl branch (that is, hexene copolymer),and a hexyl branch (that is, octene copolyme
12、r), respectively.34.2 This test method determines the methyl group (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
13、 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 11This test method is under the jurisdiction ofASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved
14、 Oct. 1, 2018. Published October 2018. Originallyapproved in 2001. Last previous edition approved in 2010 as D6645 - 01(2010).DOI: 10.1520/D6645-18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandar
15、ds volume information, refer to the standards Document Summary page onthe ASTM website.3Blitz, 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).*A Summary of Changes section appe
16、ars at the end of this standardCopyright 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 Princip
17、les for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1branch per 1000 carbons), butyl (minimum of about 5 branchesper 1000 carbons), and hexyl (minimum of about 5 branchesper 1000 carbons) bra
18、nches, respectively.Amore sensitive andless 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 ofIR calibration curves.NOTE 2For maximum sensitivity, it is recommended to view thesec
19、ond derivative of the IR spectrum to identify the comonomer type.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 o
20、f the productof plaque thickness and density) versus number of branches per1000 carbons as determined by C13 NMR spectroscopy.Although both approaches give equivalent results, the oneusing internal thickness correction is recommended in this testmethod since it is considerably simpler to execute.5.
21、Significance and Use5.1 This method determines the number of branches (that is,comonomer content) in copolymers of ethylene with 1-butene,1-hexene or 1-octene. This information can be correlated withphysical properties such as melting point, density, and stiffness,all of which depend on the degree o
22、f crystallinity of thepolymer. Differences in the comonomer content thus can havea significant effect on the final properties of products madefrom these resins.6. Interferences6.1 A conformational CH2wagging absorbance at 1368cm-1overlaps the methyl absorbance at 1378 cm-1, but does notcause signifi
23、cant interference in this test method since itsintensity is not significantly affected by the comonomercontent, but rather by the plaque thickness. The result of notcorrecting for this overlap is a positive ordinate intercept forthe calibration curve (see 10.4). Another conformational CH2wagging abs
24、orbance at 1352 cm-1does not significantlyoverlap the 1378 cm-1absorbance.6.2 The presence of most pigments will interfere with thismethod.6.3 The presence of low molecular weight hydrocarbonswill produce high results in this method due to absorbance bytheir end methyl groups at 1378 cm-1.6.4 The se
25、condary antioxidant Irgafos 1684shows an absor-bance at 768 cm-1which interferes with the identification oflow levels (that is, typically less than 5 branches per 1000carbons or less) of ethyl branches.6.5 Vinylidene groups absorb at 888 cm-1and thus caninterfere with a conclusive identification of
26、a hexene copoly-mer from its 895 cm-1resonance, depending on the relativeintensities of the two peaks.7. Apparatus7.1 Infrared Spectrophotometer, either double beam or aFourier transform (FTIR).7.1.1 Dispersive Infrared Spectrophotometer, capable ofachieving a spectral bandwidth of 4 cm-1(see Practi
27、ce E932).The instrument must be capable of scale expansion along thewavenumber axis.7.1.2 Fourier Transform Infrared Spectrometer, capable of 4cm-1resolution (see Practice E1421). The instrument must becapable of scale expansion along the wavenumber axis.7.2 Compression Molding Press, with platens c
28、apable ofbeing heated to 180C.7.3 Two Metal Plates, 150 by 150 mm or larger, of 0.5-mmthickness with smooth surfaces.7.4 Brass Shims, approximately 75 by 75 mm, of 0.3 mmthickness with an aperture in the center at least 25 by 38 mm.7.5 Micrometer (optional), with thimble graduations of0.001 mm.7.6 F
29、ilm Mounts, with apertures at least 6 by 27 mm, to holdthe specimens in the infrared spectrophotometer.8. Materials8.1 Polyethylene Terephthalate, Aluminum Foil or MatteFinished Teflon-Fibreglass Sheets.9. Hazards9.1 Caution must be used during plaque preparation tohandle the hot platens with approp
30、riate gloves for handprotection.10. Procedure10.1 Preparation of Polymer Plaque:10.1.1 Preheat the press to about 50C above the meltingpoint of the polymer.10.1.2 Place a 0.3-mm thick brass shim on the sheetmaterial chosen (see 8.1) which in turn covers a metal plate.NOTE 3When using aluminum foil,
31、place the dull side next to thepolymer to give the sample film some texture, thereby reducing fringeeffects in the infrared spectrum.10.1.3 Add polymer in sufficient quantity to completely fillthe shim aperture during pressing.10.1.4 Insert the mold assembly between the press platensand apply a slig
32、ht pressure.10.1.5 Allow the polymer to preheat for about 30 s. Applythe full press pressure at a temperature approximately 50Cabove the melting point of the polymer for 1 min or until allexudation ceases.10.1.6 Turn off the heat, turn on the cooling water, andallow the polymer to press quench at fu
33、ll pressure until thetemperature drops below 50C (or cool enough to remove themold assembly by hand).10.1.7 Select plaques that are clear for the FTIR analysis. Toavoid interference fringes in the spectrum, the plaque surfacesmust be slightly dimpled.10.2 Spectral Acquisition:4Trademark of the Ciba
34、Specialty Chemicals Co.D6645 18210.2.1 Place the polymer plaque in the infrared spectropho-tometer.10.2.2 Set the controls of the infrared spectrophotometer forquantitative conditions with a good signal-to-noise ratio and aspectral resolution (bandwidth) of 4 cm-1. For an FTIR, anapodization functio
35、n (Beer-Norton medium and Happ-Genzelhave been found to be appropriate) that gives good quantitationshall be used.10.2.3 Record the infrared spectrum from 4000 cm-1to 500cm-1.10.3 Spectral Data Reduction:10.3.1 Determine the absorbance at a fixed wavenumber(not necessarily at the apex of the 1378 cm
36、-1peak) between1378 and 1379 cm-1. A linear baseline is to be set between thevalleys present at 1400 cm-1and 1330 cm-1(see Fig. X1.1 inAppendix X1).10.3.2 Determine the area of the combination band at 2019cm-1(see Fig. X1.1 in Appendix X1). The baseline andintegration limits are to be set between th
37、e valleys on each sideof the peak (that is, typically between 1980 and 2100 cm-1).NOTE 4Several software packages are available with which macroscan be written to perform the data reduction automatically and consis-tently.10.4 Calibration:10.4.1 For a minimum of five (preferably about ten) poly-mer
38、standards containing known levels of the comonomer ofinterest, calculate the ratio of the absorbance (A) at 1378 cm-1(see 10.3.1) and the area of the combination band at 2019 cm-1(see 10.3.2) and plot:Area (1378 cm-1) / Area (2019 cm-1) versus Number ofbranches (N) per 1000 carbons.Typically, a line
39、ar regression fit will give a positive ordinateintercept (representing the contribution from the CH2waggingabsorbance at 1368 cm-1and the CH3main chain end groups)and an R2value of 0.98 or better. According to the Lambert-Beer Law:A 1378 cm21!/Area 2019 cm21! 5 aN1b (1)where:a = slope of the regress
40、ion line, andb = ordinate intercept.Depending on the exact wavenumber at which the absor-bance of the 1378 cm-1peak is measured, the slopes of theregression lines should be close to the following:ab(butene copolymers) = 0.009ah(hexene copolymers) = 0.008ao(octene copolymers) = 0.007NOTE 5The above r
41、ecommended “internal thickness correction”approach has been found to yield equivalent results to the more laborintensive approach of measuring thickness (b) to the nearest 0.01 mm anddensity (d) of the plaque and graphing A (1378 cm-1) (b d) vs. N.NOTE 6A wedge compensation or spectral subtraction u
42、sing ahomopolyethylene sample as described in Method D2238 is not required.10.5 Calculations:10.5.1 Having determined the thickness correctedabsorbance, use the equation for the appropriate regression linefitted to the calibration points to calculate the number ofbranches (N) per 1000 carbons (see 1
43、0.4). Ensure that the valueobtained is within the high and low limits of the standards. Toconvert to comonomer content, use the following expressions:Wt% 5 100NMcomNMcom11000 2 2N!228(2)Mol% 5 100Wt%McomWt%Mcom1100 2 Wt%28where:Mcom= the molecular weight of the -olefin comonomer.11. Report11.1 Compl
44、ete identification of material tested includingname, manufacturer, lot number and physical form whensampled,11.2 Date of test,11.3 Number of methyl groups per 1000 carbons and/orcomonomer content in wt % or mole % for each sample, and11.4 Any sample or spectral anomalies observed during themeasureme
45、nt.12. Precision and Bias12.1 The repeatability relative standard deviation for abutene LLDPE with a comonomer content of 4.1 mol % basedon 12 analyses over a period of two weeks is 0.9 %.12.2 The reproducibility of this test method is being deter-mined.13. Keywords13.1 branching; comonomer; FTIR; i
46、nfrared spectropho-tometry; polyethyleneD6645 183APPENDIX(Nonmandatory Information)X1. FTIR SPECTRUM OF A BUTENE COPOLYMERX1.1 Fig. X1.1 shows the FTIR spectrum for a butenecopolymer containing 17 branches per 1000 carbons.SUMMARY OF CHANGESCommittee D20 has identified the location of selected chang
47、es to this standard since the last issue(D6645 - 01(2010) that may impact the use of this standard. (October 1, 2018)(1) Removed permissive language. (2) Edited wording for improved clarity.ASTM International takes no position respecting the validity of any patent rights asserted in connection with
48、any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technic
49、al committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrig
