1、Designation: D6645 01 (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
2、 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 polye
3、thylenes 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,
4、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 limit
5、ations prior to use.NOTE 1There 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 Pr
6、actice for Sampling of Plastics3D2238 Test Methods for Absorbance of Polyethylene Dueto Methyl Groups at 1378 cm1D3124 Test Method for Vinylidene Unsaturation in Poly-ethylene by Infrared SpectrophotometryD5576 Practice for Determination of Structural Features inPolyolefins and Polyolefin Copolymers
7、 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 Performanceof Dispersi
8、ve 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,
9、 symbols, and abbreviationsused in this test method appear in Terminology E131 orIEEE/ASTM SI-10.3.2 comonomera-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 deforma
10、tion 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) bran
11、ches, 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
12、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 andles
13、s 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.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibilit
14、y 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
15、 Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.4Blitz, J. P., and McFadden, D. C., “The Characterization of Short ChainBranching in Polyethylene Using Fourier Transform Infrared Spe
16、ctroscopy,” J.Appl. Pol. Sci., 51, 13 (1994).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.NOTE 2For comonomer identification, it is recommended, for maxi-mum sensitivity, to view the second derivative of the IR spectrum.4.3 The me
17、thod 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 of the productof plaque thickness and density) versus number of branches per
18、1000 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. Significance and Use5.1 This method determines the number of branches (that
19、 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 of crystallinity of thepolymer. Differences in the comonomer content thus ma
20、y 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 significant interference in this test method since itsintensity is not significant
21、ly affected by the comonomer con-tent, 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 absorbance at 1352 cm-1does not significantlyoverlap the 1378 cm-1absorbance
22、.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 secondary antioxidant Irgafos 1685shows an absor-bance at 768 cm-1which int
23、erferes 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 mayinterfere with a conclusive identification of a hexene copoly-mer from its 895 cm-1resonance, depending on the relative
24、intensities 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 Practice E932).The instrument should be capable of scale expansion along thewav
25、enumber axis.7.1.2 Fourier Transform Infrared Spectrometer, capable of4cm-1resolution (see Practice E1421). The instrument shouldbe capable of scale expansion along the wavenumber axis.7.2 Compression Molding Press, with platens capable ofbeing heated to 180C.7.3 Two Metal Plates, 150 by 150 mm or l
26、arger, 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 Film Mounts, with apertures at least 6 by 27 mm, to holdthe specimens i
27、n 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 appropriate gloves for handprotection.10. Procedure10.1 Preparation of Polym
28、er 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, place the dull side next to thepolymer to give the sample film some te
29、xture, 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 slight pressure.10.1.5 Allow the polymer to preheat for about 30 s. Applyt
30、he 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 full pressure until thetemperature drops below 50C (or cool enough to re
31、move 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:10.2.1 Place the polymer plaque in the infrared spectropho-tometer.10.2.2 Set the controls of
32、 the infrared spectrophotometer forquantitative conditions with a good signal to noise ratio and aspectral resolution (bandwidth) of 4 cm-1. For an FTIR, anapodization function (Beer-Norton medium and Happ-Genzelhave been found to be appropriate) that gives good quantitationshould be used.10.2.3 Rec
33、ord 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-1peak) between5Trademark of the Ciba Specialty Chemicals Co.D6645 01 (2010)21378 and 1379 cm-1. A linear baseline is to be
34、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 the valleys on each sideof the peak (that is, typically between
35、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 standards containing known levels of the comonomer ofinterest,
36、 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:A (1378 cm-1) / Area (2019 cm-1) vs. Number of branches(N) per 1000 carbons.A linear regression fit should give a positive ordinateintercept (representing the co
37、ntribution 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 a N 1 b (1)where:a = slope of the regression line, andb = ordinate intercept.Depending somewhat on the exact wave
38、number at which theabsorbance of the 1378 cm-1peak is measured, the slopes ofthe regression lines should be close to the following:ab(butene copolymers) = 0.009ah(hexene copolymers) = 0.008ao(octene copolymers) = 0.007NOTE 5The above recommended “internal thickness correction” ap-proach has been fou
39、nd 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)/(bd)vs.N.NOTE 6A wedge compensation or spectral subtraction using a ho-mopolyethylene sample as described in Method D2238 is no
40、t required.10.5 Calculations:10.5.1 Having determined the thickness corrected absor-bance, use the equation for the appropriate regression line fittedto the calibration points to calculate the number of branches(N) per 1000 carbons (see 10.4). Ensure that the value obtainedis within the high and low
41、 limits of the standards. To convertto comonomer content, use the following expressions:Wt % 5 100 N McomN Mcom11000 2N!228(2)Mol % 5 100 Wt %McomWt %Mcom1100 Wt %28where:Mcom= the molecular weight of the a-olefin comonomer.11. Report11.1 Complete identification of material tested includingname, man
42、ufacturer, 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 themeasurement.12. Precision and Bias12.1 The repeatability relative
43、 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 and will be available on or before January 1, 2005.13. Keywords13.1 branching; comonomer; FTIR; infrar
44、ed spectropho-tometry; polyethyleneAPPENDIX(Nonmandatory Information)X1.See Fig. X1.1.D6645 01 (2010)3ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that de
45、termination 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 technical committee and must be reviewed every five years andif not revised, either reapproved
46、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 t
47、hat 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 copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprint
48、s (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).FIG. X1.1 FTIR Spectrum (2200 cm-1to 1200 cm-1) of a Butene Copolymer Containing 17 Branches per 1000 CarbonsD6645 01 (2010)4
