1、Designation: D 6645 01Standard Test Method forMethyl (Comonomer) Content in Polyethylene by InfraredSpectrophotometry1This standard is issued under the fixed designation D 6645; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the y
2、ear of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 byinfr
3、ared 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 S1-10, are to be regar
4、ded 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
5、 use.NOTE 1There is no similar or equivalent ISO standard.2. Referenced Documents2.1 ASTM Standards:D 792 Test Method for Density and Specific Gravity (Rela-tive Density) of Plastics by Displacement2D 1505 Test Method for Density of Plastics by the Density-Gradient Technique2D 1898 Practice for Samp
6、ling of Plastics3D 2238 Test Method forAbsorbance of Polyethylene Due tomethyl Groups at 1378 cm-12D 3124 Test Method for Vinylidene Unsaturation in Poly-ethylene by Infrared Spectrophotometry4D 5576 Practice for Determination of Structural Features inPolyolefins and Polyolefin Copolymers by Infrare
7、d Spec-troscopy5E 131 Terminology Relating to Molecular Spectroscopy6E 168 Practice for General Techniques of Infrared Quanti-tative Analysis6E 177 Practice for Use of the Terms Precision and Bias inASTM Test Methods7E 932 Practice for Describing and Measuring Performanceof Dispersive Infrared Spect
8、rophotometers6E 1421 Practice for Describing and Measuring Performanceof Fourier Transform Infrared (FT-IR) Spectrometers:Level Zero and Level One Tests6IEEE/ASTM SI-10 Standard for Use of the InternationalSystem of Units (SI): The Modern System (ReplacesASTME 380 and ANSI/IEEE Standard 268-1992)83.
9、 Terminology3.1 TerminologyThe units, symbols, and abbreviationsused in this test method appear in Terminology E 131 orIEEE/ASTM S1-10.3.2 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 13
10、77 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
11、 hexyl (thatis, octene copolymer) branches, respectively.94.2 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
12、 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,
13、 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 March 10, 2001. Published June 2001.2Annual Book of ASTM Standards, Vol 08.01.3Discon
14、tinued; see 1998 Annual Book of ASTM Standards, Vol 08.01.4Annual Book of ASTM Standards, Vol 08.02.5Annual Book of ASTM Standards, Vol 08.03.6Annual Book of ASTM Standards, Vol 03.06.7Annual Book of ASTM Standards, Vol 14.02.8Annual Book of ASTM Standards, Vol 14.04.9Blitz, J. P., and McFadden, D.
15、C., “The Characterization of Short ChainBranching in Polyethylene Using Fourier Transform Infrared Spectroscopy,” J.Appl. Pol. Sci., 51, 13 (1994).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.less ambiguous identification is obtai
16、ned by C13 NMR spec-troscopy. The latter technique is also used as a referencetechnique to provide polymer standards for the generation ofcalibration curves.NOTE 2For comonomer identification, it is recommended, for maxi-mum sensitivity, to view the second derivative of the IR spectrum.4.3 The metho
17、d 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 per100
18、0 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 is
19、,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 may h
20、avea 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 significantly
21、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.6.
22、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 16810shows anabsorbance at 768 cm-1which interfe
23、res with the identificationof low 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 relativeinte
24、nsities 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 E 932).The instrument should be capable of scale expansion along thewavenu
25、mber axis.7.1.2 Fourier Transform Infrared Spectrometer, capable of4cm-1resolution (see Practice E 1421). 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 lar
26、ger, 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 in
27、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 Polymer
28、 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 text
29、ure, 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. Applythe
30、 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 remo
31、ve 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 t
32、he infrared spectrophotometer forquantitative conditions with a good signal to noise ratio and aspectral resolution (bandwidth) of 4 cm-1. For an FTIR, an10Trademark of the Ciba Specialty Chemicals Co.D6645012apodization function (Beer-Norton medium and Happ-Genzelhave been found to be appropriate)
33、that gives good quantitationshould 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-1peak) between1378 and 1379 cm-1. A linear baseline is to be set betwe
34、en 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 1980 and
35、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, calculat
36、e 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 contributio
37、n 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 wavenumber at
38、 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 found to yie
39、ld 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 D 2238 is not requir
40、ed.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 limits
41、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, manufacture
42、r, 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 standar
43、d 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; infrared spect
44、ropho-tometry; polyethyleneAPPENDIX(Nonmandatory Information)X1.See Fig. X1.1.D6645013ASTM 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 determination of t
45、he 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 or withdrawn. Yo
46、ur 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 comment
47、s 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 reprints (single or mul
48、tiple 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).FIG. X1.1 FTIR Spectrum (2200 cm-1to 1200 cm-1) of a Butene Copolymer Containing 17 Branches per 1000 CarbonsD6645014
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