1、Designation: D6248 98 (Reapproved 2012)1Standard 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
2、 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.1NOTEReapproved with editorial changes in May 2012.1. Scope1.1 This test method covers most types of pol
3、yethylene,those ethylene plastics consisting of ethylene and a-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 w
4、ith 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.NOTE 1There is no known ISO equivalent for this standard.
5、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 Poly-ethylene by Infrared Spectroph
6、otometryE131 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 Performanceof Ultraviolet and Visible Spectrophotomet
7、ers3. 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
8、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 subtract
9、ion 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,
10、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 thr
11、ee 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-R8, sometimes referred to1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand
12、 is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved May 1, 2012. Published July 2012. Originally approvedin 1998. Last previous edition approved in 2004 as D6248 - 98 (2004). DOI:10.1520/D6248-98R12E01.2For referenced ASTM standards, visit the ASTM web
13、site, 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United Sta
14、tes.as trans-internal unsaturation; vinylidene or pendent methyl-ene, RR8C-CH2; and vinyl unsaturation, R-CH=CH2, alsoreferred to as terminal unsaturation.5.2 The type and quantity of these groups can influence thechemical and physical properties of the resin. Informationconcerning their presence ca
15、n 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 bands caused by additive presencethat overlap or interfere with unsaturatio
16、n absorbance bandsused in this test method in the range of 1050 to 850 cm1.Ifoverlapping bands occur, the method is not applicable.5.4 Interference fringes resulting from smooth sample sur-faces can cause measurement errors. This test method requiresthe use of aluminum foil in the compression moldin
17、g ofsamples to provide an adequately rough surface to minimizeinterference fringes.6. Apparatus6.1 Infrared Spectrophotometer, either double-beam, or aFourier transform (FTIR).6.1.1 Double-Beam Infrared Spectrophotometer, capable ofspectral resolution as defined in Condition C of Section III(Spectra
18、l Resolution) of the Proposed Methods for the Evalu-ation of Spectrophotometers. Also, see Practice E275 fortesting procedures. An instrument capable of scale expansionalong the wavelength (or wave number) axis is preferred.6.1.2 Fourier Transform Infrared Spectrometer, capable of4cm1resolution. The
19、 instrument should be capable of scaleexpansion along the wavelength axis.6.2 Compression Molding Press, small, with platens capableof being heated to 170 C.6.3 Two Metal Plates, 150 by 150 mm or larger, of 0.5-mmor greater thickness with smooth surfaces.6.4 Brass Shims, approximately 75 by 75 mm, o
20、f 0.5-mmthickness with an aperture in the center at least 25 by 38 mmfor most samples. A thinner shim can be used with highlyabsorbing samples.6.5 Micrometer Calipers, with thimble graduations of 0.001mm.6.6 Infrared Liquid Cell, with sodium chloride or potassiumbromide windows.6.7 Film Mounts, with
21、 apertures at least 6 by 27 mm, to holdthe specimens in the infrared spectrophotometer.7. Reagents and Materials7.1 Carbon Disulfide (CS2), reagent grade.7.2 Aluminum Foil Sheets.8. Hazards8.1 Carbon disulfide is flammable and toxic.9. Calibration9.1 Prepare at least three different solutions of eac
22、h of thestandard compounds in CS2at closely the same knownconcentration near 0.18 mol/L.9.2 Set the controls of the infrared spectrometer for quan-titative conditions with a good signal to noise ratio andsatisfactory reproducibility. Use a scanning speed sufficientlyslow to give good reproducibility
23、 of line shape. Set the slitwidth narrow enough so there is little distortion of the true lineshape. For an FTIR spectrometer, use a spectral resolution of 4cm1. Use an apodization function that gives good quantitation.Beer-Norton medium and Happ-Genzel have been found to beappropriate.9.3 Scan the
24、solutions from 1050 to 850 cm1in a 0.1-mmpath length cell which has been calibrated by interferencefringes or other methods. Cell windows made of either NaCl orKBr are suitable.9.4 Determine the integrated peak areas, A, for each stan-dard at the wavelength specified for the appropriate end group.Th
25、e baseline shall be drawn from valley to valley for the peakcentered at or near the specified wave number for each type ofunsaturation.9.5 Calculate the molar absorptivity, B for each solutionusing the known concentrations from 9.1 and the followingequation:B 5 A/C 3 T! (1)where:B = molar absorptivi
26、ty, L/mol-cm,A = integrated absorbance, measured or estimated as de-fined in 9.4,C = concentration of end group, Mol/L, andT = cell thickness, cm.9.6 For each type of unsaturation, calculate the average ofthe molar absorptivities determined in 9.5.10. Procedure10.1 Sample Preparation:10.1.1 Preheat
27、the press to 140 to 150C.10.1.2 Place a brass shim on an aluminum foil sheet, dullside up, that in turn covers a metal plate.NOTE 2Placing the dull side of the aluminum foil next to the polymergives the sample film some texture and reduces fringe effects.10.1.3 Add sufficient polymer so that the shi
28、m aperture willbe completely filled when the polymer is pressed.10.1.4 Cover with another sheet of aluminum foil, dull sidedown, and another metal plate.10.1.5 Insert the mold assembly between the press platensand apply a slight pressure.10.1.6 Allow the sample to preheat for 30 s. Apply a pressclam
29、ping pressure of 70 000 to 210 000 kPa (approximately 10000 to 30 000 psig) at 140 to 150 C for 1 min or until allexudation ceases. Use the lower pressure for 150 by 150 mmplates, and the higher pressure for 300 by 300 mm plates.10.1.7 Remove the mold from the press and allow it to coolto room tempe
30、rature. Immersion in cold water can be used toassist in the cooling.10.1.8 Using the micrometer, measure the thickness of thesample to 60.01 mm at three places within the sample beamarea. Calculate an average of the three measurements andrecord the result in centimetres.NOTE 3The thickness is given
31、here in cm in order to agree with themolar absorptivity term.10.2 Spectral Measurements:D6248 98 (2012)1210.2.1 Scan each sample slowly from 1050 to 850 cm-1.10.2.2 Measure the integrated peak area for the each peak inthe normalized spectrum at the wavelengths used to measurethe standard solutions.
32、The integrated area baseline shall bedrawn from valley to valley for the peak centered at or near thespecified wave number for each type of unsaturation.10.3 Density MeasurementMeasure the density of thepolyethylene sample by displacement, or gradient columntechnique.11. Calculation11.1 Calculate th
33、e end-group concentrations using appropri-ate molar absorptivity for each end group, using the followingequation:C 5 A/B3T! (2)where:B = average molar absorptivitiy of the standard compoundof interest as defined in 9.6, L/mol-cm,T = sample thickness, cm, andA = integrated absorbance, measured or est
34、imated, as de-fined in 10.2.2.11.2 Calculate the number of end groups per 1000 carbonatoms, V for each sample by the following equation:V 5 14 3 C/D (3)where:C = end group concentration, mol/L, calculated in 11.1, andD = density of the polyethylene sample, g/cm3, measured in11.3.1.12. Report12.1 Rep
35、ort the following information:12.1.1 Complete identification of the material tested includ-ing name, manufacturer, lot code number, and physical formwhen sampled,12.1.2 Date of test,12.1.3 Density of the material tested,12.1.4 Number of vinyl groups per 1000 carbon atoms foreach sample,12.1.5 Number
36、 of trans-vinylene groups per 1000 carbonatoms for each sample, and12.1.6 Any sample or spectral anomalies seen during themeasurements.13. Precision and Bias13.1 The repeatability standard deviation (2s) has beendetermined to be 60.0176 trans-vinylene carbon atoms per1000 total carbon atoms, and 60.
37、029 vinyl carbon atoms per1000 total carbon atoms. The reproducibility of this testmethod is being determined.13.2 No information can be presented on the bias of theprocedure in this test method because no material having anaccepted reference value is available.14. Keywords14.1 FTIR; infrared spectr
38、ophotometry; polyethylene; trans-vinylene unsaturation; vinyl unsaturationASTM 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 the validity
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