1、Designation: D 6248 98 (Reapproved 2004)Standard Test Method forVinyl and Trans Unsaturation in Polyethylene by InfraredSpectrophotometry1This standard is issued under the fixed designation D 6248; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e of revision, the year 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 most types of polyethylene,those ethylene plastics consisting of e
3、thylene 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 with its use. It is theresponsibility of the user
4、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 similar or equivalent ISO standard.2. Referenced Documents2.1 ASTM Standards:2D 792 Test
5、 Method for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD 1505 Test Method for Density of Plastics by the Density-Gradient TechniqueD 1898 Practice for Sampling of PlasticsD 3124 Test Method for Vinylidene Unsaturation in Poly-ethylene by Infrared SpectrophotometryE 1
6、31 Terminology Relating to Molecular SpectroscopyE 168 Practices for General Techniques of Infrared Quanti-tative AnalysisE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 275 Practice for Describing and Measuring Performanceof Ultraviolet, Visible, and Near Infrared Spectr
7、ophotom-etersIEEE/ASTM SI-10 Standard for Use of the InternationalSystem of Unit (SI): The Modern Metric SystemProposed Methods for the Evaluation of Spectrophotom-eters3. Terminology3.1 GeneralThe units, symbols, and abbreviations used inthis test method appear in Terminology E 131 or IEEE/ASTMSI-1
8、0.4. 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
9、 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 D 3124 mayimprove the results for very low density products.4.3 Integrated absorbance is
10、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 absorbencie
11、s.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 i
12、n any polyethylene. The threetypes are trans-vinylene, R-CH=CH-R8, sometimes referred toas trans-internal unsaturation; vinylidene or pendent methyl-ene, RR8C-CH2; and vinyl unsaturation, R-CH=CH2, alsoreferred to as terminal unsaturation.1This test method is under the jurisdiction of ASTM Committee
13、 D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved July 1, 2004. Published July 2004. Originally approvedin 1998. Last previous edition approved in 1998 as D 6248 - 98.2For referenced ASTM standards, visit the ASTM website, www.astm
14、.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 States.5.2 The ty
15、pe and quantity of these groups can influence thechemical and physical properties of the resin. Informationconcerning their presence may also be used to characterize oridentify unknown resins or blends of resins.5.3 Additives may interfere with unsaturation measure-ments. The use is cautioned to det
16、ermine which additives arepresent and if there any absorbance bands caused by additivepresence that overlap or interfere with unsaturation absorbancebands used in this test method in the range of 1050 to 850 cm1.If overlapping bands occur, the method is not applicable.5.4 Interference fringes result
17、ing from smooth sample sur-faces can cause measurement errors. This test method requiresthe use of aluminum foil in the compression molding ofsamples to provide an adequately rough surface to minimizeinterference fringes.6. Apparatus6.1 Infrared Spectrophotometer, either double-beam, or afourier tra
18、nsform (FTIR).6.1.1 Double-Beam Infrared Spectrophotometer, capable ofspectral resolution as defined in Condition C of Section III(Spectral Resolution) of the Proposed Methods for the Evalu-ation of Spectrophotometers. Also, see Practice E 275 fortesting procedures. The instrument should be capable
19、of scaleexpansion along the wavelength (or wave number) axis.6.1.2 Fourier Transform Infrared Spectrometer, capable of4cm1resolution. The 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 Tw
20、o 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, of 0.5-mmthickness with an aperture in the center at least 25 by 38 mmfor most samples. A thinner shim may be used with highlyabsorbing samples.6.5 Micrometer Calip
21、ers, with thimble graduations of 0.001mm.6.6 Infrared Liquid Cell, with sodium chloride or potassiumbromide windows.6.7 Film Mounts, with 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 Alumi
22、num Foil Sheets.8. Hazards8.1 Carbon disulfide is flammable and toxic.9. Sampling9.1 The polyethylene shall be sampled in accordance withPractice D 1898.10. Calibration10.1 Prepare at least three different solutions of each of thestandard compounds in CS2at closely the same known con-centration near
23、 0.18 mol/L.10.2 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 of line shape. Set the slitwidth narrow enough that there is little distor
24、tion of the trueline shape. For a FTIR, a spectral resolution of 4 cm1shouldbe used. An apodization function that gives good quantitationshould be used. Beer-Norton medium and Happ-Genzel havebeen found to be appropriate.10.3 Scan the solutions from 1050 to 850 cm1in a 0.1-mmpath length cell which h
25、as been calibrated by interferencefringes or other methods. Cell windows made of either NaCl orKBr are suitable.10.4 Determine the integrated peak areas, A, for eachstandard at the wavelength specified for the appropriate endgroup. The baseline shall be drawn from valley to valley for thepeak center
26、ed at or near the specified wave number for eachtype of unsaturation.10.5 Calculate the molar absorptivity, B for each solutionusing the known concentrations from 10.1 and the followingequation:B 5 A/C 3 T! (1)where:B = molar absorptivity, L/mol-cm,A = integrated absorbance, measured or estimated as
27、 de-fined in 10.4,C = concentration of end group, Mol/L, andT = cell thickness, cm.10.6 For each type of unsaturation, calculate the average ofthe molar absorptivities determined in 10.5.11. Procedure11.1 Sample Preparation:11.1.1 Preheat the press to 140 to 150C.11.1.2 Place a brass shim on an alum
28、inum 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.11.1.3 Add sufficient polymer so that the shim aperture willbe completely filled when the polymer is press
29、ed.11.1.4 Cover with another sheet of aluminum foil, dull sidedown, and another metal plate.11.1.5 Insert the mold assembly between the press platensand apply a slight pressure.11.1.6 Allow the sample to preheat for 30 s. Apply a pressclamping pressure of 70 000 to 210 000 kPa (approximately 10000 t
30、o 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.11.1.7 Remove the mold from the press and allow it to coolto room temperature. The cooling may be assisted by immer-sion in cold wat
31、er.11.1.8 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.D 6248 98 (2004)2NOTE 3The thickness is given here in cm in order to agree with themolar absor
32、ptivity term.11.2 Spectral Measurements:11.2.1 Scan each sample slowly from 1050 to 850 cm-1.11.2.2 Measure the integrated peak area for the each peak inthe normalized spectrum at the wavelengths used to measurethe standard solutions. The integrated area baseline shall bedrawn from valley to valley
33、for the peak centered at or near thespecified wave number for each type of unsaturation.11.3 Density MeasurementMeasure the density of thepolyethylene sample by displacement, or gradient columntechnique.12. Calculation12.1 Calculate the end-group concentrations using appropri-ate molar absorptivity
34、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 10.6, L/mol-cm,T = sample thickness, cm, andA = integrated absorbance, measured or estimated, as de-fined in 11.2.2.12.2 Calculate the number of end g
35、roups 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 12.1, andD = density of the polyethylene sample, g/cm3, measured in11.3.1.13. Report13.1 Report the following information:13.1.1 Complete identification of
36、the material tested includ-ing name, manufacturer, lot code number, and physical formwhen sampled,13.1.2 Date of test,13.1.3 Density of the material tested,13.1.4 Number of vinyl groups per 1000 carbon atoms foreach sample,13.1.5 Number of trans-vinylene groups per 1000 carbonatoms for each sample,
37、and13.1.6 Any sample or spectral anomalies seen during themeasurements.14. Precision and Bias14.1 The repeatability standard deviation (2s) has beendetermined to be 60.0176 trans-vinylene carbon atoms per1000 total carbon atoms, and 60.029 vinyl carbon atoms per1000 total carbon atoms. The reproduci
38、bility of this testmethod is being determined.14.2 No information can be presented on the bias of theprocedure in this test method because no material having anaccepted reference value is available.15. Keywords15.1 FTIR; infrared spectrophotometry; polyethylene; trans-vinylene unsaturation; vinyl un
39、saturationASTM 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 of any such patent rights, and the riskof infringement of such r
40、ights, 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. Your comments are invited either for revision of this standard or for addition
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42、TM 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 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).D 6248 98 (2004)3
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