1、Designation: D3124 98 (Reapproved 2011)Standard Test Method forVinylidene Unsaturation in Polyethylene by InfraredSpectrophotometry1This standard is issued under the fixed designation D3124; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, 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 is applicable to all types of polyethyl-enes, those ethylene plastics consisting
3、of ethylene anda-olefin copolymers longer than propylene, and blends of theabove in any 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 u
4、ser 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 to this standard.2. Referenced Documents2.1 ASTM Standards:2D79
5、2 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 Practice for Sampling of PlasticsE131 Terminology Relating to Molecular SpectroscopyE168 Practices for General Techniques of
6、 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 SpectrophotometersIEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units (the Modernized Metric Syst
7、em)Proposed Methods for Evaluation of Spectrophotometers33. Terminology3.1 GeneralThe units, symbols, and abbreviations used inthis test method appear in Terminology E131 or StandardIEEE/ASTM SI 10.4. Summary of Test Method4.1 The band at 888 cm-1(11.26 m) is characteristic ofvinylidene groups (1, 2
8、).4It is the strongest vinylidene bandand is due to the deformation vibrations of the C - H bonds inthe CH2group.4.2 This band is overlapped by absorption at 11.25 to 11.07m (889 to 903 cm-1) from vibrations of terminal methylgroups on alkyl groups longer than ethyl. By using a bromi-nated sample in
9、 the reference beam of a double-beam spectro-photometer along with an untreated sample in the samplebeam, the methyl absorption is cancelled out. For spectrom-eters with computerized spectral manipulation capabilities, thesame effect may be accomplished by subtraction of thebrominated spectra from t
10、he untreated spectra. The bromina-tion destroys the vinylidene unsaturation in the sample (1) inthe reference beam but leaves the methyl absorption intact.Thus, the methyl absorption is eliminated because it appears inboth the sample and reference beams. The vinylidene absorp-tion is then seen witho
11、ut interference in the difference spec-trum.4.3 Integrated absorbance, instead of the usual absorbanceat the band peak, is used in this test method. Integratedabsorbance is found by integrating the spectrum over theabsorbance band when the spectrum is plotted as absorbanceversus frequency, in cm-1.
12、A very good approximation tointegrated absorbance is obtained by multiplying the absor-bance at the band peak by the band half-width, the width of theband in cm-1at an absorbance equal to 50 % of the peakabsorbance. This approximation may be used for this testmethod if integrated absorbance is not a
13、vailable. Most spectralmanipulation software contains algorithms for adequately de-termining baseline corrected integrated absorbances. Integratedabsorbance is used because it is more nearly constant for aseries of materials containing the same absorbing group indifferent environments, or in differe
14、nt states of aggregation. It1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods(Section D20.70.08).Current edition approved Feb. 1, 2011. Published March 2011. Originallyapproved in 1972. Last prev
15、ious edition approved in 2003 as D3124 98(2003).DOI: 10.1520/D3124-98R11.2For referenced ASTM standards, visit the ASTM website, 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 A
16、STM website.3Proceedings. Am. Soc. Testing Mats., ASTEA, Vol 58, 1958, pp. 472494.4The boldface numbers in parentheses refer to the list of references at the end ofthis test method.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.is i
17、ndependent of changes in line shape. Peak absorbances arequite dependent on line shape factors, especially line width,which depends on the state of aggregation. Calibration with aliquid sample for measurements on solid-state samples is notsatisfactory using peak absorbances but is satisfactory using
18、integrated absorbances (1, 3).4.4 Calibration is performed using a solution of 2,3-dimethyl-1,3-butadiene in a liquid cell of known thickness.This liquid has two vinylidene groups per molecule. Threedifferent solutions are prepared and their measurements aver-aged to obtain greater accuracy.5. Signi
19、ficance and Use5.1 There are three types of olefinic groups present insufficient concentrations to warrant consideration, one or moreof which can normally be found in any polyethylene (4). Thethree types are: trans-vinylene, R - CH = CH - R8, sometimesreferred to as transinternal unsaturation; vinyl
20、idene or pendentmethylene, RR8C=CH2; and vinyl unsaturation,R-CH=CH2, also referred 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 may also be used to characterize oridentify u
21、nknown resins or blends of resins.5.3 Vinylidene unsaturation represents the major portion ofthe unsaturation present in most low-density polyethylenes.5.4 Infrared spectroscopy can be used for the determinationof unsaturation in polyethylene (1, 3, 5). The values deter-mined by infrared agree with
22、those determined by IC1 uptake(5).6. Apparatus6.1 Infrared Spectrophotometer, Either Double Beam orFourier Transform (FTIR):6.1.1 Double-beam infrared spectrophotometer, capable ofspectral resolution as defined by Condition C of Section III(Spectral Resolution) of the Proposed Methods for Evaluation
23、of Spectrophotometers. Also, see Practice E275 for testingprocedures. The instrument should be capable of scale expan-sion along the wavelength (or wave number) axis.56.1.2 Fourier transform infrared spectrometer, capable of4-cm-1resolution and scale expansion along the wavelengthaxis.5,66.2 Compres
24、sion-Molding Press, small, with platens ca-pable of being heated to 170C.6.3 Two Metal Plates, 150 by 150 mm or larger, of 0.5-mmthickness with smooth surfaces, preferably chromium plated.6.4 Brass Shims, approximately 75 by 75 mm, of 0.5-mmthickness with an aperture in the center at least 25 by 38
25、mm.6.5 Micrometer Calipers, with thimble graduations of 0.001mm.6.6 Infrared Liquid Cell, with sodium chloride or potassiumbromide windows, 0.1-mm spacing, calibrated.6.7 Film Mounts, with apertures at least 6 by 27 mm, to holdthe specimens in the infrared spectrophotometer.6.8 Glass Stoppered Flask
26、s, 150-mL.6.9 Vacuum Oven.7. Reagents and Materials7.1 Bromine, reagent grade.7.2 Carbon Disulfide (CS2), reagent grade.7.3 Poly(ethylene terephthalate) or Aluminum Sheets, 80 by80 mm, or slightly larger to cover brass shims.7.4 Standard Compound, 2,3-dimethyl-1,3-butadiene (liq-uid) of high purity,
27、 five 1-mL vials.78. Hazards8.1 Bromine is toxic and corrosive. Bromine treatmentshould be carried out in a hood or other ventilated space.Neoprene gloves should be worn and adequate eye protectionemployed. Bromine-treated samples should be exposed to astream of air for 24 h or more to remove surplu
28、s brominebefore measurement in order to protect the operator andequipment. Samples previously treated with bromine shouldnever be stored with materials which will be damaged bybromine.9. Sampling9.1 The polyethylene shall be sampled in accordance withPractice D1898.10. Calibration10.1 Prepare at lea
29、st three different solutions of the standardcompound in CS2at closely the same known concentrationnear 0.18 mol/L (14.8 g/L). Calculate the exact vinylideneconcentrations (two times the molar concentrations) and recordthe values.10.2 Set the controls of the infrared spectrometer for quan-titative co
30、nditions with a good signal to noise ratio andsatisfactory reproducibility. Use a sufficiently expanded chartscale such that line width can be measured accurately. Use ascanning speed sufficiently slow to give good reproducibility ofline shape. Set the slit width narrow enough that there is littledi
31、stortion of the true line shape. Record the instrument condi-tions used. For a FT-IR, a spectral resolution of 4 cm-1shouldbe 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 935
32、 to 847 cm-1(10.70 to 11.80m) in the 0.1-mm sodium chloride cell which has beencalibrated by interference fringes or other adequate method.For a FT-IR, expand the scale of the transformed and convertedabsorbance spectra from 935 to 847 cm-1.NOTE 2Practice E275, paragraph 21.5, describes the interfer
33、encefringe method of calibrating the thickness of infrared cells.10.4 For the FTIR, calculate the baseline corrected inte-grated absorbance of the 888-cm-1(11.26-m) band. For adouble-beam IR without integration capability, measure the5Perkin-Elmer Models 21, 125, 221, and 421 spectrophotometers and
34、BeckmanIR-4 and IR-9 spectrophotometers have been found satisfactory for this purpose.6FT-IR instruments made by a variety of manufacturers that have spectralresolutions of at least 2 cm-1have been found adequate for these purposes.7Obtainable from Chemical Sales Co., 4692 Kenny Rd., Columbus, OH 43
35、221.D3124 98 (2011)2absorbance maximum intensity of the same band using thebaseline technique. Then, measure the band width, in cm-1,athalf intensity of the band. Multiply the two measurements toget an estimate of the integrated area.NOTE 3Practice E168 describes a suitable procedure for measuringth
36、e absorbance.10.5 Calculate the molar absorptivity, B, for each solutionusing the known concentrations from 10.1 and the followingequation:B 5 A/C 3 L! (1)where:B = molar absorptivity, L/mol-cm,A = integrated absorbance, measured or estimated as de-fined in 10.4,C = concentration of vinylidene group
37、, mol/L, andL = cell thickness, cm.10.6 Calculate the average molar absorptivity from thevalues obtained 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 a polyethylene terephthalate oraluminum sheet, which in turn covers a metal plate
38、.11.1.3 Add polymer in sufficient quantity to completely fillthe shim aperture during pressing.11.1.4 Cover with another sheet of polyethylene terephtha-late or aluminum and another metal plate.11.1.5 Insert the mold assembly between the press platensand apply a slight pressure.11.1.6 Allow the samp
39、le to preheat for 30 s. Apply the fullpress pressure at 140 to 150C for 1 min or until all exudationceases.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 water.11.1.8 Release the pressure and remove the sample.11.1.9 U
40、sing the micrometer, measure the thicknesses of thesample to 60.01 mm at three places within the sample beamarea. Calculate an average of the three measurements andrecord in centimetres.11.1.10 Repeat 11.1.1-11.1.9 until two pairs of sampleshave been obtained such that for each pair the members do n
41、otdiffer by more than 2 % in thickness. Use one member of eachpair for bromination in 11.2. Set the other member of each pairaside for use in 11.3 without bromination.11.2 Bromination:11.2.1 Two alternate bromination test methods, solution orvapor phase, may be employed. The solution test method use
42、sa solution of bromine in carbon tetrachloride. The vapor-phasetest method uses the vapor above liquid bromine.NOTE 4The vapor-phase test method is recommended for anysamples that show solubility in carbon tetrachloride.11.2.2 Solution Test Method:11.2.2.1 Place the samples in a 5 % by volume soluti
43、on ofbromine in carbon tetrachloride for 3 h. This reaction should beperformed in the dark or in a flask which has been blackenedto exclude light.11.2.2.2 Remove the samples from the bromine solution.Suspend freely and dry in a vacuum oven at room temperatureovernight. The films should then have a p
44、ale yellow color.11.2.3 Vapor Phase Test Method:11.2.3.1 Cut a portion of the sample film to fit snugly in themouth of a 150-cm3glass stoppered flask.11.2.3.2 Hold one end of the film with forceps and push itinto the neck of the flask containing a few cubic centimetres ofliquid bromine so that the g
45、reater part of the film is suspendedin bromine vapor in the body of the flask. The film should beheld by the edges at the narrow part of the neck.NOTE 5The following method of suspending the film above thebromine seems preferable. Find a ground glass joint which will fit theflask. Form it into a sto
46、pper with a hook drawn out from the bottom.Perforate the film at one end and attach to the hook before closing the flaskwith this stopper.11.2.3.3 Stopper the flask with a short ground stopper andleave this assembly at room temperature (23C) for 2 h. After2 h, remove the film using forceps.11.2.3.4
47、Place the bromine-treated film on a watch glass andallow it to remain in the draught of the hood until most of theabsorbed bromine has been removed and the film is pale yellowin color.11.3 Spectral Measurements:11.3.1 Use samples of brominated and unbrominated mate-rials in pairs such that the thick
48、ness does not differ by morethan 62 %. Errors in the true integrated vinylidene absorbancewill result if thickness differences are larger or if brominationis incomplete.11.3.2 Place the unbrominated sample in the sample beamand its brominated counterpart in the reference beam.11.3.3 Scan the samples
49、 slowly from 935 to 847 cm-1(10.70to 11.80 m), employing the instrument conditions recordedpreviously in 10.2 and 10.3. For a FT-IR, the instrumentconditions described in 10.2 and 10.3 should be used.11.3.4 For the peak at 888-cm-1(11.26 m) measure theintegrated absorbance, or estimate the integrated area employ-ing the procedure used in 10.4.11.3.5 Repeat 11.3.1-11.3.4 for replicate samples.11.3.6 Measure the density of the polyethylene sample bydisplacement or gradient column technique.12. Calculation12.1 Calculate the vinylidene concentrations using the fol-lowi
