ASTM D3124-98(2003)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D3124–98 (Reapproved 2003)
Standard Test Method for
Vinylidene Unsaturation in Polyethylene by Infrared
Spectrophotometry
This standard is issued under the fixed designation D3124; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This test method is applicable to all types of polyethyl- 3.1 General—The units, symbols, andabbreviationsusedin
enes, those ethylene plastics consisting of ethylene and this test method appear in Terminology E131 or Standard
a-olefin copolymers longer than propylene, and blends of the IEEE/ASTM SI 10.
above in any ratio.
4. Summary of Test Method
1.2 The values stated in SI units are to be regarded as the
-1
4.1 The band at 888 cm (11.26 µm) is characteristic of
standard.
1.3 This standard does not purport to address all of the vinylidene groups (1, 2). It is the strongest vinylidene band
and is due to the deformation vibrations of the C - H bonds in
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- the CH group.
4.2 This band is overlapped by absorption at 11.25 to 11.07
priate safety and health practices and determine the applica-
-1
bility of regulatory limitations prior to use. Specific hazards µm (889 to 903 cm ) from vibrations of terminal methyl
groups on alkyl groups longer than ethyl. By using a bromi-
statements are given in Section 8.
nated sample in the reference beam of a double-beam spectro-
NOTE 1—There is no similar or equivalent ISO standard.
photometer along with an untreated sample in the sample
beam, the methyl absorption is cancelled out. For spectrom-
2. Referenced Documents
eters with computerized spectral manipulation capabilities, the
2.1 ASTM Standards:
same effect may be accomplished by subtraction of the
D792 Test Methods for Density and Specific Gravity (Rela-
brominated spectra from the untreated spectra. The bromina-
tive Density) of Plastics by Displacement
tion destroys the vinylidene unsaturation in the sample (1) in
D1505 Test Method for Density of Plastics by the Density-
the reference beam but leaves the methyl absorption intact.
Gradient Technique
Thus, the methyl absorption is eliminated because it appears in
D1898 Practice for Sampling of Plastics
both the sample and reference beams. The vinylidene absorp-
E131 Terminology Relating to Molecular Spectroscopy
tion is then seen without interference in the difference spec-
E168 Practices for General Techniques of Infrared Quanti-
trum.
tative Analysis
4.3 Integrated absorbance, instead of the usual absorbance
E177 Practice for Use of the Terms Precision and Bias in
at the band peak, is used in this test method. Integrated
ASTM Test Methods
absorbance is found by integrating the spectrum over the
E275 Practice for Describing and Measuring Performance
absorbance band when the spectrum is plotted as absorbance
of Ultraviolet and Visible Spectrophotometers
-1
versus frequency, in cm . A very good approximation to
IEEE/ASTM SI 10 Standard for Use of the International
integrated absorbance is obtained by multiplying the absor-
System of Units (the Modernized Metric System)
bance at the band peak by the band half-width, the width of the
Proposed Methods for Evaluation of Spectrophotometers
-1
band in cm at an absorbance equal to 50 % of the peak
absorbance. This approximation may be used for this test
method if integrated absorbance is not available. Most spectral
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
manipulation software contains algorithms for adequately de-
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods
terminingbaselinecorrectedintegratedabsorbances.Integrated
(Section D20.70.08).
Current edition approved March 10, 2003. Published April 2003. Originally
absorbance is used because it is more nearly constant for a
approved in 1972. Last previous edition approved in 1998 as D3124 – 98. DOI:
series of materials containing the same absorbing group in
10.1520/D3124-98R03.
2 different environments, or in different states of aggregation. It
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. The boldface numbers in parentheses refer to the list of references at the end of
Proceedings. Am. Soc. Testing Mats., ASTEA, Vol 58, 1958, pp. 472–494. this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D3124–98 (2003)
is independent of changes in line shape. Peak absorbances are 6.7 Film Mounts,withaperturesatleast6by27mm,tohold
quite dependent on line shape factors, especially line width, the specimens in the infrared spectrophotometer.
which depends on the state of aggregation. Calibration with a 6.8 Glass Stoppered Flasks, 150-mL.
liquid sample for measurements on solid-state samples is not 6.9 Vacuum Oven.
satisfactory using peak absorbances but is satisfactory using
7. Reagents and Materials
integrated absorbances (1, 3).
4.4 Calibration is performed using a solution of 2,3-
7.1 Bromine, reagent grade.
dimethyl-1,3-butadiene in a liquid cell of known thickness.
7.2 Carbon Disulfide (CS ), reagent grade.
This liquid has two vinylidene groups per molecule. Three
7.3 Poly(ethylene terephthalate) or Aluminum Sheets, 80 by
different solutions are prepared and their measurements aver-
80 mm, or slightly larger to cover brass shims.
aged to obtain greater accuracy.
7.4 Standard Compound, 2,3-dimethyl-1,3-butadiene (liq-
uid) of high purity, five 1-mL vials.
5. Significance and Use
8. Hazards
5.1 There are three types of olefinic groups present in
sufficient concentrations to warrant consideration, one or more 8.1 Bromine is toxic and corrosive. Bromine treatment
of which can normally be found in any polyethylene (4). The should be carried out in a hood or other ventilated space.
three types are: trans-vinylene, R - CH = CH - R8, sometimes Neoprene gloves should be worn and adequate eye protection
referred to as transinternal unsaturation; vinylidene or pendent employed. Bromine-treated samples should be exposed to a
methylene, RR8C=CH ; and vinyl unsaturation, stream of air for 24 h or more to remove surplus bromine
R-CH=CH , also referred to as terminal unsaturation. before measurement in order to protect the operator and
5.2 The type and quantity of these groups can influence the equipment. Samples previously treated with bromine should
chemical and physical properties of the resin. Information never be stored with materials which will be damaged by
concerning their presence may also be used to characterize or bromine.
identify unknown resins or blends of resins.
9. Sampling
5.3 Vinylidene unsaturation represents the major portion of
the unsaturation present in most low-density polyethylenes.
9.1 The polyethylene shall be sampled in accordance with
5.4 Infrared spectroscopy can be used for the determination Practice D1898.
of unsaturation in polyethylene (1, 3, 5). The values deter-
10. Calibration
mined by infrared agree with those determined by IC1 uptake
(5).
10.1 Prepare at least three different solutions of the standard
compound in CS at closely the same known concentration
6. Apparatus
near 0.18 mol/L (14.8 g/L). Calculate the exact vinylidene
6.1 Infrared Spectrophotometer, Either Double Beam or concentrations(twotimesthemolarconcentrations)andrecord
Fourier Transform (FTIR): the values.
6.1.1 Double-beam infrared spectrophotometer, capable of 10.2 Set the controls of the infrared spectrometer for quan-
spectral resolution as defined by Condition C of Section III titative conditions with a good signal to noise ratio and
(Spectral Resolution) of the Proposed Methods for Evaluation satisfactory reproducibility. Use a sufficiently expanded chart
of Spectrophotometers. Also, see Practice E275 for testing scale such that line width can be measured accurately. Use a
procedures. The instrument should be capable of scale expan- scanningspeedsufficientlyslowtogivegoodreproducibilityof
sion along the wavelength (or wave number) axis. line shape. Set the slit width narrow enough that there is little
6.1.2 Fourier transform infrared spectrometer, capable of distortion of the true line shape. Record the instrument condi-
-1 -1
4-cm resolution and scale expansion along the wavelength tions used. For a FT-IR, a spectral resolution of 4 cm should
5,6
axis. be used. An apodization function that gives good quantitation
6.2 Compression-Molding Press, small, with platens ca- should be used. Beer-Norton medium and Happ-Genzel have
pable of being heated to 170°C. been found to be appropriate.
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6.3 Two Metal Plates, 150 by 150 mm or larger, of 0.5-mm 10.3 Scanthesolutionsfrom935to847cm (10.70to11.80
thickness with smooth surfaces, preferably chromium plated. µm) in the 0.1-mm sodium chloride cell which has been
6.4 Brass Shims, approximately 75 by 75 mm, of 0.5-mm calibrated by interference fringes or other adequate method.
thickness with an aperture in the center at least 25 by 38 mm. ForaFT-IR,expandthescaleofthetransformedandconverted
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6.5 Micrometer Calipers, with thimble graduations of 0.001 absorbance spectra from 935 to 847 cm .
mm.
NOTE 2—Practice E275, paragraph 21.5, describes the interference
6.6 Infrared Liquid Ce
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