ASTM D3124-98(2019)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D3124 − 98 (Reapproved 2019)
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 E168 Practices for General Techniques of Infrared Quanti-
tative Analysis
1.1 This test method is applicable to all types of
E177 Practice for Use of the Terms Precision and Bias in
polyethylenes, those ethylene plastics consisting of ethylene
ASTM Test Methods
and α-olefin copolymers longer than propylene, and blends of
E275 Practice for Describing and Measuring Performance of
the above in any ratio.
Ultraviolet and Visible Spectrophotometers
1.2 The values stated in SI units are to be regarded as the
IEEE/ASTM SI 10 Standard for Use of the International
standard.
System of Units (the Modernized Metric System)
1.3 This standard does not purport to address all of the
Proposed Methods for Evaluation of Spectrophotometers
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3.1 General—The units, symbols, and abbreviations used in
mine the applicability of regulatory limitations prior to use.
this test method appear in Terminology E131 or Standard
Specific hazards statements are given in Section 8.
IEEE/ASTM SI 10.
NOTE 1—There is no known ISO equivalent to this standard.
4. Summary of Test Method
1.4 This international standard was developed in accor-
–1
4.1 The band at 888 cm (11.26 µm) is characteristic of
dance with internationally recognized principles on standard-
vinylidene groups (1, 2). It is the strongest vinylidene band
ization established in the Decision on Principles for the
and is due to the deformation vibrations of the C - H bonds in
Development of International Standards, Guides and Recom-
the CH group.
mendations issued by the World Trade Organization Technical
4.2 This band is overlapped by absorption at 11.25 to 11.07
Barriers to Trade (TBT) Committee.
–1
µm (889 to 903 cm ) from vibrations of terminal methyl
groups on alkyl groups longer than ethyl. By using a bromi-
2. Referenced Documents
nated sample in the reference beam of a double-beam spectro-
2.1 ASTM Standards:
photometer along with an untreated sample in the sample
D792 Test Methods for Density and Specific Gravity (Rela-
beam, the methyl absorption is cancelled out. For spectrom-
tive Density) of Plastics by Displacement
eters with computerized spectral manipulation capabilities, the
D1505 Test Method for Density of Plastics by the Density-
same effect may be accomplished by subtraction of the
Gradient Technique
brominated spectra from the untreated spectra. The bromina-
D1898 Practice for Sampling of Plastics (Withdrawn 1998)
tion destroys the vinylidene unsaturation in the sample (1) in
E131 Terminology Relating to Molecular Spectroscopy
the reference beam but leaves the methyl absorption intact.
Thus, the methyl absorption is eliminated because it appears in
both the sample and reference beams. The vinylidene absorp-
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
tion is then seen without interference in the difference spec-
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods
trum.
(Section D20.70.08).
Current edition approved Nov. 1, 2019. Published November 2019. Originally
4.3 Integrated absorbance, instead of the usual absorbance
approved in 1972. Last previous edition approved in 2011 as D3124 – 98(2011).
at the band peak, is used in this test method. Integrated
DOI: 10.1520/D3124-98R19.
absorbance is found by integrating the spectrum over the
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. Proceedings. Am. Soc. Testing Mats., ASTEA, Vol 58, 1958, pp. 472-494.
3 5
The last approved version of this historical standard is referenced on The boldface numbers in parentheses refer to the list of references at the end of
www.astm.org. this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3124 − 98 (2019)
absorbance band when the spectrum is plotted as absorbance 6.1.2 Fourier transform infrared spectrometer, capable of
–1 –1
versus frequency, in cm . A very good approximation to 4-cm resolution and scale expansion along the wavelength
6,7
integrated absorbance is obtained by multiplying the absor- axis.
bance at the band peak by the band half-width, the width of the
6.2 Compression-Molding Press, small, with platens ca-
–1
band in cm at an absorbance equal to 50 % of the peak
pable of being heated to 170°C.
absorbance. This approximation may be used for this test
6.3 Two Metal Plates, 150 by 150 mm or larger, of 0.5-mm
method if integrated absorbance is not available. Most spectral
thickness with smooth surfaces, preferably chromium plated.
manipulation software contains algorithms for adequately de-
terminingbaselinecorrectedintegratedabsorbances.Integrated
6.4 Brass Shims, approximately 75 by 75 mm, of 0.5-mm
absorbance is used because it is more nearly constant for a thickness with an aperture in the center at least 25 by 38 mm.
series of materials containing the same absorbing group in
6.5 Micrometer Calipers, with thimble graduations of 0.001
different environments, or in different states of aggregation. It
mm.
is independent of changes in line shape. Peak absorbances are
6.6 Infrared Liquid Cell, with sodium chloride or potassium
quite dependent on line shape factors, especially line width,
bromide windows, 0.1-mm spacing, calibrated.
which depends on the state of aggregation. Calibration with a
liquid sample for measurements on solid-state samples is not
6.7 Film Mounts,withaperturesatleast6by27mm,tohold
satisfactory using peak absorbances but is satisfactory using
the specimens in the infrared spectrophotometer.
integrated absorbances (1, 3).
6.8 Glass Stoppered Flasks, 150-mL.
4.4 Calibration is performed using a solution of 2,3-
6.9 Vacuum Oven.
dimethyl-1,3-butadiene in a liquid cell of known thickness.
This liquid has two vinylidene groups per molecule. Three
7. Reagents and Materials
different solutions are prepared and their measurements aver-
7.1 Bromine, reagent grade.
aged to obtain greater accuracy.
7.2 Carbon Disulfide (CS ), reagent grade.
5. Significance and Use
7.3 Poly(ethylene terephthalate) or Aluminum Sheets, 80 by
80 mm, or slightly larger to cover brass shims.
5.1 There are three types of olefinic groups present in
sufficient concentrations to warrant consideration, one or more
7.4 Standard Compound, 2,3-dimethyl-1,3-butadiene (liq-
of which can normally be found in any polyethylene (4). The
uid) of high purity, five 1-mL vials.
three types are: trans-vinylene, R - CH = CH - R', sometimes
8. Hazards
referred to as transinternal unsaturation; vinylidene or pendent
methylene, RR'C = CH ; and vinyl unsaturation,
2 8.1 Bromine is toxic and corrosive. Bromine treatment
R-CH=CH , also referred to as terminal unsaturation.
2 should be carried out in a hood or other ventilated space.
Neoprene gloves should be worn and adequate eye protection
5.2 The type and quantity of these groups can influence the
employed. Bromine-treated samples should be exposed to a
chemical and physical properties of the resin. Information
stream of air for 24 h or more to remove surplus bromine
concerning their presence may also be used to characterize or
before measurement in order to protect the operator and
identify unknown resins or blends of resins.
equipment. Samples previously treated with bromine should
5.3 Vinylidene unsaturation represents the major portion of
never be stored with materials which will be damaged by
the unsaturation present in most low-density polyethylenes.
bromine.
5.4 Infrared spectroscopy can be used for the determination
9. Sampling
of unsaturation in polyethylene (1, 3, 5). The values deter-
mined by infrared agree with those determined by IC1 uptake 9.1 The polyethylene shall be sampled in accordance with
(5).
Practice D1898.
10. Calibration
6. Apparatus
10.1 Prepare at least three different solutions of the standard
6.1 Infrared Spectrophotometer, Either Double Beam or
compound in CS at closely the same known concentration
Fourier Transform (FTIR): 2
near 0.18 mol/L (14.8 g/L). Calculate the exact vinylidene
6.1.1 Double-beam infrared spectrophotometer, capable of
concentrations(twotimesthemolarconcentrations)andrecord
spectral resolution as defined by Condition C of Section III
the values.
(Spectral Resolution) of the Proposed Methods for Evaluation
of Spectrophotometers. Also, see Practice E275 for testing 10.2 Set the controls of the infrared spectrometer for quan-
procedures. The instrument should be capable of scale expan- titative conditions with a good signal to noise ratio and
sion along the wavelength (or wave number) axis. satisfactory reproducibility. Use a sufficiently expanded chart
FT-IR instruments made by a variety of manufacturers that have spectral
6 -1
Perkin-Elmer Models 21, 125, 221, and 421 spectrophotometers and Beckman resolutions of at least 2 cm have been found adequate for these purposes.
IR-4 and IR-9 spectrophotometers have been found satisfactory for this purpose. Obtainable from Chemical Sales Co., 4692 Kenny Rd., Columbus, OH 43221.
...