ASTM D3124-98(2011)
(Test Method)Standard Test Method for Vinylidene Unsaturation in Polyethylene by Infrared Spectrophotometry
Standard Test Method for Vinylidene Unsaturation in Polyethylene by Infrared Spectrophotometry
SIGNIFICANCE AND USE
There are three types of olefinic groups present in sufficient concentrations to warrant consideration, one or more of which can normally be found in any polyethylene (4). The three types are: trans-vinylene, R - CH = CH - R′, sometimes referred to as transinternal unsaturation; vinylidene or pendent methylene, RR′C = CH2; and vinyl unsaturation, R - CH = CH2, also referred to as terminal unsaturation.
The type and quantity of these groups can influence the chemical and physical properties of the resin. Information concerning their presence may also be used to characterize or identify unknown resins or blends of resins.
Vinylidene unsaturation represents the major portion of the unsaturation present in most low-density polyethylenes.
Infrared spectroscopy can be used for the determination of unsaturation in polyethylene (1, 3, 5). The values determined by infrared agree with those determined by IC1 uptake (5).
SCOPE
1.1 This test method is applicable to all types of polyethylenes, those ethylene plastics consisting of ethylene and α-olefin copolymers longer than propylene, and blends of the above in any ratio.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazards statements are given in Section 8.
Note 1—There is no known ISO equivalent to this standard.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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 2011)
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 System of Units (the Modernized Metric System)
Proposed Methods for Evaluation of Spectrophotometers
1.1 This test method is applicable to all types of
polyethylenes, those ethylene plastics consisting of ethylene
3. Terminology
and α-olefin copolymers longer than propylene, and blends of
3.1 General—The units, symbols, and abbreviations used in
the above in any ratio.
this test method appear in Terminology E131 or Standard
1.2 The values stated in SI units are to be regarded as the
IEEE/ASTM SI 10.
standard.
4. Summary of Test Method
1.3 This standard does not purport to address all of the
-1
safety concerns, if any, associated with its use. It is the
4.1 The band at 888 cm (11.26 µm) is characteristic of
responsibility of the user of this standard to establish appro-
vinylidene groups (1, 2). It is the strongest vinylidene band
priate safety and health practices and determine the applica-
and is due to the deformation vibrations of the C - H bonds in
bility of regulatory limitations prior to use. Specific hazards
the CH group.
statements are given in Section 8.
4.2 This band is overlapped by absorption at 11.25 to 11.07
-1
NOTE 1—There is no known ISO equivalent to this standard.
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.
E168 Practices for General Techniques of Infrared Quanti- Thus, the methyl absorption is eliminated because it appears in
tative Analysis both the sample and reference beams. The vinylidene absorp-
E177 Practice for Use of the Terms Precision and Bias in tion is then seen without interference in the difference spec-
ASTM Test Methods trum.
E275 Practice for Describing and Measuring Performance of
4.3 Integrated absorbance, instead of the usual absorbance
Ultraviolet and Visible Spectrophotometers
at the band peak, is used in this test method. Integrated
IEEE/ASTM SI 10 Standard for Use of the International
absorbance is found by integrating the spectrum over the
absorbance band when the spectrum is plotted as absorbance
-1
versus frequency, in cm . A very good approximation to
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
integrated absorbance is obtained by multiplying the absor-
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods
(Section D20.70.08). bance at the band peak by the band half-width, the width of the
-1
Current edition approved Feb. 1, 2011. Published March 2011. Originally
band in cm at an absorbance equal to 50 % of the peak
approved in 1972. Last previous edition approved in 2003 as D3124 – 98(2003).
absorbance. This approximation may be used for this test
DOI: 10.1520/D3124-98R11.
method if integrated absorbance is not available. Most spectral
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 (2011)
manipulation software contains algorithms for adequately de- 6.4 Brass Shims, approximately 75 by 75 mm, of 0.5-mm
terminingbaselinecorrectedintegratedabsorbances.Integrated thickness with an aperture in the center at least 25 by 38 mm.
absorbance is used because it is more nearly constant for a
6.5 Micrometer Calipers, with thimble graduations of 0.001
series of materials containing the same absorbing group in
mm.
different environments, or in different states of aggregation. It
6.6 Infrared Liquid Cell, with sodium chloride or potassium
is independent of changes in line shape. Peak absorbances are
bromide windows, 0.1-mm spacing, calibrated.
quite dependent on line shape factors, especially line width,
which depends on the state of aggregation. Calibration with a 6.7 Film Mounts,withaperturesatleast6by27mm,tohold
liquid sample for measurements on solid-state samples is not
the specimens in the infrared spectrophotometer.
satisfactory using peak absorbances but is satisfactory using
6.8 Glass Stoppered Flasks, 150-mL.
integrated absorbances (1, 3).
6.9 Vacuum Oven.
4.4 Calibration is performed using a solution of 2,3-
dimethyl-1,3-butadiene in a liquid cell of known thickness.
7. Reagents and Materials
This liquid has two vinylidene groups per molecule. Three
7.1 Bromine, reagent grade.
different solutions are prepared and their measurements aver-
aged to obtain greater accuracy. 7.2 Carbon Disulfide (CS ), reagent grade.
7.3 Poly(ethylene terephthalate) or Aluminum Sheets, 80 by
5. Significance and Use
80 mm, or slightly larger to cover brass shims.
5.1 There are three types of olefinic groups present in
7.4 Standard Compound, 2,3-dimethyl-1,3-butadiene (liq-
sufficient concentrations to warrant consideration, one or more
uid) of high purity, five 1-mL vials.
of which can normally be found in any polyethylene (4). The
three types are: trans-vinylene, R - CH = CH - R', sometimes
8. Hazards
referred to as transinternal unsaturation; vinylidene or pendent
8.1 Bromine is toxic and corrosive. Bromine treatment
methylene, RR'C = CH ; and vinyl unsaturation,
should be carried out in a hood or other ventilated space.
R-CH=CH , also referred to as terminal unsaturation.
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.
6. Apparatus
10. Calibration
6.1 Infrared Spectrophotometer, Either Double Beam or
10.1 Prepare at least three different solutions of the standard
Fourier Transform (FTIR):
compound in CS at closely the same known concentration
6.1.1 Double-beam infrared spectrophotometer, capable of
near 0.18 mol/L (14.8 g/L). Calculate the exact vinylidene
spectral resolution as defined by Condition C of Section III
concentrations(twotimesthemolarconcentrations)andrecord
(Spectral Resolution) of the Proposed Methods for Evaluation
the values.
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-
6 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
6.1.2 Fourier transform infrared spectrometer, capable of
-1 scale such that line width can be measured accurately. Use a
4-cm resolution and scale expansion along the wavelength
6,7 scanningspeedsufficientlyslowtogivegoodreproducibilityof
axis.
line shape. Set the slit width narrow enough that there is little
6.2 Compression-Molding Press, small, with platens ca-
distortion of the true line shape. Record the instrument condi-
-1
pable of being heated to 170°C.
tions used. For a FT-IR, a spectral resolution of 4 cm should
be used. An apodization function that gives good quantitation
6.3 Two Metal Plates, 150 by 150 mm or larger, of 0.5-mm
thickness with smooth surfaces, preferably chromium plated. should be used. Beer-Norton medium and Happ-Genzel have
been found to be appropriate.
Perkin-Elmer Models 21, 125, 221, and 421 spectrophotometers and Beckman
IR-4 and IR-9 spectrophotometers have been found satisfactory for this purpose.
7 8
FT-IR instruments made by a
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