ASTM D3124-98

Standard Test Method for Vinylidene Unsaturation in Polyethylene by Infrared Spectrophotometry

SCOPE
1.1 This test method is applicable to all types of polyethylenes and blends of polyethylenes.
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 problems, 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 similar or equivalent ISO standard.

General Information

• Status: Historical
• Publication Date: 09-Mar-1998
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.70 - Analytical Methods

Relations

• Replaced By: ASTM D3124-98(2003) - Standard Test Method for Vinylidene Unsaturation in Polyethylene by Infrared Spectrophotometry
• Effective Date: 10-Mar-2003
• Referred By: ASTM D6248-21 - Standard Test Method for Vinyl and Trans Unsaturation in Polyethylene by Infrared Spectrophotometry
• Effective Date: 10-Mar-1998
• Referred By: ASTM D5576-00(2021)e1 - Standard Practice for Determination of Structural Features in Polyolefins and Polyolefin Copolymers by Infrared Spectrophotometry (FT-IR)
• Effective Date: 10-Mar-1998
• Referred By: ASTM D6645-18 - Standard Test Method for Methyl (Comonomer) Content in Polyethylene by Infrared Spectrophotometry
• Effective Date: 10-Mar-1998

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 3124 – 98
Standard Test Method for
Vinylidene Unsaturation in Polyethylene by Infrared
Spectrophotometry
This standard is issued under the fixed designation D 3124; 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 (e) 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, and abbreviations used in
enes, those ethylene plastics consisting of ethylene and this test method appear in Terminology E 131 or Practice
a-olefin copolymers longer than propylene, and blends of the E 380.
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.
vinylidene groups (1, 2). It is the strongest vinylidene band
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the and is due to the deformation vibrations of the C - H bonds in
the CH group.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- 4.2 This band is overlapped by absorption at 11.25 to 11.07
-1
μm (889 to 903 cm ) from vibrations of terminal methyl
bility of regulatory limitations prior to use. Specific hazards
statements are given in Section 8. groups on alkyl groups longer than ethyl. By using a bromi-
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
D 792 Test Methods for Density and Specific Gravity (Rela-
2 brominated spectra from the untreated spectra. The bromina-
tive Density) of Plastics by Displacement
tion destroys the vinylidene unsaturation in the sample (1) in
D 1505 Test Method for Density of Plastics by the Density-
2 the reference beam but leaves the methyl absorption intact.
Gradient Technique
Thus, the methyl absorption is eliminated because it appears in
D 1898 Practice for Sampling of Plastics
3 both the sample and reference beams. The vinylidene absorp-
E 131 Terminology Relating to Molecular Spectroscopy
tion is then seen without interference in the difference spec-
E 168 Practices for General Techniques of Infrared Quanti-
3 trum.
tative Analysis
4.3 Integrated absorbance, instead of the usual absorbance
E 177 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
E 275 Practice for Describing and Measuring Performance
absorbance band when the spectrum is plotted as absorbance
of Ultraviolet, Visible, and Near Infrared Spectrophotom-
-1
versus frequency, in cm . A very good approximation to
eters
integrated absorbance is obtained by multiplying the absor-
E 380 Practice for Use of the International System of Units
bance at the band peak by the band half-width, the width of the
(the Modernized Metric System)
-1
band in cm at an absorbance equal to 50 % of the peak
Proposed Methods for Evaluation of Spectrophotometers
absorbance. This approximation may be used for this test
method if integrated absorbance is not available. Most spectral
manipulation software contains algorithms for adequately de-
termining baseline corrected integrated absorbances. Integrated
This test method is under the jurisdiction of ASTM Committee D-20 on Plastics
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods
absorbance is used because it is more nearly constant for a
(Section D20.70.08).
series of materials containing the same absorbing group in
Current edition approved March 10, 1998. Published December 1998. Originally
different environments, or in different states of aggregation. It
published as D 3124 – 72. Last previous edition D 3124 – 93.
Annual Book of ASTM Standards, Vol 08.01.
Annual Book of ASTM Standards, Vol 03.06.
4 6
Annual Book of ASTM Standards, Vol 14.02. 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.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 3124
is independent of changes in line shape. Peak absorbances are 6.7 Film Mounts, with apertures at least 6 by 27 mm, to hold
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
5.1 There are three types of olefinic groups present in 8. Hazards
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.
5.3 Vinylidene unsaturation represents the major portion of
9. Sampling
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 D 1898.
of unsaturation in polyethylene (1, 3, 5). The values deter-
mined by infrared agree with those determined by IC1 uptake
10. Calibration
(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 (two times the molar concentrations) and record
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 E 275 for testing
scale such that line width can be measured accurately. Use a
procedures. The instrument should be capable of scale expan-
7 scanning speed sufficiently slow to give good reproducibility of
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
-1
distortion of the true line shape. Record the instrument condi-
4-cm resolution and scale expansion along the wavelength
-1
8 tions used. For a FT-IR, a spectral resolution of 4 cm should
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.
6.3 Two Metal Plates, 150 by 150 mm or larger, of 0.5-mm
-1
10.3 Scan the solutions from 935 to 847 cm (10.70 to 11.80
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.
For a FT-IR, expand the scale of the transformed and converted
6.5 Micrometer Calipers, with thimble graduations of 0.001
-1
absorbance spectra from 935 to 847 cm .
mm.
6.6 Infrared Liquid Cell, with sodium chloride or potassium
NOTE 2—Practice E 275, paragraph 21.5, describes the interference
fringe method of calibrating the thickness of infrared cells.
bromide windows, 0.1-mm spacing, calibrated.
10.4 For t
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