ASTM D6248-21

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: D6248 − 21
Standard Test Method for
Vinyl and Trans Unsaturation in Polyethylene by Infrared
Spectrophotometry
This standard is issued under the fixed designation D6248; 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 E177 Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
1.1 This test method covers most types of polyethylene,
E275 Practice for Describing and Measuring Performance of
those ethylene plastics consisting of ethylene and α-olefin
Ultraviolet and Visible Spectrophotometers
comonomers longer than propylene, and blends of the above in
any ratio.
3. Terminology
1.2 The values stated in SI units are to be regarded as the
3.1 General—The units, symbols, and abbreviations used in
standard.
this test method appear in Terminology E131.
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 4. Summary of Test Method
responsibility of the user of this standard to establish appro-
–1
4.1 The band at 965 cm is characteristic of the trans-
priate safety, health, and environmental practices and deter- –1
vinylene substituted group. The band at 908 cm is character-
mine the applicability of regulatory limitations prior to use.
istic of the terminal vinyl group.
Specific hazards statements are given in Section 8.
4.2 These bands are not seriously overlapped by interfering
–1
NOTE 1—There is no known ISO equivalent for this standard.
groups from the polymer. The vinyl absorbance at 908 cm is
1.4 This international standard was developed in accor-
close to the absorbance band from terminal methyl groups on
–1
dance with internationally recognized principles on standard-
chains longer than ethyl, at 895 cm . This interference is
ization established in the Decision on Principles for the
minimal for most products. Inclusion of the bromination and
Development of International Standards, Guides and Recom-
spectral subtraction step from Test Method D3124 has been
mendations issued by the World Trade Organization Technical
found to improve the results for some very low density
Barriers to Trade (TBT) Committee.
products.
4.3 Integrated absorbance is used in this test method.
2. Referenced Documents
Integrated absorbance is found by integrating the spectrum
2.1 ASTM Standards:
over the absorbance band when the spectrum is plotted as
D792 Test Methods for Density and Specific Gravity (Rela-
–1
absorbance versus frequency, in cm . Most spectral manipu-
tive Density) of Plastics by Displacement
lation software contains algorithms for adequately determining
D1505 Test Method for Density of Plastics by the Density-
baseline corrected integrated absorbencies.
Gradient Technique
4.4 Calibration is performed using a solution of 1-octene for
D3124 Test Method for Vinylidene Unsaturation in Polyeth-
normal vinyl groups, and trans-3-hexene for trans-vinylene
ylene by Infrared Spectrophotometry
groups.
E131 Terminology Relating to Molecular Spectroscopy
E168 Practices for General Techniques of Infrared Quanti-
5. Significance and Use
tative Analysis
5.1 There are three types of olefinic groups present in
sufficient concentrations to warrant consideration, one or more
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
of that can normally be found in any polyethylene. The three
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.
Current edition approved Nov. 15, 2021. Published December 2021. Originally
types are trans-vinylene, R-CH=CH-R', sometimes referred to
ɛ1
approved in 1998. Last previous edition approved in 2012 as D6248 - 98 (2012) ,
as trans-internal unsaturation; vinylidene or pendent
which was withdrawn January 2021 and reinstated in November 2021. DOI:
methylene, RR'C-CH2; and vinyl unsaturation, R-CH=CH2,
10.1520/D6248-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or also referred to as terminal unsaturation.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
5.2 The type and quantity of these groups can influence the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. chemical and physical properties of the resin. Information
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6248 − 21
concerning their presence can also be used to characterize or slow to give good reproducibility of line shape. Set the slit
identify unknown resins or blends of resins. width narrow enough so there is little distortion of the true line
shape. For an FTIR spectrometer, use a spectral resolution of 4
5.3 Additivescaninterferewithunsaturationmeasurements.
–1
cm .Useanapodizationfunctionthatgivesgoodquantitation.
The use is cautioned to determine which additives are present
Beer-Norton medium and Happ-Genzel have been found to be
and if there any absorbance bands caused by additive presence
appropriate.
that overlap or interfere with unsaturation absorbance bands
–1 –1
used in this test method in the range of 1050 to 850 cm .If 9.3 Scan the solutions from 1050 to 850 cm in a 0.1-mm
overlapping bands occur, the method is not applicable. path length cell which has been calibrated by interference
fringes or other methods. Cell windows made of either NaCl or
5.4 Interference fringes resulting from smooth sample sur-
KBr are suitable.
faces can cause measurement errors. This test method requires
the use of aluminum foil in the compression molding of
9.4 Determine the integrated peak areas, A, for each stan-
samples to provide an adequately rough surface to minimize dard at the wavelength specified for the appropriate end group.
interference fringes.
The baseline shall be drawn from valley to valley for the peak
centered at or near the specified wave number for each type of
6. Apparatus
unsaturation.
6.1 Infrared Spectrophotometer, either double-beam, or a
9.5 Calculate the molar absorptivity, B for each solution
Fourier transform (FTIR).
using the known concentrations from 9.1 and the following
6.1.1 Double-Beam Infrared Spectrophotometer, capable of
equation:
spectral resolution as defined in Condition C of Section III
B 5 A/C 3 T (1)
~ !
(Spectral Resol
...