ASTM D6645-01(2010)

Standard Test Method for Methyl (Comonomer) Content in Polyethylene by Infrared Spectrophotometry

SIGNIFICANCE AND USE
This method determines the number of branches (that is, comonomer content) in copolymers of ethylene with 1-butene, 1-hexene or 1-octene. This information can be correlated with physical properties such as melting point, density, and stiffness, all of which depend on the degree of crystallinity of the polymer. Differences in the comonomer content thus may have a significant effect on the final properties of products made from these resins.
SCOPE
1.1 This test method covers the determination of methyl groups (that is, comonomer content) in polyethylenes by infrared spectrophotometry. The test method is applicable to copolymers of ethylene with 1-butene, 1-hexene, or 1-octene having densities above 900 kg/m3. High-pressure low-density polyethylenes (LDPE) and terpolymers are excluded.
1.2 The values stated in SI units, based on , 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.
Note 1—There is no known ISO equivalent to this standard.

General Information

• Status: Historical
• Publication Date: 31-Dec-2009
• ICS: 19.100 - Non-destructive testing
• ICS: 83.080.20 - Thermoplastic materials
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.70 - Analytical Methods

Relations

• Replaced By: ASTM D6645-18 - Standard Test Method for Methyl (Comonomer) Content in Polyethylene by Infrared Spectrophotometry
• Effective Date: 01-Oct-2018

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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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: D6645 − 01 (Reapproved 2010)
Standard Test Method for
Methyl (Comonomer) Content in Polyethylene by Infrared
Spectrophotometry
This standard is issued under the fixed designation D6645; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E168Practices for General Techniques of Infrared Quanti-
tative Analysis
1.1 This test method covers the determination of methyl
E177Practice for Use of the Terms Precision and Bias in
groups (that is, comonomer content) in polyethylenes by
ASTM Test Methods
infrared spectrophotometry. The test method is applicable to
E932PracticeforDescribingandMeasuringPerformanceof
copolymers of ethylene with 1-butene, 1-hexene, or 1-octene
3 Dispersive Infrared Spectrometers
having densities above 900 kg/m . High-pressure low-density
E1421Practice for Describing and Measuring Performance
polyethylenes (LDPE) and terpolymers are excluded.
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
1.2 The values stated in SI units, based on IEEE/ASTMSI-
eters: Level Zero and Level One Tests
10, are to be regarded as the standard.
IEEE/ASTMSI-10 Standard for Use of the International
1.3 This standard does not purport to address all of the
System of Units (SI): The Modern System
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 3. Terminology
priate safety and health practices and determine the applica-
3.1 Terminology—The units, symbols, and abbreviations
bility of regulatory limitations prior to use.
used in this test method appear in Terminology E131 or
IEEE/ASTMSI-10.
NOTE 1—There is no known ISO equivalent to this standard.
3.2 comonomer—α-olefin monomer. In this test method,
2. Referenced Documents
comonomer refers to 1-butene, 1-hexene, and 1-octene only.
2.1 ASTM Standards:
D792Test Methods for Density and Specific Gravity (Rela-
4. Summary of Test Method
tive Density) of Plastics by Displacement -1 -1
4.1 The band located between 1377 cm and 1379 cm is
D1505Test Method for Density of Plastics by the Density-
due to a deformation vibration of the –CH group. Bands at
Gradient Technique -1
approximately772cm (branchmethylenerockingmode),895
D1898Practice for Sampling of Plastics (Withdrawn 1998)
-1 -1
cm (methyl rocking mode), and 785 cm (branch methylene
D2238TestMethodsforAbsorbanceofPolyethyleneDueto
rocking mode) are characteristic of ethyl (that is, butene
−1
Methyl Groups at 1378 cm
copolymer), butyl (that is, hexene copolymer), and hexyl (that
D3124Test Method forVinylidene Unsaturation in Polyeth-
is, octene copolymer) branches, respectively.
ylene by Infrared Spectrophotometry
4.2 This test method determines the methyl (that is,
D5576Practice for Determination of Structural Features in
comonomer)contentofapolyethylenecopolymerbasedonthe
Polyolefins and Polyolefin Copolymers by Infrared Spec-
-1
IR absorbance at 1378 cm from a pressed plaque. The
trophotometry (FT-IR)
comonomer type has to be known and a calibration curve has
E131Terminology Relating to Molecular Spectroscopy
to be available prior to the analysis. If the comonomer is not
-1 -1
known a priori, the presence of bands at 772 cm , 895 cm ,
-1
ThistestmethodisunderthejurisdictionofASTMCommitteeD20onPlastics
and 785 cm can be used to identify ethyl (minimum of 1
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.
branchper1000carbons),butyl(minimumofabout5branches
Current edition approved Jan. 1, 2010. Published January 2010. Originally
per 1000 carbons), and hexyl (minimum of about 5 branches
approved in 2001. Last previous edition approved in 2001 as D6645-01. DOI:
10.1520/D6645-01R10. per1000carbons)branches,respectively.Amoresensitiveand
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. Blitz, J. P., and McFadden, D. C., “The Characterization of Short Chain
The last approved version of this historical standard is referenced on Branching in Polyethylene Using Fourier Transform Infrared Spectroscopy,” J.
www.astm.org. Appl. Pol. Sci., 51, 13 (1994).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6645 − 01 (2010)
less ambiguous identification is obtained by C13 NMR spec- 7.1.1 Dispersive Infrared Spectrophotometer, capable of
-1
troscopy. The latter technique is also used as a reference achieving a spectral bandwidth of 4 cm (see Practice E932).
technique to provide polymer standards for the generation of The instrument should be capable of scale expansion along the
calibration curves. wavenumber axis.
7.1.2 Fourier Transform Infrared Spectrometer,capableof4
NOTE 2—For comonomer identification, it is recommended, for maxi-
-1
cm resolution(seePracticeE1421).Theinstrumentshouldbe
mum sensitivity, to view the second derivative of the IR spectrum.
capable of scale expansion along the wavenumber axis.
4.3 Themethodiscalibratedbyplottingabsorbanceat1378
-1
7.2 Compression Molding Press, with platens capable of
cm per unit area of the methylene combination band at 2019
-1
being heated to 180°C.
cm (thatis,internalthicknesscorrectionapproach)orperunit
of spectral cross-section (that is, the reciprocal of the product
7.3 Two Metal Plates, 150 by 150 mm or larger, of 0.5-mm
ofplaquethicknessanddensity)versusnumberofbranchesper
thickness with smooth surfaces.
1000 carbons as determined by C13 NMR spectroscopy.
7.4 Brass Shims, approximately 75 by 75 mm, of 0.3 mm
Although both approaches give equivalent results, the one
thickness with an aperture in the center at least 25 by 38 mm.
using internal thickness correction is recommended in this test
7.5 Micrometer (optional), with thimble graduations of
method since it is considerably simpler to execute.
0.001 mm.
5. Significance and Use
7.6 Film Mounts,withaperturesatleast6by27mm,tohold
the specimens in the infrared spectrophotometer.
5.1 Thismethoddeterminesthenumberofbranches(thatis,
comonomer content) in copolymers of ethylene with 1-butene,
8. Materials
1-hexene or 1-octene. This information can be correlated with
physicalpropertiessuchasmeltingpoint,density,andstiffness,
8.1 Polyethylene Terephthalate, Aluminum Foil or Matte
all of which depend on the degree of crystallinity of the Finished Teflon-Fibreglass Sheets.
polymer. Differences in the comonomer content thus may have
9. Hazards
a significant effect on the final properties of products made
from these resins.
9.1 Caution must be used during plaque preparation to
handle the hot platens with appropriate gloves for hand
6. Interferences
protection.
6.1 A conformational CH wagging absorbance at 1368
-1 -1
10. Procedure
cm overlapsthemethylabsorbanceat1378cm ,butdoesnot
cause significant interference in this test method since its 10.1 Preparation of Polymer Plaque:
intensity is not significantly affected by the comonomer
10.1.1 Preheat the press to about 50°C above the melting
content, but rather by the plaque thickness. The result of not point of the polymer.
correcting for thi
...