ASTM D6645-18
(Test Method)Standard Test Method for Methyl (Comonomer) Content in Polyethylene by Infrared Spectrophotometry
Standard Test Method for Methyl (Comonomer) Content in Polyethylene by Infrared Spectrophotometry
SIGNIFICANCE AND USE
5.1 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 can 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 IEEE/ASTM SI-10, 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
Note 1: There is no known ISO equivalent to this standard.
1.4 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.
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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: D6645 − 18
Standard Test Method for
Methyl (Comonomer) Content in Polyethylene by Infrared
1
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* D5576Practice for Determination of Structural Features in
Polyolefins and Polyolefin Copolymers by Infrared Spec-
1.1 This test method covers the determination of methyl
trophotometry (FT-IR)
groups (that is, comonomer content) in polyethylenes by
E131Terminology Relating to Molecular Spectroscopy
infrared spectrophotometry. The test method is applicable to
E168Practices for General Techniques of Infrared Quanti-
copolymers of ethylene with 1-butene, 1-hexene, or 1-octene
3 tative Analysis
having densities above 900 kg/m . High-pressure low-density
E177Practice for Use of the Terms Precision and Bias in
polyethylenes (LDPE) and terpolymers are excluded.
ASTM Test Methods
1.2 The values stated in SI units, based on IEEE/ASTMSI-
E932PracticeforDescribingandMeasuringPerformanceof
10, are to be regarded as the standard.
Dispersive Infrared Spectrometers
1.3 This standard does not purport to address all of the
E1421Practice for Describing and Measuring Performance
safety concerns, if any, associated with its use. It is the of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
responsibility of the user of this standard to establish appro-
eters: Level Zero and Level One Tests
priate safety, health, and environmental practices and deter- IEEE/ASTMSI-10Standard for Use of the International
mine the applicability of regulatory limitations prior to use.
System of Units (SI): The Modern System
NOTE 1—There is no known ISO equivalent to this standard.
3. Terminology
1.4 This international standard was developed in accor-
3.1 Terminology—The units, symbols, and abbreviations
dance with internationally recognized principles on standard-
used in this test method appear in Terminology E131 or
ization established in the Decision on Principles for the
IEEE/ASTMSI-10.
Development of International Standards, Guides and Recom-
3.2 comonomer—α-olefin monomer. In this test method,
mendations issued by the World Trade Organization Technical
comonomer refers to 1-butene, 1-hexene, or 1-octene only.
Barriers to Trade (TBT) Committee.
4. Summary of Test Method
2. Referenced Documents
-1 -1
2
4.1 The band located between 1377 cm and 1379 cm is
2.1 ASTM Standards:
due to a deformation vibration of the –CH group. Bands at
3
D792Test Methods for Density and Specific Gravity (Rela-
-1
approximately772cm (branchmethylenerockingmode),895
tive Density) of Plastics by Displacement
-1 -1
cm (methyl rocking mode), and 785 cm (branch methylene
D1505Test Method for Density of Plastics by the Density-
rocking mode) are characteristic of an ethyl branch (that is,
Gradient Technique
butenecopolymer),abutylbranch(thatis,hexenecopolymer),
D2238TestMethodsforAbsorbanceofPolyethyleneDueto
3
−1
and a hexyl branch (that is, octene copolymer), respectively.
Methyl Groups at 1378 cm
D3124Test Method forVinylidene Unsaturation in Polyeth- 4.2 This test method determines the methyl group (that is,
ylene by Infrared Spectrophotometry
comonomer)contentofapolyethylenecopolymerbasedonthe
-1
IR absorbance at 1378 cm from a pressed plaque. The
comonomer type has to be known and a calibration curve has
1
ThistestmethodisunderthejurisdictionofASTMCommitteeD20onPlastics
to be available prior to the analysis. If the comonomer is not
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods. -1 -1
known a priori, the presence of bands at 772 cm , 895 cm ,
Current edition approved Oct. 1, 2018. Published October 2018. Originally
-1
and 785 cm can be used to identify ethyl (minimum of 1
approved in 2001. Last previous edition approved in 2010 as D6645-01(2010).
DOI: 10.1520/D6645-18.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Blitz, J. P., and McFadden, D. C., “The Characterization of Short Chain
Standards volume information, refer to the standard’s Document Summary page on Branching in Polyethylene Using Fourier Transform Infrared Spectroscopy,” J.
the ASTM website. Appl. Pol. Sci., 51, 13 (1994).
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6645 − 01 (Reapproved 2010) D6645 − 18
Standard Test Method for
Methyl (Comonomer) Content in Polyethylene by Infrared
1
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. 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 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
3
above 900 kg/m . High-pressure low-density polyethylenes (LDPE) and terpolymers are excluded.
1.2 The values stated in SI units, based on IEEE/ASTM SI-10, 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
NOTE 1—There is no known ISO equivalent to this standard.
1.4 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.
2. Referenced Documents
2
2.1 ASTM Standards:
D792 Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
D1505 Test Method for Density of Plastics by the Density-Gradient Technique
3
D1898 Practice for Sampling of Plastics (Withdrawn 1998)
−1
D2238 Test Methods for Absorbance of Polyethylene Due to Methyl Groups at 1378 cm
D3124 Test Method for Vinylidene Unsaturation in Polyethylene by Infrared Spectrophotometry
D5576 Practice for Determination of Structural Features in Polyolefins and Polyolefin Copolymers by Infrared Spectrophotom-
etry (FT-IR)
E131 Terminology Relating to Molecular Spectroscopy
E168 Practices for General Techniques of Infrared Quantitative Analysis
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E932 Practice for Describing and Measuring Performance of Dispersive Infrared Spectrometers
E1421 Practice for Describing and Measuring Performance of Fourier Transform Mid-Infrared (FT-MIR) Spectrometers: Level
Zero and Level One Tests
IEEE/ASTM SI-10 Standard for Use of the International System of Units (SI): The Modern System
3. Terminology
3.1 Terminology—The units, symbols, and abbreviations used in this test method appear in Terminology E131 or IEEE/
ASTM SI-10.
3.2 comonomer—α-olefin monomer. In this test method, comonomer refers to 1-butene, 1-hexene, andor 1-octene only.
1
This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.
Current edition approved Jan. 1, 2010Oct. 1, 2018. Published January 2010October 2018. Originally approved in 2001. Last previous edition approved in 20012010 as
D6645 - 01.D6645 - 01(2010). DOI: 10.1520/D6645-01R10.10.1520/D6645-18.
2
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.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
D6645 − 18
4. Summary of Test Method
-1 -1
4.1 The band located between 1377 cm and 1379 cm is due to a deformation vibration of the –CH group. Bands at
3
-1 -1 -1
approximately 772 cm (branch methylene rocking mode), 895 cm (methyl rocking mode), and 785 cm (branch methylene
rocking mode) are characteristic of an ethyl branch (that is, butene copolymer), a butyl branch (that is, hexene copolymer), and
3
a hexyl branch (that is, octene copolymer) branches, copolymer), respectively.
4.2 This test method determines the methyl group (that is, comonomer) content of a polyethylene copolymer based on the IR
-1
absorbance at 1378 cm
...
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