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ASTM D2238-92(2012)e1

Historical Revision

Standard Test Methods for Absorbance of Polyethylene Due to Methyl Groups at 1378 cm<sup>&minus;1</sup> (Withdrawn 2021)

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1.1 These test methods cover measurement by infrared absorption spectrophotometry of the 1378.4-cm−1 (7.255-μm) band in polyethylene due to methyl groups. (1, 2, 4-7)2 Two test methods are covered:

1.1.1 Test Method A uses compensation with a standard sample film or wedge of known methyl content.

1.1.2 Test Method B uses compensation with a wedge of polymethylene or a polyethylene of known low methyl content.

1.2 These test methods are applicable to polyethylenes of Types I (density 910 to 925 kg/m3), II (density 926 to 940), and III (density 941 to 965).

Note 1—For determination of density, see Specifications D1248.
Note 2—In cases of Type III polyethylene with densities greater than 0.950 g/cm3, different results are obtained with the two test methods.

1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.4 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 7.

Note 3—There is no known ISO equivalent to this standard.

4.1 When interpreted with the aid of appropriate calibration data, either test method can be used to compare the total methyl contents of polyethylenes made by similar processes. Such information can be interpreted in terms of specific alkyl groups with the aid of data on infrared absorption at certain other wavelengths (3).

Note 4—The bias of determination of the concentration of total alkyl groups depends on knowing the concentrations of methyl and ethyl branches present, since these branches have anomalously high absorptivities per group at 1378 cm−1 (7.25 μm).

4.2 Knowledge of total methyl groups in polyethylene, when combined with data on molecular weight and on reactive end groups such as vinyl, can lead to assignment of end-group structures and can shed light upon polymerization mechanisms.

4.3 Data on total methyl groups in polyethylene can be correlated qualitatively with certain polymer properties such as melting point, density, stiffness, and other mechanical properties that are closely dependent on the degree of crystallinity of the polymer.

4.4 These test methods are especially suitable for research. They have not been tested for use in manufacturing control.
SDO ASTM: ASTM International
Document Number D2238
Publication Date Dec. 1, 2012
Language en - English
Page Count 7
Revision Level 92(2012)e1
Supercedes
Committee D20.70
Publish Date Document Id Type View
Sept. 1, 2022 D2238-22 Revision
Dec. 1, 2012 D2238-92R12E01 Revision
July 1, 2004 D2238-92R04 Reaffirmation
March 10, 1999 D2238-92R99 Reaffirmation