ASTM D2238-22

4.1?When interpreted with the aid of appropriate calibration data, either test method is acceptable for use to compare the total methyl contents of polyethylenes made by similar processes. Data on infrared absorption at certain other wavelengths is potentially useful for information on certain other wavelengths (7).

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

4.3?Qualitative correlations are possible between data on total methyl groups in polyethylene 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.

1.1?These test methods cover measurement by infrared absorption spectrophotometry of the 1378 cm^?1 (7.25 ?m) band in polyethylene due to methyl groups. (1, 2, 3-6)2 Two test methods are covered:

1.2?These test methods are applicable to polyethylenes of Types I (density 0.910 to 0.925 g/cm³), II (density 0.926 to 0.940 g/cm³), and III (density 0.941 to 0.965 g/cm³).

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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Note 3:?There is no known ISO equivalent to this standard.