ASTM  D6645 Methyl (Comonomer) Content in Polyethylene by Infrared Spectrophotometry

Scope:

The determination of methyl groups (that is, comonomer content) in polyethylenes using infrared spectrophotometry is covered by this ASTM D6645 test technique. This method determines the number of branches (comonomer content) in ethylene with 1-butene, 1-hexene, or 1-octene  copolymers. Physical parameters like melting temperature, density, and stiffness, all of which are dependent on the degree of crystallinity of the polymer, can be associated with this information. As a result, variations in comonomer content may have a considerable impact on the ultimate qualities of goods created using these resins. The ASTM D6645 test method is simple,  direct, fast, and accurate.

Procedure:

The methyl content of ethylene and copolymers of other monomers (propane, butylene, and hexylene) are examined using the ASTM D6645 approach. The ratio X of the absorbance value of the peak areas (the baseline range of methyl absorption peaks is selected to be from 1400 cm^-1to  1330 cm^-1) of methyl characteristic peaks (from 1378 cm^-1to 1379 cm^-1) of the polyethylene samples copolymerized by ethylene and different monomers (propene, butylene, and hexylene). A fourier transform infrared spectrometer is used to determine the absorbance value of the peak areas of the copolymerized polyethylene characteristic peaks (from 2100 cm^-1to 1980 cm^-1). Then,  using the regression formula Y=KX+b, the methyl content Y percent is estimated, where K and b  are constants obtained from the infrared spectrum of the standard samples.

Specimen size:

Plaques with satisfactory surface polish and uniformity are used as test specimens for ASTM D6645. 

Data:

In ASTM D6645, any sample or spectral anomalies observed during the measurement are reported.

The concentration of methyl content in polyethylene is reported in SI units and is considered as standard.

Conclusion:

The determination of methyl groups (that is, comonomer content) in polyethylenes using infrared spectrophotometry is covered by this ASTM D6645 test technique.