ASTM D6474 Molecular Weight Distribution and Molecular Weight Averages of Polyolefins

Scope:

The ASTM D6474 standard procedure determines the molecular weight distribution and averages of polyethylene (excluding LDPE) and polypropylene resins. It can analyze polyethylenes (excluding LDPE) and polypropylenes that dissolve in 1,2,4 trichlorobenzene (TCB) at 140 °C.
Variations in molecular weight and molecular weight distribution significantly influence the physical properties of these resins, such as morphology, strength, melt flow, and other characteristics. As a result, these disparities also impact the ultimate properties of products manufactured from these resins.

Procedure:

In this ASTM test method, identified as D6474, a solvent dissolves a polyolefin sample and is injected into a chromatographic column filled with a solid substrate. This technique separates the molecules in the solution based on their size. The elution of the separated molecules from the column occurs in the order of their concentration, and they are subsequently detected and recorded. The timings of receipt are calibrated to determine molecular weights. The data on molecular weight concentration is then utilized to calculate average molecular weight parameters and molecular weight distribution.

Specimen Size:

For the ASTM D6474 test process, a finely ground polymer is employed as a test specimen.

Data:

As the α-olefin comonomer content in linear low-density polyethylene increases, the accuracy of the molecular weight results declines, i.e., they become increasingly underrated, according to the ASTM D6474 test technique.

Conclusion:

The ASTM D6474 test procedure measures the molecular weight averages and molecular weight distribution of polyethylene (excluding LDPE) and polypropylene resins.