Vinylidene Unsaturation in Polyethylene by Infrared Spectrophotometry ASTM D3124

Vinylidene Unsaturation in Polyethylene by Infrared Spectrophotometry ASTM D3124

ASTM D3124 test method covers every sort of polyethylene such as ethylene plastics, α-olefin copolymers that are longer than propylene, and the mixture of these in any ratio. It determines the effect of unsaturation of vinylidene by using reagents like bromine, carbon disulfide, and 2, 3-dimethyl-1,3-butadiene. The final results of the test method are expressed in SI units.


    ASTM D3124 test method studies the characteristics of the vinylidene group. The chemical and physical properties of the resin affected by the different types of olefinic groups are determined. The information obtained from the study can help in identifying and characterizing unknown resins or other blends of it. Vinylidene unsaturation plays a significant role in low-density polyethylenes and can be detected by infrared spectroscopy. 

    Test Procedure:

    The sample is prepared and preheated to be placed in a brass shim filled with polymer on polyethylene terephthalate that covers the metal plate. The mold assembly is pressed by placing it between the press platens, and then the sample is removed after cooling. The thickness of the sample is measured through a micrometer, and the process is repeated by initiating bromination and other test methods.

    Specimen Size : 

    Brass Shims, approximately 75 by 75 mm, of 0.5-mm thickness with an aperture in the center at least 25 by 38 mm.


    Molar absorption of the solutions can be calculated as follows, with the standard being the SI Units:
    B ꞊ (A/C × L)
    Where: B = molar absorptivity, L/mol-cm
    A = integrated absorbance, measured or estimated
    C = concentration of vinylidene group, mol/L
    L = cell thickness, cm.


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