ASTM D6248-98 Test for Vinyl and Trans Unsaturation in Polyethylene by Infrared Spectrophotometry

Scope:

There are three types of olefinic groups (unsaturation) present in sufficient concentrations in any polyethylene. These three types of unsaturation are trans-vinylene, vinylidene, and vinyl unsaturation or terminal unsaturation. ASTM D6248-98 test method is used to measure these unsaturations using Infrared spectrophotometry. The type and quantity of olefinic groups influence the chemical and physical properties of the resin. Also, Olefinic groups can be used to characterize or identify unknown resins or blends of resins. 

Test Procedure:

ASTM D6248-98 uses infrared Spectrophotometry. Infrared spectrophotometry is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms. In this test, the infrared spectrum of a sample is recorded by passing a beam of infrared light through the sample. When the frequency of the IR is the same as the vibrational frequency of a bond or collection of bonds, absorption occurs. Examination of the transmitted light reveals how much energy was absorbed at each frequency. The entire wavelength range is measured using a Fourier transform instrument and then a transmittance or absorbance spectrum is generated using a dedicated procedure.

Data:

The following information is reported:

The density of the material tested, end-group concentrations, number of vinyl groups per 1000 carbon atoms for each sample, number of trans-vinylene groups per 1000 carbon atoms for each sample, and any sample or spectral anomalies seen during the measurements.