Analysis of Antioxidants in Polyethylene Using Supercritical Fluid Extraction/Supercritical Fluid Chromatography and Infrared Detection

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Abstract
Supercritical fluid extraction using 100% carbon dioxide is able to remove antioxidant additives from flaked polyethylene. SFE appears to be more selective for the lower-range low-MW polymer than Soxhlet-type extraction. This yields a chromatogram with less interference from low-MW polymer peaks in the region where the additive components elute. Infrared detection is able to locate peaks corresponding to distinct types of additives by generating chromatograms from chemically specific regions of the SFC/IR data. Infrared spectra are sufficient for identification of additives and determination of the oxidation state of phosphorus-containing antioxidants.