Chemical recycling of polyethylene in oxygen-enriched supercritical CO2

Thermal oxidation of polyethylene was carried out in oxygen-enriched sc CO2 and in pure oxygen under a pressure of 215 and 14 bar, respectively. Oxygen to polymer weight ratio was varied. At lower oxygen content, the products were brown to dark brown pastes; at higher oxygen content, the products were dark yellow to dark-brown liquids. For the oligomeric fraction of the products, the data on molecular weights obtained by means of diffusion-ordered NMR and gel permeating chromatography was compared. Thermogravimetric analysis demonstrated that oxygen content strongly affects the yield of volatile products. The volatile products were further analyzed by means of H-1, C-13 NMR, gas chromatography-mass spectrometry and potentiometric titration. All the results obtained suggest that sc CO2 influence is more pronounced at lower oxygen to polymer mass ratio, which may be useful for carrying out chemical recycling of polyethylene through thermal oxidation while minimizing the amount of oxygen required.

Automated summary

The thermal oxidation of polyethylene was studied in oxygen-enriched supercritical CO2 and pure oxygen environments, showing that the oxygen content strongly affects the product characteristics. The volatile products were analyzed using various techniques, revealing that supercritical CO2 has a more pronounced influence at lower oxygen to polymer mass ratios.