Decontamination of volatile compounds from post-consumer recycled HDPE via supercritical CO2: Unravelling the critical role of co-solvent molecular structure.

This study systematically evaluates supercritical CO2 (scCO2) extraction for the decontamination of volatile compounds from post-consumer recycled high-density polyethylene (rHDPE), with a focus on co-solvent effects. Time-resolved extraction revealed that contaminant load strongly influenced removal efficiency, and flakes achieved 15% higher performance than pellets due to thinner morphology and reduced re-embedding. Co-solvent assistance further enhanced efficiency, with p-xylene, ethylbenzene, and cyclohexanone achieving up to 35% improvement compared to neat scCO2. Hansen Solubility Parameter (HSP) analysis indicates that solvent compatibility with HDPE is a necessary but insufficient factor for the enhanced decontamination efficiency, and further molecular descriptor analysis provided additional mechanistic insight, highlighting aromaticity, polarizability, rigidity, and topological complexity as key determinants of enhanced efficiency. Aromatic co-solvents facilitated contaminant release through π-electron delocalization and planar rigidity, while cyclohexanone achieved broad solvation capacity via polar functionality and favorable topological descriptors. These results reveal structure-performance relationships that may inform co-solvent selection and contribute to the understanding of scCO2-based decontamination strategies for rHDPE.