Application of solvent-based dissolution method for recycling of ocean plastics and removal of selected persistent organic contaminants

Ocean plastic pollution represents a critical environmental challenge, with polyolefins accumulating in oceans while acting as a vector for hazardous additives and sorbed persistent organic pollutants. Conventional mechanical recycling cannot remove embedded contaminants and causes progressive polymer degradation, limiting closed-loop implementation. This study investigates solvent-based decontamination of ocean high-density polyethylene (HDPE) through dissolution-precipitation and multi-stage washing, comparing fresh-solvent and counter-current configurations. The ocean HDPE sample was spiked with 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV-328) and di(2-ethylhexyl) phthalate (DEHP) (approximately 10,000 μg/g) to simulate worst-case contamination by dissolving in xylene at 108 °C and precipitation via cooling and further aided by addition of an anti-solvent (isopropanol) at 40 °C. The spiked polymer underwent six sequential washing cycles at 40 °C using xylene-isopropanol (1:1 w /w). Removal efficiencies were quantified by GC–MS, while polymer integrity was evaluated using X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), high-temperature gel permeation chromatography (HT-GPC), differential scanning calorimetry (DSC), and melt flow measurements. Dissolution-precipitation (DP) stage achieved 76% contaminant removal by eliminating diffusion barriers. Further sequential washing increased total removal to 99.98% for both contaminants leaving residual concentrations (in the dry polymer) of 2.14 ± 0.12 μg/g for UV 328 and 3.30 ± 0.06 μg/g for DEHP via the fresh-solvent washing method. 99.83% removal was achieved by counter current extraction method while reducing the demand of solvent recovery by 83%. The recycled HDPE showed preserved molecular weight, removal of inorganic contaminants (>78%), and processability characteristics comparable to reported recycled PE, demonstrating solvent-based decontamination as a viable pathway for ocean plastic waste recycling.