Surfactant-free synthesis of polyethylene nanoparticles: toward more realistic model nanoplastics

Abstract

Nanoplastics have recently been identified across diverse environmental compartments and are now considered a new class of emerging pollutants. Among them, polyethylene (PE) is the most predominant polyolefin detected in both micro- and nanoplastic forms. Accurate environmental and toxicological assessment of PE nanoplastics requires representative model particles; however, their development remains challenging due to PE's semi-crystalline nature, which hinders top-down fabrication, and the gaseous state of its monomer, which complicates bottom-up synthesis involving high pressure and temperature. In this study, we report the surfactant-free radical aqueous emulsion polymerization of ethylene as a viable route to synthesize model PE nanoparticles with tunable surface charges (anionic or cationic) and narrow size distributions (50–150 nm, extended up 200 nm via seeded polymerization). To mimic oxidative environmental aging, copolymer nanoparticles incorporating polar monomers (vinyl acetate or carbon monoxide) were also produced. These materials exhibit variable surface charges, particle sizes, and carbonyl indices, offering structurally and chemically relevant models for investigating the environmental behavior and toxicity of PE-based nanoplastics.