Harnessing Colloidal Dispersion for Laccase-Driven Enzymatic Depolymerization of Polystyrene

Abstract

Polystyrene (PS) is one of the most widely used synthetic polymers, with annual global production of around 20 million tons. However, its robust C─C backbone renders it highly recalcitrant to (bio)chemical depolymerization, and no sustainable re-/up-cycling method has yet been developed. Here, we establish a proof-of-concept for the efficient depolymerization of PS under mild aqueous conditions, using a laccase–mediator system (LMS) composed of Trametes versicolor laccase, 1-hydroxybenzotriazole (HBT), and ambient oxygen. To overcome substrate accessibility issues, PS is formulated into colloidally stable nanoparticles, promoting interfacial remote biocatalysis. Under such conditions, up to 99.9% decrease in molar mass is achieved from an initial PS of over 2 million g mol−1, synthesized by ab initio free-radical emulsion polymerization. This colloidal dispersion strategy is also effective for commercial PS and expanded PS waste processed by post-dispersion in surfactant-containing aqueous media. Mechanistic studies suggest that LMS-mediated depolymerization proceeds via HBT radical diffusion into PS nanoparticles, triggering hydrogen atom transfer (HAT)-based oxidation and β-scissions of PS chains. This approach provides an efficient method for PS depolymerization using aqueous conditions, ambient O2 and a native enzyme without harsh solvents or experimental conditions.