Harnessing Colloidal Dispersion for Laccase-Driven Enzymatic Depolymerization of Polystyrene.

From the paper

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.