Enabling Downstream Recycling: Separation and Debromination of Polymeric Brominated Flame Retardants from Polystyrene

Abstract

Brominated flame retardants (BFRs) have been widely used to enhance fire resistance in polymeric materials; however, conventional small-molecule BFRs raise significant environmental and health concerns due to their persistence, bioaccumulation, and toxicity. To address these issues, polymeric BFRs such as brominated polystyrene (Br-PS) and brominated styrene-butadiene-styrene (Br-SBS) block copolymer have been developed as alternative, more stable flame retardants to replace the conventional BFRs. In this study, we explored effective strategies for the treatment and valorization of these polymeric BFRs. Initially, we investigated degradation through pyrolysis, using Br-PS as a model substrate. However, this approach proved inefficient, as it yielded a mixture of brominated and nonbrominated aromatic compounds with negligible recovery of valuable monomers such as styrene. Alternatively, we developed a two-step strategy combining selective separation and catalytic hydrodebromination (HDB). By employing a solvent separation method using methyl ethyl ketone (MEK) or ethyl acetate (EtOAc) as polystyrene (PS) solvents, we selectively isolated Br-PS and Br-SBS with high purities and mass recovery efficiencies (>99% purity, 99 wt %, respectively, for both BFRs), while PS was efficiently recovered from solution (>99% purity, 96 wt %). The isolated polymeric BFRs were then subjected to catalytic HDB under mild conditions using Pd/C (5 wt %). This approach effectively depleted the majority of halogen content, achieving 90 mol % debromination and yielding polymers with substantially reduced bromine levels, which are suitable for subsequent recycling. Overall, our integrated separation and catalytic debromination strategy offers a selective and efficient pathway for the valorization of polymeric BFR-containing materials, enabling their safe reintegration into plastic recycling schemes.