Decontaminating Plastic Recyclates via Solvothermal Extraction of Brominated Flame Retardants

Removing hazardous additives, such as brominated flame retardants (BFRs), from plastics is essential for mitigating the environmental burden of BFR-contaminated plastic recyclates. In this study, bromine-rich acrylonitrile–butadiene–styrene (ABS) and high-impact polystyrene (HIPS) samples from a recycling facility were extracted in an autoclave using mixtures of water, isopropanol (IPA), and sodium hydroxide (NaOH) as solvents. The total bromine content of the samples was quantified by X-ray fluorescence (XRF), while organic additives were analyzed using direct insertion probe mass spectrometry (DIP-MS). Initial characterization revealed the presence of multiple BFRs and other additives in both recyclates. Through process optimization, covering extraction time, temperature, and solvent composition, the solvothermal extraction methods proved effective in removing these additives. For the ABS sample, the H2O/IPA/NaOH extraction allowed efficient bromine removal (94%) at 125 °C, while for r-HIPS, the highest bromine removal (69%) was achieved through repeated extractions using IPA/NaOH at 100 °C. Intriguingly, extraction selectivity could be tuned by adjusting the extraction conditions and solvent composition. Overall, the findings highlighted that the extraction process should be optimized for each specific waste composition. The applied protocol, utilizing relatively mild conditions and environmentally friendly solvents, holds the potential for enhancing plastic recyclability and reducing the environmental impact of BFRs.