Solvent-Based Recycling of HIPS/ABS: Impact of Fractionation on Pyrolysis Process and Monomer Recovery

Acrylonitrile–butadiene–styrene (ABS) and high-impact polystyrene (HIPS) are the dominant polymeric components of waste electrical and electronic equipment (WEEE), yet their separation remains challenging using conventional methods. Here, we report a simple and selective solvent-based strategy for separating ABS from HIPS/ABS blends using propylene carbonate (PrC) as a targeted solvent. PrC selectively solubilizes ABS, enabling its recovery with 99% purity and 90–93 wt % mass recovery while leaving HIPS unaffected (>99% purity, ∼100 wt % recovery) without altering the chemical integrity of either polymer. The method is applicable to both model polymer blends and real WEEE samples. The recovered HIPS fractions can subsequently be processed to isolate pure polystyrene (PS) matrices. To demonstrate the recycling potential of the separated streams, pyrolysis of the isolated HIPS and PS matrices increased styrene yields by up to 25 wt % compared with the starting HIPS/ABS blends. Catalytic pyrolysis of the PS matrices over a mixed-metal oxide Fe–K/ZrO2 further enhanced styrene production, achieving yields up to 31 wt % higher than those from untreated HIPS/ABS mixtures. This integrated solvent fractionation and catalytic upgrading strategy could improve the valorization of WEEE-derived plastics and facilitate complementary mechanical and chemical recycling.