High‐strength composites by thiocracking of high‐polypropylene‐content mixed waste

Abstract Mixed‐material municipal waste poses a persistent end‐of‐life management challenge because the heterogeneous composition limits efficient separation and recycling. After disposal, mixed‐material waste often fragments into microplastics, associated with adverse effects for both terrestrial and aquatic organisms. Herein, we report a one‐pot thiocracking strategy to upcycle mixed plastic waste comprising predominantly polystyrene with polypropylene content (31 wt%) an order of magnitude higher than any prior thiocracked mixture. Thiocracking with elemental sulfur yields PWS 90 , a composite with compressive and flexural strengths of 18.2 ± 0.4 MPa and 3.30 ± 0.13 MPa, respectively. These properties are comparable to those of ordinary Portland cement (compressive strength ≥17 MPa, flexural strength ca 3.7 MPa), the most common material for building and infrastructure applications globally. This work is the first demonstration of successful incorporation of high quantities of polypropylene into high‐sulfur materials without loss of mechanical properties. The synthesis strategy also proves to have a very low E‐factor (0.074) and a reduced global warming potential (+0.07 kg CO 2 e kg −1 compared to ca +1.0 kg CO 2 e kg −1 for ordinary Portland cement), making it a potentially sustainable and environmentally friendly route to high‐strength goods. © 2026 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.