Valorization of Unused, Expired Surgical Masks in Polymer-Modified Bitumens Using Maleic Anhydride as a Compatibilizer

In this study, polypropylene (PP) recovered from unused, expired surgical masks was evaluated as a substitute for virgin PP in polymer-modified bitumen (PMB). Unlike previous studies that incorporated whole masks or mixed polymer residues into bitumen, this work focuses specifically on recovering and functionalizing the polypropylene layers of surgical masks to directly replace virgin PP in PMB formulations. To improve the compatibility between PP and the bituminous matrix, maleic anhydride (MAH) and a maleic anhydride-grafted compatibilizer (AUS) were incorporated through different blending strategies. Five PMB formulations (0.5–5 wt.% polymer content) were prepared from B70/100 reference bitumen. ATR/FT-IR confirmed the absence of thermo-oxidative degradation during mixing. Viscosity, penetration force and softening behaviour tests at 10–40 °C identified the MAH-functionalized mask-derived PP (PMB_MMAH) as the best-performing formulation. Compared to the base bitumen, this formulation increased the softening point by ~10–15 °C, raised viscosity by ~20–30%, and reduced penetration by up to 25%. These results demonstrate that mask-derived PP can provide a sustainable alternative to virgin PP while ensuring comparable or improved technical performance. Further studies will evaluate long-term ageing behaviour and environmental impact.