Upcycling Post‐Consumer Polystyrene Into Thermo‐Reactive Interfacial Modifiers for High‐Performance Wood–Polymer Composites

ABSTRACT The valorization of post‐consumer polymer waste into high‐performance functional materials remains a central challenge in sustainable polymer engineering. In this study, waste polystyrene foam was chemically transformed via sequential nitration, reduction, and blocked‐isocyanate functionalization to produce reactive interfacial modifiers for coumarone–indene resin–based wood–polymer composites (WPCs). Structural evolution was confirmed using FTIR, 1 H NMR, and XPS analyses. Thermal characterization revealed deblocking behavior consistent with thermally activated carbamate dissociation. Incorporation of aminated polystyrene increased tensile strength by 64.8% compared to the control, while blocked‐isocyanate‐functionalized polystyrene enabled a balanced enhancement in strength (21.6%) and elongation (141%), indicating improved interfacial compatibility. Thermal stability and surface hardness were also improved relative to unmodified systems. The results suggest that chemically engineered waste polystyrene can function as a reactive compatibilizer, offering a sustainable strategy for enhancing WPC performance while advancing circular polymer utilization.