Effects of Flame‐Retardant Additives in Recycling and 3D Printing Filament Production of Polystyrene

Flame retardants incorporated during plastic production to improve its properties can affect plastic recycling and product application. The aim of this study is to explore the effects of flame‐retardant additives in recycling and 3D printing filament production of polystyrene. Samples of the 2017 model polystyrene, both with the flame‐retardant additive (PS‐FR) and without (PS), were sourced from an old printer and crushed into an appropriate flake size. Although the FTIR identification and chemical composition of the sample remain intact, flame retardants have a significant impact on thermal behavior: PS‐FR showed an earlier commencement of degradation (280°C) and a lower glass transition temperature (98°C) than PS (300°C and 102°C, respectively). Material processing was affected, evidenced by a significantly lower melt flow rate for PS‐FR (4.6 ± 0.1 g/10 min) compared with PS (5.7 ± 0.2 g/10 min). Similarly, filament diameter of extruded PS‐FR is considerably higher (1.92 ± 0.02 mm) than PS (1.76 ± 0.02 mm), which limits the application of filament for 3D printing. As expected, PS‐FR compression‐molded plates demonstrated superior flame resistance. Crucially, flame retardants altered mechanical properties: PS‐FR exhibited higher tensile modulus (2020 ± 39.21 MPa) and tensile strength (19 ± 0.32 MPa), indicating increased rigidity and load‐bearing capacity. These findings highlight the critical trade‐offs between fire safety, end‐of‐life polystyrene processing, application, and mechanical performance imposed by flame retardants in recycled polystyrene.