Thermo-catalytic conversion of PET waste into turbostratic graphene-like nanosheets with tailored crystallinity and electrical performance for reinforcement of semi-crystalline thermoplastics

Official URL: https://dx.doi.org/10.1021/acssuschemeng.6c01039

The upcycling of post-consumer PET bottles into carbon-based reinforcements enables their reuse as high-value additives for semi-crystalline polymers, offering a sustainable alternative to downcycling. In this study, we demonstrate a circular upcycling pathway converting PET bottles into turbostratic graphene-like sp2-carbon nanosheets with controlled structural ordering, enabling multifunctional reinforcement thermoplastic matrices. The process is based on a thermo-catalytic route involving talc-supported pyrolysis, using iron (Fe)-assisted chemical activation and zinc (Zn)-assisted physical blending to tailor the structure and properties of the resulting sp2-carbon materials. Structural analyses indicate that the Fe-derived sample exhibits relatively higher structural ordering, reflected by sharper XRD features and a higher XRD-derived relative sp2-carbon ordering index, while the Zn-derived sample shows lower ordering and more pronounced structural disorder. The observed stacking characteristics are interpreted as limited stacking thickness inferred from XRD coherence length, rather than exact layer counts. Raman analysis further confirms the presence of partially oxidized turbostratic sp2-carbon structures, characterized by broad and non-single-component 2D features. XPS analysis reveals higher carbon purity in the Zn-derived material (86.2 atom %) compared to the Fe-derived counterpart (82.2 atom %), correlating with improved oxidative stability. Electrical measurements show that the Fe-derived material reaches an effective bulk conductivity of 0.44 S/cm, exceeding that of the Zn-derived sample (0.14 S/cm). When incorporated at 0.5 wt % into PP, PA66, and PET, the turbostratic graphene-like sp2-carbon nanosheets function as both nucleating and reinforcing agents. Mechanical testing reveals improvements of 21−28% in PP flexural properties, 31% in PA66 tensile modulus, and 26% in PET tensile strength. Life-cycle assessment indicates up to 98% reduction in CO2 emissions compared to the conventional reduced graphene oxide production route considered as a benchmark.