A Direct Synthesis Route of Thermally Expanded Graphene for Electrically Conductive PEEK Polymer Composites with Environmental Assessment Analysis

This study presents a rapid and chemical-free synthesis of thermally expanded graphene (TEG), which is a lightweight carbon material, via 5-minute single-step thermal exfoliation of commercially available expandable graphite. The resulting TEG exhibits ultralow density of 0.0195 g/mL and a significant volumetric expansion ratio (32-fold), indicative of a porous network structure. Structural analyses confirmed the effective removal of oxygen-containing groups (C/O ratio increased from 4.7 to 79.0), restoration of conjugated graphitic domains (I2D/IG value of 0.57), the material's thermal robustness (single major decomposition stage beginning at 595 °C), and the formation of wrinkled layers with microholes resulting from gas release. Importantly, a life cycle assessment (LCA) revealed a moderate global warming potential (0.0233 kg CO₂-eq/g), substantially lower than that of reduced graphene oxide (rGO) and carbon nanotubes (CNTs). For the first time, TEG was incorporated into polyetheretherketone (PEEK) to fabricate conductive polymer composites, achieving an electrical conductivity of 0.003381 S/cm at 10 wt.% loading. These findings highlight TEG as a sustainable and high-performance conductive filler for advanced thermoplastic applications in polymer matrices.