Transition Metal Catalyzed Carbonization of Polyetherimide/Graphite Nanocomposites

The development of technologies based on carbon structures derived from polymeric precursors, such as ultramicroporous carbon molecular sieve membranes (CMSMs) and structural foams, relies on optimizing the pyrolysis parameters and precursor composition. This fundamental study investigates the pyrolysis of graphite (Gr)-enhanced polyetherimide (PEI) systems, catalyzed by transition metals (Fe, Co, Ni) using thermogravimetric analysis (TGA) under nitrogen within the framework of an I-optimal response surface design. Factors included Gr content (0–100 phr), heating rate (10–20 °C/min), and catalyst type. The main research aim was to maximize char yields and elucidate the chemical mechanisms of carbonization. The results indicate that Gr-enhanced PEI nanocomposites containing Fe or Co at 100 phr Gr, pyrolyzed at 10 °C/min, achieved maximum char yields, approximately 55–57% higher than the neat PEI and 11–12% higher than the PEI/Gr nanocomposites without catalyst. Moreover, significant interactions were detected between the Gr content and catalyst type, as well as heating rate and catalyst type. Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) of the optimal samples revealed the mechanisms for char formation in the presence of Gr, Fe, and Co. Specifically, XPS revealed photoemission peaks at C 1s (∼285.1 eV) and N 1s (∼399.5 eV), highlighting the preservation of the carbonaceous backbone and nitrogen-rich PEI functional groups, alongside evidence of metal integration. Raman spectroscopy demonstrated that Co catalyst enhanced graphitization with reduced defect density, while Fe induced significant disorder due to stronger Fe–N and Fe–C interactions. XRD confirmed the graphitic nature of the resulting carbonaceous structures and the absence of distinct metal carbide or oxide phases, emphasizing the catalytic role of Fe and Co in modifying local graphitic environments. While scaling up and long-term thermal stability of these systems remain challenging, these findings provide a framework for the systematic design of carbon structures with tailored properties.