Hydrogen-peroxide intercalated expanded graphite facilitates large enhancement in thermal conductivity of polyetherimide/graphite nanocomposites

In this work, we prepared expanded graphite (EG) filler using hydrogen peroxide (H₂O₂) as an oxidizing agent to study its impact on the thermal conductivity (k) of polyetherimide (PEI) composite, compared to EG prepared using sodium chlorate (NaClO₃). Sulfuric acid was used as the primary intercalating agent for both synthesis routes. The use of H₂O₂ prepared EG (EG-H₂O₂) led to a remarkable ∼4030% enhancement (9.5 Wm⁻¹K⁻¹) in k of the PEI/EG composite, while the use of NaClO₃ prepared EG (EG-NaClO₃) led to a much smaller enhancement of ∼2190% (5.3 Wm⁻¹K⁻¹), at 10 wt% EG composition compared to k_PEI (∼0.23 Wm⁻¹K⁻¹). Such findings exceed the current state-of-art in EG-based polymer composites. Detailed characterization was performed to understand the properties of EG-H₂O₂ and EG-NaClO₃. Raman analysis revealed that H₂O₂ resulted in relatively defect-free EG (I_D/I_G ratio ∼0.04), thus preserving the k of graphite (∼2000 Wm⁻¹K⁻¹). Use of NaClO₃, however, led to a large defect density (I_D/I_G ratio ∼0.25), yielding graphite with significantly diminished k. Furthermore, through-plane thermal diffusivity of EG-H₂O₂ paper was measured to be 9.5 mm²s^-1 while that of NaClO₃ case was measured to be 6.7 mm²s^-1, thus directly confirming the beneficial impact of H₂O₂ in preserving the high k of graphene. X-ray photoelectron spectroscopy (XPS) revealed that the higher number of defects in EG-NaClO₃ are due to the higher degree of oxidation induced by NaClO₃. The results demonstrate the potential of EG-H₂O₂ as an efficient filler for achieving high thermal conductivity polymer composites.