Carbon-carbon composites from polyetherimide matrix precursors via high-pressure stabilization in press (HiPSiP)

Despite the attractively high carbon yields (∼70%) of aromatic thermoplastics, like polyetherimide (PEI), thermoplastic matrix precursors for carbon–carbon composites have seen limited study due to thermal processing challenges. These materials melt during heating, and without containment, deform and lose structural integrity. Another major challenge is gas evolution during stabilization and carbonization, generating voids. This study introduces a new stabilization method, termed high-pressure stabilization in press (HiPSiP), which is performed directly during a compression molding process. After initial molding at 280 °C and 10 MPa for 30 min, the pressure and temperature is ramped up to 100 MPa and 510 °C and held for 1–3 h inside the mold before cooling. After HiPSiP, the matrix no longer exhibits thermoplastic behavior, due to cross-linking of the polymer chains. This prevents distortion and gas-induced decompaction during subsequent carbonization. Carbonized samples reached a density of 1.53 g/cm 3 and achieved short beam strength of 28.4 ± 0.6 MPa, one of the highest to the authors’ best knowledge without the use of any densification cycles. Characterization was performed for thermal, microstructural, chemical, and mechanical properties, using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), optical microscopy, scanning electron microscopy (SEM), powder x-ray diffraction (PXRD), elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), and short beam strength testing. Comparisons are made against samples stabilized under ambient pressure in air, and non-stabilized samples.