Interface diffusion and morphology of aerospace grade epoxy co-cured with thermoplastic polymers

Interfaces formed during the co-curing of an aerospace grade epoxy resin in contact with PEI, PES, and PSU surfaces are examined in this work. The interface found in each scenario is characterized by optical microscopy, and low voltage Scanning Electron Microscopy (SEM) using Energy-Dispersive X-ray spectroscopy (EDX) where applicable. Atomic Force Microscopy (AFM) in tapping mode is also used for high resolution imaging of the interface. The spatial resolution and limitations for each microanalysis technique are defined, and results are interpreted accordingly. The morphology of each interface obtained is correlated with a thermodynamic approach based on the Hansen Solubility Parameter (HSP), which considers dispersion forces, polar forces, hydrogen bonding, and ionic forces between the two materials. The limitations of the HSP thermodynamic approach for this study are discussed. Significant interdiffusion of more than 50 μm is found with PES, PEI and PSU. Nevertheless, a phase separation mechanism was evidenced only for PEI and PSU, and could not be detected with PES. Larger interdiffusion was observed with PSU than PEI.