Process dependent interface strengthening, de-icing and EMI shielding performance in PEEK/CF laminates

Abstract

Carbon fiber (CF)/polyetheretherketone (PEEK) laminates are emerging as a potential material for aero structural applications, thereby offering tough competition to the traditional Fiber reinforced polymers. The additional advantages like high production rate, recyclability, weldability, higher damage tolerance and prolonged service life at high temperatures make them a popular choice over traditional carbon fiber reinforced epoxy (CFRE) laminates. PEEK based laminates offer unique advantages, but the properties largely depend on the processing parameters (temperature and pressure cycles, holding time, etc.), which control both diffusion of PEEK into CF and the interfacial adhesion between CF and PEEK at a given volume fraction of CF. Our results begin to suggest that the interfacial adhesion between PEEK and CF depends largely on the temperature as manifested from interlaminar shear strength (ILSS) and flexural strength (FS) recorded for different pressure cycles. For a given temperature, increasing the pressure cycle influences the mechanical properties more than the holding time. In addition, beyond a certain temperature the viscosity drops, and the interface is weakened because of the decrease in matrix volume. The laminate fabricated using the optimized parameters showed an ILSS of 66 MPa and FS of 658 MPa, which is significantly higher than the traditional CFRE. The fractography analysis complements the results obtained manifesting in bare CF at temperatures >410 °C and a thick layer of PEEK on CF at < 410 °C, suggesting that at optimum temperatures the PEEK diffuses well through all the layers of CF. The laminates were also studied for deicing applications using Joule heating. A de-icing time of 30 s at a low voltage of 4 V and rapid heat dissipation, together with a high total shielding effectiveness (SET) of 47.5 dB, makes these laminates potential candidates for aerostructures.