Feasibility study on ultrasonic-assisted processing techniques for the value-retention of hybrid thermoplastic–thermoset composites

The integration of high-performance thermoplastics in fiber-reinforced polymers with thermoset matrices offers the possibility of using existing manufacturing processes and at the same time incorporating the advantages of thermoplastics. These include higher fracture toughness, weldability and reprocessability. Among exisiting high-performance thermoplastics, polyetherimide (PEI) stands out due to its amorphous structure, which provides good compatibility with thermosets. This study investigates the integration of a PEI interlayer within carbon fiber-reinforced epoxy prepregs to evaluate the feasibility of value-retention and multiple circular use of hybrid thermoplastic-thermoset laminates via power ultrasonics. A novel ultrasonic-assisted separation method employing a cutting tool enabled controlled pre-crack initiation and propagation along the PEI interface, resulting in clean and repeatable separation. Subsequent displacement-controlled ultrasonic reconsolidation of the separated laminates, facilitated by a PEI film as energy director, led to uniform melt generation and a 55% increase in lap-shear strength compared to time-controlled reconsolidation experiments. Furthermore, double cantilever beam (DCB) testing revealed a 250% enhancement in the critical energy release rate (G I,C ) for laminates with PEI interlayer, demonstrating significantly improved fracture toughness. These findings underscore the dual functionality of the PEI interlayer, not only as a toughening agent but also as an enabler for reprocessing and reusing by power ultrasonics. The demonstrated approach offers a compelling pathway for sustainable composite design, particularly for aerospace applications where mechanical performance and end-of-use circularity options are critical. • PEI interlayer enables sharp interlaminar ultrasonic separation in hybrid composite laminates. • Displacement-controlled reconsolidation improves lap-shear strength by 55%. • PEI interlayer boosts fracture toughness with 250% rise in critical energy release rate. • Ultrasonic-assisted processing holds potential in circularity of hybrid aerospace composites.