The re-manufacture and repairability of poly(ether ether ketone) discontinuous carbon fibre composites

A major limitation of carbon fibre-reinforced polymers is their unsuitability for repair and recycling processes due to the common employment of thermoset resin matrices and continuous fibres. Advanced thermoplastic discontinuous fibre moulding compounds (DFMCs) now offer an alternative for high-performance components. Although DFMCs cannot match the raw performance of continuous fibre reinforcement, compression-moulding techniques developed at the University of Exeter enable poly(ether ether ketone) (PEEK) matrix DFMCs to challenge the mechanical properties of aluminium in thick-section components, an application area outside the scope of thermoset composites. This previous research also identified that PEEK DFMC components are far less likely to suffer significant breakage of the fibres during fracture, suggesting that the material is highly suited to repair through simple remoulding, using heat and pressure to re-melt and consolidate the resin along the fracture path returning it to its original strength and stiffness. This offers an exciting capacity for repair and recyclability. This paper investigates this further, utilising a series of three-point bending samples loaded to fracture before being reheated and pressurised then tested again. Multiple reprocessing approaches are investigated, including the use of additional material to act as repair packs, re-pressing to induce significant flow and simple remoulding. This study shows that composites can be repaired with minimal loss of mechanical performance even when significant fracture occurs. The application of repair packs actually increases performance, reaching a flexural modulus of ca 80 GPa after three fracture cycles and a maximum bending stress of ca 900 MPa. (c) 2021 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Automated summary

The study shows that PEEK matrix DFMCs have good repair performance, and simple reshaping through re-melting and applying pressure can restore the composite material to its original strength and stiffness. Additionally, the application of repair packs and re-molding methods do not lead to significant loss of mechanical performance even after repeated fracture cycles.